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PMD-100 was one with selectable dither

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From page 14 of the PMD-100 datsheet:

Dither Modes

The PMD-100 provides 8 different output dithers in Program mode. All dither levels are available for output data widths from 16 to 24 bits at 8 Fs and 4 Fs oversampling rates only. Dither must be disabled if the 2 Fs oversampling rate is selected (as well as 24 bit mode must be selected when the 2 Fs oversampling rate is selected). There are seven levels of high-frequency weighted dither (modes 0-6) plus minimum amplitude white triangular PDF dither (mode 7). Modes 0 and 7 are minimum amplitude dithers which correct quantizing errors only, whereas modes 1 through 6 are increasing levels of high-frequency weighted dither designed to smooth out non-linearity errors in multi-bit DAC’s (Modes 0 or 7 are appropriate for single-bit DAC’s). The HF weighted dithers put the dither energy above the audio spectrum, where most of it is later filtered out by the analog low-pass filter following the DAC. In general, multi-bit DAC’s behave better with high levels of dither, but some analog circuits following the DAC may have problems with transient intermodulation distortion (TIM) when confronted with high levels of high frequency energy. The best dither level for a particular circuit implementation must be determined empirically.

Dither Notes:
1) Dither level 6 is the highest level of high-frequency weighted dither available with the PMD-100.
2) In Stand-Alone Mode, dither mode 0 (minimum high frequency weighted) is available. Setting pin 4 DITH low will disable all dither including programmed dither and should be used only for test purposes.




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Topic - upsampling article - solidgore 08:08:38 08/22/03 ( 47)