syn08 said:
I´m still suprised that some common (common as i thought they were) terms are used and interpreted in quite different ways around the world.
I only found a (federal standard? ) for definition here:
http://www.its.bldrdoc.gov/fs-1037/dir-037/_5509.htm
http://www.its.bldrdoc.gov/fs-1037/dir-017/_2542.htm
The definitions for THD and IM-Distorsion rely on different input signal content; while THD uses only one (of course variable) input frequency, IM-tests are made by two or more frequencies.
Therefore in our hypothetical case it is only one fundamental in the input signal, that creates an IM-product, as the second input frequency is a hidden one (in this case caused by jitter).
So the answer to your question would be "no", as a 19+20 kHz IMD test contains two input frequencies.
BTW, regarding the "linear distorsions"; is it really useless to seperate signal alterations that create no spectral content from signal alterations that only change amplitude or phase?
In the end the merit of technical terms is the common meaning- if enough people are convinced the definitions may be changed.
PHEONIX said:
Hi Arthur. I now have electrical performance goals that equate with inaudibility of the amp itself. This makes the design process much more focussed and successful.
An issue with speakers is that they have their own sonic signatures and their signature is not independent of the amp used to drive them (they interact). To critically assess an amp by listening requires enough familiarity with the speakers used to be able to discriminate the speaker distortion from the amp distortion. For amplifier evaluation, I think familiarity with the speakers is more important than which speakers you use, provided the speakers are reasonably well designed. The source is much more important; use the best you can sensibly afford.
Brian
We, pioneers of audio design, make our definitions of audio 'deviations' as we go. 'Linear distortion' is one such definition. Works for me!
Just like Otala defined: TIM. It could also be called SID, 'Slope distortion' etc. TIM is just a definition.
'Linear distortion' denotes the effects that dielectric absorption gives you, that is NOT easily measureable with an older type wave or spectrum analyser. This sort of distortion used to be VERY BOTHERSOME to users of analog computers.
We found it somewhat effecting audio listeners, sometimes as a 'sweetener' or 'forgiver' of poorly recorded material. Other times, it deviated the path leading to audio accuracy, and was best, removed.
Just like Otala defined: TIM. It could also be called SID, 'Slope distortion' etc. TIM is just a definition.
'Linear distortion' denotes the effects that dielectric absorption gives you, that is NOT easily measureable with an older type wave or spectrum analyser. This sort of distortion used to be VERY BOTHERSOME to users of analog computers.
We found it somewhat effecting audio listeners, sometimes as a 'sweetener' or 'forgiver' of poorly recorded material. Other times, it deviated the path leading to audio accuracy, and was best, removed.
I have heard the term linear distortion used to represent frequency response variations in the past. That distinguishes it from non-linear distortions. Amplitude dependent frequency response changes would be a bit of a conundrum here, especially if they don't have a corresponding harmonic generation.
'Linear distortion' shows up in the 'time domain' more clearly than in the 'frequency demain'. This is why it is so obscure with conventional measurements.
It is more like comparing two graphical images on a screen and noting subtle difference between them, especially if you subtract the two images from each other.
It is more like comparing two graphical images on a screen and noting subtle difference between them, especially if you subtract the two images from each other.
1audio said:
Yes. According to the definition of "linear distortion" a filter is distorting the signal. The notion is obviously important in telecom and other areas where the phase relationships are critical, but to call this a "distortion" in audio is certainly not appropriate.
BTW, I haven't ever seen a shred of evidence about DA inducing linear distortions. To me, this is one of John's pet peeves.
john curl said:
Unfortunately JC, you haven't offered anything beyond blank statements. Again, the topic is "DA induces linear distortions".
I have offered you my own work, published in Journal of Applied Physics in the mid 90's, together with references and citations, which clearly proves that DA is fundamentally a nonlinear phenomena, which consequently introduces non linear distortions. Obviously you haven't bothered to take a look, which is not at all suprising given your approach of anything that contradicts your 40 years old experience.
The funny thing is that DA in capacitors that we normally use in audio for signal transmission is modeled by paralleled ideal caps and idealized resistors. This was done by Dow, in the 1950's for analog computer simulation and adopted by Bob Pease (remember him?) on his 1980's paper. DA, the stuff that we ACTUALLY measure, was emulated on SPICE in the early 1980's by Scott Wurcer, who contributes here.
It is true that IT IS A MODEL, but what we actually measure is a deviation of up to 10% or
(-40dB) and the computer simulation closely emulates real measurements, YET the nonlinear distortion is 0, by inspection in the computer model, and normally below -100dB in measurements of real devices. Therefore, there is often a range of 1000 times or MORE deviation from linear distortion and what we measure as nonlinear distortion.
Yet, everyone must know that DA is a physical mechanism, and that by definition, must contain SOME nonlinearity. This appears to be where you come in.
Well, clue us in!
It is true that IT IS A MODEL, but what we actually measure is a deviation of up to 10% or
(-40dB) and the computer simulation closely emulates real measurements, YET the nonlinear distortion is 0, by inspection in the computer model, and normally below -100dB in measurements of real devices. Therefore, there is often a range of 1000 times or MORE deviation from linear distortion and what we measure as nonlinear distortion.
Yet, everyone must know that DA is a physical mechanism, and that by definition, must contain SOME nonlinearity. This appears to be where you come in.
Well, clue us in!
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