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RE: Me too

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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  • RE: Me too - Tony Lauck 11/14/1518:20:24 11/14/15 (0)


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