I know DSP's are available for loudspeaker frequency response
compensation, typically combined with a non-time-coherent "room
correction" function.

Is anything similar available for treating loudspeaker distortion?
(actually whole-of-system distortion, but measured as what comes out
of the speaker and hopefully dominated by the speaker's distortion
contribution).

I don't mean a research tool for speaker designers. I mean something
that can be used in the home or studio to reduce distortion from
existing systems.

Stand-alone or PC-based.

I imagine something that fits in the audio chain between the sound
source and the amplifier. It might generate its own test signals and
analyse the speaker output through a microphone. It could treat
harmonic distortion by mapping a number of harmonics of measured
distortion against signal amplitude against signal frequency. It could
then generate a compensating map of out-of-phase harmonics. Then when
playing music through the system, it could apply the compensating map
real-time to the incoming music signal.

Of course it would be sensible to combine such a function in the same
DSP as is used for frequency response compensation.

Am I dreaming, or describing a real product?

Grant

This would be feasible for a speaker manufacturer to do for a specific speaker,
but a general-purpose unit would be a lot further off. The big problem is the
multitude of different distortion mechanisms, their nonlinear nature, and their
natural dependence on frequency and other conditions. For example, around a
reflex enclosure's tuning frequency, displacement is very low, so
displacement-related drops to near zero, but distortion from flux displacement
in the pole pieces reaches a maximum. Even if this was all modeled, it changes
with the enclosure Q, the placement in the room, barometric pressure,
temperature, and aging of the driver, etc. In short - it's way too hard for me,
and, I suspect, for most designers.

On the other hand, Philips' (and others) old "motional feedback" method,
although necessarily tightly integrated with the driver, is probably a better
bet to get some improvement at least; still not general-purpose, though.

On 4 Sep 2003 20:35:32 -0700, (Grant Sellek)
wrote:

I know DSP's are available for loudspeaker frequency response
compensation, typically combined with a non-time-coherent "room
correction" function.

Is anything similar available for treating loudspeaker distortion?
(actually whole-of-system distortion, but measured as what comes out
of the speaker and hopefully dominated by the speaker's distortion
contribution).

I don't mean a research tool for speaker designers. I mean something
that can be used in the home or studio to reduce distortion from
existing systems.

Stand-alone or PC-based.

I imagine something that fits in the audio chain between the sound
source and the amplifier. It might generate its own test signals and
analyse the speaker output through a microphone. It could treat
harmonic distortion by mapping a number of harmonics of measured
distortion against signal amplitude against signal frequency. It could
then generate a compensating map of out-of-phase harmonics. Then when
playing music through the system, it could apply the compensating map
real-time to the incoming music signal.

Of course it would be sensible to combine such a function in the same
DSP as is used for frequency response compensation.

Am I dreaming, or describing a real product?

Grant

Regards,
Tony (remove "_" from email address to reply)

In article ,
Ethan Winer ethan at ethanwiner dot com wrote:
Grant,

Great question, and really great answers from Tony. You are absolutely
correct that loudspeaker distortion is very important (and rarely
specified!) - it's much more important than many folks realize. Here's my
take:

First, the notion that DSP can compensate for room acoustics problems is a
myth. EQ and other electronics can help a little, in a few special cases.
But the biggest room problem is a series of many peaks and dips in the low
frequency response. These peaks and dips change depending on where the
speakers are placed, and where you are in the room. This simply cannot be
compensated for by electronics. For a similar reason - all the stuff Tony
said - DSP can correct only some of the causes of speaker distortion.

Not so. It is certainly possible, though not necessarily easy,
to deconvolve the room response for a selected listening region.
This HAS been done successfully though, as I said, it is neither
simple and easy to derive the deconvolution function, nor is it
simple to implement, often requiring quite of bit of horsepower.

One way to reduce loudspeaker distortion is to include the loudspeaker's
voice coil in the power amp's negative feedback loop. Mackie does this in
their HR series speakers, as do some other manufacturers. This allows the
amplifier to compensate for incorrect cone movement directly, with much more
control than is possible with an external DSP unit.

No, it can ONLY reduce those non-linearities that are
accurately reflected in the non-linear behavior of the Dl
product of the driver. It completely ignores mechanical
non-linearities that do no manifest themselves in the electrical
domain.

--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |

On Fri, 5 Sep 2003 11:01:36 -0400, "Ethan Winer" ethan at ethanwiner
dot com wrote:

First, the notion that DSP can compensate for room acoustics problems is a
myth.

Tell that to Behringer, TACT and Meridian..................

EQ and other electronics can help a little, in a few special cases.
But the biggest room problem is a series of many peaks and dips in the low
frequency response. These peaks and dips change depending on where the
speakers are placed, and where you are in the room. This simply cannot be
compensated for by electronics.

Of course it can - you just need a microphone placed at the listening
position. Heck, B&O (of all people!) just launched a speaker which
contains its own microphone, and adjusts its bass response depending
where it's placed in the room.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Dick,

It is certainly possible, though not necessarily easy, to deconvolve the
room response for a selected listening region.

It really isn't possible. The problem is the many peaks and dips caused by
reflections off the room boundaries. Those dips can be very deep, and they
are position dependent. So even if you have enough amplifier and speaker
capability to overcome a 15 dB dip at 75 Hz, as soon as you apply that
correction you'll have a terrible peak a foot or two away. Maybe you could
make that work if you mix while sitting in a dentist chair with your head
clamped into position...

it can ONLY reduce those non-linearities that are accurately reflected in
the non-linear behavior of the Dl product of the driver.

I don't know what "D1" is, but you are correct that including the voice coil
in the feedback loop cannot overcome every possible source of distortion.
But if you can hit the main sources and reduce the distortion from 5% to
less than 1%, (I'm just guessing at those figures) I'd say that's a
worthwhile goal.

--Ethan

In article ,
Ethan Winer ethan at ethanwiner dot com wrote:
Dick,

It is certainly possible, though not necessarily easy, to deconvolve the
room response for a selected listening region.

It really isn't possible. The problem is the many peaks and dips caused by
reflections off the room boundaries. Those dips can be very deep, and they
are position dependent. So even if you have enough amplifier and speaker
capability to overcome a 15 dB dip at 75 Hz, as soon as you apply that
correction you'll have a terrible peak a foot or two away.

False, what you are claiming is a physical impossibility. If you
have a dip at 75 Hz, the CLOSEST a peak could be is 1/4
wavelength away. You have to go through 90 degrees of phase
rotation for this to occur. Further, the only way that a "15 dB
dip could have a correspondong "terrible peak" is if the
absorbtion coefficient of the room boundaries is damned near 0
(it isn't) and if ALL the energy is concentrated into the
primary nodes (it isn't).

Indeed, is HAS been done QUITE successfully in just the range of
frequencies you're claiming that it's impossible in. It ain't
cheap, and it's computationally quite expensive, tobe sure, but
it has been done.

Maybe you could
make that work if you mix while sitting in a dentist chair with your head
clamped into position...

Maybe you could actually study the physics of the situation a
bit more and actually SEE what REALLY happens in real rooms.
Even in the worst case scenario you describe, the area over
which the correction is valid is quite a bit larger than you
claim, encompassing a volume at least 15 times your claim.

it can ONLY reduce those non-linearities that are accurately reflected in
the non-linear behavior of the Dl product of the driver.

I don't know what "D1" is, but you are correct that including the voice coil
in the feedback loop cannot overcome every possible source of distortion.

Sorry, type, it's Bl (as in Bee-el), the electromagnetic
transduction parameter of the motor system.

But if you can hit the main sources and reduce the distortion from 5% to
less than 1%, (I'm just guessing at those figures) I'd say that's a
worthwhile goal.

Well, yes, you are guessing at the figures, and the numbers that
result give a woefully inadequate picture of the situation.

For the most part, the distortion produced by the non-linear
behavior of the electrical and mechanical system is excurion
dependent. Right away that tells us what's important and what's
not. Below the system resonance (usually corresponding to system
cutoff), since the system is stiffness controlled, the
suspension non-linearities and the magnetic non-linearites
together play the dominat role in determining the production of
spurious components due to non-linearity. THat may not seem
important, but consider that much of the resulting distortion
components wind up above cutoff.

Above resonance, in the mass-controlled region, the magnetic
system non-linearities dominate, BUT, since the excursion goes
as the inverse square of the frequency, it becomes a fairly
irrelevant once you get up into the region where much of the
real energy is being produced. There, you have non-linearities
in the diaphragm itself, and those simply are NOT reflected at
all in the electrical domain and are thus non-correctable by
your scheme.


--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |

Richard,

If you have a dip at 75 Hz, the CLOSEST a peak could be is 1/4 wavelength
away.

Not so at all, though maybe I could have chosen my words better. By "peak" I
meant the enormous boost caused by the applied EQ, not a natural peak due to
the wave in the room. An acoustic null in a room is very sharp - both in
frequency and the location where the level is at a minimum. Moving just a
few inches away from the null spot yields a huge difference in level. So
boosting a low frequency by 15 dB will cause a big increase in that
frequency nearby in the room where the naturally occurring null is not so
deep.

If you've never experimented with low frequency sine waves in a room - and
it sounds like you haven't - I suggest you play 80 Hz (or any low frequency
your speakers can reproduce cleanly) and walk toward and away from the rear
wall. At a point 1/4 wavelength from every boundary there is a deep null.
(Since the floor and ceiling are also boundaries and they all combine, you
may have to stand up tall or crouch down to find the place where the null is
most complete.) Even with a decent amount of bass trapping installed you can
easily hear and measure these nulls. But especially in a room without bass
traps the effect is very obvious.

Indeed, is HAS been done QUITE successfully

No need to shout. Maybe if you define "quite successfully" as "it seemed to
help a little." Seriously, besides the response/position problem, and the
inability to eliminate echoes and ringing, yet another room problem you
cannot solve with DSP is excessive reverb at low frequencies. This is one of
the biggest problems for mixing engineers in small untreated rooms because
it makes bass instruments sound muddy with the notes ill-defined. There's no
way can you reduce reverb time with DSP.

those simply are NOT reflected at all in the electrical domain and are
thus non-correctable by your scheme.

Hey, it's not my scheme! I'm just reporting what an EE friend said Mackie
does. You gave a lot of explanations, but it would have been even better had
you included real world figures of speaker distortion and how much it can be
improved by various methods. Without any supporting data it sounds like
you're guessing as much as I was. :-)

you are hypothesizing more and more pathologically absurd scenarios.

No need for name calling either. Please let's keep the discussion
professional and courteous.

How many listening rooms suffer from flutter echoes and ringing of a
sufficient Q to cause the problems you describe? Careful, I HAVE measured a
number of rooms. Have you?

Yes, acoustic treatment is my business and I have measured lots of rooms.

As soon as you get even one "boing" caused by echoes between parallel
surfaces, you have exceeded what can be controlled electronically. This is
especially a problem with the now-common (and inept) practice of treating
home theaters by leaving the upper walls completely bare. So as soon as a
gun goes off in an action movie, how could DSP leave the sound of the bullet
intact but prevent the sound from bouncing off the walls?

The only practical solution for all of these problems - peaks and dips
caused by acoustic interference, excessive reverb, flutter echo and
ringing - is broadband acoustic treatment. Even if it is possible to at
least reduce room effects a little, by your own admission (earlier) it
requires huge resources and thus huge expense. So why even bother to pursue
that angle, when acoustic treatment is so much simpler, less expensive, and
does a much better job?

--Ethan

On Fri, 5 Sep 2003 14:37:57 -0400, "Ethan Winer" ethan at ethanwiner
dot com wrote:

Stewart,

Tell that to Behringer, TACT and Meridian ... you just need a microphone
placed at the listening position. Heck, B&O (of all people!) just launched a
speaker which contains its own microphone

See my answer to Dick. It's not possible unless you don't mind being
strapped into a chair with your head clamped in place so it can't move even
one inch. If that's acceptable then okay, I concede. :-)

Dick already answered that point, which simply is not true. Meridian
and TACT have offered excellent room-correction for several years, and
works very effectively over movements of several feet, as should be
obvious from simple consideration of the wavelengths involved.

Two other room problems that cannot be compensated for with DSP are flutter
echoes and ringing. Yes, you can make a really deep and really narrow notch
at the ring frequencies. But the tones are still there and still sustain
after the sound source stops. And any legitimate musical content at that
frequency will be removed. And there's really no way to get rid of echoes
using electronics.

Agreed, except that *serious* flutter echoes and ringing are very rare
in domestic rooms (as opposed to commercial concrete shells), and in
any event, it's not hard to deal with those by choosing suitable
furnishings. You can drop the Q of such echoes to negilgible values by
the simple hanging of a couple of wall rugs, and by carpeting the
floor.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Stewart,

Meridian and TACT have offered excellent room-correction for several years


How do you define excellent? More to the point, how can any electronic
device reduce reverb time or eliminate echoes? I had heard of the Meridian
system and I just looked up their PDF article again. Since they offer
several graphs as proof the system works, should I be suspicious that none
of the graph legends are readable?

I had never heard of TACT so I looked them up too, but found nothing
meaningful in the way of explanations. Maybe I'm biased against an
electronic solution because I manufacture and sell high performance acoustic
treatment. But the idea of using DSP to control the three common and
fundamental room problems - low frequency peaks and dips, echo and reverb,
and ringing - makes no sense. How can you possibly get rid of even a little
echo with DSP? Okay, I suppose you could generate an equal and opposite
echo, and time it to arrive at the listening position. But again, as soon as
you move your head an inch or two the sound is much worse. And what a kludge
that is compared to the standard proven solutions.

Agreed, except that *serious* flutter echoes and ringing are very rare in
domestic rooms

I deal with smallish recording studios all the time, and I assure you that
after low frequency peaks and dips, echoes and ringing are the second most
common complaint.

You can drop the Q of such echoes to negilgible values by the simple
hanging of a couple of wall rugs, and by carpeting the floor.

Which is my whole point. Why bother with the complexity of DSP when you can
do a much better job with conventional treatment? I didn't notice prices on
either of those other sites, but I assume the cost for those DSP boxes is
much higher than conventional treatment, yes?

--Ethan

On Sat, 6 Sep 2003 06:51:01 -0400, "Ethan Winer" ethan at ethanwiner
dot com wrote:

Richard,

If you have a dip at 75 Hz, the CLOSEST a peak could be is 1/4 wavelength
away.

Not so at all, though maybe I could have chosen my words better. By "peak" I
meant the enormous boost caused by the applied EQ, not a natural peak due to
the wave in the room. An acoustic null in a room is very sharp - both in
frequency and the location where the level is at a minimum.

Actually no, it isn't in any halfway reasonable domestic environment.

Moving just a
few inches away from the null spot yields a huge difference in level. So
boosting a low frequency by 15 dB will cause a big increase in that
frequency nearby in the room where the naturally occurring null is not so
deep.

Could we have that again, in English please?

If you've never experimented with low frequency sine waves in a room - and
it sounds like you haven't - I suggest you play 80 Hz (or any low frequency
your speakers can reproduce cleanly) and walk toward and away from the rear
wall. At a point 1/4 wavelength from every boundary there is a deep null.
(Since the floor and ceiling are also boundaries and they all combine, you
may have to stand up tall or crouch down to find the place where the null is
most complete.) Even with a decent amount of bass trapping installed you can
easily hear and measure these nulls. But especially in a room without bass
traps the effect is very obvious.

Firstly, I would *strongly* suggest that you avoid intimating that
Dick Pierce has not 'been there and done that' regarding loudspeaker
or room measurements. Secondly, what you are claiming simply does not
happen except in the most pathologically horrendous rooms (think
cube).
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sat, 6 Sep 2003 13:45:38 -0400, "Ethan Winer" ethan at ethanwiner
dot com wrote:

Stewart,

Meridian and TACT have offered excellent room-correction for several years

How do you define excellent?

Able to correct for room resonance effects and loudspeaker response
errors.

More to the point, how can any electronic
device reduce reverb time or eliminate echoes?

It can't, but these are easily corrected by other means.

I had heard of the Meridian
system and I just looked up their PDF article again. Since they offer
several graphs as proof the system works, should I be suspicious that none
of the graph legends are readable?

No, since the system is effective in reality.

I had never heard of TACT so I looked them up too, but found nothing
meaningful in the way of explanations. Maybe I'm biased against an
electronic solution because I manufacture and sell high performance acoustic
treatment.

Oh, could there perhaps be a conflict of interest here? :-)

But the idea of using DSP to control the three common and
fundamental room problems - low frequency peaks and dips, echo and reverb,
and ringing - makes no sense.

Actually, it makes perfect sense, at least for the first one. The
other two (which are actually the same thing, if you understand
acoustics) are very easily controlled without resorting to overpriced
'audiophile' solutions.

How can you possibly get rid of even a little
echo with DSP?

You can't, but you can with a $20 rug hung on the wall or thrown on
the floor..........

Okay, I suppose you could generate an equal and opposite
echo, and time it to arrive at the listening position. But again, as soon as
you move your head an inch or two the sound is much worse. And what a kludge
that is compared to the standard proven solutions.

That's absolute garbage. DSP solutions work over several feet, as
should be obvious if you consider the basic physics of the situation.

Agreed, except that *serious* flutter echoes and ringing are very rare in
domestic rooms

I deal with smallish recording studios all the time, and I assure you that
after low frequency peaks and dips, echoes and ringing are the second most
common complaint.

And this relates to domestic situations, exactly how?

You can drop the Q of such echoes to negilgible values by the simple
hanging of a couple of wall rugs, and by carpeting the floor.

Which is my whole point. Why bother with the complexity of DSP when you can
do a much better job with conventional treatment? I didn't notice prices on
either of those other sites, but I assume the cost for those DSP boxes is
much higher than conventional treatment, yes?

Certainly, but they don't attempt to deal with slap echo, which can be
controlled for a few tens of dollars by the intelligent use of floor
rugs and wall drapes, to the taste of the owner. Now, what do you
charge for your 'audiophile' room treatments, and what do they look
like?

Ethan, you're a troll attempting to push your room treatments on
people who don't know any better. This is probably not the best place
to make your sales pitch.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Both Ethan and Dick Pierce know exactly what they are talking about. Ethan
is a legend in the acoustic treatment community. Dick is a legend in the
Loudspeaker and Bass Cabinet reviewing, educating community.

They are both looking at this question their very different perspectives and
are arguing because their views of acoustic reproduction are very different.

I have seen excellent uses of DSP that blew me away. Dick has too. In fact
he has tested and reviewed them.

I have seen excellent uses of bass traps, Helm-Holtz resonators, Acoustic
Foam and Acoustic diffusors that blew me away. Ethan has tested these
systems and designs very competent acoustic solutions. He writes excellent
articles for DIY'ers and frugal professionals.

I think there are things that both solutions can provide that the other
cannot. DSP cannot correct EVERY negative aspect of an acoustic space, nor
can acoustic treatment.

Let's just have some peace and return to discussing this and stop picking
fights.

- FLINT

In article ,
Stewart Pinkerton wrote:
How can you possibly get rid of even a little
echo with DSP?

You can't, but you can with a $20 rug hung on the wall or thrown on
the floor..........

Except at the low frequencies (below a few hundred hertz) which are
most problematic due to the near omni-polar response of most speakers
resulting in a lower ratio of direct sound to the reverberant field. This
is made worse by the relatively close spacing of the equal loudness curves.

--
a href="http://www.poohsticks.org/drew/"Home Page/a
The Congress shall assemble at least once in every Year, and such Meeting
shall be on the first Monday in December, unless they shall by Law appoint a
different Day.

Ethan Winer wrote:

Stewart,

Tell that to Behringer, TACT and Meridian ... you just need a microphone
placed at the listening position. Heck, B&O (of all people!) just launched a
speaker which contains its own microphone

See my answer to Dick. It's not possible unless you don't mind being
strapped into a chair with your head clamped in place so it can't move even
one inch. If that's acceptable then okay, I concede. :-)

Two other room problems that cannot be compensated for with DSP are flutter
echoes and ringing. Yes, you can make a really deep and really narrow notch
at the ring frequencies. But the tones are still there and still sustain
after the sound source stops. And any legitimate musical content at that
frequency will be removed. And there's really no way to get rid of echoes
using electronics.

Echoes, flutters, and ringing are all effects that can be modeled
perfectly as a linear system. Within certain constraints (minimum phase,
well-conditioned), they can be removed. The concept is called deconvolution
or inverse filtering.

One of those constraints is the listener position, as you have stated. Of
course that constraint is dependent on the frequencies at which the correction
is being applied, so if you're talking about low-frequency EQ, the "head lock"
problem is not present. The other serious constraint I didn't hear you mention
is that the equalization is only valid for a single listener.
--
% Randy Yates % "...the answer lies within your soul
%% Fuquay-Varina, NC % 'cause no one knows which side
%%% 919-577-9882 % the coin will fall."
%%%% % 'Big Wheels', *Out of the Blue*, ELO
http://home.earthlink.net/~yatescr

On Sat, 6 Sep 2003 18:09:27 -0600, (Drew
Eckhardt) wrote:

In article ,
Stewart Pinkerton wrote:
How can you possibly get rid of even a little
echo with DSP?

You can't, but you can with a $20 rug hung on the wall or thrown on
the floor..........

Except at the low frequencies (below a few hundred hertz) which are
most problematic due to the near omni-polar response of most speakers
resulting in a lower ratio of direct sound to the reverberant field. This
is made worse by the relatively close spacing of the equal loudness curves.

Well yes, and that's where DSP solutions become *extremely* useful.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 07 Sep 2003 04:28:45 GMT, Randy Yates wrote:

Ethan Winer wrote:

Stewart,

Tell that to Behringer, TACT and Meridian ... you just need a microphone
placed at the listening position. Heck, B&O (of all people!) just launched a
speaker which contains its own microphone

See my answer to Dick. It's not possible unless you don't mind being
strapped into a chair with your head clamped in place so it can't move even
one inch. If that's acceptable then okay, I concede. :-)

Two other room problems that cannot be compensated for with DSP are flutter
echoes and ringing. Yes, you can make a really deep and really narrow notch
at the ring frequencies. But the tones are still there and still sustain
after the sound source stops. And any legitimate musical content at that
frequency will be removed. And there's really no way to get rid of echoes
using electronics.

Echoes, flutters, and ringing are all effects that can be modeled
perfectly as a linear system. Within certain constraints (minimum phase,
well-conditioned), they can be removed. The concept is called deconvolution
or inverse filtering.

Interesting, I didn't know that. I would still tend to use acoustic
treatment to remedy reflection effects, combined with DSP room
correction to sort out eigentones.

One of those constraints is the listener position, as you have stated. Of
course that constraint is dependent on the frequencies at which the correction
is being applied, so if you're talking about low-frequency EQ, the "head lock"
problem is not present. The other serious constraint I didn't hear you mention
is that the equalization is only valid for a single listener.

Ah the loneliness of the true audiophile! :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"flint" wrote in message
...
Both Ethan and Dick Pierce know exactly what they are talking about. Ethan
is a legend in the acoustic treatment community. Dick is a legend in the
Loudspeaker and Bass Cabinet reviewing, educating community.

They are both looking at this question their very different perspectives
and
are arguing because their views of acoustic reproduction are very
different.

I have seen excellent uses of DSP that blew me away. Dick has too. In fact
he has tested and reviewed them.

I have seen excellent uses of bass traps, Helm-Holtz resonators, Acoustic
Foam and Acoustic diffusors that blew me away. Ethan has tested these
systems and designs very competent acoustic solutions. He writes excellent
articles for DIY'ers and frugal professionals.

I think there are things that both solutions can provide that the other
cannot. DSP cannot correct EVERY negative aspect of an acoustic space, nor
can acoustic treatment.

FWIW I'll second this!

I admire both guys for the good stuff they do in their respective areas of
audio.

Left to my own choices, I follow what Ethan says about room acoustics first,
and when you have the room with the acoustics of your dreams or merely the
best you can do because of other constraints, then start thinking about the
DSP-based room enhancements.

Dick,

Your grasp of acoustical physics is, well, underwhelming.

I freely admit that I am not a physicist nor a mathematician. But I am
technically minded, and I have plenty of practical hands-on experience with
this stuff.

Please, for the gathered crowd, show how high the Q of such a resonance
must be to make your assertion true.

You are confusing the Q of the frequency response at a given location with
the size of that location. If you find a spot in the room where the response
is down 15 dB at 100 Hz, a high Q will make the dip less severe at 101 Hz.
But even with a low Q the depth of the null can be very deep - theoretically
infinite - and the size of the "zone" where the null is that deep can be
very small. If you move away just a little from where the null is deepest
the level will come back up quite a bit.

EW: There's no way can you reduce reverb time with DSP.

RP: Wanna bet? Again, do you understand the principal of deconvolution?

You are correct that deconvolution involves complex math I do not
understand. But please explain in plain English the mechanism by which DSP
can remove echoes and reverb. I can see how DSP could create equal and
opposite echoes, and maybe even equal and opposite reverb (if you have a
Cray). But how could this be applied in a typical room and not suffer from
the "move your head one inch" restriction? This is the crux of the matter:
How is a complex solution having severe positional restrictions sensible,
when the problem can be solved better and much less expensively using bass
traps and fiberglass panels?

And you STILL did not answer the question: how many listening rooms in
domestic situations suffer from the problems you describe?

All of them!

If the response in the room is linear, and it contains finite energy, it
is correctable.

Yeah, okay, theoretically for a tiny zone. But not only is the zone tiny,
for everyone outside the zone the correction will make things many times
worse.

--Ethan

Stewart,

EW: An acoustic null in a room is very sharp - both in frequency and the
location where the level is at a minimum.

SP: Actually no, it isn't in any halfway reasonable domestic environment.


Yes, it really is. And it's so easy to prove I don't know why we're arguing
about it. Take a sine wave oscillator or test tone CD and play it through
your system. Or a friend's system. Or a system in ANY room without adequate
acoustic treatment. Now walk around the room very slowly listening for drops
in level. You will immediately see that at any reasonable frequency (say, 80
Hz to 4 KHz) there are many locations that have severe drops in level, and
those locations are extremely restricted in size. Moving your head even one
inch at mid/high frequencies is enough to go from full level to a nearly
complete cancellation. At low frequencies the size of the null zone is
larger, but still very small - if you move to the adjacent seat on the couch
the level can change many dB.

EW: So boosting a low frequency by 15 dB will cause a big increase in
that frequency nearby in the room where the naturally occurring null is not
so deep.

SP: Could we have that again, in English please?

Let's say at the listening position you measure a 15 dB dip at 80 Hz. So you
set the room EQ to boost 80 Hz by 15 dB. Now in that precise spot the level
at 80 Hz is back to normal. But now in the adjacent seat the level is 8 dB
higher than normal because the dip was only 7 dB there initially, but that
location is also receiving the 15 dB of EQ boost.

I would *strongly* suggest that you avoid intimating that Dick Pierce has
not 'been there and done that' regarding loudspeaker or room measurements.

I had never heard of Richard Pierce before meeting him here, and I have no
idea what he's done or what he knows. I gladly discuss these issues and
assess all points on their merit, without regard to who said them.

what you are claiming simply does not happen except in the most
pathologically horrendous rooms (think cube).

You are very wrong. The peaks and dips I describe happen in every home-sized
room with exactly the severity I described. And they happen at ALL
frequencies, not just those related to the room dimensions. It's a
surprisingly common misconception, even among acoustics people, that peaks
and nulls occur only at modal frequencies. Please do as I suggest and play
some sine waves and walk around. Also see this excellent article by studio
designer Wes Lachot:

www.recording.org/users/acoustics/waves_wl.html

--Ethan

On Sun, 7 Sep 2003 11:38:28 -0400, "Ethan Winer" ethan at ethanwiner
dot com wrote:

Dick,

Your grasp of acoustical physics is, well, underwhelming.

I freely admit that I am not a physicist nor a mathematician. But I am
technically minded, and I have plenty of practical hands-on experience with
this stuff.

Please, for the gathered crowd, show how high the Q of such a resonance
must be to make your assertion true.

You are confusing the Q of the frequency response at a given location with
the size of that location. If you find a spot in the room where the response
is down 15 dB at 100 Hz, a high Q will make the dip less severe at 101 Hz.
But even with a low Q the depth of the null can be very deep - theoretically
infinite - and the size of the "zone" where the null is that deep can be
very small. If you move away just a little from where the null is deepest
the level will come back up quite a bit.


You are confusing standing waves with bulk resonances. The change in
level along a standing waves - in a and out of nulls - is governed by
a Cosine law, as is normal with the amplitude of any two co-frequency
signals sliding over each other. So the change in level between two
points is not governed by an idea of a Q factor. The one aspect in
which the room makes a difference is in the depth of the null. For an
infinite null you need perfect reflectivity. For a deep null, you need
good reflectivity, and a parallel wall area big enough to reflect
essentially plane waves.

It is in the Helmholtz mode that a room can have a Q factor, and that
does not behave as you describe here.
EW: There's no way can you reduce reverb time with DSP.

RP: Wanna bet? Again, do you understand the principal of deconvolution?

You are correct that deconvolution involves complex math I do not
understand. But please explain in plain English the mechanism by which DSP
can remove echoes and reverb. I can see how DSP could create equal and
opposite echoes, and maybe even equal and opposite reverb (if you have a
Cray). But how could this be applied in a typical room and not suffer from
the "move your head one inch" restriction? This is the crux of the matter:
How is a complex solution having severe positional restrictions sensible,
when the problem can be solved better and much less expensively using bass
traps and fiberglass panels?

The room is simply a complex transmission line, with an amplitude and
delay response. If it can be measured, then its conjugate can be
synthesised and placed in series with the signal. It seems
counter-intuitive, but this does indeed result in the elimination of
all the unflatnesses and echoes that have been measured. How big a
volume of the room you can treat in this way depends on how high a
frequency you need to go to, and how bad the room is to begin with.
Certainly up to a couple of hundred Hz shouldn't be a problem, and if
you can't sort the room out otherwise above that frequency, you are
really in trouble.

And you STILL did not answer the question: how many listening rooms in
domestic situations suffer from the problems you describe?

All of them!

If the response in the room is linear, and it contains finite energy, it
is correctable.

Yeah, okay, theoretically for a tiny zone. But not only is the zone tiny,
for everyone outside the zone the correction will make things many times
worse.

--Ethan

d

_____________________________

http://www.pearce.uk.com

In article ,
Ethan Winer ethan at ethanwiner dot com wrote:
Dick,

Your grasp of acoustical physics is, well, underwhelming.

I freely admit that I am not a physicist nor a mathematician. But I am
technically minded, and I have plenty of practical hands-on experience with
this stuff.

Please, for the gathered crowd, show how high the Q of such a resonance
must be to make your assertion true.

You are confusing the Q of the frequency response at a given location with
the size of that location.

Sir, there is n such thing as "the Q of the frequency response."
The question I asked is perfectly valid

If you find a spot in the room where the response
is down 15 dB at 100 Hz, a high Q will make the dip less severe at 101 Hz.
But even with a low Q the depth of the null can be very deep - theoretically
infinite - and the size of the "zone" where the null is that deep can be
very small. If you move away just a little from where the null is deepest
the level will come back up quite a bit.

Sorry, sir, your statment is simply nonsensical mathematically.,

EW: There's no way can you reduce reverb time with DSP.

RP: Wanna bet? Again, do you understand the principal of deconvolution?

You are correct that deconvolution involves complex math I do not
understand. But please explain in plain English the mechanism by which DSP
can remove echoes and reverb. I can see how DSP could create equal and
opposite echoes, and maybe even equal and opposite reverb (if you have a
Cray).

Actually, modern DSP chips are far more effcieicnt at this sort
of thing than a general purpose Cray.

Beyond that, you have just stated that what you first claimed
impossible is in fact quite possible.

But how could this be applied in a typical room and not suffer
from the "move your head one inch" restriction?

BECAUSE YOU SIMPLY CANNOT HAVE A THE LEVEL OF SUCH CHNAGE OVER
THE SPACE OF AN INCH IF THE WAVELENGTH IS MANY FEET LONG.

You have already admitted you do not understand "complex math."
Are you admitting that you do not understand this as well?

How is a complex solution having severe positional restrictions sensible,
when the problem can be solved better and much less expensively using bass
traps and fiberglass panels?

That is NOT the crux of the issue: you have made a number of
incorrect and nonsensical technical assertions, and simply
failed to support them with anything other than reassertions

If the response in the room is linear, and it contains finite energy, it
is correctable.

Yeah, okay, theoretically for a tiny zone. But not only is the zone tiny,
for everyone outside the zone the correction will make things many times
worse.

Sir, you have now made this wrong statement at least a half
dozen times, and if you make it another half dozen, it will
STILL not get any less wrong.

--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |

In article ,
Ethan Winer ethan at ethanwiner dot com wrote:
about it. Take a sine wave oscillator or test tone CD and play it through
your system. Or a friend's system. Or a system in ANY room without adequate
acoustic treatment. Now walk around the room very slowly listening for drops
in level. You will immediately see that at any reasonable frequency (say, 80
Hz to 4 KHz) there are many locations that have severe drops in level, and
those locations are extremely restricted in size.

Moving your head even one
inch at mid/high frequencies is enough to go from full level to a nearly
complete cancellation.

Mr. Winer, this is MOST dishonest of you. You first stated in
your assertion that these nulles were extremely sharp at
frequencies of 70 Hz. Now, all of a suddenm you have TOTALLY
changed the scenario by stating that these phenomenon occur at
"mid/high frequencies."

I am sorry, but you've now gone from vagueness and imprecise
claims to simpl,y changing your assertions in midstram.

You have already admitted you do not understand the physics and
methematics that are crucial to the topic, what more is there
for you to admit?

I had never heard of Richard Pierce before meeting him here, and I have no
idea what he's done or what he knows. I gladly discuss these issues and
assess all points on their merit, without regard to who said them.

They are not my ideas, kinf sir, they are basic and fundamental
concepts of acoustics going all the way back to the wave
equation. YOu are arguing against that, and there's a couple of
centuries of pretty well-founded science and evdience that
suggests your assertions are way off the amrk.

--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |

Don,

the change in level between two points is not governed by an idea of a Q
factor.

But that's exactly what *I* said! That Q is a frequency bandwidth concept,
versus the physical size of the null zone and how far away you have to move
for the null to not be as deep.

this does indeed result in the elimination of all the unflatnesses and
echoes that have been measured.

But the echo level and arrival time is different for every location in the
room. Move one foot away and the arrival time changes by 1 millisecond. So
how many milliseconds would you have the DSP use to remove echoes for all
three seats on my living room couch? And how would the EQ boost that's
applied for my seat affect the seats on either side?

--Ethan

Thanks for the educational discussion on room correction. Much
appreciated.

Returning to my original question about treating loudspeaker
distortion with DSP, nobody mentioned whether there was a real product
available, even if it only tackled one tyupe of distortion (e.g.
harmonic distortion) and not all of the varied speaker distortions
mentioned. Any comment?

I would be quite satisfied to only treat one listening space in the
room. The problems of catering for multiple listeners do not
especially concern me. Although I noticed that pro EQ tools like SIA
Smaart sometimes can average corrections over a number of listening
positions, which may be useful for EQ work. But it may be a moot
point. If distortions emitted from the speaker (irrespective of their
origin in the audio reproduction chain) were being reduced, I thought
this improvement would not be dependent on listening position. Is that
right?

Grant


My original post:
================================================== ==================
I know DSP's are available for loudspeaker frequency response
compensation, typically combined with a non-time-coherent "room
correction" function.

Is anything similar available for treating loudspeaker distortion?
(actually whole-of-system distortion, but measured as what comes out
of the speaker and hopefully dominated by the speaker's distortion
contribution).

I don't mean a research tool for speaker designers. I mean something
that can be used in the home or studio to reduce distortion from
existing systems.

Stand-alone or PC-based.

I imagine something that fits in the audio chain between the sound
source and the amplifier. It might generate its own test signals and
analyse the speaker output through a microphone. It could treat
harmonic distortion by mapping a number of harmonics of measured
distortion against signal amplitude against signal frequency. It could
then generate a compensating map of out-of-phase harmonics. Then when
playing music through the system, it could apply the compensating map
real-time to the incoming music signal.

Of course it would be sensible to combine such a function in the same
DSP as is used for frequency response compensation.

Am I dreaming, or describing a real product?
================================================== ==================

On Sun, 7 Sep 2003 11:27:06 -0400, "Ethan Winer" ethan at ethanwiner
dot com wrote:

Stewart,

what do you charge for your 'audiophile' room treatments, and what do they
look like? Ethan, you're a troll attempting to push your room treatments on
people who don't know any better. This is probably not the best place to
make your sales pitch.

That's not true, and it's unfair to accuse me of that. What's your
affiliation, BTW?

I don't think that I was the one who said that, and I have no
commercial interest in audio. You OTOH certainly do, so perhaps you
are indeed just trying to 'knock' DSP room-correction. My take is
pretty much the same as Arny's - find a good room, give it some basic
acoustic treatment, and leave the LF stuff to DSP.

I've been championing the importance of acoustic treatment since the late
1970s. I've been selling bass traps and broadband absorbers for less than a
year. I jumped into this thread only because it irks me to see half-baked
solutions touted as workable. The original poster accepted the claim that
DSP is a reasonable way to cure the peaks and dips caused by acoustic
interference, and that's what I addressed.

Unfortunately for your argument, DSP in fact *is* a reasonable way to
cure the peaks and dips caused by acoustic interference.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Sun, 7 Sep 2003 11:43:49 -0400, "Ethan Winer" ethan at ethanwiner
dot com wrote:

Stewart,

EW: An acoustic null in a room is very sharp - both in frequency and the
location where the level is at a minimum.

SP: Actually no, it isn't in any halfway reasonable domestic environment.


Yes, it really is. And it's so easy to prove I don't know why we're arguing
about it. Take a sine wave oscillator or test tone CD and play it through
your system. Or a friend's system. Or a system in ANY room without adequate
acoustic treatment. Now walk around the room very slowly listening for drops
in level. You will immediately see that at any reasonable frequency (say, 80
Hz to 4 KHz) there are many locations that have severe drops in level, and
those locations are extremely restricted in size. Moving your head even one
inch at mid/high frequencies is enough to go from full level to a nearly
complete cancellation. At low frequencies the size of the null zone is
larger, but still very small - if you move to the adjacent seat on the couch
the level can change many dB.

Thgis is utter rubbish. Firstly, you will *never* exceed a 10dB
difference in any normal domestic living room, secondly, moving your
head an inch at 4kHz will certainly *not* achieve anything approaching
a complete cancellation in any real-word room, and thirdly, at low
frequencies (which I'll take to be less than 100Hz) you would have to
move about three feet to go from reinforcement to partial cancellation
- and even then there won't be 'many dB' of difference. As you say,
this is trivially easy to prove with an oscillator and a microphone.

EW: So boosting a low frequency by 15 dB will cause a big increase in
that frequency nearby in the room where the naturally occurring null is not
so deep.

SP: Could we have that again, in English please?

Let's say at the listening position you measure a 15 dB dip at 80 Hz. So you
set the room EQ to boost 80 Hz by 15 dB. Now in that precise spot the level
at 80 Hz is back to normal. But now in the adjacent seat the level is 8 dB
higher than normal because the dip was only 7 dB there initially, but that
location is also receiving the 15 dB of EQ boost.

However, you will *never* find a 15dB null in any normal domestic
living room.

I would *strongly* suggest that you avoid intimating that Dick Pierce has
not 'been there and done that' regarding loudspeaker or room measurements.

I had never heard of Richard Pierce before meeting him here, and I have no
idea what he's done or what he knows. I gladly discuss these issues and
assess all points on their merit, without regard to who said them.

Actually, you are doing no such thing in this thread, as Dick has
pointed out on several occasions. You are ducking, diving and spraying
wild assertions all over the place, none of which bear any relation to
very well known acoustic principles.

what you are claiming simply does not happen except in the most
pathologically horrendous rooms (think cube).

You are very wrong. The peaks and dips I describe happen in every home-sized
room with exactly the severity I described.

No, that is simply *not* the case.

And they happen at ALL
frequencies, not just those related to the room dimensions.

Absolute garbage. These effects may be *noticeable* at a few tens of
Hertz, but they rapidly avearage out by the lower midrange, except in
the most pathologically unrealistic rooms, such as a concrete and
glass commercial property.

It's a
surprisingly common misconception, even among acoustics people, that peaks
and nulls occur only at modal frequencies. Please do as I suggest and play
some sine waves and walk around.

I've been there and done that on several occasions. You are talking
rubbish.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Stewart,

you will *never* find a 15dB null in any normal domestic living room.

Please see my other post.

No, that is simply *not* the case.
Absolute garbage.
You are talking rubbish.

C'mon Stewart, tell us how you REALLY feel!

:-)

--Ethan

Grant,

nobody mentioned whether there was a real product available, even if it
only tackled one tyupe of distortion

The closest thing I'm aware of is the pre-distortion scheme for analog tape
I already mentioned. Other than something like that, or what Mackie appears
to do putting the speaker voice coil in the power amp's feedback loop, I'm
not aware of any such commercial devices. Not that there isn't or couldn't
be such a device.

SIA Smaart sometimes can average corrections over a number of listening
positions, which may be useful for EQ work.

Averaging is really not as useful as you might think. This was discussed in
detail recently in John Sayers' acoustics forum
(www.johnlsayers.com/phpBB2/index.php, Studio Design section) where a
similar "discussion" erupted over the validity of pink noise versus sine
wave testing. The problem with pink noise is that it averages all
frequencies within a third octave (usually) band. But within a single band
there could be a deep null and also a big peak. So the averaged measurement
shows a reassuringly flat response that *completely hides* response
variations as large as 20 dB!

--Ethan

"Stewart Pinkerton" wrote in message
...

On Sun, 7 Sep 2003 11:43:49 -0400, "Ethan Winer" ethan at ethanwiner
dot com wrote:

Yes, it really is. And it's so easy to prove I don't know why we're
arguing
about it. Take a sine wave oscillator or test tone CD and play it through
your system. Or a friend's system. Or a system in ANY room without
adequate
acoustic treatment. Now walk around the room very slowly listening for
drops
in level. You will immediately see that at any reasonable frequency (say,
80
Hz to 4 KHz) there are many locations that have severe drops in level,
and
those locations are extremely restricted in size. Moving your head even
one
inch at mid/high frequencies is enough to go from full level to a nearly
complete cancellation. At low frequencies the size of the null zone is
larger, but still very small - if you move to the adjacent seat on the
couch
the level can change many dB.

Been there, done that, it works. I'm not sure I've seen this work well as
high as 4 KHz, but I've definitely seen strong effects at 400 Hz.

This is utter rubbish. Firstly, you will *never* exceed a 10dB
difference in any normal domestic living room, secondly, moving your
head an inch at 4kHz will certainly *not* achieve anything approaching
a complete cancellation in any real-word room, and thirdly, at low
frequencies (which I'll take to be less than 100Hz) you would have to
move about three feet to go from reinforcement to partial cancellation
- and even then there won't be 'many dB' of difference.

Been there, done that and seen and heard the nulls. Not complete nulls, but
20-30 dB nulls, easy. It's a simple experiment since all you need is a pure
sine wave source.

As you say,
this is trivially easy to prove with an oscillator and a microphone.

Yes, and Ethan describes a relevant experiment in another post and I've done
similar things.

EW: So boosting a low frequency by 15 dB will cause a big increase in
that frequency nearby in the room where the naturally occurring null is
not
so deep.

SP: Could we have that again, in English please?

Let's say at the listening position you measure a 15 dB dip at 80 Hz. So
you
set the room EQ to boost 80 Hz by 15 dB. Now in that precise spot the
level
at 80 Hz is back to normal. But now in the adjacent seat the level is 8
dB
higher than normal because the dip was only 7 dB there initially, but
that
location is also receiving the 15 dB of EQ boost.

However, you will *never* find a 15dB null in any normal domestic
living room.

I wish. If you measure with pure tones, you will find nulls deeper than
that. However, the relevance of a single null is questionable. This is a
major reason why swept tones, warble tones, and noise and other means are
popularly used for measuring the frequency response of loudspeakers in
reverberant rooms.

I would *strongly* suggest that you avoid intimating that Dick Pierce
has
not 'been there and done that' regarding loudspeaker or room
measurements.

I can only presume that people are agreeing loudly or missing the meaning of
words and sentences.

I had never heard of Richard Pierce before meeting him here, and I have
no
idea what he's done or what he knows. I gladly discuss these issues and
assess all points on their merit, without regard to who said them.

IME Dick Pierce is a trustworthy source of audio knowledge. But, so is Ethan
Winer.

I've learned from life that it's not always correct to presume that when two
people appear to disagree, that one of them is absolutely wrong. FWIW George
Middius, Ed Shain and David Weil among others used to play this childish
game on RAO with JJ and I, and as wrong as it was then, its at least that
wrong here, now.

Let's stick to the facts, eh?

Arny,

the relevance of a single null is questionable. This is a major reason why
swept tones, warble tones, and noise and other means are popularly used

See my other post about the suitability of sine waves for testing. In fact,
I have lately come to the conclusion that sine waves are perhaps the ONLY
worthwhile test if you really want the brutal truth about a room. The
problem with pink noise and swept sine waves, unless they are very narrow
and swept very slowly, is too many different frequencies are all lumped
together in one measured band. As you know, just a couple of Hertz is enough
to make a large difference in the response. I can measure 15 dB nulls in my
room all day long, yet a pink noise test shows my room as being flat within
just a dB or two across most of the range. I love showing the pink noise
graph to my friends, but I know it's pure fiction! :-)

Let's stick to the facts, eh?

Yes. Thanks for keeping that in the forefront.

--Ethan

Arny,

AFAIK current "revealed truth" among those who *know* is that 1/12 octave
is warranted.

I doubt even 1/12th octave is narrow enough. Here's a figure from my
Acoustics FAQ showing what my partner and I measured in his 10x16 foot
control room using sine waves:

www.ethanwiner.com/response.gif

Look at the region starting at 125 Hz in the top half. If you measure first
at 160 Hz and then 1/12th octave above that (169.5 Hz) you'll have gone from
a deep null to its adjacent peak. So at those frequencies in that room
you'll get the results expected. But in a room where the peaks and dips
start just a few Hertz lower or higher, readings at those same frequencies
will measure flat because one reading is on the upside and the other is on
the downside. And that completely hides the 10 dB difference that's actually
present.

--Ethan

"Ethan Winer" ethan at ethanwiner dot com wrote in message
...
Arny,

Please get back when you do some sine-wave measurements of your own. You
might be surprised!

Yes, and I'm still hoping some of the other naysayers will try it too.


It sure did get quiet around here, all of a sudden...

;-)

Ethan Winer wrote:
[...]
And again, even if the frequency response errors can be corrected with EQ,
that does nothing for the lack of clarity on notes played by bass
instruments dues to excessive LF reverb.

And again, the process implemented using DSP is not EQ in the sense
you are thinking. But you are certainly free to believe whatever you
wish.
--
% Randy Yates % "...the answer lies within your soul
%% Fuquay-Varina, NC % 'cause no one knows which side
%%% 919-577-9882 % the coin will fall."
%%%% % 'Big Wheels', *Out of the Blue*, ELO
http://home.earthlink.net/~yatescr

Randy,

the process implemented using DSP is not EQ in the sense you are thinking.
But you are certainly free to believe whatever you wish.

Then talk to me! :-)

If I'm missing something important, explain so I'll learn. Don't just hit
and run. And explain How and What room correcting DSP can do, not just say
"It fixes the problems" because that explains nothing. If you were to ask me
how bass traps and absorbers solve room problems, I could easily explain it
in great detail!

Room nulls are very deep and they change depth and frequency over very small
distances. So I can't see how electronics can compensate unless you put your
head in a vise, which no sane person would accept. Last week the group
argued whether nulls are really that deep and change 15-20 dB over a few
inches. The premise being that DSP doesn't need to correct for such serious
anomalies. I showed that all rooms do in fact vary that much over tiny
distances, so now the burden is back on the DSP promoters to explain how
such severe nulls can be corrected for all listeners on the couch.

Severe nulls are just the start. Much harder to solve are echoes and reverb.
How can DSP remove echoes and reverb that are floating around a room for
more than a pinpoint sized area? This is the crux of it. Explain that
sufficiently and you'll be well on your way toward convincing me. Heck, you
don't have to explain anything at all - just tell me where I can audition
one of these things in a lousy sounding room so I can switch the DSP on and
off and hear the change for myself. My ears are very attuned to poor rooms
and how they sound after adding bass traps and other treatment. If a DSP
solution can really do the same thing, I'll change my opinion on a dime the
moment I hear it.

--Ethan

Ethan Winer wrote:

Randy,

the process implemented using DSP is not EQ in the sense you are thinking.
But you are certainly free to believe whatever you wish.

Then talk to me! :-)

If I'm missing something important, explain so I'll learn. Don't just hit
and run. And explain How and What room correcting DSP can do, not just say
"It fixes the problems" because that explains nothing. If you were to ask me
how bass traps and absorbers solve room problems, I could easily explain it
in great detail!

Is it not possible that a topic may be complex enough that one or two usenet news
postings won't even come close to describing it in enough depth that one really
understands it?

This type of topic is usually covered in a one-semester engineering course called
"Linear System Theory" or "Fourier Transforms" or some such. The relevent concepts
involved are the definition of a linear, time-invariant system, the description
of such systems by their impulse response, the operation of such systems through
the operation of convolution (in the time domain), and various properties such
systems (e.g., causality, stability, invertibility, etc.), and various properties
and elementary results of Fourier transforms (both discrete-time and continuous-time).

If you really want to understand at this level, I suggest you read the relevent
parts of the book "Signals and Systems" by Oppenheim et al. There is a more
recent equivalent by this author, "Discrete-Time Signal Processing," but I much
prefer the older book.

Also, I have stated in no uncertain terms that such a system is going to be
listener-position dependent. Why do you insist on asking me to describe a
solution which is not?

Ethan, I don't mean to be rude or excessively inaccessible, but really - why
must everything be elementary? It ain't. Besides, I DID attempt to lead you
to the path of understanding by throwing out a few of the concepts (e.g.,
convolution), but it (understandably) didn't stick.
--
% Randy Yates % "...the answer lies within your soul
%% Fuquay-Varina, NC % 'cause no one knows which side
%%% 919-577-9882 % the coin will fall."
%%%% % 'Big Wheels', *Out of the Blue*, ELO
http://home.earthlink.net/~yatescr

Y'know, several days ago, someone made a comment about how this
thread has suddenly gone silent, as if it was somehow a sign
that the other side had somehow lost.

In article ,
Rusty Boudreaux wrote:
"Ethan Winer" ethan at ethanwiner dot com wrote in message
...
If I'm missing something important, explain so I'll learn.
Don't just hit and run. And explain How and What room
correcting DSP can do,

Like Dick Pierce and others have said, deconvolution.

Like Randy Yates said, and like many others have said, if Mr.
Winer would just take the time to explore beyond his narrow
viewpoint.

Measure the impulse response of a room, invert it, and convolve
with the incoming audio. If done properly with enough horsepower
you get perfect results at ANY point in the room.

To "deconvolve" the acoustics of a room:
y(n)=hroom(z)*x(n)

http://www.isip.msstate.edu/publicat...e_4773/lecture
s/current/lecture_19/

Here's some recorded examples of correcting audio from a very
echoy lounge. The program was written by an undergrad EE student
for a class...so this is far from perfect...but it will show how
reverb and echos are reduced.

http://www.cs.caltech.edu/~ashman/ee...oject107c.html

More explanations:
http://www.clsp.jhu.edu/seminars/abs...997/soong.html
http://www.cs.tut.fi/~temmi/MSc_Thesis/Abstract.html
http://www.iop.org/EJ/abstract/0957-0233/12/1/311
http://www.google.com/search?q=audio+deconvolution

So I can't see how electronics can compensate unless
you put you head in a vise, which no sane person would accept.

Yes, it has become quite apparent that you can't see this, and
that's where your problem is. YOu have, again no insult
intended, a VERY limited view of this topic, and you can't see
beyond so thus you assume there is nothing beyond it to see.

distances, so now the burden is back on the DSP promoters to
explain how such severe nulls can be corrected for all
listeners on the couch.

No. The burden is on you to research and understand
deconvolution.

Indeed, the "DSP promoters" HAVE already done that, and there
is extensive description of this in the literature should you
care to engage in the effort. People like myself are NOT going
to do it in this forum because it is a complex topic that
also requires some willingness on the other participant to do
the work.

Severe nulls are just the start. Much harder to solve are
echoes and reverb.

Nope, just deconvolve the room. Done.

How can DSP remove echoes and reverb that are floating around a
room for
more than a pinpoint sized area?

Deconvolution.

Mr. Winer, does the word "deconvolution" sound at all familiar?

Now, to see if you HAVE done the work necessary for you to
understand the process, see if you can answer this question:
deconvolution techniques can be made to work quite well for
small rooms, but a heretofore undiscussed property makes the
solution for very large acoustic spaces (such as cathedrals,
auditoria, stadia) much more difficult. And, as a hint, it's
not, per se, a CORRECTION problem by a measurement problem that
is based on the assumption of stationary signals.

If you can understand even the question, you're halfway there.

Now, go do the homework.

--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |

Randy,

Is it not possible that a topic may be complex enough that one or two
usenet news postings won't even come close to describing it in enough depth
that one really understands it?

All I'm asking for is an explanation of the concepts, not for you to hold my
hand through a bunch of higher math. When someone truly understands an
advanced process, they should be able to explain the basics in plain
English. For example, if the DSP you promote works be creating equal and
opposite echoes, then say so. Or say whatever it does do. Over the years
I've been guided by people a lot smarter than me, and the one common trait
all the real experts shared was being able to explain complex matters in
simple terms. I now strive to do that myself, to help others who know less
than me. See my mini-book "The Hardware Tutor" where I explain the basics of
analog and digital electronics in mechanical terms with no math. It's about
1/3 of the way down the page on my Articles page:

www.ethanwiner.com/articles.html

If you really want to understand at this level

No, I really don't. All I want is a plain-English explanation. Or just tell
me where I can hear such a system at work. Do stores demo these things?

I have stated in no uncertain terms that such a system is going to be
listener-position dependent. Why do you insist on asking me to describe a
solution which is not?

Because if this system is dependant on the listenener remaining in one very
small place, then it is not viable! It may work in theory, but it's destined
to remain more of a technical curiosity than a practical solution. I have
asked repeatedly how wide an area can be realistically included in the
correction zone, and all I've gotten back is "it depends." That would be an
acceptable answer if it also included a range. Like, "We've been able to
perfectly correct an area 3x8 feet in a room that's at least 20x30 feet." Or
whatever.

Remember, this all started when I objected to the notion that DSP is a
PRACTICAL solution to room problems. Then y'all insulted me, and claimed
it's physically impossible for a null to vary by 15 dB across four inches. I
hope you're not still disputing that!

Don't get me wrong, I love science and math and theory. And I'm here to
learn too. But we all must be able to disinguish a cool lab experiment from
a practical solution.

--Ethan

Richard D Pierce wrote:

Y'know, several days ago, someone made a comment about how this
thread has suddenly gone silent, as if it was somehow a sign
that the other side had somehow lost.

In article ,
Rusty Boudreaux wrote:
"Ethan Winer" ethan at ethanwiner dot com wrote in message
...
If I'm missing something important, explain so I'll learn.
Don't just hit and run. And explain How and What room
correcting DSP can do,

Like Dick Pierce and others have said, deconvolution.

Like Randy Yates said, and like many others have said, if Mr.
Winer would just take the time to explore beyond his narrow
viewpoint.

Measure the impulse response of a room, invert it, and convolve
with the incoming audio. If done properly with enough horsepower
you get perfect results at ANY point in the room.

To "deconvolve" the acoustics of a room:
y(n)=hroom(z)*x(n)

http://www.isip.msstate.edu/publicat...e_4773/lecture
s/current/lecture_19/

Here's some recorded examples of correcting audio from a very
echoy lounge. The program was written by an undergrad EE student
for a class...so this is far from perfect...but it will show how
reverb and echos are reduced.

http://www.cs.caltech.edu/~ashman/ee...oject107c.html

More explanations:
http://www.clsp.jhu.edu/seminars/abs...997/soong.html
http://www.cs.tut.fi/~temmi/MSc_Thesis/Abstract.html
http://www.iop.org/EJ/abstract/0957-0233/12/1/311
http://www.google.com/search?q=audio+deconvolution

So I can't see how electronics can compensate unless
you put you head in a vise, which no sane person would accept.

Yes, it has become quite apparent that you can't see this, and
that's where your problem is. YOu have, again no insult
intended, a VERY limited view of this topic, and you can't see
beyond so thus you assume there is nothing beyond it to see.

distances, so now the burden is back on the DSP promoters to
explain how such severe nulls can be corrected for all
listeners on the couch.

No. The burden is on you to research and understand
deconvolution.

Indeed, the "DSP promoters" HAVE already done that, and there
is extensive description of this in the literature should you
care to engage in the effort. People like myself are NOT going
to do it in this forum because it is a complex topic that
also requires some willingness on the other participant to do
the work.

Severe nulls are just the start. Much harder to solve are
echoes and reverb.

Nope, just deconvolve the room. Done.

This sounds very interesting. How is this done in practice?
Are there products available that would allow an audiophile to do this
and about how much would it cost?

George Deliz

In article ,
Ethan Winer ethan at ethanwiner dot com wrote:
Richard,

as if it was somehow a sign that the other side had somehow lost.

My goal is not to argue and "take sides." And I've said repeatedly that I'm
here to learn. But are you still maintaining that peaks and nulls cannot
vary by 15 dB across a span of four inches?

Now, Mr. Winer, I did not say that, did I?

What I said was in direct refutation of YOUR claim of such
variations at 70 Hz over a span of one inch.


--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |

In article ,
Ethan Winer ethan at ethanwiner dot com wrote:
Thanks. The math is way over my head, but I did glean this nugget from one
of those referenced pages:

"However, in the above single- and multi-channel approaches, the requirement
that the room impulse response needs to be identified first renders the
solution not readily applicable to a real situation."

What that means is that there is no such thing as a one-size-
fits-all solution. Since the impulse response contains all the
information needed to fully characterize the linear response of
ANY system, and since each system (i.e., room) has its own
unique impulse response, you need to measure the impulse
response for that room.

--
| Dick Pierce |
| Professional Audio Development |
| 1-781/826-4953 Voice and FAX |
| |