IN A DITHER

Your Personal Studio Buyer's Guide 2001 is great! Not so much because of its comprehensive product listings, but because of the very interesting "Digital
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Your Personal Studio Buyer's Guide 2001 is great! Not so much because of its comprehensive product listings, but because of the very interesting "Digital Audio" article, which discussed the necessity of dithering. The idea of dithering in the analog domain, before digitizing the mixdown, is paradoxical to me: after all, everyone's obsession is getting the cleanest sound possible for recording. But the author's arguments make sense.

The best test is to try this idea with various audio material. But the article doesn't say where to get gear that allows analog dithering (as a master insert or whatever). I've browsed the Internet, but I haven't come across anything related so far. Could you list some resources for dithering/noise-shaping hardware?

Also, are you recommending only dithering of the analog signal before digitizing it? Or does noise shaping serve the same purpose? Thanks for an excellent article.Alexei Reznickvia e-mail

Alexei - Input dithering is performed automatically in modern analog-to-digital converters (ADCs) within digital audio systems. You can certainly experiment with adding white noise to an analog signal before sending it into a digital system, but this is not generally advisable. Most manufacturers of digital systems have already determined the best way to dither the input signal, and adding your own noise will probably compromise the sound quality more than it might help in the digitization process.

Noise shaping does not serve the same purpose. This process is normally applied to a digital signal whose word length must be reduced before being converted into an analog signal. In this case, the digital signal is first dithered by adding artfully selected "pseudo" random numbers to each sample. Then the extra bits are removed, and the resulting white noise is shifted to the high end of the audible spectrum and beyond. Because our hearing is relatively insensitive to such high frequencies, we perceive less of the noise, even though its amplitude is higher than it was as white noise spread evenly throughout the entire audible spectrum.

Whereas analog input dithering is applied in the ADC, digital output dithering and noise shaping are applied to a digital signal before it is converted into analog form by a digital-to-analog converter (DAC). All digital signal processors (DSPs) perform internal digital dithering, because the results of their computations have more bits than the final output signal, but this process is not generally under user control. You're most likely to find user-controllable digital dithering and noise shaping in high-end, outboard DACs and computer-based digital audio software packages.