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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: RE: Non Oversampling (NOS) DAC's posted by Todd Krieger on September 1, 2012 at 01:32:38:
Uh...no. The roll-off is due to the zero-order hold operation of most DAC chips. Which is more commonly known as, sample and hold operation. It has nothing to do with whether the DAC is R2R (so,ethin which I'd unintentionally suggested due to clumsy writing), or sigma-delta. Nor is it due to modulation. It would be interesting to know where you came by this notion, Todd. Perhaps, you are thinking of sigma-delta modulation. Which is a related topic, but not the cuase of the roll-off effect. The roll-off has to do with the 'stair-step' like shape of most D/A converter outputs.The high-frequency roll-off shape and transition frequency are a function of the sample rate at which the converter is running. The higher the sample rate, the more brief is the hold period. The hold period is the flat 'step' part of the output 'stair-step' waveform. Depending on the implementation of the oversampling utilized with a given sigma-delta converter, the reason such a converter might exhibit less roll-off has to do with it having a higher effective sample rate. This is also the reason why a true NOS converter, one running at the native rate of the input samples and not utilizing any external or internal oversampling interpolation, will exhibit the most severe in-band roll-off effect.
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Ken Newton
Edits: 09/01/12 09/01/12
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- RE: Non Oversampling (NOS) DAC's - knewton 10:24:05 09/01/12 (0)
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