Walter Knapp wrote:
> The real culprit, and I think what Rich was getting at is
overdriving in
> pre and A/D. He is right, this is common. It will be just as
common in
> the new solid state digitals. It's a matter of teaching folks to
handle
> digital recording. There's still a lot of recording advice
floating
> around that's straight from analog recording and ruins digital
> recordings. We need to root that out.
Yes, overdriving in pre and A/D is much more critical in digital
equipment than in analog tape recordings. Overdriving an analog tape
recorder may add a few regular harmonics only. Instead, overdriving
digital equipment will lead to additional irregular (mirrored)
harmonics. This kind of distortion results from alias effects in the
digital sampling process. Analog clipping within the pre-amplifier
and the A/D input stage may produce very high-frequency harmonics
reaching the ultrasonic domain. During normal operation, high-
frequency components would be removed by the integrated anti-alias
filter of the recorder. However, when this anti-alias circuit is
overdriven, that low-pass filter will fail. As a result, all the
requency components higher than one half of the sampling rate will
be folded down into the audible range. These "mirrored" harmonics
are responsible for the extremely unpleasant distortions.
Raimund
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