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RE: Do measurements matter? - linked article

Posted by morricab (S) on January 26, 2015 at 07:18:52

In Reply to: RE: Do measurements matter? - linked article posted by beppe61 on January 26, 2015 at 03:14:43:

You are thinking about this in the same way an engineer would typically look at this: distortion bad so I use my bag of tricks to reduce that distortion so that wave in = wave out. However, you have to realize that ALL amplification devices are inherently NON-linear and this means that they will all make extra harmonics in addition to the main signal and to one degree or another distort the waveform. That is the imperfect world we live in...no such thing as a truly linear amplification device.

Then in the 1930s a guy discovered that if you use negative feedback, suddenly the whole mess seems to disappear and it became standard engineering practice...along with push/pull circuits that partially cancel out even order distortion.

However, it was noticed by some that sound quality did not take a leap forward as someone who is obssessed with HOW MUCH distortion was present would have assumed. In fact, some felt that there was a big problem with the now orthodox view of applying feedback to "linearize" a circuit. No forethought was done to address if what was being done in the name of lower distortion was actually lower sounding to the listener.

This got some people thinking about HOW distortion is reduced and what side effects there are from those approaches and what it might be doing sonically that has a negative impact on perceived quality. It turns out that people are quite tolerant of even a few % 2nd order harmonic but may well be intolerant of < 0.1% ninth harmonic or even less tolerant of even higher orders.

Obviously a truly distortion free signal is desireable but it is not really possible at least not with current technology. What masquerades as almost "zero" distortion has been shown by Crowhurst and others to be nothing of the sort, which along with signal modulated noise floors, dynamic distortion, noise burst etc. seems that the distortion is shifted around but not really eliminated.

Your confusion arises from the thining that what is on the scope is what you hear...it is not really the case because also the scope doesn't often have the resolution necessary to show you all the really tiny distortions that seem innocent but may be very damaging to the sound.

Some distortions are fatiguing and some are simply invisible to your ear brain as they are masked by the ear/brains own mechanisms and distortions. High order harmonics are almost always fatiguing because it takes very high SPLs to generate them in your own ear and they are associated therefore with loudness. I think it is these high order harmonics that are the most damaging to soundstage and full 3d stereo imaging. They bring the perception of highs forward and thus shorten the depth and flatten the images.

Many no feedback amps, whatever their other flaws, have good long term listenability because they are creating a distortion pattern that is closer to nature and often have exceptionally 3d imagining and depth of soundstage because of a relative lack of high order harmonics that damage such perception.

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