Paul,

If you have an imperfect D/A converter, oversampling can help some---providing, say, 3dB more SNR every time you double the sample rate. But generally speaking, oversampling is primarily used to simplify the filtering process that has to occur after D/A conversion. The FAQ that you posted has a good explanation of this.

In order to mitigate the effects of an imperfect D/A converter, the two most common approaches are
1) to 'overspec' the part---for example, to use an 18- or 20-bit converter even when only 16 is required. In my work (not audio), we have a 14-bit A/D converter that we expect to see 12 "effective" bits from; a 12-bit D/A that we expect 11 "effective" bits from; etc.
2) to go completely the other direction, and use the 'reduced' bit techniques (like 1-bit sigma/delta or delta/sigma D/As) and crank up the sample rate accordingly.

One very good point that FAQ makes is that any of these techniques can be employed in a lousy product. I think the 1-bit techniques were first employed to make cheaper products; but now the Sony Super Audio CD (SACD) format uses a highly oversampled 1-bit storage format. Weird.

For another example of a high-quality 1-bit solution, check out the TACT Millennium digital amplifier. Basically, it uses a high-power 1-bit D/A converter for each audio channel. There are no analog amplification stages! Increasing the volume simply changes the voltage levels for the 1s and 0s. In the end, most of the quantization noise is shaped way up into the inaudible range, and a very gentle low-pass filter is all that is needed to clean up the signal. WOW! (OK I'm a nerd, I like that stuff)


Michael Grant
12GB Green
080000266