[Mike Rivers]

On 2/9/2012 12:54 PM, wrote:

Mxmanic is doing this as a hobby, no doubt because he found
low cost software which permits him to dabble, and now
thinks it qualifies him to tell professionals how they
should be doing their jobs.

Not really. He's telling us how he'd solve a problem if only
his tools would work the way he expects them to work . . .
which they don't, quite.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mxsmanic]

Frank Stearns writes:

I'm amazed at the number of recordings showing a 15,750 hz spike from a CRT
monitor.

Really? That's pretty interesting. I used to be able to hear that sound from
CRTs. Nowadays they have much higher scan rates, so I don't hear it very often
(but I can still hear it on headphones, so it's not my ears). Surprisingly,
even when I was a teenager, most people couldn't hear it--I'd walk into a
classroom and ask why the TV was still on, even though there was no picture,
and people thought I was imagining things. Which makes it hard to understand
how a so-called Mosquito is really supposed to work.

Anyway, it's interesting that the sound of nearby CRTs is getting recorded.
Surely that has declined somewhat with the advent of flat panels, though,
right?

Heck, even one of my own pipe organ recordings managed to acoustically pick up
15,200 hz or so from a closed-circuit 9" video monitor that was up on the organ
console. The organ was a tracker, which meant the console was part of the organ, and
the organ was way up in a loft. The monitor allowed the organist to watch a
conductor's position down on the main floor of the church. The monitor was probably
1970s vintage; seems high-volume flyback noise was pretty common in those days.

And easier to hear when the CRT had no signal, because the free-running
horizontal scan rate was somewhat lower than the synchronized rate.

First video production room I walked into -- with all those various CRTs -- made my
eyes water and my teeth hurt because of all the flyback noise.)

I've had similar experiences. I've been in equipment rooms filled with modems
that had similar high-frequency noise, although I don't know where it came
from. Mainframe computers used to make a lot of noise like this, too.

But a few things to consider: I don't think very many folks hear a flyback spike
embedded in a recording -- they're typically 20-40 dB down, and usually well-masked
by lots of energy at surrounding frequencies.

I don't recall ever hearing it on music. I seem to remember hearing it on
other types of recordings.

Even with the narrowest Q you might have on an EQ, it's damn near impossible to
notch out a single frequency like that. A 1/12 octave notch at 15K is going to put
quite a dip in your spectrum up there -- and you *will* hear that, whereas the
single offending freq you well might not.

It's something that I will look for. And it's the sort of thing that I'd want
to remove, which is what might make a spectrum analysis handy, since 15 kHz
can be hard to hear.

The analyzer can also help you find system problems. I had a noisy full-sine UPS
that was putting out spikes at 19.5K and 26K and sometimes (oh the horror) 10.5K.
Worse, it was injecting this crap into the building ground! Zooming in I saw
additional "sidebands" on these spikes at 60 and 120 Hz intervals. The spectrum
analyzer was a very useful tool to investigate this.

What do you do when you have a recording with that kind of noise?

To their discredit, the issue was never resolved and the UPS was abandoned in favor
of lighter, cheaper systems that were dead quiet, even when fully powering the
loads. (I've also seen that 19.5K spike in a few other commercial recordings; I'm
guessing they had the same defective UPS running during the recording!)

I didn't think that audio systems had a need for UPS systems, unless it's
really, really important to hear the entire song.

[Mxsmanic]

Mike Rivers writes:

You can't say "the guitar is out of tune?

I guess I could, but I don't know how to tune it.

Also, sometimes the errors are more complex, and I'm not sure who is making
the mistake. In some cases, the "mistakes" are deliberate, as when the
Manhattan Transfer sings "A Nightingale Sang in Berkeley Square," which
contains a lot of unusual intervals.

Well, you see, there are tools for people like you who want
to make music but don't have the skills or experience.

I'm a music listener, rather than a music maker. I record ambient sounds or
speech, mostly, for my little touristy videos. Indeed, I avoid recording any
kind of music, because copyright trolls on YouTube will latch onto it to make
fraudulent infringement claims.

This is true. That principle is even used in warfare. Make
the enemy want to **** and he'll have something else on his
mind than fighting a war. But think: How is such a sound
going to creep into your recording?

That's the mystery. When I record street scenes, I see an awful lot of
low-frequency noise, but I have no idea where most of it is coming from. In
real life, I also hear it (based on comparisons I've done), but for whatever
reason, I don't notice it as much. Really low frequencies seem to be something
that you notice unconsciously, even when you can hear them.

Somebody could hear it, probably a lot of people could.

I recall it being around 30 kHz, so the number of people actually hearing it
would be too small to explain a general restlessness. But maybe it affected
them in some other way than through hearing alone. Apparently it was very
loud.

Maybe there was no engineer manning the controls. Maybe
there was and he couldn't hear it. Maybe he could hear it,
did everything he could to eliminate or reduce it and still
couldn't get rid of it.

In the story I read, someone looked at a graphic equalizer or something and
noticed a huge spike at a very high frequency.

I used to do shows in an auditorium in a Government building
where, every hour, something would be sent along the power
lines to correct all the clocks. It caused a whistle in the
PA system for about 30 seconds and then it was gone. I
noticed it, as did some people in the audience. They
probably thought I did something to cause it.

Thank goodness we don't need systems like that now, although they are probably
still in use. There are other gadgets that send junk over power lines, too. I
guess nobody worries about interference.

And the way to do that is to know that your equipment is
working properly and simply not make noises like that.

But sometimes the noise is coming from something that isn't yours, and it's a
surprise.

But what you're talking about is a problem that you can
eliminate at the source. Using a spectrum analyzer to find
it after the fact is only helping you to put a Band Aid on
it, not fix the problem.

For field recordings, I don't have a spectrum analyzer handy.

Yeah, but can you dance to it? For a realistic perspective,
check out Flanders & Swann's "A Song of Reproduction."

http://youtu.be/7fJmmDkvQyc

Well, places like discos already use similar concepts. But you could design
something much more detailed, like a spectrum analyzer, that would provide
enough information to understand things like speech, for a trained observer.

[Mxsmanic]

Mike Rivers writes:

I know many audio engineers, both live and studio, that have
hearing loss and still manage to do good work. They don't
look at a spectrum analyzer to see what they can't here,
though.

So what do they do? And did they damage their hearing from their work, or did
they lose it for other reasons?

But the best way to handle
problems like "loud noise at 18 kHz" is to avoid them in the
first place. Where might such a noise enter the recording
process? It isn't likely to come from anyone's vocal cords
or an instrument. It likely means something is broken.

Well, if the room is filled with old-style CRTs, what can you do?

[Mxsmanic]

writes:

Mxmanic is doing this as a hobby, no doubt because he found
low cost software which permits him to dabble ...

... and now thinks it qualifies him to tell professionals how
they should be doing their jobs.

No. But I do notice that some professionals who lack confidence in their own
abilities feel threatened any time someone they consider external to the
profession starts to ask questions or make any assertions at all. Those who
are not insecure remain undisturbed.

This is true in many, many professions, not just professional audio. There are
always a lot of people who aren't as competent as they'd like people to think,
and apparently they worry about being "exposed."

Finally for Mxmanic: Folks such as MIke and i aren't just
trying to urniate in your cornflakes just to have something
to do. Neophytes lurk here for useful information, and
they're endeavoring to put their product out before the
public, even if self produced and self engineered. Hence,
we have to do whatever we can to dispel myths and
misinformation. I'm not the gentlest at doing so. Sorry
'bout that.

I am impervious to taking offense, so you need not worry. I know what I know,
and I also have an excellent idea of what I don't know.

[Mxsmanic]

Richard Webb writes:

Have you ever mixed live for broadcast or for paying customers?

No.

Did you just decide to dabble in audio once you found low cost
software? I'd guess the later.

I don't know that dabble is the right word, but I do take an interest in many
technologies, including audio recording, and the availability of low-cost
equipment of good quality has allowed me to investigate audio recording to a
much greater extent than I would have been able to forty years ago, without
having to dedicate my professional life to it to do so.

IN the era that Mike's referencing most folks didn't have
spectrum analysis tools readily available as I said, ears
and the monitoring chain were what was used to make those
decisions. Mike is one of us in this group who's made his
daily bread working in audio, and we got some neophyte
basement tinkerer going to tell him he's full of ****?

If my posts bother you, don't read them. There are plenty of other people who
know what they are talking about and don't mind discussing their work with
neophytes.

Still, if you're going to cause money to change hands you need a better
monitoring chain it sounds like.

The only money that has changed hands has gone from my hands into the hands of
audio equipment dealers, and my budget is very small.

... if you're playing and tinkering for your own good time, have at it,
but expect the professionals in this group to challenge such assertions
when you make them here.

That's fine with me, and it would certainly be more productive than your
sophomoric invective, which wastes both my time and yours.

[Mxsmanic]

Arny Krueger writes:

Been there done that, but we're talking *really* loud, like over 120 dB SPL.
That doesn't happen with recordings, as a rule. For openers, they rarely get
played that loud, and in many cases if they were played that loud, the 30
KHz tone that created 120 dB SPL would quickly fry the tweeter, which has
happened in the real world.

I don't recall the specifics of the (apocryphal) story I read, but it did
mention that the very-high-frequency noise was also very loud. The one thing
it didn't explain is where a noise like that could have been coming from, as I
recall.

[[email protected]]

Mike Rivers writes:
On 2/9/2012 12:54 PM, wrote:
Mxmanic is doing this as a hobby, no doubt because he found
low cost software which permits him to dabble, and now
thinks it qualifies him to tell professionals how they
should be doing their jobs.
Not really. He's telling us how he'd solve a problem if only
his tools would work the way he expects them to work . . .
which they don't, quite.

Yep, that too, and in a group frequented by folks in
production, especially that might be visited by those who
are learning it's important to dispel such misconceptions.
Note the recent thread on the pro-audio list re audio snake
oil.

What we have here is a man who has only one tool, and that's
a hammer, so everything appears to require a sharp blow.

Can't recall where I first heard it but, "when the only tool
you have is a hammer everything begins to look like a nail."

He does bring up an interesting point, older crt devices. I
was thinking more along the lines of misadjusted tape
machine as was Frank in one post.
Regards,



Richard webb,

replace anything before at with elspider

[Frank Stearns]

Mxsmanic writes:

Frank Stearns writes:

I'm amazed at the number of recordings showing a 15,750 hz spike from a CRT
monitor.

Really? That's pretty interesting. I used to be able to hear that sound from
CRTs. Nowadays they have much higher scan rates, so I don't hear it very often

That, and better construction of the deflection yokes. But CRTs are so last-century.
Not that many around any more, but you still find them, like that pipe organ
monitor.

Anyway, it's interesting that the sound of nearby CRTs is getting recorded.
Surely that has declined somewhat with the advent of flat panels, though,
right?

There are a few different paths where flyback can get into a recording:

1. acoustically, through microphones. That's fairly rare, as the monitor will have
to be in pretty crappy shape to put out that much acoustical volume, the mics have
to be pretty good and in just the right spot. Move a small diaphram mic 1/4" to
1/2" and you'd see the 15.75K level swing probably some 30 dB. A large diaphragm
would have less variance, though probably a good 3-6 dB. (15.75K has a wavelength of
0.86 inches). A lot depends on how the sound is radiated from the monitor.

2. Inductively or electrostatically by way of unbalanced (or poorly balanced)
circuits going near a monitor.

3. Infiltration due to bad grounds or other poor practices in the facility. Older
wiring can introduce a series of potential "gotchas".

How can you tell how the spike got in? Generally, if acoustically, you'll typically
see the spike bouncing around in amplitude. If electronically, typically the spike
is rock solid and does not vary in amplitude. This is what I've typically seen when
commercial recordings have it. There were one or more CRT monitors or TVs in the
studio or machine room or some place, dumping crap into a susceptable audio circuit.
(And you can believe that a lot of even famous studios have some pretty
"interesting" wiring practices.)

But a few things to consider: I don't think very many folks hear a flyback spike
embedded in a recording -- they're typically 20-40 dB down, and usually well-masked
by lots of energy at surrounding frequencies.

I don't recall ever hearing it on music. I seem to remember hearing it on
other types of recordings.

Music will usually mask the flyback, unless it's really, really bad. Spoken word or
solo instruments with not a lot of HF content would be less able to mask such noise.

Even with the narrowest Q you might have on an EQ, it's damn near impossible to
notch out a single frequency like that. A 1/12 octave notch at 15K is going to put
quite a dip in your spectrum up there -- and you *will* hear that, whereas the
single offending freq you well might not.

It's something that I will look for. And it's the sort of thing that I'd want
to remove, which is what might make a spectrum analysis handy, since 15 kHz
can be hard to hear.

Well, you might find it very difficult to remove. To minimize sonic damage you'd
need a notch filter with something like a 1/1000 (or smaller) octave width. I am not
a DSP expert; not even sure if you can do that.


The analyzer can also help you find system problems. I had a noisy full-sine UPS
that was putting out spikes at 19.5K and 26K and sometimes (oh the horror) 10.5K.
Worse, it was injecting this crap into the building ground! Zooming in I saw
additional "sidebands" on these spikes at 60 and 120 Hz intervals. The spectrum
analyzer was a very useful tool to investigate this.

What do you do when you have a recording with that kind of noise?

At 19.5K, we lived with it. It was actually discovered by a friendly competitor with
his S.A.; darn decent of him to let me know. The 15.75 was never audible.

To their discredit, the issue was never resolved and the UPS was abandoned in favor
of lighter, cheaper systems that were dead quiet, even when fully powering the
loads. (I've also seen that 19.5K spike in a few other commercial recordings; I'm
guessing they had the same defective UPS running during the recording!)

I didn't think that audio systems had a need for UPS systems, unless it's
really, really important to hear the entire song.

That's not the issue. The UPS is used during location recording. If you only have
one shot at something, you don't want a recording hardware glitch due to a momentary
power company hiccup (or outright outage), nor some idiot accidently switching off
the AC outlet used for your gear or disconnecting your AC cord. After hundreds and
hundreds of location gigs, all of the above have happened at one time or another --
not often but they did. The USP saved the day each time. Without it there would have
either been a hole in the recording or a complete loss. Oh, and as a side
benefit, most UPS provide basic power filtering and protection. THAT'S why I carry a
UPS!

Frank
Mobile Audio

--

[Trevor]

"Arny Krueger" wrote in message
...
A loud ultrasonic noise could still affect listeners, even if they
couldn't actually hear the sound.

Been there done that, but we're talking *really* loud, like over 120 dB
SPL. That doesn't happen with recordings, as a rule. For openers, they
rarely get played that loud, and in many cases if they were played that
loud, the 30 KHz tone that created 120 dB SPL would quickly fry the
tweeter,


Live sound speakers too at 120dB 30kHz!!! May very well be possible with a
jet engine whine I guess.

Trevor.

[Trevor]

"Arny Krueger" wrote in message
...
because the opportunities to work through live sound situations with FFTs
and the like are pretty limited.

What makes you say that? Been doing live gigs with a laptop recorder and FFT
analyser for many years, as have many sound engineers I know. Sure you don't
want to have to look at them much during the gig, but invaluable for set up
IMO.

Trevor.

[Mxsmanic]

Frank Stearns writes:

Well, you might find it very difficult to remove. To minimize sonic damage you'd
need a notch filter with something like a 1/1000 (or smaller) octave width. I am not
a DSP expert; not even sure if you can do that.

If you know it's actually from a CRT, couldn't you superimpose a signal of
exactly the same frequency and opposite phase and remove it, without affecting
anything else? Like astromomers do when they use extremely narrow filters to
completely remove the yellow light from low-pressure sodium-vapor streetlights
(which have an extremely monochromatic light).

Oh, and as a side benefit, most UPS provide basic power filtering and protection.
THAT'S why I carry a UPS!

That's the main reason why I put my computers on a UPS, although the battery
back-up is nice, too. But they weigh a ton--they must be a hassle to lug
around on location.

[[email protected]]

On 2012-02-09 said:
snip
There are a few different paths where flyback can get into a
recording:
1. acoustically, through microphones. That's fairly rare, as the
monitor will have
to be in pretty crappy shape to put out that much acoustical volume,
the mics have
to be pretty good and in just the right spot. Move a small diaphram
mic 1/4" to 1/2" and you'd see the 15.75K level swing probably some
30 dB. A large diaphragm
would have less variance, though probably a good 3-6 dB. (15.75K
has a wavelength of
0.86 inches). A lot depends on how the sound is radiated from the
monitor.

Right, and as you note, rare.

2. Inductively or electrostatically by way of unbalanced (or poorly
balanced) circuits going near a monitor.
3. Infiltration due to bad grounds or other poor practices in the
facility. Older
wiring can introduce a series of potential "gotchas".
How can you tell how the spike got in? Generally, if acoustically,
you'll typically
see the spike bouncing around in amplitude. If electronically,
typically the spike
is rock solid and does not vary in amplitude. This is what I've
typically seen when
commercial recordings have it. There were one or more CRT monitors
or TVs in the
studio or machine room or some place, dumping crap into a
susceptable audio circuit.

Right, and if your inputs and outputs are few you may be
able to eliminate this with some ferrite chokes. When I've
found something like this in two-way radio systems'
transmitters I've used the snap on ferrites effectively.

(And you can believe that a lot of even famous studios have some
pretty "interesting" wiring practices.)
snip
I didn't think that audio systems had a need for UPS systems,
unless it's really, really important to hear the entire song.
That's not the issue. The UPS is used during location recording. If
you only have
one shot at something, you don't want a recording hardware glitch
due to a momentary
power company hiccup (or outright outage), nor some idiot
accidently switching off

Something truncated your post, but I use one on location,
it's a don't leave home without it piece of gear for on site
recording, especially when recording to hard disk. Even if
the other gear isn't protected by it the recorder *must* be.
This way at least we can stop, and save our work to that
point. IN the case of folks like Frank and myself, folks
are paying good money to be recorded.





Richard webb,

replace anything before at with elspider

[Frank Stearns]

Mxsmanic writes:

Frank Stearns writes:

Well, you might find it very difficult to remove. To minimize sonic damage you'd
need a notch filter with something like a 1/1000 (or smaller) octave width. I am not
a DSP expert; not even sure if you can do that.

If you know it's actually from a CRT, couldn't you superimpose a signal of
exactly the same frequency and opposite phase and remove it, without affecting
anything else? Like astromomers do when they use extremely narrow filters to
completely remove the yellow light from low-pressure sodium-vapor streetlights
(which have an extremely monochromatic light).

Interesting idea, and perhaps worth a try, but here are the difficulties I see:

- exact waveform of the interference... it's likely not going to be perfectly
symmetrical, as your inverted "cancel" signal will be. As a result, the residual
might be worse. That is, you might wind up with some sharply peaked and spikey
waveforms hanging around. And remember, it'd be tough to go look at just this one hz
because it's buried in program.

- the easiest way to set this up would be another mix channel with an oscillator.
You'd precisely match this to the interference hz which, as I've seen, is rarely
exactly at 15.75K. So you'd have nudge that around as you look for a null, or have a
*very* high-res spectrum analyzer (higher than I've ever seen).

You're also hoping that the hz of the source interference isn't drifting a hz or two
back and forth. When it drifts away from your cancel frequency, kiss your
null goodbye.

You'd also have a delay plug-in on that channel to get the signal exactly at the
perfect null point. Pressing the "polarity" button on the channel isn't going to
mean a thing -- you have no idea as to the timing of the original interference.

Problem is, the delay plug-in will be stepped in samples, which might be far too
coarse of a timing step to get the waveform nudged to perfect nulling, especially if
the data is at 44.1Khz.

- if the spike entered multiple channels at various delays and levels of a
multitrack recording, you might very well have to pair up a nuller channel with
each program channel.

Attempting to null just the two track might prove impossible. If indeed the spike
entered from multiple points at slightly different delays, not to mention what
reverb, pitch correction, or other effects applied to the original mix channels
would do to the noise signal, you're done before you begin. You'd really need
access to the original multi-tracks to make this feasible.

All this tedium assumes you HEAR the problem in the first place.

Now, if you couldn't do this in DSP with a super narrow notch nulling is worth a
try. You might get lucky. You'd certainly get some good exercise with your spectrum
analyzer.

(A super narrow notch would allow for some hz drift of the interference and wouldn't
care at all about timing.)


Oh, and as a side benefit, most UPS provide basic power filtering and protection.
THAT'S why I carry a UPS!

That's the main reason why I put my computers on a UPS, although the battery
back-up is nice, too. But they weigh a ton--they must be a hassle to lug
around on location.

I miswrote that -- filtering was NOT the main reason I carried a UPS, it was ALL
things considered regarding the UPS.

My original noisy double-sine unit was 55 pounds in its own box. Yes, a pain. But
happily, its replacement was 15 pounds and fits in a 1U rack space.

My full-blown kit, 24-track primary and 24-track backup, plus microphone preamps,
goes into 3 cases (two 4U and one 6U) and weighs about 60 pounds per case. Add
another 250 pounds in snakes, cabling, microphones, and stands. 15 pounds out of all
that weight is a *very small* safety tax to pay.

Frank
Mobile Audio

--

[Mxsmanic]

Frank Stearns writes:

Interesting idea, and perhaps worth a try, but here are the difficulties I see:

- exact waveform of the interference... it's likely not going to be perfectly
symmetrical, as your inverted "cancel" signal will be. As a result, the residual
might be worse. That is, you might wind up with some sharply peaked and spikey
waveforms hanging around. And remember, it'd be tough to go look at just this one hz
because it's buried in program.

Hmm ... yes. But perhaps the sound of horizontal sync in CRTs follows a
predictable pattern. A sawtooth wave, perhaps, since that's what the sync
signal looks like internally.

If it were a big problem, it might be worth having a tool specifically to deal
with it, although with the declining use of CRTs (particularly those with low
scan rates), it's probably too late to care.

- the easiest way to set this up would be another mix channel with an oscillator.
You'd precisely match this to the interference hz which, as I've seen, is rarely
exactly at 15.75K. So you'd have nudge that around as you look for a null, or have a
*very* high-res spectrum analyzer (higher than I've ever seen).

Yeah, it would be somewhat specialized. And you'd probably need NTSC and PAL
versions. And the free-running sync of the CRTs will indeed be slightly
different (lower in frequency) than the synchronized rate.

You're also hoping that the hz of the source interference isn't drifting a hz or two
back and forth. When it drifts away from your cancel frequency, kiss your
null goodbye.

If it's receiving a signal, the signal would have to be pretty stable in
frequency, as it is piloted by the signal source. If it's not receiving a
signal, it could drift a lot.

But other things have just occurred to me. If they are computer monitors, and
not just television sets, you have a new problem, because the noise could be
at any one of many different frequencies. Most latter-day computer CRTs have
scan rates so high that they are well out of the audio range, but older
interlaced monitors do indeed produce noise comparable to that of TV sets. But
you'd have to be able to adjust the frequency a lot.

You'd also have a delay plug-in on that channel to get the signal exactly at the
perfect null point. Pressing the "polarity" button on the channel isn't going to
mean a thing -- you have no idea as to the timing of the original interference.

Problem is, the delay plug-in will be stepped in samples, which might be far too
coarse of a timing step to get the waveform nudged to perfect nulling, especially if
the data is at 44.1Khz.

You could compute and sample a waveform at a very high rate and then compute
the samples that would be needed at a lower rate to cancel the noise with a
given phase, I think (?).

- if the spike entered multiple channels at various delays and levels of a
multitrack recording, you might very well have to pair up a nuller channel with
each program channel.

This is looking more and more expensive, even in software.

All this tedium assumes you HEAR the problem in the first place.

Well, you might see it in the spectrum.

My original noisy double-sine unit was 55 pounds in its own box. Yes, a pain. But
happily, its replacement was 15 pounds and fits in a 1U rack space.

My full-blown kit, 24-track primary and 24-track backup, plus microphone preamps,
goes into 3 cases (two 4U and one 6U) and weighs about 60 pounds per case. Add
another 250 pounds in snakes, cabling, microphones, and stands. 15 pounds out of all
that weight is a *very small* safety tax to pay.

Agreed. I'm limited to what I can carry on my person, which is just a few
pounds.

[Anahata]

On Fri, 10 Feb 2012 02:41:34 +0100, Mxsmanic wrote:

If you know it's actually from a CRT, couldn't you superimpose a signal
of exactly the same frequency and opposite phase and remove it, without
affecting anything else? Like astromomers do when they use extremely
narrow filters to completely remove the yellow light from low-pressure
sodium-vapor streetlights (which have an extremely monochromatic light).

They use a filter (which is what Frank was suggesting in the first
place); they don't add an equal and opposite waveform, which would be
impossible as the original sodium light is not coherent.

You could do it the way you suggest for CRT line frequency. You'd need a
phased locked loop to generate a tone that matched the interference. You
only need a sine wave to cancel out the 18kHz fundamental. Harmonics at
36 kHz and above can be more conventially filtered.

Better to keep the interference out in the first place though, as
everyone has said.

--
Anahata
-+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827

[Anahata]

On Fri, 10 Feb 2012 12:33:58 +0100, Mxsmanic wrote:


Hmm ... yes. But perhaps the sound of horizontal sync in CRTs follows a
predictable pattern. A sawtooth wave, perhaps, since that's what the
sync signal looks like internally.

You've no idea what it will look like when it's been picked up by your
audio system. But (as mentioned in my previous post) the waveform is
determined by harmonics outside the audible range which can be knocked
out with a low pass filter.

If it were a big problem, it might be worth having a tool specifically
to deal with it

Like some tape recorders that used to have a "MPX filter" to remove the
19kHz pilot tone in case you were recording from FM radio?

--
Anahata
-+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827

[Mike Rivers]

On 2/9/2012 6:37 PM, Mxsmanic wrote:

I know many audio engineers, both live and studio, that have
hearing loss and still manage to do good work.

So what do they do? And did they damage their hearing from their work, or did
they lose it for other reasons?

People can suffer hearing loss from many reasons including
just getting old. Some do have accelerated hearing loss due
to exposure to loud music as part of their work. Some were
in loud bands, lost their hearing there, and moved into
engineering and production. Lots of reasons.

As to what they do - they depend on experience, knowing how
they hear "good" recordings, understand the kind of music
that they're producing, and they are aware of what might be
unexpected. They ask for other opinions - few engineers,
even those with golden ears, work entirely without
consulting others. Maybe it's the band or musician they're
recording (the customer must be satisfied), maybe it's
another engineer, assistant, or intern working on the
session, maybe it's the mastering house. And some simply
move into roles where they don't need golden ears.

Now if you're making your own music and producing yourself
on a desert island and you have no idea what it actually
sounds like, well, I really don't have a good answer for you
other than to just play for fun and don't worry about what
others think. Or send it to someone else to polish it up.

Well, if the room is filled with old-style CRTs, what can you do?

Turn them off or find another place to work. You wouldn't
try to record a lead vocal track on a busy street corner,
would you? Unless you wanted that for an effect, of course.

This is a perfect example of knowing what you're doing.
Actually, the problem you're more likely to have with CRTs
in a recording environment isn't with the horizontal sweep
frequency, which is really too high to be picked up by most
microphones unless they're just inches away. You're more
likely to get very noticeable low-mid buzz from the vertical
sweep being picked up by a guitar pickup. If you're really
worried about the horizontal sweep frequency, you could
simply filter everything above 15 kHz. What else would you
be recording that has usable musical content up there? You
probably could live without the CRTs while recording the
triangle solo.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mike Rivers]

On 2/9/2012 6:41 PM, Mxsmanic wrote:

I do notice that some professionals who lack confidence in their own
abilities feel threatened any time someone they consider external to the
profession starts to ask questions or make any assertions at all. Those who
are not insecure remain undisturbed.

And some are just naive. But you're right - there are a lot
of people who are insecure about their work, and live in
fear that someone will hear something that they missed. This
goes away with experience, and if it doesn't, then you're
REALLY in the wrong business. This mostly tends to be a
"gear" thing rather than a "stray noises" thing, though.

Novices are frequently asking if they should get a better
mic preamp, when what they really need is better monitoring
so they can make that decision themselves. Mostly, if there
are real problems with their work, it's with how they're
working and not what they're working with.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mike Rivers]

On 2/9/2012 6:35 PM, Mxsmanic wrote:

I'm a music listener, rather than a music maker. I record ambient sounds or
speech, mostly, for my little touristy videos.

This explains a lot. You should have mentioned this earlier.

When I record street scenes, I see an awful lot of
low-frequency noise, but I have no idea where most of it is coming from. In
real life, I also hear it (based on comparisons I've done), but for whatever
reason, I don't notice it as much. Really low frequencies seem to be something
that you notice unconsciously, even when you can hear them.

Well, this is what's really there. Why not record them and
make use of them? Or, alternatively, be aware that they're
present in your recordings and, if inappropriate, simply use
a different recording or filter so that you get the effect
that you want.

I recall it being around 30 kHz, so the number of people actually hearing it
would be too small to explain a general restlessness. But maybe it affected
them in some other way than through hearing alone. Apparently it was very
loud.

Are you talking about a recording? Or about something in
real life? If you live adjacent to an artillery test range,
you most likely will be exposed to high amplitude low
frequency energy now and then. People who live adjacent to
Camp Pendelton get used to it. But recording something like
this (which isn't easy to do well) might be effective in one
of your videos.

In the story I read, someone looked at a graphic equalizer or something and
noticed a huge spike at a very high frequency.

Movies are better than ever.

But sometimes the noise is coming from something that isn't yours, and it's a
surprise.

Some recordings just turn out to be unusable. So you do it
again, or make the best of what you have.

For field recordings, I don't have a spectrum analyzer handy.

Are you also blind? Do you have no friends to work with who
can help you out with your hearing impairment, or confidence
impairment?

Well, places like discos already use similar concepts. But you could design
something much more detailed, like a spectrum analyzer, that would provide
enough information to understand things like speech, for a trained observer.

People who study speech and hearing indeed do use tools like
spectrum analysis. But that's science, not recording
technology. Different tools for different purposes.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mike Rivers]

On 2/9/2012 8:41 PM, Mxsmanic wrote:

If you know it's actually from a CRT, couldn't you superimpose a signal of
exactly the same frequency and opposite phase and remove it, without affecting
anything else?

No two are alike. It's a good theory that doesn't work in
practice.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mike Rivers]

On 2/9/2012 8:41 PM, Mxsmanic wrote:

If you know it's actually from a CRT, couldn't you superimpose a signal of
exactly the same frequency and opposite phase and remove it

Actually, I have a better answer than what I just posted. If
you have a sample of the noise that's fairly well isolated,
there are "noise cancellation" programs that, in a more
sophisticated version of what you propose, do what you're
dreaming about. They work by analyzing the spectrum of the
sample of the noise that you want to remove and subtracting
that from the program material. It can work fairly well for
things like line frequency hum or the noise of a fan (but
not the wind) from an air conditioner. But the more
frequencies that are involved in the noise source (and CRT
sweep noise isn't just a single frequency) the less
effective the noise reduction can be without damaging the
primary program material.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Frank Stearns]

Mike Rivers writes:

sweep being picked up by a guitar pickup. If you're really
worried about the horizontal sweep frequency, you could
simply filter everything above 15 kHz. What else would you
be recording that has usable musical content up there? You

Gawk! Mike! Are you sure about that???

With many program sources, I agree with you (including a run-of-the-mill pickup).

But others, say piano, acoustic guitar (recorded with good microphones or some of
the newer super-good-sounding pickups), drums, choral/orchestral, et al, it'd hurt
to lop off the upper half of the last octave. Up there you have some sweet
harmonics, some useful pick and attack noise, and so on.

I have done the narrow notch thing and wasn't keen on the results (you could
definitely hear that something was gone), so going to even more removal makes me
hesitate, unless I knew that as you say, no usable musical content was up there on
that particular track.

YMMV.

Frank
Mobile Audio
--

[Frank Stearns]

Mike Rivers writes:

On 2/9/2012 8:41 PM, Mxsmanic wrote:

If you know it's actually from a CRT, couldn't you superimpose a signal of
exactly the same frequency and opposite phase and remove it

Actually, I have a better answer than what I just posted. If
you have a sample of the noise that's fairly well isolated,
there are "noise cancellation" programs that, in a more
sophisticated version of what you propose, do what you're
dreaming about. They work by analyzing the spectrum of the
sample of the noise that you want to remove and subtracting
that from the program material. It can work fairly well for

Mike, have you run across a particular package that does this really well? I've got
a couple different venues that have some specific noise spectra between 90 and 110
hz. (I know; weird frequency range. Seems to be some sort of "blow across the coke
bottle" resonance in the air returns which appear to be too small for the volume of
the halls. In one hall you can stand about four feet from one of the two returns,
release a piece of paper from chest height, and it quickly sails to the grill and
smack, becomes a prisoner.)

I've messed with the periodic noise removal tool in sound forge and it seems
completely useless for this. (And I have recorded some nice samples of this noise
when it was just me in the hall. Even though it sounds like periodic noise, perhaps
it's too chaotic? The analyzer shows a fair amount of random bouncing at that hz
range; turbulance in the resonate cavity of the return shaft, no doubt.)

Be curious to hear any product recommendations you might have. Maybe there's a
really smart one that could keep adjusting itself to variations in the noise
spectra.

Thanks in advance,
Frank
Mobile Audio

--

[Arny Krueger[_4_]]

"Frank Stearns" wrote in message
acquisition...
Mike Rivers writes:

On 2/9/2012 8:41 PM, Mxsmanic wrote:

If you know it's actually from a CRT, couldn't you superimpose a signal
of
exactly the same frequency and opposite phase and remove it

Actually, I have a better answer than what I just posted. If
you have a sample of the noise that's fairly well isolated,
there are "noise cancellation" programs that, in a more
sophisticated version of what you propose, do what you're
dreaming about. They work by analyzing the spectrum of the
sample of the noise that you want to remove and subtracting
that from the program material. It can work fairly well for

Mike, have you run across a particular package that does this really well?
I've got
a couple different venues that have some specific noise spectra between 90
and 110
hz. (I know; weird frequency range. Seems to be some sort of "blow across
the coke
bottle" resonance in the air returns which appear to be too small for the
volume of
the halls. In one hall you can stand about four feet from one of the two
returns,
release a piece of paper from chest height, and it quickly sails to the
grill and
smack, becomes a prisoner.)

I've messed with the periodic noise removal tool in sound forge and it
seems
completely useless for this. (And I have recorded some nice samples of
this noise
when it was just me in the hall. Even though it sounds like periodic
noise, perhaps
it's too chaotic? The analyzer shows a fair amount of random bouncing at
that hz
range; turbulance in the resonate cavity of the return shaft, no doubt.)

Be curious to hear any product recommendations you might have. Maybe
there's a
really smart one that could keep adjusting itself to variations in the
noise
spectra.

Cool Edit Pro and Audition have a DTMF tone removal tool that is very
effective for removing narrowband noises and tones if you manually change
its center frequencies, which is fully supported.

If you can find a DTMF tone removal plug in with similar ease of use, it
might be just as good.

[Arny Krueger[_4_]]

"Frank Stearns" wrote in message
acquisition...
Mike Rivers writes:

sweep being picked up by a guitar pickup. If you're really
worried about the horizontal sweep frequency, you could
simply filter everything above 15 kHz. What else would you
be recording that has usable musical content up there? You

Gawk! Mike! Are you sure about that???

With many program sources, I agree with you (including a run-of-the-mill
pickup).

But others, say piano, acoustic guitar (recorded with good microphones or
some of
the newer super-good-sounding pickups), drums, choral/orchestral, et al,
it'd hurt
to lop off the upper half of the last octave. Up there you have some sweet
harmonics, some useful pick and attack noise, and so on.

Yes, but through the magic of the ear's masking, you may never notice their
loss in a DBT.

I pretty well predict that you will notice their loss in a sighted
evaluation, until you get really comfortable with the easily regrettable
results in the DBT.

It is pretty well known that brick walling at 16 KHz is usually benign.

You can test things like this using any of the software DBT test
controllers, such as the one that is a plug-in for the Foobar music player
freeware.

[Scott Dorsey]

Mxsmanic wrote:
I'm a music listener, rather than a music maker. I record ambient sounds or
speech, mostly, for my little touristy videos. Indeed, I avoid recording any
kind of music, because copyright trolls on YouTube will latch onto it to make
fraudulent infringement claims.

Then, out of curiosity, what are you doing in an audio production newsgroup?
And what makes you think you can tell people in an audio production newsgroup
how to do their jobs?

That's the mystery. When I record street scenes, I see an awful lot of
low-frequency noise, but I have no idea where most of it is coming from. In
real life, I also hear it (based on comparisons I've done), but for whatever
reason, I don't notice it as much. Really low frequencies seem to be something
that you notice unconsciously, even when you can hear them.

I can take NYC for about two days because of the constant rumble everywhere.
I can't help but notice it. I suspect people who live there all the time get
used to it. I can stop in a quiet office building and feel the subway going
by. And yes, it goes into everything, which is why you need good monitoring.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Frank Stearns]

"Arny Krueger" writes:

snips

It is pretty well known that brick walling at 16 KHz is usually benign.

Eeeeekkkk!!!! Arny, my man! "Well known" to what people smoking what kind of rope?!

Seems to me someone going for that would have to have limited monitoring, a
poor room, or have perhaps been conditioned to the 16K brick wall used in most
MP3 encodes, even the higher bit-rate ones, to make a pronouncement like that.

As a classical and acoustic music engineer, I can assure you that 16-20K **IS**
significant, and I'd take a long walk of a short pier before lopping it off.

You can test things like this using any of the software DBT test
controllers, such as the one that is a plug-in for the Foobar music player
freeware.

Something that huge is bloody obvious in my room. And with one exception, all of my
clients would immediately hear it as well (they wouldn't have to see a damn thing,
either).

My favorite mastering engineer would bring me the white jacket with the really long
sleeves if I did something like that. He doesn't use a spectrum analyzer, and
sometimes chides me when I ask for certain changes numerically. He's totally an
"ear" guy and is well aware of the suggestive nature of the visual component.

I can just see him if I brought in a master like that. He'd swing around in his
chair, lean forward, glare and me, and say, "WTF happened to this?"

No, thanks. I'll maintain to 20K. Not much point in going a whole lot higher, I
agree, but you're cutting pretty deep into bone at 16K -- at least for the kind of
work I do. With a lot of pop/rock even 14K is probably fine, perhaps even preferable
so as to remove nasty artifacts from over-processing, clipping, etc., but not with
acoustic sources that are to be maintained in hi-fi.

Frank
Mobile Audio
--

[ChrisCoaster]

On Feb 6, 10:28*pm, Mxsmanic wrote:
I installed a freeware plug-in on Sound Forge that provides a spectrum
analysis. When I analyze something, it seems like there's a lot of sound
energy at low frequencies, even though I don't seem to be hearing that much at
the low end. There's a "slope" adjustment in the analyzer, but I'm not sure
what it does--can someone explain it to me?

I tried generating some white noise and then adjusting the slope so that the
spectrum was relatively flat (since I presume that white noise contains equal
amounts of sound energy at all frequencies), but I'm not sure that this
accomplished what I want. I'd just like to see the actual sound levels for
each frequency.

If it makes a difference, the audio editing program is Sound Forge (the Audio
Studio version) and the plug-in is VOXengo SPAN.
___________________
I have Audacity - can analyze the same way. I believe it analyzes
based on the "presence" or energy level at certain frequencies vs the
volume of what we actually hear in a given song. Bass contains more
energy and thus the mountains skewed to the left in most of my cases.
If you see a really tall HUMP or peak between 50 & 100Hz then you're
probably analyzing a rap song; the lows were purposely pumped up in
post.

I purposely EQd a "normal" song - without the hip-hop hump(!) just to
see - and hear - what it would sound like "flat", but the result was
tinny and thin sounding, even if the spectro was less skewed and
flatter than before. Why? Our ears are not programmed to hear that
way. If you are EQing a project in post and it has any outstanding
peaks or dips across its spectro there is probably something wrong or
too much EQ is being used in that location.

-CC

[Mxsmanic]

Mike Rivers writes:

No two are alike. It's a good theory that doesn't work in
practice.

The horizontal sync is locked on all receivers that are capturing the same
broadcast signal.

[Mxsmanic]

Mike Rivers writes:

Well, this is what's really there. Why not record them and
make use of them?

If it's really there, I don't have a problem with it. I just want to make sure
that the equipment is not exaggerating it. It seems less obvious in real life
than it does on the recording, but perhaps that's just because I'm listening
to the recording away from the original environment. When I monitor it during
recording, I don't seem to notice it.

Are you talking about a recording? Or about something in
real life?

It was a concert, so I presume the sound was live.

If you live adjacent to an artillery test range,
you most likely will be exposed to high amplitude low
frequency energy now and then. People who live adjacent to
Camp Pendelton get used to it. But recording something like
this (which isn't easy to do well) might be effective in one
of your videos.

I think it would be interesting to analyze a recording of a sonic boom, but
those are hard to come by these days (I did hear them a lot when I was
little).

Are you also blind? Do you have no friends to work with who
can help you out with your hearing impairment, or confidence
impairment?

I can see. I have no one to work with. I lack confidence in domains about
which I don't have a high level of knowledge, which seems very logical to me.

[Mxsmanic]

Scott Dorsey writes:

Then, out of curiosity, what are you doing in an audio production
newsgroup?

It seemed like a good source of information.

And what makes you think you can tell people in an audio production newsgroup
how to do their jobs?

I don't recall saying anything either way.

I can take NYC for about two days because of the constant rumble everywhere.
I can't help but notice it. I suspect people who live there all the time get
used to it. I can stop in a quiet office building and feel the subway going
by. And yes, it goes into everything, which is why you need good monitoring.

A subway line runs under my apartment building, and sometimes I can hear the
subway (faintly) passing below. Maybe I'll try recording it sometime, and see
how it turns out.

[Mxsmanic]

Mike Rivers writes:

Turn them off or find another place to work. You wouldn't
try to record a lead vocal track on a busy street corner,
would you? Unless you wanted that for an effect, of course.

But you could be shooting a documentary in a TV studio, and then you'd have
CRTs all around, and they probably could not be shut off. Of course, that's a
rather contrived example.

[Scott Dorsey]

Mxsmanic wrote:

I think it would be interesting to analyze a recording of a sonic boom, but
those are hard to come by these days (I did hear them a lot when I was
little).

http://ntrs.nasa.gov and also the NTIA database will have plenty of papers
with pictures of N-wave waveforms. Since you can't actually reproduce them,
they _are_ best just viewed as time domain plots.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Mxsmanic wrote:
Mike Rivers writes:

Turn them off or find another place to work. You wouldn't
try to record a lead vocal track on a busy street corner,
would you? Unless you wanted that for an effect, of course.

But you could be shooting a documentary in a TV studio, and then you'd have
CRTs all around, and they probably could not be shut off. Of course, that's a
rather contrived example.

That's what engineers do every day.

And unfortunately as people move around in the studio, the noise waveforms
from the monitors change.

That's why we have notch filters.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Richard Webb[_3_]]

On Fri 2012-Feb-10 07:15, Mike Rivers writes:
I do notice that some professionals who lack confidence in their own
abilities feel threatened any time someone they consider external to the
profession starts to ask questions or make any assertions at all. Those who
are not insecure remain undisturbed.

Sometimes asking the right questions will help the neophyte
learn however. As an old instructor once taught me, asking
questions is good, asking the right question can mvoe you
toward understanding g.

And some are just naive. But you're right - there are a lot of
people who are insecure about their work, and live in
fear that someone will hear something that they missed. This goes
away with experience, and if it doesn't, then you're
REALLY in the wrong business. This mostly tends to be a
"gear" thing rather than a "stray noises" thing, though.

INdeed, and one thing that may help mxmanic with the type of thing he does is to consider how he intends to use the
captured sound, then decide how much massaging to do with
it.


As a simple example, he can think of that dense arrangement
he hears where the acoustic guitar is more apparent from
just the sound of strumming. The track in isolation
probably doesn't sound that great, or that much like an
acoustic guitar, but when blended with the otehr parts of
the arrangement in the mix does just what one wants the
acoustic guitar to do.

That's where the monitoring environment ears and knowledge
can all come together. Often the trick is knowing what
should be worried about and what can be safely ignored
because in the final production it's going to be a nonissue. A good example of that was the discussion of crt scan noise. As Frank noted, in most musical arrangements it's a
nonissue, but if the piece is a single instrument or spoken
word only it becomes one.

What it often boils down to is the old adage "don't sweat
the small stuff."

HEre's an example for him from a project I did about a
decade ago.

Gospel group, the keyboard player had a little bit of a
ground loop problem with one of his keyboards he used on the session. For most of their album project it was a nonissue, that hummmmmm buried in the mix. But, there was one
selection where that keyboard was all alone naked for the
first eight bars. When we went to mixing I bugged him more
than once about bringing in that keyboard sans the rest of
his rig and retracking the intro, and even though we weren't doing the customary billing by the hour he refused. hE was
quite happy with it, but those eight bars drove me crazy
every time I listened to the intro.

I knew i was going to be present during the mastering
however, so I let it ride, mixed the album, and went to the
mastering session. When we came to that track we did the
transfer, then applied a filter to the intro which wasn't
applied once the rest of the ensemble started to play. I
captured enough of the noise in isolation even as I did the
mix so that we could tailor the filter to the hum's exact
characteristics. My only concern then was whether the
filter would negatively impact the tone of the keyboard.

Yeah I know, only eight bars, and he was happy as a clam
with the whole project, but I never would have been happy
with that one going out the door with my name on it and that hum present ,g.


Regards,
Richard
--
| Remove .my.foot for email
| via Waldo's Place USA Fidonet-Internet Gateway Site
| Standard disclaimer: The views of this user are strictly his own.

[Frank Stearns]

Mxsmanic writes:

Mike Rivers writes:

No two are alike. It's a good theory that doesn't work in
practice.

The horizontal sync is locked on all receivers that are capturing the same
broadcast signal.

True, but you might well get some waveform distortions (based on how the sync signal
got into your audio) that would make cancellation much less than what the
theoretical ideal.

Over the years I've been down the cancellation route on a number of different issues
and indeed, theory is way better than practice.

The problem is, to get an effective cancellation for any application, the target and
inverted cancel signal must be exactly in step -- amplitude, timing,
frequency/waveform -- to do any good. And in the real world, it's durn difficult to
get all three. Usually you're very lucky to get two right, or even one.

Assuming you can take the spectral hit and get a narrow enough notch, the notch will
likely be the better practical solution -- assuming, of course, you can't go back
and correct the initial problem.

Frank
Mobile Audio

--

[Mike Rivers]

On 2/10/2012 2:31 PM, Mxsmanic wrote:

The horizontal sync is locked on all receivers that are capturing the same
broadcast signal.

Kid's got an answer for everything, it seems.

The frequency may be the same, but not all transformers are
the same. It's not the sweep that makes the noise, it's all
the things rattle around that aren't supposed to be transducer.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mike Rivers]

On 2/10/2012 2:36 PM, Mxsmanic wrote:

If it's really there, I don't have a problem with it. I just want to make sure
that the equipment is not exaggerating it.

Why would your equipment be exaggerating a particular
frequency range? Sure, mics aren't perfectly flat, but you
should know their characteristics before you go to work.

It seems less obvious in real life
than it does on the recording, but perhaps that's just because I'm listening
to the recording away from the original environment.

This is true with just about every recording. You capture
one sound field and play it back in a different environment.
Accurate monitors in a room with some care toward acoustic
accuracy at the listening position goes a long way toward
making things sound like they did when you were there, but
you'll never get an exact match.

I think it would be interesting to analyze a recording of a sonic boom, but
those are hard to come by these days (I did hear them a lot when I was
little).

Bob Katz used to have a recording of a Cape Canaveral
reocket launch that he recorded (with permission) at fairly
close range. www.digido.com

I can see. I have no one to work with. I lack confidence in domains about
which I don't have a high level of knowledge, which seems very logical to me.

In that case, you need to get some friends and get some
confidence. Your friends don't need golden ears, just play
them the recording and ask them what they hear.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Mxsmanic]

Mike Rivers writes:

The frequency may be the same, but not all transformers are
the same. It's not the sweep that makes the noise, it's all
the things rattle around that aren't supposed to be transducer.

But they should all rattle at the same frequency, since the sync frequency is
locked.