Computer Audio Asylum

Music servers and other computer based digital audio technologies.

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RE: Anyone heard Apple's 24 bit Beatles FLAC rips from the USB?

Posted by Tony Lauck on December 15, 2009 at 08:24:40:
"1 bit is not pcm."

PCM with some word length and DSD represent an analog signal with the same mathematical formulation. (Discrete time sampled data, samples quantized to a finite number of discrete values. With n bit PCM, there are 2^n discrete values. For n=1 there are two values, +1 and -1. DSD is just 1 bit PCM.) There are known tradeoffs between bit depth and sample rate and this is how modern converters are built. If you are hung up on mechanism rather than on function then you won't see the common framework into which the various formats fit.

The commonality in the formats can easily be seen with minimalist DACs for these formats: for example a traditional NOS DAC with minimal filtering and a DSD DAC made with a flip flop with minimal filtering. When a NOS DAC is playing low level PCM material the same components are working as with the minimalist DSD DAC, albeit at a lower sample rate. Were you to clock a NOS DAC at 2.8 MHz then you could use it as a DSD DAC. You would take the DSD signal and treat each bit as +1 or -1, and then sign extend it to get the necessary input to the NOS DAC.