Feedback in audio esp wrt op-amps.

[William Sommerwerck]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:46CC9BE3.7165B596@hotmail.com...

William Sommerwerck wrote:

William Sommerwerck wrote:

When I worked at Rupert Neve..

When and where was this ?

Neve Connecticut, USA. 1983, I think.

Bethel presumably? Did you ever meet Robin Porter.
I was told he'd spent some time at RN Inc.

Bethel, yes, right across from Mallory/Duracell.

The name doesn't ring a bell. I've forgotten the names of the people I
worked with. Hope none of them is reading this!

 

[William Sommerwerck]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:46CC9B77.D796A0CD@hotmail.com...

William Sommerwerck wrote:

It seems to make a lot more sense to apply NFB
in rather more moderate amounts to
a gain stage that's already quite linear.

I first read this rule in the '60s.

Where did you originally come across it?

In an "Electronics World" article about the new JBL solid-state amp with a
"T" output stage. The author explicitly stated the principle -- get the
circuit as linear and wideband as possible before applying feedback.

 

[Eeyore]

William Sommerwerck wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote
William Sommerwerck wrote:
William Sommerwerck wrote:

When I worked at Rupert Neve..

When and where was this ?

Neve Connecticut, USA. 1983, I think.

Bethel presumably? Did you ever meet Robin Porter.
I was told he'd spent some time at RN Inc.

Bethel, yes, right across from Mallory/Duracell.

The name doesn't ring a bell.

Just thought I'd ask. He was UK based but I'd just heard he spent some time over
there. We worked in the same dept (operations/custom engineering) and we had
even been on the same course at uni but not in the same year.

What was your role there btw ?

Graham

 

[Eeyore]

William Sommerwerck wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote
William Sommerwerck wrote:

It seems to make a lot more sense to apply NFB
in rather more moderate amounts to
a gain stage that's already quite linear.

I first read this rule in the '60s.

Where did you originally come across it?

In an "Electronics World" article about the new JBL solid-state amp with a
"T" output stage. The author explicitly stated the principle -- get the
circuit as linear and wideband as possible before applying feedback.

Right. I think I've come across the article online. I also read Wireless World
back then too. I may have saved it somewhere. I do recall smiling slightly when
I read it recently on account of a certain element of 'old thinking' it
embodied. Makes you realise how far we've advanced over the years.

Graham

 

[isw]

In article <1bednZh-GfJoxVHbnZ2dnUVZ_qmlnZ2d@comcast.com>,
"William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

The spectrum is important, in fact it is critical. In many cases, 2nd
order
distortion is hard to hear, particularly when listening to solo
instruments.
This is due to concurrent spectral masking in the human ear.

Higher order harmonics are not so well masked as 2nd, so the ear can
pick them out, even when they are relatively small.

The audibility of harmonic distortion might also depend on tuning. In a
system using whole-number ratios, harmonic distortion of all orders might be
less audible than in a tempered system.

Most instruments produce overtones as well as -- or instead of --
harmonics. They don't fall directly on multiples of the fundamental no
matter what tuning is used.

Isaac

 

[Eeyore]

isw wrote:

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

The spectrum is important, in fact it is critical. In many cases, 2nd
order distortion is hard to hear, particularly when listening to solo
instruments. This is due to concurrent spectral masking in the human ear.

Higher order harmonics are not so well masked as 2nd, so the ear can
pick them out, even when they are relatively small.

The audibility of harmonic distortion might also depend on tuning. In a
system using whole-number ratios, harmonic distortion of all orders might be
less audible than in a tempered system.

Most instruments produce overtones as well as -- or instead of --
harmonics. They don't fall directly on multiples of the fundamental no
matter what tuning is used.

The technical definition of an overtone is no different from a harmonic other than
its number.

1st overtone = 2nd harmonic etc.

That itself has no relation to the production of 'harmonics' that are not integer
multiples of the fundamental. I'd like to see some more evidence of this alleged
behaviour too.

Graham

 

[Paul Stamler]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:KsudnVwrG9OoLVHbnZ2dnUVZ_jydnZ2d@comcast.com...

It seems to make a lot more sense to apply NFB
in rather more moderate amounts to
a gain stage that's already quite linear.

I first read this rule in the '60s.

Where did you originally come across it?

In an "Electronics World" article about the new JBL solid-state amp with a
"T" output stage. The author explicitly stated the principle -- get the
circuit as linear and wideband as possible before applying feedback.

The principle wasn't new, though; Norman Crowhurst was talking about it in
the 1950s.

That was an interesting design; I remember it as sounding good, but it's
been a really long time since I heard one.

Peace,
Paul

 

[Mr.T]

"Scott Dorsey" <kludge@panix.com> wrote in message
news:fahilt$h9v$1@panix2.panix.com...

Yes, but do you understand what I said, or are you just choosing to
ignore
the difference between parallel circuits and series circuits?

I understand what you said, but it isn't really relevant except in the
case of the equalizer mentioned by another person in this thread, or if
you want to handwave about the number of individual op-amps in all the
channel strips on that SSL.

Not me, but isn't that what you are doing?

Pop the cover on an SSL 4000 and count the number of individual gain
stages
from the front to the back, then into the tape mchine and back again.
There
are lots.

Sure, BUT it is still very unusual to have more than 100 in series with the
audio chain, just as I originally stated.
I guess you could possibly achieve it, *IF* that was your aim. And it would
probably still measure fairly blameless in any case.

While you're staring at all the chips next time, why not actually shove a
test signal in and measure the result at the output. I think you will not
find any significant problems unless it is broken.

MrT.

 

[Peter Larsen]

Arny Krueger wrote:

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
newstydnbFbio9jFlHbnZ2dnUVZ_gOdnZ2d@comcast.com...

The audibility of harmonic distortion might also depend on tuning.
In a system using whole-number ratios, harmonic distortion of all
orders might be less audible than in a tempered system.

Why might that be?

Masking effects -- or lack thereof. For example, in such a system, the
third
harmonic would fall exactly on a scale note, whereas under our current
system, the third harmonic comes _very_ close, but not exactly.

Masking is not *that* frequency-sensitive.

This is not about masking, it is about pitch, and pitch is acutely
heard.


Kind regards

Peter Larsen

 

[Peter Larsen]

Eeyore wrote:

The audibility of harmonic distortion might also depend on tuning.
In a system using whole-number ratios, harmonic distortion of all
orders might be less audible than in a tempered system.

But who's still using those old tunings ?

There are people here knowing vastly more about music than I do, but all
instruments that allow intonation are in my understanding likely to use
or at least approximate those scales unless playing with a tempered
instrument. After all, that is what the intonation advantage is about.

I've heard the difference it makes to how the music sounds btw (at college 30
yrs ago) and it's quite remarkable.

Listen to a good string quartet Graham, the purity of tone they offer
can be astounding. Or a solo violin playing solo, add a piano and the
player will intonate differently, and the very same violin now sound
grungy because it has to follow the piano.

Graham

Kind regards

Peter Larsen

 

[Arny Krueger]

"Peter Larsen" <SPAMSHIELD_plarsen@mail.tele.dk> wrote in message
news:46CD36A5.B521F6EA@mail.tele.dk...

Arny Krueger wrote:

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
newstydnbFbio9jFlHbnZ2dnUVZ_gOdnZ2d@comcast.com...

The audibility of harmonic distortion might also depend on tuning.
In a system using whole-number ratios, harmonic distortion of all
orders might be less audible than in a tempered system.

Why might that be?

Masking effects -- or lack thereof. For example, in such a system, the
third
harmonic would fall exactly on a scale note, whereas under our current
system, the third harmonic comes _very_ close, but not exactly.

Masking is not *that* frequency-sensitive.

This is not about masking, it is about pitch, and pitch is acutely
heard.

True, but...

You've got to reliably perceive a sound before you can tell what pitch it
is. Masking can keep you from totally perceiving a certain sound in any
way.

As I said before, many musical instruments have overtones that are not
exactly harmonically related to the fundamental. The usual rules of masking
apply to those overtones, as well.

Bottom line, the audibility of nonlinear distortion is not contingent on
different types of musical scales or whether you use A=440 or some other
base pitch.

 

[Arny Krueger]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:46CD01A2.F28D9D7B@hotmail.com...

isw wrote:

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

The spectrum is important, in fact it is critical. In many cases, 2nd
order distortion is hard to hear, particularly when listening to solo
instruments. This is due to concurrent spectral masking in the human
ear.

Higher order harmonics are not so well masked as 2nd, so the ear can
pick them out, even when they are relatively small.

The audibility of harmonic distortion might also depend on tuning. In a
system using whole-number ratios, harmonic distortion of all orders
might be
less audible than in a tempered system.

Most instruments produce overtones as well as -- or instead of --
harmonics. They don't fall directly on multiples of the fundamental no
matter what tuning is used.

The technical definition of an overtone is no different from a harmonic
other than
its number.

1st overtone = 2nd harmonic etc.

Overtones are a superset of the set of harmonics:

Wikipedia:

"

Overtone:

An overtone is a sinusoidal component of a waveform, of greater frequency
(usually an integer number multiple) than its fundamental frequency. The
term is usually used in music, rather than wave physics. (see standing wave)

Harmonic:
In acoustics and telecommunication, the harmonic of a wave is a component
frequency of the signal that is an integer multiple of the fundamental
frequency. For example, if the frequency is f, the harmonics have frequency
2f, 3f, 4f, etc. The harmonics have the property that they are all periodic
at the signal frequency, and due to the properties of Fourier series, the
sum of the signal and its harmonics is also periodic at that frequency.

Many oscillators, including the human voice, a bowed violin string, or a
Cepheid variable star, are more or less periodic, and thus can be decomposed
into harmonics.

Most passive oscillators, such as a plucked guitar string or a struck drum
head or struck bell, naturally oscillate at several frequencies known as
overtones. When the oscillator is long and thin, such as a guitar string, a
trumpet, or a chime, the overtones are still integer multiples of the
fundamental frequency. Hence, these devices can mimic the sound of singing
and are often incorporated into music. Overtones whose frequency is not an
integer multiple of the fundamental are called inharmonic and are often
perceived as unpleasant.

The untrained human ear typically does not perceive harmonics as separate
notes. Instead, they are perceived as the timbre of the tone. In a musical
context, overtones which are not exactly integer multiples of the
fundamental are known as inharmonics. Inharmonics which are not close to
harmonics are known as partials. Bells have more clearly perceptible
partials than most instruments. Antique singing bowls are well known for
their unique quality of producing multiple harmonic overtones or
multiphonics.

The tight relation between overtones and harmonics in music often leads to
their being used synonymously in a strictly musical context, but they are
counted differently leading to some possible confusion.

"

That itself has no relation to the production of 'harmonics' that are not
integer
multiples of the fundamental. I'd like to see some more evidence of this
alleged
behaviour too.

See the Wikipedia article about harmonics, above.

In general, percussion instruments (including stringed instruments that use
struck or plucked strings) have equations of motion that are nonlinear
enough that there are inharmonic overtones.

 

[Peter Larsen]

Eeyore wrote:

Peter Larsen wrote:

Eeyore wrote:

The audibility of harmonic distortion might also depend on tuning.
In a system using whole-number ratios, harmonic distortion of all
orders might be less audible than in a tempered system.

But who's still using those old tunings ?

There are people here knowing vastly more about music than I do, but all
instruments that allow intonation are in my understanding likely to use
or at least approximate those scales unless playing with a tempered
instrument. After all, that is what the intonation advantage is about.

That's not what we're talking about.

True, this is about audibiity of distortion and the subtopic whether
audibility is increased due to musical dissonance between distortion
components and actual tones and overtones.

The example that makes me prone to aassume that William has a point is
the experience of overall improvement of tonal purity in recorded music
once 50 Hz hum and its overtones have been filtered out.

IF this tonal purity issue applies also for distortion components, then
out of tune distortion could be a cause of general grungyness to a
larger extent than in tune distortion, out of tune nad in tune
constituting references to the tempered scale.

You can tune most instruments to these scales.

Unless they have to play with tempered instruments.

So as to not spread this over multiple follow ups I will toss in a
comment to Dick here: the point made, I think it was by William, is
about disharmonic harmonic distortion possibly being more audible than
harmonic distortion, harmonic distortion will occur on frequencies that
are disharmonic compared to a tempered tuning as I have understood this,
consequently it is not about masking of the distortion components per
se. But I probably have a lot to learn about also this.

Graham

Kind regards

Peter Larsen

 

On Aug 22, 4:34 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

William Sommerwerck wrote:
The spectrum is important, in fact it is critical. In many cases, 2nd
order distortion is hard to hear, particularly when listening to solo
instruments. This is due to concurrent spectral masking in the human ear.

Higher order harmonics are not so well masked as 2nd, so the ear can
pick them out, even when they are relatively small.

The audibility of harmonic distortion might also depend on tuning. In a
system using whole-number ratios, harmonic distortion of all orders might be
less audible than in a tempered system.

But who's still using those old tunings ?

Almost every performer of music written in those times when
these tunings prevailed. Almost all modern performances
of Baroque music and some early classical music pays
attention to this detail. Many modern pipe organs that are
based on historical models use variations of these
temperements.

That being said, the point that the harmonics may be "on"
or "off" is somewhat silly, because it assumes masking
ONLY occurs for exact frequency matches. In fact, masking
is quite broad.

 

[Eeyore]

Peter Larsen wrote:

Eeyore wrote:

The audibility of harmonic distortion might also depend on tuning.
In a system using whole-number ratios, harmonic distortion of all
orders might be less audible than in a tempered system.

But who's still using those old tunings ?

There are people here knowing vastly more about music than I do, but all
instruments that allow intonation are in my understanding likely to use
or at least approximate those scales unless playing with a tempered
instrument. After all, that is what the intonation advantage is about.

That's not what we're talking about.

You can tune most instruments to these scales.

Graham

 

[Arny Krueger]

<dpierce@cartchunk.org> wrote in message
news:1187869334.034035.85910@m37g2000prh.googlegroups.com...

On Aug 22, 4:34 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:
William Sommerwerck wrote:
The spectrum is important, in fact it is critical. In many cases, 2nd
order distortion is hard to hear, particularly when listening to solo
instruments. This is due to concurrent spectral masking in the human
ear.

Higher order harmonics are not so well masked as 2nd, so the ear can
pick them out, even when they are relatively small.

The audibility of harmonic distortion might also depend on tuning. In a
system using whole-number ratios, harmonic distortion of all orders
might be
less audible than in a tempered system.

That being said, the point that the harmonics may be "on"
or "off" is somewhat silly, because it assumes masking
ONLY occurs for exact frequency matches.

I suspect that some might believe that masking might be less for
non-harmonic overtones because they sound dissonant to some ears. This is
the obvious inverse of what you said.

In fact, masking is quite broad.

Agreed. When a sound is masked it is not perceived, so whether its harmonic
or not is irrelevant.

 

[William Sommerwerck]

Agreed. When a sound is masked it is not perceived, so whether
its harmonic or not is irrelevant.

Arny, this is "proof by assumption".

The issue is whether harmonic distortion is less audible in a tuning system
using whole-number ratios.

Given the claimed "broadness" of masking effects, I'm willing to accept the
idea that tuning has little or no effect on the audibility of harmonic
distortion. What I originally posted was speculation.

 

[Arny Krueger]

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:AcydnWbue_755FDbnZ2dnUVZ_oaonZ2d@comcast.com...

Agreed. When a sound is masked it is not perceived, so whether
its harmonic or not is irrelevant.

Arny, this is "proof by assumption".

No, it is proof by construction.

The issue is whether harmonic distortion is less audible in a tuning
system
using whole-number ratios.

Right, and the answer is generally known in informed circles. That knowlege
is based on both logic and observation.

Given the claimed "broadness" of masking effects, I'm willing to accept
the
idea that tuning has little or no effect on the audibility of harmonic
distortion. What I originally posted was speculation.

I'm happy to accept it as speculation. No harm, no foul if speculation turns
out to fail logical and practical tests. That one reason we call it
speculation and not fact. ;-)

 

[Scott Dorsey]

Mr.T <MrT@home> wrote:

"Scott Dorsey" <kludge@panix.com> wrote in message
news:fahilt$h9v$1@panix2.panix.com...
Yes, but do you understand what I said, or are you just choosing to
ignore
the difference between parallel circuits and series circuits?

I understand what you said, but it isn't really relevant except in the
case of the equalizer mentioned by another person in this thread, or if
you want to handwave about the number of individual op-amps in all the
channel strips on that SSL.

Not me, but isn't that what you are doing?

No.

Pop the cover on an SSL 4000 and count the number of individual gain
stages
from the front to the back, then into the tape mchine and back again.
There
are lots.

Sure, BUT it is still very unusual to have more than 100 in series with the
audio chain, just as I originally stated.
I guess you could possibly achieve it, *IF* that was your aim. And it would
probably still measure fairly blameless in any case.

Pull the cover on an SSL 4000 and look inside. Or just look at the
schematic.

While you're staring at all the chips next time, why not actually shove a
test signal in and measure the result at the output. I think you will not
find any significant problems unless it is broken.

Well, what comes out sure sounds a whole lot different than what went in,
so I would suspect a measurement would indicate that too.

Bob Pease has a wonderful classroom demo in which he shows a 1 KC square
wave through a fairly clean op-amp stage, then through a hundred, and
then through a huge board with a thousand op-amps on it. A small error
gets exaggerated substantially.
--scott

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

 

[Scott Dorsey]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

That's not what we're talking about.

You can tune most instruments to these scales.

Except the piano, which you can't really tune to _any_ scale...
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."