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Music servers and other computer based digital audio technologies.

Clocking

When you listen to digital audio you are listening to a clock, just like you are listening to a turntable when you listen to an LP. The quality of this clock is more important than any other component involved in the conversion from digital to analog. (By "clock" I include the crystal, the associated oscillator and clock distribution circuitry and the power supply for all this associated circuitry.)

If a DAC includes a properly integrated async USB interface the clock involved will be local to the digital to analog conversion chip and the associated USB input circuitry will be clocked by this local clock. The USB input circuitry will have buffering circuits that reclock the signals sent over USB. As a result there won't be any direct coupling from the USB cable and the clock that runs the D/A chip. If a DAC accepts SPDIF the DAC will be forced to run on the clock provided by the SPDIF source. Unless this clock is very high quality and run by a very low noise power supply it will have significant jitter. In addition, even if this clock happened to be magically perfect the SPDIF cable will add jitter. An SPDIF DAC is forced to work with a jittery input signal and this precludes the best possible results. For this reason a properly integrated USB DAC can be expected to work better than an SPDIF DAC connected to an external source of SPDIF. (The only exception would be if the DAC exported a clock that could be used to control the SPDIF source, but this is not standardized and is certainly not the case with the Halide Bridge, as can be seen by the photo.)

If one has an existing DAC that one likes then it may be that an external USB to SPDIF bridge will work better than an SPDIF source that's internal to a computer. It may also be the case that even with a poor SPDIF source an SPDIF DAC sounds better than an another DAC with an integrated async USB interface because the clock is not the only important component in a DAC.

Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar


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