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Posted By

TLC
on 2007-01-07
18:53:10
 Re: SID-supported software ???

Bionic: the only problem with sigma-delta D/As is, that they need to operate at very high frequency to provide reasonable slew rates (since slew rate is the key here to achieve low distortion and low noise). For a 16-bit 44.1Khz sigma-delta dac, one would ideally need 65535*44100 = 2.89Ghz internal sampling frequency to be able to do a full magnitude step in one sampling cycle. ...Not even commonly used "so-called" hifi but otherwise professional DACs are up to this task. Lower operational frequency is acceptable, as long as the available slew rate (limited by the resolution and the operational frequency together) is "high enough". Otherwise, one introduces distortion. With something like the SID where sharp/high amplitude waveforms are generated, keeping high slew rate should be mandatory, to avoid this distortion. (That's why I'm also suspecting this behind the DTV's bad sound quality... With a cheap FPGA (or this ASIC), the usual operating freq is in the order of 10Mhz's, maybe, 1-200Mhz at the top, with extra attention). ...BTW, high-end DACs are usually still multi-bit DACs of some sort (see the PCM1704 and the PCM1796 from Burr-Brown)... as it seems, "true" high dynamic range with low overall noise is still hard to achieve with sigma-delta dac's.



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