Re: Re: Re: Re: Re: Re: Harold S. Black.
I beg to differ. Music is very transitive and if you feed information from the past into the stream of the present the resulting is a hall of mirrors effect. The hall of mirrors produces distortion products that are not "natural" and are detected by the ear-brain super-computer at much lower levels than more natural distortions (does feedback lower distortion -- or just move it around so that it appears elsewhere in another form?)
dave
nw_avphile said:
I beg to differ. Music is very transitive and if you feed information from the past into the stream of the present the resulting is a hall of mirrors effect. The hall of mirrors produces distortion products that are not "natural" and are detected by the ear-brain super-computer at much lower levels than more natural distortions (does feedback lower distortion -- or just move it around so that it appears elsewhere in another form?)
dave
Re: Re: Re: Re: Re: Re: Re: Harold S. Black.
1 - The Cheever document is essentially a way to quantify "euphonic distortion"--distortion we find more pleasing (or less objectionable). There's nothing wrong with that, and I never said that low NFB amps don't have higher levels of distortion (which some seem to enjoy). We're back to amplifiers as art. If you WANT more distortion, and less accuracy, then by all means use less NFB as that's one way to get it.
2 - The main premise of the Cheever document was to attempt to resolve the apparent conflict with what the high-end tweak press reports (in this case Stereophile) and with what can be objectively measured. With respect to euphonic distortion, that's fine, but with respect to low distortion amps, the real issue seems to be the high-end press and their psychologically biased non-blind listening (the very subject of this thread).
3 - If you look at the credibility of Stereophile, as a whole, much of what they publish really doesn't stand up very well to even common sense. They claim the most outrageous differences from things that have been shown time and time again don't make any difference at all. Obviously not everyone will agree with me on this point, but if you look at the greater community at large, and not just within the esoteric crowd that has a big investment in high-end audio, my views are in the majority.
4 - So, IMHO, the Cheever document is built on a very shaky foundation to begin with--subjective biased comments that don't stand up well to blind listening results. In other words: Garbage In-Garbage Out.
I did, or at least much of it. I didn't see anything to refute what I've said about NFB. I have the following comments:Brett said:
1 - The Cheever document is essentially a way to quantify "euphonic distortion"--distortion we find more pleasing (or less objectionable). There's nothing wrong with that, and I never said that low NFB amps don't have higher levels of distortion (which some seem to enjoy). We're back to amplifiers as art. If you WANT more distortion, and less accuracy, then by all means use less NFB as that's one way to get it.
2 - The main premise of the Cheever document was to attempt to resolve the apparent conflict with what the high-end tweak press reports (in this case Stereophile) and with what can be objectively measured. With respect to euphonic distortion, that's fine, but with respect to low distortion amps, the real issue seems to be the high-end press and their psychologically biased non-blind listening (the very subject of this thread).
3 - If you look at the credibility of Stereophile, as a whole, much of what they publish really doesn't stand up very well to even common sense. They claim the most outrageous differences from things that have been shown time and time again don't make any difference at all. Obviously not everyone will agree with me on this point, but if you look at the greater community at large, and not just within the esoteric crowd that has a big investment in high-end audio, my views are in the majority.
4 - So, IMHO, the Cheever document is built on a very shaky foundation to begin with--subjective biased comments that don't stand up well to blind listening results. In other words: Garbage In-Garbage Out.
Re: Re: Re: Re: Re: Re: Re: Harold S. Black.
AmpOutput = AmpInput*Gain + All Forms of Errors and Distortion
All Forms of Errors and Distortion = AmpOutput - AmpInput*Gain
Well please explain why high NFB doesn't show up as some kind of distortion in a null difference test using real transitive music driving real reactive speakers? Or are you suggesting that it should? Again:planet10 said:
AmpOutput = AmpInput*Gain + All Forms of Errors and Distortion
All Forms of Errors and Distortion = AmpOutput - AmpInput*Gain
Re: Re: Re: Re: Re: Harold S. Black.
The simplest analogy i can use is hose filled with water, ( to represent electrons in our linear negative feedback audio amp.), and attached to a tap at one end, (which then reperesents our signal source).
As soon as the tap is opened, water must flow out the open end of the hose instantaneously...there can be no delay in the initial response....
However, turning the tap off cannot result in instant cessation of water flow out the hose due to inertia, momentum, etc, etc.....
This was the point i was trying to make.....ie:.....you cannot have delayed feedback for a stable negative feedback audio power amp..........the output, and by implication and the fraction thereof that is fed back, must respond instanteneously to input stimuli, even though it may, in charging and discharging design and parasitic time constants, take longer to complete it's response....
I think you'll find we are discussing linear time invariant systems here......DSP arrangements can be routinely persuaded to accomodate delays of a fortnight++++
planet10 said:
The simplest analogy i can use is hose filled with water, ( to represent electrons in our linear negative feedback audio amp.), and attached to a tap at one end, (which then reperesents our signal source).
As soon as the tap is opened, water must flow out the open end of the hose instantaneously...there can be no delay in the initial response....
However, turning the tap off cannot result in instant cessation of water flow out the hose due to inertia, momentum, etc, etc.....
This was the point i was trying to make.....ie:.....you cannot have delayed feedback for a stable negative feedback audio power amp..........the output, and by implication and the fraction thereof that is fed back, must respond instanteneously to input stimuli, even though it may, in charging and discharging design and parasitic time constants, take longer to complete it's response....
traderbam said:
Think! How do digital control systems work? Very big time delays here around the feedback loop. Look up "z transforms" on the net.
I think you'll find we are discussing linear time invariant systems here......DSP arrangements can be routinely persuaded to accomodate delays of a fortnight++++
Trouble in paradise...
I don't have the time at the moment to do a blow-by-blow analysis of the document but I promise to look at it more closely and see if I missed some other points. But you're partly right, when it seemed the very premise was based on non-blind listening--from the esoteric tweak press at that--my respect for the rest of what the author had to say dropped several notches.
If somewhere later in the document are the results of well designed blind listening tests that collaborate what the author is saying about what is heard versus what is measured, I will very much change my views. Without that, however, it's not too far from doing a study on what the National Enquirer reports about Michael Jackson's love life. The study might be entirely valid, but the premise is based on subjective gossip.
Yikes! I wasn't trying to attack you, and I agree with the above statement. But along with mikek (see post #401), I think the "what is heard" part of your statement above is largely based on comments of the high-end press in the Cheever document. Hence I think it's very valid to call into question the validity of "what was heard"? I doubt the staff at MIT is familiar with Stereophile so it doesn't surprise me it passed their inspection.Brett said:
I don't have the time at the moment to do a blow-by-blow analysis of the document but I promise to look at it more closely and see if I missed some other points. But you're partly right, when it seemed the very premise was based on non-blind listening--from the esoteric tweak press at that--my respect for the rest of what the author had to say dropped several notches.
If somewhere later in the document are the results of well designed blind listening tests that collaborate what the author is saying about what is heard versus what is measured, I will very much change my views. Without that, however, it's not too far from doing a study on what the National Enquirer reports about Michael Jackson's love life. The study might be entirely valid, but the premise is based on subjective gossip.
Re: Re: Re: Re: Re: Re: Harold S. Black.
Well, I don't we are discussing linear time invariant systems. I believe the open loop gain of an audio power amp and the gains of the transistors are nonlinear, that's whole point of using negative feedback. I won't get into the instantaneous semantic discussion, will point out that there is a phase shift (several poles worth) in the open loop gain of an amplifier and therefore in phase delay around the feedback loop. Some of these poles shift with signal level due to changes in Ft with current and transistor capacitances that are a function of the signal voltage across them. I believe I read the statement that a feedback system is either stable or an oscillator somewhere in this thread. This is not true as it ignores the whole issue of phase margin.
Novel use of the hose analogy and mention linear time invariant systems in the same post though, its good too see you taking a two pronged approach to all this but for the fact that neither one really describes what is happening in the negative feedback loop.
mikek said:
The simplest analogy i can use is hose filled with water, ( to represent electrons in our linear negative feedback audio amp.), and attached to a tap at one end, (which then reperesents our signal source).
As soon as the tap is opened, water must flow out the open end of the hose instantaneously...there can be no delay in the initial response....
However, turning the tap off cannot result in instant cessation of water flow out the hose due to inertia, momentum, etc, etc.....
This was the point i was trying to make.....ie:.....you cannot have delayed feedback for a stable negative feedback audio power amp..........the output, and by implication and the fraction thereof that is fed back, must respond instanteneously to input stimuli, even though it may, in charging and discharging design and parasitic time constants, take longer to complete it's response....
I think you'll find we are discussing linear time invariant systems here......DSP arrangements can be routinely persuaded to accomodate delays of a fortnight++++
Well, I don't we are discussing linear time invariant systems. I believe the open loop gain of an audio power amp and the gains of the transistors are nonlinear, that's whole point of using negative feedback. I won't get into the instantaneous semantic discussion, will point out that there is a phase shift (several poles worth) in the open loop gain of an amplifier and therefore in phase delay around the feedback loop. Some of these poles shift with signal level due to changes in Ft with current and transistor capacitances that are a function of the signal voltage across them. I believe I read the statement that a feedback system is either stable or an oscillator somewhere in this thread. This is not true as it ignores the whole issue of phase margin.
Novel use of the hose analogy and mention linear time invariant systems in the same post though, its good too see you taking a two pronged approach to all this but for the fact that neither one really describes what is happening in the negative feedback loop.
Re: Re: Re: Re: Re: Re: Re: Re: Harold S. Black.
Well, I think it's pretty much a non-issue in that context. Though Jinji Kimura would probably disagree seeing as that's his whole reason for keeping the feedback loop as small as possible in his Gaincard amplifier.
I try to keep all conductive loops, not just feedback loops, as small as possible because smaller conductive loops mean less susceptibility to interfering noise. And while I don't mind a bit of signal-related distortion, I don't care at all for non-signal-related noise.
And hey, keeping things small conserves resources too.
se
nw_avphile said:
Well, I think it's pretty much a non-issue in that context. Though Jinji Kimura would probably disagree seeing as that's his whole reason for keeping the feedback loop as small as possible in his Gaincard amplifier.
I try to keep all conductive loops, not just feedback loops, as small as possible because smaller conductive loops mean less susceptibility to interfering noise. And while I don't mind a bit of signal-related distortion, I don't care at all for non-signal-related noise.
And hey, keeping things small conserves resources too.
se
Re: Re: Re: Re: Re: Re: Re: Re: Re: Harold S. Black.
That's good design practice (that's often NOT followed in audio layouts). It also reduces ESD susceptibility. In digital design (especially if you want the equipment to meet the FCC part B requirements for radiation) it becomes essential.Steve Eddy said:
Re: Re: Re: Re: Re: Re: Re: Harold S. Black.
...no fred, you cannot have several poles worth of phase shift in a stable linear system...that is a contradiction in terms....
.....and for a system which cannot be used open-loop, the inherent non-linearity of the individual components is academic...the purpose of the global feedback loop, of course, is render such negligible...
...in other words the applied signal does not give two hoots what the open-loop linearity of your system amounts to.....it does not even 'know' you've applied feedback.......
Fred Dieckmann said:
...no fred, you cannot have several poles worth of phase shift in a stable linear system...that is a contradiction in terms....
.....and for a system which cannot be used open-loop, the inherent non-linearity of the individual components is academic...the purpose of the global feedback loop, of course, is render such negligible...
...in other words the applied signal does not give two hoots what the open-loop linearity of your system amounts to.....it does not even 'know' you've applied feedback.......
Re: Re: Re: Re: Re: Re: Re: Re: Harold S. Black.
No. Electrons don't flow, they drift under the influence of the applied field which propagates as a transverse wave down the length of the conductors at a finite speed.
The electrons don't take on any drift until the field reaches them. And because the field propagates at a finite speed, there will be a delay between the application of a field at one end of the line and its influencing the electrons at the end of the line.
In other words, the electrons at one end of the cable don't start dribbling out the instant you apply a field at the other end. There is a delay, which will be the propagation speed of the wave divided by the length of the line.
So, given an ideal propagation speed of 300 million meters per second, if your line is 300 million meters long, it will take 1 second before the wave reaches the end of the line and the electrons take on any drift.
se
mikek said:
No. Electrons don't flow, they drift under the influence of the applied field which propagates as a transverse wave down the length of the conductors at a finite speed.
The electrons don't take on any drift until the field reaches them. And because the field propagates at a finite speed, there will be a delay between the application of a field at one end of the line and its influencing the electrons at the end of the line.
In other words, the electrons at one end of the cable don't start dribbling out the instant you apply a field at the other end. There is a delay, which will be the propagation speed of the wave divided by the length of the line.
So, given an ideal propagation speed of 300 million meters per second, if your line is 300 million meters long, it will take 1 second before the wave reaches the end of the line and the electrons take on any drift.
se
Re: Re: Re: Re: Re: Re: Re: Re: Re: Harold S. Black.
http://shaping.ru/download/pdffile/Hydrodynamic.pdf
www.radioelectronicschool.com/downloads/howfast.pdf
Steve Eddy said:
http://shaping.ru/download/pdffile/Hydrodynamic.pdf
www.radioelectronicschool.com/downloads/howfast.pdf
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Harold S. Black.
These are irrelevant. They only deal with the movement of electrons under the influence of an applied field. What you don't seem to be grasping here is that the applied field propagates at a finite velocity down the line and that the electrons at the end of the line, don't do anything until that force reaches them.
se
mikek said:
These are irrelevant. They only deal with the movement of electrons under the influence of an applied field. What you don't seem to be grasping here is that the applied field propagates at a finite velocity down the line and that the electrons at the end of the line, don't do anything until that force reaches them.
se
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Harold S. Black.
If that were the case, then propagation velocity would have to be infinte. And propagation velocity is not infinite. You apply an "EMF" at one end of the line and the electrons at the other end of the line won't "experience" it until some time later.
More germane, the "EMF" at the output of the amplifier takes a certain, non-zero amount of time to propagate from the output back to the input. That time being the propagation velocity divided by the length of the feedback loop.
Which means that feedback is ALWAYS delayed by some amount.
se
mikek said:
If that were the case, then propagation velocity would have to be infinte. And propagation velocity is not infinite. You apply an "EMF" at one end of the line and the electrons at the other end of the line won't "experience" it until some time later.
More germane, the "EMF" at the output of the amplifier takes a certain, non-zero amount of time to propagate from the output back to the input. That time being the propagation velocity divided by the length of the feedback loop.
Which means that feedback is ALWAYS delayed by some amount.
se
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.