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In Reply to: RE: Me too posted by A.Wayne on November 14, 2015 at 03:39:50
Well, when an amp clips then it is of course not making the same distortion pattern it was before it was clipping...that is why one should avoid clipping. That being said it has been demonstrated that an amp without negative feedback will recover from clipping much fast than one with a lot of feedback. Clipping recovery can go a long way towards masking clipping because it is usually at high volume levels where our hearing is less sensitive...if it is short enough.
Follow Ups:
I agree. The pattern of clipping is important.
I was given some clipped recordings to restore and I started doing some experiments by taking clean digital recordings (24/96) and deliberately clipping them and then doing listening tests. In most cases clipping one cycle of the waveform will be inaudible, while the same clipping applied to multiple cycles will be audible. If one note is clipped it may be hard to notice the harshness and it may appear as just a bit more dynamics by the musicians. However, if the damage repeats for several notes then it can be perceived as a defect, either with the recording or the musicianship. In some cases repeated distortion won't be perceived as a deficiency in the sound quality or musicianship, but the listener will get a headache from listening. (I didn't try to do any scientific tests to "prove" these conclusions, because they appeared to be completely obvious.)
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
It doesn't get worse than digital clipping....
Go Rossi ......
Some of the tapes I worked on had analog clipping and they sounded different than digital clipping. In one case, the analog clipping wasn't really on the tape, it was a very, very hot metal cassette tape and with the gain knob on my cassette player cranked up the analog output stage of the Nak cassette deck was clipping. After I discovered this situation though careful listening I changed my procedures and ran the gain up on my ADC and ran the gain down on my tape deck. (There wasn't any S/N problem due to loss of bit depth when recording 24 bit audio from cassette tape.)
The problem with digital clipping is that it voids the preconditions for the Nyquist theorem to be applicable. As a gross example of that, consider a 1000 Hz sine wave. With purely analog clipping one will get a series of odd harmonics, 3000, 5000, 7000, etc... But if you take a digital square wave (+1 and -1 samples at 1000 Hz) one will get all kinds of alias products that will be at odd frequencies, including beat tones below the 1000 Hz fundamental. These will show up on a spectrum plot (FFT) and will also be clearly audible, especially if you use a sweep tone. A sweep tone with analog distortion will move in one direction. A sweep tone with digital distortion due to aliasing will have "birdies" moving in the opposite distortion.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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