John Curl's Blowtorch preamplifier part II - Page 2423 - diyAudio
 John Curl's Blowtorch preamplifier part II
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Join Date: Nov 2008
Location: Oakmont PA
Quote:
 Originally Posted by DF96 Last time I looked, differentiation and integration were linear transformations so can't introduce distortion. They do, of course, modify frequency response. Sorry, am I "jumping on the Fourier bandwagon"? Silly me, to think that mathematics might actually tell us something useful about "the real world"!
Normally when I get responses like this I assume the problem is that English is not their native language and the error is in translation. The word "Linear" has multiple meanings and apparently you haven't even bothered to test the math for your comment.

But to make this clear If you take the first derivative of a square wave you get a Dirac Delta function. If you take the integral you get a triangle wave.

Now if you care to listen to these you will find they do not sound the same.

If you would like to look at the the Fourier representation they are quite different.

If you would like to describe the difference in harmonic components and the resultant distortion you would see that they are not "Linear!"

Last edited by simon7000; 6th July 2012 at 02:57 PM.

diyAudio Member

Join Date: Jan 2004
Location: dorchester ma
Quote:
 Originally Posted by RNMarsh I can not cover the past all over again... as someone said -- time is running out. All was discussed in detail with John C. and W.Jung and others at the time and a long time before the invitation. Check the Proceedings (1995) and then get back to me. I am adding this in here to help make a more complete picture and the history of the capacitor issue. Thx - Richard (Dick) Marsh
I don't have the proceedings right now and I didn't mean to contradict anything there only point out that a simple passive circuit that has a second order non-linearity that can differentate between music and sine waves is extraordinary. I was involved in the bridge null test with John and Walt, it is very powerful, but when I wanted to discuss how to use it to extract the Pease ladder model for the cap no one was interested. After all they were making 5 1/2 - 6 1/2 digit integrating A/D's by some simple compensation techniques. I never found DA alone to do anymore than cause minor frequency response deviations and as usual one had to insert truely horrible examples to get large results. Is high DA an indicator of high voltage coefficient, I don't know?

I have not changed my mind on the matter at all. This work was very useful but most of the time it pointed out the awful components or bad things that folks knew to avoid in the first place. As a justification for substituting a good \$2 film cap with an \$80 hand made teflon one I don't agree (and never have).

BTW I disliked that DSP conference because David Rich expected an onslaught of objectivism aimed at debunking the audiophile "myths". I didn't cooperate, if you remember I even said good things about SET amps which incited a member of the audience to think I spoke against feedback. David Rich never spoke to me again. You also might remember when I pointed out the conventional I/V had rising output impedance that was an open door for RFI the feathers also flew. Don't knock the 5532.
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"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

Last edited by scott wurcer; 6th July 2012 at 03:25 PM.

 6th July 2012, 03:12 PM #24223 diyAudio Member   Join Date: May 2007 They don't sound the same because they represent very different frequency responses, but a triangle, square and Dirac delta have exactly the same frequency components and can (in an ideal world) be transformed back and forth with no loss or addition of information by purely linear circuits. No distortion needed! You have helped me make my point. At frequencies several decades above its rolloff point a low pass filter is virtually indistinguishable from an integrator. If an integrator introduced distortion then all opamp and standard SS power amp circuits would be useless for audio. Integrators and differentiators really don't create distortion, but they do fiddle with frequency response in a major way. However, a coupling cap is chosen to alter frequency response either in a selected way or as little as possible so the 'differentiation' aspect of it is minimal. You really ought to think through what you are saying before confusing people with misunderstandings about calculus.
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Join Date: Jan 2004
Location: dorchester ma
Quote:
 Originally Posted by simon7000 If you would like to describe the difference in harmonic components and the resultant distortion you would see that they are not "Linear!"
A square wave by one definition is a maximally distorted sine wave and integration or differentiation are simple first order filtering functions. BTW the derivative of a square wave is a train of +/- impulses the spectrum simply the square waves filtered by a first order zero, The tri-wave simply the square wave filtered by a first order pole. Integration and differentiation do not distort i.e. they do not create new harmonics.

In Fourier space the integral or derivative of a series sum of sines or cosines are just another sum of sines or cosines (at the same omegas).

(Sorry DF96 out outdrew me by seconds I guess)
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

Last edited by scott wurcer; 6th July 2012 at 03:27 PM.

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Join Date: Nov 2008
Location: Oakmont PA
Quote:
 Originally Posted by scott wurcer A square wave by one definition is a maximally distorted sine wave and integration or differentiation are simple first order filtering functions. BTW the derivative of a square wave is a train of +/- impulses the spectrum simply the square waves filtered by a first order zero, The tri-wave simply the square wave filtered by a first order pole. Integration and differentiation do not distort i.e. they do not create new harmonics. In Fourier space the integral or derivative of a series sum of sines or cosines are just another sum of sines or cosines (at the same omegas).
Scott,

I am aware that they are all a series of odd harmonics, however the amplitude of each of the harmonics changes. If you compare the original amplitude to the post process amplitudes of each harmonic, the difference is the definition of classic harmonic distortion as used in audio.

The process is reversible, but the issue was that when you pass a sine wave through a capacitor the current is a cosine wave. That is also called phase shift or a lagging response. The result looks and sounds the same.

When you pass a complex waveform, particularly one that is not periodic, the derivative is by the audio use of the word distorted. Even though the spectrum is the same the waveform is not. That may not not look or sound the same.

ES

 6th July 2012, 03:49 PM #24226 diyAudio Member   Join Date: May 2007 Changing the shape of a waveform by using a filter does not correspond to the normal audio use of the term 'distorted', as no new frequency components are introduced. Comparing 'before' and 'after' harmonic amplitudes can be a useful way of detecting distortion provided that there is little or no filtering going on as well. Strictly speaking, you should also see how harmonic amplitudes vary with signal level: a filter will give fixed ratios of out/in, while distortion will give varying ratios. I think you may be confusing methods of measuring harmonic distortion with definitions of what HD actually is. What if you want to avoid 'Fourier' (although I can't think why you would)? Then perhaps you could define distortion as some change in the waveform which cannot be brought about by any linear filter. Filters do change the sound, which may be why they are used, but 'change' and 'distortion' are not synonyms.
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Quote:
 Originally Posted by simon7000 Scott, If you compare the original amplitude to the post process amplitudes of each harmonic, the difference is the definition of classic harmonic distortion as used in audio. ES
Sorry ED we don't just disagree this time, you're wrong . By that definition any filter has distortion and an RIAA is nothing but distortion except at exactly 1kHz.

This is definately not any definition of harmonic distortion, there are NO NEW HARMONICS.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

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Join Date: Nov 2008
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Quote:
 Originally Posted by scott wurcer Sorry ED we don't just disagree this time, you're wrong . By that definition any filter has distortion and an RIAA is nothing but distortion except at exactly 1kHz. This is definately not any definition of harmonic distortion, there are NO NEW HARMONICS.
Scott,

The issue is slipping into the side argument.

The issue is that any capacitor is driven by a source resistance and into a load resistance and why that places limits on the circuit performance.

As any source resistance produces a finite current the charging and discharging of the capacitor is exponential not linear. Now when the amplitudes of the harmonics are varied so will the charging current available for those harmonics. That deviation is what I started with. It is not an issue with a single sine wave. Yes I know it is a very small side effect.

Now some designers use capacitors of at least ten times the value required to pass the designed low frequency cut-off citing improvements from this. Others have used high impedance loads. Both approaches reduce the issue.

The reason why I am looking at the issue is that of a musical note's ADSR (Attack, Decay, Sustain, and Release) provides a high level (or full scale for practical purposes) sharp initial envelope that is of very low frequency and is not continuous. It is the modulation between that and the "tone" (or carrier frequency) that creates artifacts that are not as low in level.

diyAudio Member

Join Date: May 2007
Quote:
 Originally Posted by simon7000 creates artifacts
No. A filter can't create anything. This is the basic fact you seem to miss. A CR circuit, even with DA, is just a filter. It might be a more complicated filter than an ideal CR, but it is still a filter. Dielectric or resistor nonlinearity is a separate issue. No matter how unlike the output waveform is from the input or how much it sounds different, there is no distortion. If it sounds too different then it merely means that the frequency rolloff is in the wrong place.

The charging of a cap from a square wave had better be exponential, not linear, otherwise it will introduce distortion through slew-rate-limiting. There is no "modulation" between a transient and a tone, as filters are linear.

diyAudio Member

Join Date: Jan 2004
Location: dorchester ma
Quote:
 Originally Posted by simon7000 Scott, The issue is slipping into the side argument. The issue is that any capacitor is driven by a source resistance and into a load resistance and why that places limits on the circuit performance.
Yes, the issue is that the best AC voltage across a cap is no AC voltage. But the true distortion at the -3dB point is due to dielectric properties other than just DA even though they might be related. As for -120dB artifacts being audible please read Dick Burwen's editorial in Linear Audio. Finishing half your beer is more audible in more ways than one.

EDIT - Probably more audible if it was a glass of beer.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

Last edited by scott wurcer; 6th July 2012 at 04:41 PM.

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