[Roy W. Rising[_2_]]

A minus B Protocol:

Sum the out-of-phase, level-matched outputs of two test subjects. Listen
to the residual artifacts at *normal* (!) monitor level. If they're not
audible, they don't matter. If they are audible, which device is
contributing them the most ... and why?

Let the new mudwar begin! (I will watch from the sidelines.)

--
~ Roy
"If you notice the sound, it's wrong!"

[Arny Krueger]

"Roy W. Rising" wrote in message
...
A minus B Protocol:

Sum the out-of-phase, level-matched outputs of two test subjects. Listen
to the residual artifacts at *normal* (!) monitor level. If they're not
audible, they don't matter. If they are audible, which device is
contributing them the most ... and why?

Let the new mudwar begin! (I will watch from the sidelines.)

This is old news, been tried many times. It is rarely the silver bullet
that might be hoped for.

The problem is that you can have relatively large instantaneous differences,
even when both UUTs are each reasonably sonically accurate.

A good example of this would involve broadband but moderate frequency and
phase response situations; and time delays, even those down in the range of
a few dozen microseconds.

IOW you can have a device that has as little as a few dozen microseconds
latency, and when you subtract its output from something that has
appreciably less latency, the difference you get will be very easy to hear.
However, latency in that range is rarely a big audible problem. So, the
relatively large difference signal you get with instantaneous subtraction is
misleading.

You'd think this method would be OK for power amps because they are pretty
good in the cosmic scheme of things. But, when David Hafler was using a
signal subtraction-based methodology to promote his amplifiers some years
back, he ended up having to fix up the phase response of his own products in
ways that really didn't do much for how they sounded under normal
conditions.

A similar idea that works more generally involves putting the signal through
the piece of equipment several times, which adds another layer of noise and
distortion each run-through.

You can find examples of applications of this methodology at
http://www.pcabx.com/product/amplifiers/index.htm . I by pushed the test
signals through these amps enough times so that their characteristic sonic
colorations are reasonably easy to hear. You can then back off on the
number of repetitions until you stop hearing the amp's colorations. In every
case, that happens by the time the number of reps is one.

I did a similar thing at http://www.pcabx.com/product/soundcard/index.htm .
At least one of the audio interfaces was so good that it wasn't practical to
increase the number of reps to the point where the coloration of the sound
card was easy to hear. Others were so bad that even one rep had audible
consequences.

Well, that is what I heard back when I was working with these pages on the
PCABX site. Maybe you have more sensitive ears than I did back then. Here is
a relatively easy opportunity to listen for yourself, and reach your own
conclusions.

[Scott Dorsey]

Roy W. Rising wrote:
A minus B Protocol:

Sum the out-of-phase, level-matched outputs of two test subjects. Listen
to the residual artifacts at *normal* (!) monitor level. If they're not
audible, they don't matter. If they are audible, which device is
contributing them the most ... and why?

Let the new mudwar begin! (I will watch from the sidelines.)

Sometimes colorations in the summing device become a problem, and in
the modern digital world where devices have latency it can sometimes
be a problem to deal with proper nulling.

But, this can be a very, very revealing test, and quantitative measurements
of the difference signals can be extremely useful, as well as qualitative
listening.

Doing this test on lossy encoding systems is absolutely fascinating and
gives you a real window into how they work.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

You'd think this method would be OK for power amps because they
are pretty good in the cosmic scheme of things. But, when David
Hafler was using a signal subtraction-based methodology to promote
his amplifiers some years back, he ended up having to fix up the
phase response of his own products in ways that really didn't do
much for how they sounded under normal conditions.

Crown developed what they called a "null amplifier" that (supposedly)
performed this test correctly. Dr. Clayton Barclay, late of Crown, told me
that the Crown PL-1 amplifier could get close to a 90dB null on program
material. I've been trying to get my hands on a null amplifier, but they're
hard to come by.

Having to compensate for the amplifier's phase errors is an old problem. As
it's a static error *, and can in principle be compensated for with an
all-pass network, it's not significant.

* Well, not quite... As the average power level rises and the amplifier's
bandwidth narrows, the phase shift will increase.


You can find examples of applications of this methodology at
http://www.pcabx.com/product/amplifiers/index.htm. I by pushed the test
signals through these amps enough times so that their characteristic sonic
colorations are reasonably easy to hear. You can then back off on the
number of repetitions until you stop hearing the amp's colorations. In
every
case, that happens by the time the number of reps is one.

Well, well, well... Isn't _that_ convenient. That doesn't produce even the
faintest "Hmmm..." response?

[hank alrich]

Roy W. Rising wrote:

A minus B Protocol:

Sum the out-of-phase, level-matched outputs of two test subjects. Listen
to the residual artifacts at *normal* (!) monitor level. If they're not
audible, they don't matter. If they are audible, which device is
contributing them the most ... and why?

Let the new mudwar begin! (I will watch from the sidelines.)

Troublemaker!

--
ha
Iraq is Arabic for Vietnam

[Arny Krueger]

"William Sommerwerck" wrote in message
. ..

You can find examples of applications of this methodology at
http://www.pcabx.com/product/amplifiers/index.htm. I by pushed the test
signals through these amps enough times so that their characteristic
sonic
colorations are reasonably easy to hear. You can then back off on the
number of repetitions until you stop hearing the amp's colorations. In
every case, that happens by the time the number of reps is one.

Well, well, well... Isn't _that_ convenient. That doesn't produce even the
faintest "Hmmm..." response?

Hey, I didn't make the universe, I just report on it. ;-)

The methology used to do some of the amp tests involved a speaker simulator
that was designed to be reasonable but get amps to be as audibly different
as possible, and it came darn close. For example, my speaker simulator is
about twice as tough as the one that Stereophile used. I'm not out there
trying to make SET amps, some other tubed amps, and other kinds of
inherently poor amps (e.g. some switchmode amps) look as good as possible.

We've gotten some positive results with repetitions = 2. So, some
amp/speaker combinations are pretty close to the edge. OTOH, such
differences as were heard with a reasonble number of repetitions were pretty
subtle, not so strong that they would get the usual "yecch" response that we
often see reported.

The strongest reason why otherwise good SS power amps have any audible
coloration at all often relates to the inductor network that most SS power
amps have in series with their output terminal. Some amp makers have found
that the bigger they make this inductor, the fewer amps come back in
warranty. So they want to make it as big as possible within reason. This
part is usually sized to just barely have reasonably flat response up to 20
KHz with a resistive load. If you have certain kinds of speaker loads, the
inductor will have a stronger resonance than planned, and cause larger
variations above 10 KHz.

[Les Cargill]

Scott Dorsey wrote:

Roy W. Rising wrote:

A minus B Protocol:

Sum the out-of-phase, level-matched outputs of two test subjects. Listen
to the residual artifacts at *normal* (!) monitor level. If they're not
audible, they don't matter. If they are audible, which device is
contributing them the most ... and why?

Let the new mudwar begin! (I will watch from the sidelines.)


Sometimes colorations in the summing device become a problem, and in
the modern digital world where devices have latency it can sometimes
be a problem to deal with proper nulling.

But, this can be a very, very revealing test, and quantitative measurements
of the difference signals can be extremely useful, as well as qualitative
listening.

Doing this test on lossy encoding systems is absolutely fascinating and
gives you a real window into how they work.
--scott


With lossy encoders, you can save the original PCM and diff
it with the output. Add a single sample FS pulse to synch by.

--
Les Cargill

[Steven Sullivan]

Roy W. Rising wrote:
A minus B Protocol:

Sum the out-of-phase, level-matched outputs of two test subjects. Listen
to the residual artifacts at *normal* (!) monitor level. If they're not
audible, they don't matter. If they are audible, which device is
contributing them the most ... and why?

Let the new mudwar begin! (I will watch from the sidelines.)

--
~ Roy
"If you notice the sound, it's wrong!"

you mean, like this?


http://libinst.com/Audio%20DiffMaker.htm


___
-S
"As human beings, we understand the world through simile, analogy,
metaphor, narrative and, sometimes, claymation." - B. Mason