What we imagine we're looking for here is to mimic
the distortion of air on the presumption that this
will be less offensive than some other form of
distortion. As such we want the second harmonic
character of the output to give slightly higher pressure
variation on compression (+) than rarefaction (-).
You don't like this theory? I've got others.
the distortion of air on the presumption that this
will be less offensive than some other form of
distortion. As such we want the second harmonic
character of the output to give slightly higher pressure
variation on compression (+) than rarefaction (-).
You don't like this theory? I've got others.
It's always seemed to me like a good theory in that it agrees withNelson Pass said:
the well established observation that even fairly large doses of
second harmonic distortion are pretty innocuous.
Still, I wonder if the addition (or at least non-elimination from an
active amplifying system) of in-phase (additive or expansive)
third harmonic distortion might also be desirable. I'm supposing
here that, on their way from the microphone to the speaker,
audio signals undergo a systemic distortion consisting mainly of
anti-phase (subtractive or compressive) third harmonic as a result
of limited diaphragm elasticities and an accumulation of small
nonlinear conductive losses.
As far as I know, these passive sources of distortion don't
otherwise get compensated for or corrected out of the system.
I don't know what fundamental characteristic (besides theRobPhill33 said:
even harmonic nature) of air to which you make reference,
unless it is absolute phase.
I would say that absolute phase is certainly an easy tweak,
regardless of what you might imagine of its audibility.
There are other things, such as dispersion (different frequencies
propagating at different velocities) and also high frequency
attenuation (the sonic difference in top end between front
row and 15 rows back)
One of the most interesting things about dispersion is that it
seems to be something you can mimic a bit in a circuit, so that
the bright top end of close-mic'd recordings can be taken down
a notch, and it improves the perception of the recording. Of
course it doesn't do a thing for something recorded from the
back of the hall....
Unfortunately, I don't know of any ordinary form of distortionJoe Berry said:
which reverses the odd order compression effect. You can,
however, avoid it by amplifying with single-ended Class A
circuits.
Perhaps I have misunderstood, you said earlier
Whatever is done to the second harmonic (larger gain at higher current) must also be done to the fundemental, correct? Unless I am way off, which is likely, the fundemental would exhibit slightly higher pressure on compression, as would 2nd,3rd,etc. harmonics. I was wondering if this is beneficial to the fundemental alone, or is the subsequent improvement in the 2nd harmonic distortion the primary audable difference?
Hi all,
I did once calculate the distortion product of a 120dB SPL sine wave as I was interested by nelson's theory. I think I even posted it in one of the threads of DIYaudio.com. It was much less then 1% if I remeber correctly. It is very easy to calculate once you know the amount of absolute presure variance of a 120dB sine wave.... I don't remeber anymore. I used a book: ' Fundamentals of the physiology of hearing' which is part of the audiologist curriculum in The Netherlans.
Furthermore I commented that I don't agree with Nelson's theory (but I stil love him ) . I think that a clever man as him should realize that the non-linrearities of the ear-drum, oval & round-membrane, cochlear fluids and the rest are orders of magnitudes larger. This non-linear behavior of the inner-ear-organ is used everday in hospistal practise to investigated the possible hearing defects in just born babies. Furthermore the masking effect that takes place in out hearing organ is conviniently left out of Nelson's theory. Still, I hope I once will have enough savings to get my a Pass amplifier
gr,
Thijs
I did once calculate the distortion product of a 120dB SPL sine wave as I was interested by nelson's theory. I think I even posted it in one of the threads of DIYaudio.com. It was much less then 1% if I remeber correctly. It is very easy to calculate once you know the amount of absolute presure variance of a 120dB sine wave.... I don't remeber anymore. I used a book: ' Fundamentals of the physiology of hearing' which is part of the audiologist curriculum in The Netherlans.
Furthermore I commented that I don't agree with Nelson's theory (but I stil love him
) . I think that a clever man as him should realize that the non-linrearities of the ear-drum, oval & round-membrane, cochlear fluids and the rest are orders of magnitudes larger. This non-linear behavior of the inner-ear-organ is used everday in hospistal practise to investigated the possible hearing defects in just born babies. Furthermore the masking effect that takes place in out hearing organ is conviniently left out of Nelson's theory. Still, I hope I once will have enough savings to get my a Pass amplifier gr,
Thijs
Nelson Pass said:
Ah, thanks for the reality check. I went back to a simulation file
where I thought I had seen an example of "expansive" third
harmonic. I was disappointed to note that the distortion residual
had been buffered by an inverter, which caused it to display as
in-phase when in fact it wasn't. Oh well ...
Maybe it's time to trot out one of those "other ideas" you keep
teasing us with, if there is one that applies here.
Nelson's theory has always appealed to me for its simplicity, and set me off on my voyage of discovery back in '92 with the Zen amplifier. However, a 1% variation in 'elasticity' of air over a complete 100 dBL cycle would probably yield a lot less than 0.1% H2 and that figure would certainly not be audible.
Nonetheless the fact remains that some amps sound a lot more 'natural' than others, given all other components are not changed and a meaningful AB test is performed. So there's likely something else here......
Nelson's suggestion that using SE circuits fixes the problem is also true from my experience. SE does sound palpably different to PP - but both can sound very, very good. Problem is getting any meaningful power from an SE circuit. How many of us use single cylinder engines in our cars??
It might well be that the good sound is related to spectral distribution of the distortion. Given that the PP output stage cancels its own even order distortions (or at least most of them), then it makes good sense to concentrate on making the OP stage as transparent as possible and accepting that the quality of the sonics largely derives from the input and voltage amplifier circuitry, particularly the latter.
Certainly it does appear that the ear is far more sensitive to higher, odd order distortions than we realize, and if these can be removed utterly - automatic with SE and zero global feedback - we are certainly on the right track.
Cheers,
Hugh
Nonetheless the fact remains that some amps sound a lot more 'natural' than others, given all other components are not changed and a meaningful AB test is performed. So there's likely something else here......
Nelson's suggestion that using SE circuits fixes the problem is also true from my experience. SE does sound palpably different to PP - but both can sound very, very good. Problem is getting any meaningful power from an SE circuit. How many of us use single cylinder engines in our cars??
It might well be that the good sound is related to spectral distribution of the distortion. Given that the PP output stage cancels its own even order distortions (or at least most of them), then it makes good sense to concentrate on making the OP stage as transparent as possible and accepting that the quality of the sonics largely derives from the input and voltage amplifier circuitry, particularly the latter.
Certainly it does appear that the ear is far more sensitive to higher, odd order distortions than we realize, and if these can be removed utterly - automatic with SE and zero global feedback - we are certainly on the right track.
Cheers,
Hugh
AKSA said:
Okay, but I'm no longer sure which problem we are talking about.
The (hypothetical) compressive odd harmonic problem I described
earlier had to do with the passive components of a signal chain.
When Nelson stated earlier that SE circuits avoid this problem, I
think he is referring to the same phenomenon, but in the active
context of an amp, preamp, etc.
Maybe it is possible to address both problems at the same time.
I recall that Hamm's AES paper from the early '70s, on why tubes
and transistors sound different, noted that a fundamental tone
compressed by the addition of third harmonic could be reopened
by adding some second harmonic to the mix.
It may be, then, that single-ended circuits don't just *avoid* the
problem of odd harmonics in the active circuits that inlcude them.
Perhaps, by adding some second harmonic to the mix, they also
help to *correct* for odd harmonic distortion added to the signal
elsewhere in the reproducing chain.
Brilliant! So the adage quoted so often that goes "adding in second order distortion is not the aim or should not be" may be in error. Are you saying that perfectly amplifying a signal is only desirable if it does'nt have some thirds distortion already intrained, otherwise, actually dirtying up the signal with a little second harmonic distorts the signal but corrects the message. The vail falls away...
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