Nelson Pass said:Yes, well the real fact is that we don't know all that much about
hearing. Steven Dear (the bat guy) has been pointing me in a lot
of interesting directions, and it continues to be be very fascinating,
but mostly the conclusion I have to draw is that we don't really
even know what we don't know.
The ear is not really a microphone, and the neural networks which
process the feed from the ear do not really resemble any analog or
digital system we are familiar with.
We vaguely understand that high order distortions are more
audible, but we are operating in the realm of "ironic" engineering,
to steal a phrase from John Horgan, in which we are speculating
without either much in the way of facts or even decent theories
which suggest good experiments. Sort of like literary criticism.
Ironic engineering come in the flavors "naive" and "sophisticated",
the former having strong beliefs in the "truth" of things like
harmonic distortion analysis, and the latter more sceptical, maybe
having listened to audio with single ended tube amps and such.
So does the drunk really appreciate the limitations of his search
method? Maybe he does, but likes working where the light is.
Why should we seek to achieve a perfect signal through the amplifier if it's invariably going to be distorted through the loudspeaker and room?
Isn't it (sometimes) possible for example that the distortion from an amplifier cancels out the distortion of the room in a way that's favorable not only to the ear but in measurements?
Nelson Pass said:
Or as I put it elsewhere:
............................................................
Experts knowledge limit.
Yeah, we sure can have doubt about what is true and what is not.
And how little we seem to know.
On one hand we have one of our best (Curl)
saying he is concerned with higher order harmonic distortion
at the 0.001 % level (-100dB)
and if he is concerned it must mean we can hear it, as it is audio we are talking about.
On the other hand we have one with great knowledge
after spent half his life in research and work with sound and related matters (Geddes)
that say some sounds we can not even perceive at 20.000 % (-30dB) harmonic distortion level.
So, here I am today.
I am not so sure about anything.
And I can not see any good investigations happen,
that in the near future can contribute to make me less confused
about human sound perception.
Lineup
probably will not know close to truth about sound during his lifetime
Professor smith said:
..and one must not forget that the recording itself has plenty of distortion as well....
I recently asked an artist who has mixed its own CD why I could hear unpleasant distortion (so I called it) on its CD and he replied that he had noticed also but could not get rid of it in the mix and he said that "..it is only rock & roll" after all..."
My point is that there is absolutely no similarity between recording/mixing process between different pieces of music and the latters suffer from overcompression, saturation distortion and all sort of things... Since we are used to that, we probably only noticed the worst sound productions....
The latter one from some writings I feel it to hear about my yammering not being totally futile after all here possibly.
Somebody knows it, how large an the distortion of the human ear?
And this moreover individually apparently different!
Not spoken because of the effects of the cerebral factor which cannot be neglected apparently.
That I believe it, even not so much processed topic, than the distortion of the ear.
I do not know it, how large an amplifier's distortion, which disturbs anybody already, may be.
I am not anxious whatever because of this.
Szervusz Lineup!
I very much likes your avatar, your signature and what you write!
You know that I will be there beside you on that day, and I hold your shoulder with my hand!
Gyuri
Somebody knows it, how large an the distortion of the human ear?
And this moreover individually apparently different!
Not spoken because of the effects of the cerebral factor which cannot be neglected apparently.
That I believe it, even not so much processed topic, than the distortion of the ear.
I do not know it, how large an amplifier's distortion, which disturbs anybody already, may be.
I am not anxious whatever because of this.
Szervusz Lineup!
I very much likes your avatar, your signature and what you write!
You know that I will be there beside you on that day, and I hold your shoulder with my hand!
Gyuri
Already for a long time is eager to get from me some thoughts, may interest somebody possibly.
All of this all audio fuss is similar to the Search of the Holy Grál mostly possibly or search to the GUT.
I believe it about my own part accordingly, the above one from among two any of the soon ones will be,
rather than an audio like that chain, the one that produces a totally realistic sound.
Not talking about it, that not only the sound, but it would be necessary to give back the sound environment.
From among these on that of any of the levels impossible, because how can be expected it, that an any kind of loudspeaker, (let us talk about this now only) could be able to give back the sound of single Guarnieri, Amati or Stradivari. Since we do not know even it punctually, for what these its secret! Beside this for this the unfortunate audio chain we call it, it is necessary to reproduce an organ's, a full orchestra's, a human song's or a rock concert's sound sometimes.
All this together with sound environment, in a relatively little room!
Not, we chase dreams, but this much better, as if we would find the perfect answer.
All of this all audio fuss is similar to the Search of the Holy Grál mostly possibly or search to the GUT.
I believe it about my own part accordingly, the above one from among two any of the soon ones will be,
rather than an audio like that chain, the one that produces a totally realistic sound.
Not talking about it, that not only the sound, but it would be necessary to give back the sound environment.
From among these on that of any of the levels impossible, because how can be expected it, that an any kind of loudspeaker, (let us talk about this now only) could be able to give back the sound of single Guarnieri, Amati or Stradivari. Since we do not know even it punctually, for what these its secret! Beside this for this the unfortunate audio chain we call it, it is necessary to reproduce an organ's, a full orchestra's, a human song's or a rock concert's sound sometimes.
All this together with sound environment, in a relatively little room!
Not, we chase dreams, but this much better, as if we would find the perfect answer.
Nelson,
Very nice article.
As I compare the two graphs showing the effects of NFB on higher order harmonic distortion, I might conclude that source degeneration NFB is greatly superior to NFB applied to the gate of the gain device. It looks like the starting points for the two graphs are different, the source degeneration graph starts with relatively high amounts of 3rd and 4rth order harmonics.
Could you comment on how these two forms of NFB compare?
Thanks,
JJ
Very nice article.
As I compare the two graphs showing the effects of NFB on higher order harmonic distortion, I might conclude that source degeneration NFB is greatly superior to NFB applied to the gate of the gain device. It looks like the starting points for the two graphs are different, the source degeneration graph starts with relatively high amounts of 3rd and 4rth order harmonics.
Could you comment on how these two forms of NFB compare?
Thanks,
JJ
Gyuri said:
Me not worried, too. About amplifier distortion levels.
Think amplifier distortion is only a minor issue, in 90 % of sound systems.
Yes, sometimes I change my avatar and my signature message.
If you really take a closer look at yourself
then I think a lot would discover,
reason you discuss in this COMMUNITY is not all what it appear to be.
Maybe it is not that amplifier thing.
Maybe that amplifier thing is a good excuse for get something.
Something you need.
... like a friend or two, some body that reply to you
jupiterjune said:
These are not apples-to-apples comparison, and you will note that
I did not include the degenerated example in the article.
However it supports my own opinion that degeneration is not the
same as loop feedback. Some opine that degeneration causes
creation of higher order harmonics, but I haven't seen it yet.
It is accordingly presumably. I did an interesting experiment once.
Different clear sine with a lower frequency waves I cranked up to the loudspeakers. Since I do not have a gauge microphone, only this cheapo ear of mine, I had to rely on this. It was possible to map the strengthening and the extinctions walking round because of that wonderfully in the room. On different frequencies, different places.
Gyuri
Different clear sine with a lower frequency waves I cranked up to the loudspeakers. Since I do not have a gauge microphone, only this cheapo ear of mine, I had to rely on this. It was possible to map the strengthening and the extinctions walking round because of that wonderfully in the room. On different frequencies, different places.
Gyuri
janneman said:
I agree, you'll have areas of pressure reinforcement and canceling creating peaks and dips in the response based on room shape, size, and listener position. In general things that absorb sound are not flat in frequency absorption. So the type and quantity of that treatment can also alter the frequency response in the diffuse field (the area back away from the speakers where moving away no longer lowers the sound level)
If you have something in the room that is excited at natural frequency and resonates, it may then emit harmonics of the resonance, and that would the only exception I can think of. An obvious example of this is the loudspeaker cabinet itself. But could also be the glass in picture frames or windows, or shelves. I had a problem with loose glass panes in a fireplace door for instance. A slow sine sweep of the room can find these.
In general, I disagree with the group of people tend to state the room and speaker is where 99% of the problems are, and all you need is a cheap receiver and superb loudspeakers with extensive room treatment. These are the same guys that insist a single distortion measurement qualifies that cheap receiver. Not that one can ignore room and speakers, but it's not "everything".
Whatever here true it, that a chain so strong, than the weakest link. Is seems to me accordingly, if we exchange only a chain link for a better one after all sometimes however the audio in a audio chain, as if the whole chain would be stronger.
I feel some contradiction here.
At the same time my opinion the quality of the two ends of a shackle the most determining one in the look of the tone quality.
Gyuri
I feel some contradiction here.
At the same time my opinion the quality of the two ends of a shackle the most determining one in the look of the tone quality.
Gyuri
Nelson Pass said:
I got the impression from the article that many-staged circuits were more naughty than NFB? Because the more stages you add the worse the problems get, but keep adding NFB and eventually things start to turn around.
I also got the impression that if a designer did it the hard way, and developed a multi-stage circuit with 80dB of NFB, and solved the side-effects like instability, that there is nothing to complain about?
Hi Nelson
I've read the article and liked it much. Good work!
One thing just makes me think:
1. Class (A)B produces high amount of high-order harmonics
2. Negative feedback, to a degree, creates the higher order harmonics out of lower order hamonics of open loop characteristics.
These are points we all agree I believe. But the real point is: do the phenomena mentioned above add up?
I bet negative feedback may increse 7th harmonic of the single ended class A amplifier, but any amount of feedback does reduce 7th harmonic of the class B stage, because much of 7th hamonic was already there.
What do you think?
I've read the article and liked it much. Good work!
One thing just makes me think:
1. Class (A)B produces high amount of high-order harmonics
2. Negative feedback, to a degree, creates the higher order harmonics out of lower order hamonics of open loop characteristics.
These are points we all agree I believe. But the real point is: do the phenomena mentioned above add up?
I bet negative feedback may increse 7th harmonic of the single ended class A amplifier, but any amount of feedback does reduce 7th harmonic of the class B stage, because much of 7th hamonic was already there.
What do you think?
Hard to say.
Of course the intent of the article was more along the lines of shaking
thinking up rather than pointing the way.
It's pretty clear that most anything you do will alter the complexity - when
you apply correction to a pre-existing harmonic, you still get other stuff as
well.
If the other stuff is more audible we need to consider whether it's because
the distortion is less musical or because it helps create the formation of
larger distortion peaks.
I did a little work improving the model since the article, starting with Boyk's
trumpet spectrum carried out to the 50th harmonic in approximately the
same amplitudes as his data.
http://www.cco.caltech.edu/~boyk/spectra/spectra.htm
I added normalization (not in the original sims) which sets the peak signal
value to 1.00, making the results much more realistic (and less dramatic),
and then ran this through models of single and multiple stages with
harmonics out to the 10th, declining in amplitude at 3 dB per harmonic.
Just playing around with this model, I decided that you probably want to
start thinking in terms of a 10 to 1 margin when talking about static
distortion versus dynamic - in other words, you can expect to see distortion
peaks with music on the order of 10 times that which you see with a single
tone assuming that both signal waves have the same size peak amplitude.
Is the ear sensitive to peak distortion? That would support the greater
audibility of higher order harmonics, but I don't know.
If you drive the distortion low enough, does it become audible? You would
reasonably expect so, but that is not supported by the anecdotal observations
of many audiophiles.
Of course the intent of the article was more along the lines of shaking
thinking up rather than pointing the way.
It's pretty clear that most anything you do will alter the complexity - when
you apply correction to a pre-existing harmonic, you still get other stuff as
well.
If the other stuff is more audible we need to consider whether it's because
the distortion is less musical or because it helps create the formation of
larger distortion peaks.
I did a little work improving the model since the article, starting with Boyk's
trumpet spectrum carried out to the 50th harmonic in approximately the
same amplitudes as his data.
http://www.cco.caltech.edu/~boyk/spectra/spectra.htm
I added normalization (not in the original sims) which sets the peak signal
value to 1.00, making the results much more realistic (and less dramatic),
and then ran this through models of single and multiple stages with
harmonics out to the 10th, declining in amplitude at 3 dB per harmonic.
Just playing around with this model, I decided that you probably want to
start thinking in terms of a 10 to 1 margin when talking about static
distortion versus dynamic - in other words, you can expect to see distortion
peaks with music on the order of 10 times that which you see with a single
tone assuming that both signal waves have the same size peak amplitude.
Is the ear sensitive to peak distortion? That would support the greater
audibility of higher order harmonics, but I don't know.
If you drive the distortion low enough, does it become audible? You would
reasonably expect so, but that is not supported by the anecdotal observations
of many audiophiles.
There are several problems relating to feedback (to be interpreted broadly as published specifications, else why bother with feedback?) vs. sound quality in the listening room.
1) Most people don't have any earthly idea what real music sounds like. The only thing they compare amps to are other amps, which leaves them decidedly at sea when it comes to deciding which ones sound more like real music.
2) High feedback tends to give--amongst other things--a little bit of forwardness in the upper midrange. The problem here is that this is a region where we're genetically programmed to be excited...is that sussuration in the grass just the wind or an approaching predator?...and people think it conveys "more detail."
3) In the context of DIY stuff, the majority of builders are just so damned pleased to hear music come out of something they built with their own two hands that they don't care if it sounds like elephant flatulance...it's their elephant flatulence, and they're ecstatic. Note that I'm not saying people shouldn't be proud of, and excited by, their efforts...it's just that a lot of people never actually listen critically. It's theirs and it's perfect...so there!
4) Regardless of how much they protest to the contrary, most people aren't detail-oriented enough to notice the little things that make the difference. They listen to the overall envelope of the music and don't dwell on the fine textures. I've got a buddy who's like this. He's got some older, fairly decent equipment, but he doesn't really appreciate it because half the time he puts on music, then listens from the next room. You're not going to hear the differences in imaging, high end extension, and detail that way.
5) It's not necessary, but it's often helpful to listen (critically, not just hearing it cranked wide open at a party) to lots of different pieces of equipment. That way you can box in what is and is not achievable with current technology. If the only animal you've ever seen is a dog, you might be under the impression that all animals look like dogs. On first seeing a sea urchin, you might not even recognize it as an animal. But if you've seen whales and aardvarks and bears and eagles and earth worms and microbes you're both more open minded and less easily fooled.
6) Much ado is made of people who 'hear what they expect to hear' when listening to high end equipment, with the implication (often not even implied) that there's nothing there to hear. Note, however, that the converse is just as true--if not moreso--in that if someone goes in to listen to a piece of equipment with good distortion specifications, and if they're prone to thinking that standard distortion specs are all they need, then they've already decided that the amp sounds fantastic before the first note is played.
There are other factors as well, but what I'm trying to get at it that, honestly, the majority of listeners don't really listen closely enough to notice if one circuit really sounds more like music than another. It's good enough for background music and it's good enough for parties, so they figure it's top notch. That per se isn't a problem. It's when they start insisting that 'good enough' means that's all there is to hear and that others need not attempt to wring that last iota of performance out of their circuits that I begin to have a problem with their approach and their attitude.
Nelson's distortion writeup might help shed light on some of the implications of negative feedback. Others have attempted to discover why the published specifications don't always match what you hear, but so far no one has managed to find a complete explanation. In the meantime, I've settled for using as little negative feedback as possible, sometimes as low as 0dB (GR-25), sometimes low single digits (around 5 to 8dB) and sometimes as high as 15 to 20dB. Above that, it begins to be too intrusive. If I find that I need more than that to whip a circuit into shape, I start asking myself whether the circuit needs a basic redesign. More and more, I'm coming to the conclusion that the circuit is fundamentally flawed and either needs reworking or junking.
One more thing. In most areas of life people are skeptical if someone offers them something for nothing. And they should be. So why is it that those same people swallow whole the concept that negative feedback extracts no price?
Just something to think about.
Grey
1) Most people don't have any earthly idea what real music sounds like. The only thing they compare amps to are other amps, which leaves them decidedly at sea when it comes to deciding which ones sound more like real music.
2) High feedback tends to give--amongst other things--a little bit of forwardness in the upper midrange. The problem here is that this is a region where we're genetically programmed to be excited...is that sussuration in the grass just the wind or an approaching predator?...and people think it conveys "more detail."
3) In the context of DIY stuff, the majority of builders are just so damned pleased to hear music come out of something they built with their own two hands that they don't care if it sounds like elephant flatulance...it's their elephant flatulence, and they're ecstatic. Note that I'm not saying people shouldn't be proud of, and excited by, their efforts...it's just that a lot of people never actually listen critically. It's theirs and it's perfect...so there!
4) Regardless of how much they protest to the contrary, most people aren't detail-oriented enough to notice the little things that make the difference. They listen to the overall envelope of the music and don't dwell on the fine textures. I've got a buddy who's like this. He's got some older, fairly decent equipment, but he doesn't really appreciate it because half the time he puts on music, then listens from the next room. You're not going to hear the differences in imaging, high end extension, and detail that way.
5) It's not necessary, but it's often helpful to listen (critically, not just hearing it cranked wide open at a party) to lots of different pieces of equipment. That way you can box in what is and is not achievable with current technology. If the only animal you've ever seen is a dog, you might be under the impression that all animals look like dogs. On first seeing a sea urchin, you might not even recognize it as an animal. But if you've seen whales and aardvarks and bears and eagles and earth worms and microbes you're both more open minded and less easily fooled.
6) Much ado is made of people who 'hear what they expect to hear' when listening to high end equipment, with the implication (often not even implied) that there's nothing there to hear. Note, however, that the converse is just as true--if not moreso--in that if someone goes in to listen to a piece of equipment with good distortion specifications, and if they're prone to thinking that standard distortion specs are all they need, then they've already decided that the amp sounds fantastic before the first note is played.
There are other factors as well, but what I'm trying to get at it that, honestly, the majority of listeners don't really listen closely enough to notice if one circuit really sounds more like music than another. It's good enough for background music and it's good enough for parties, so they figure it's top notch. That per se isn't a problem. It's when they start insisting that 'good enough' means that's all there is to hear and that others need not attempt to wring that last iota of performance out of their circuits that I begin to have a problem with their approach and their attitude.
Nelson's distortion writeup might help shed light on some of the implications of negative feedback. Others have attempted to discover why the published specifications don't always match what you hear, but so far no one has managed to find a complete explanation. In the meantime, I've settled for using as little negative feedback as possible, sometimes as low as 0dB (GR-25), sometimes low single digits (around 5 to 8dB) and sometimes as high as 15 to 20dB. Above that, it begins to be too intrusive. If I find that I need more than that to whip a circuit into shape, I start asking myself whether the circuit needs a basic redesign. More and more, I'm coming to the conclusion that the circuit is fundamentally flawed and either needs reworking or junking.
One more thing. In most areas of life people are skeptical if someone offers them something for nothing. And they should be. So why is it that those same people swallow whole the concept that negative feedback extracts no price?
Just something to think about.
Grey