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What are the differences of PCM vs DSD?

 

Direct-Stream Digital is simply a 1-bit digital audio format that is based on the Sigma-Delta encoding/decoding architecture, and in practice is commonly referred to as a DSD recording/file. Many are not aware though that whether they are employed in the processing of PCM or DSD signals, all modern DAC chips are actually based on the same basic Sigma-Delta architecture. In short, the only real question is whether we're sending a PCM or DSD signal to be decoded by a Sigma-Delta DAC. With respect to PCM, a typical DAC applies multi-bit modulation for converting incoming data into a Sigma-Delta signal, and then that signal is processed by a following Low-Pass Filter stage. DSD decoding skips the Sigma-Delta conversion part of the process as the signal is directly decoded by the DAC, after which it is then processed by the Low-Pass Filter stage. The differences between the two processes are relatively minimal and somewhat akin to comparing 10 dimes with a 1-dollar bill and trying to determine which is better. In one case where you have a coin purse, 10 dimes is better. In the case where you have a wallet though, the dollar bill is preferable. In either case, you still have the exact same amount of currency. Likewise in the case of PCM vs. DSD, you still have the same amount of data being processed. It's simply a matter of how the decoding hardware (DAC) was constructed as to which format is preferable. Therefore, no matter how you view it DSD and PCM are nothing more than different ways of looking at the exact same thing. While there are differences, where and when the data is converted is of little practical importance with respect to the end result. In fact, during the recording process virtually all DSD recording are first converted into PCM for mixing, equalization and other "artistic" processing. Upon completion, the data is then converted back to DSD format and manufactured into discs of "so called" DSD recordings (SACD) for distribution to consumers. In addition, the majority of DSD recordings are actually converted from original PCM masters. One should note that most all such back-and-forth conversion is performed via software – not hardware. In similar fashion, during DSD playback from a PC both the uDAC3 and Icon DAC employ a computer-resident ASIO driver along with a special USB communications chip that is contained within the NuForce product. Together, each of these works in cooperation with the other for achieving real-time DSD to PCM conversion. One should also note that the interestingly enough, the DSD format was originally developed to facilitate conversion to the 44.1kHz CD standard. Hence, the PCM equivalent of a 2.8Mhz DSD file would be manifest as an 88.2kHz file at 20-bit resolution. Compared to a 24-bit PCM file, DSD delivers a dynamic range that is actually 24dB less. Similarly, a "double" 5.6Mhz DSD file is the equivalent of a PCM file recorded at 176.4kHz and 20-bit resolution. Direct-Stream Digital is simply a 1-bit digital audio format that is based on the Sigma-Delta encoding/decoding architecture, and in practice is commonly referred to as a DSD recording/file. Many are not aware though that whether they are employed in the processing of PCM or DSD signals, all modern DAC chips are actually based on the same basic Sigma-Delta architecture. In short, the only real question is whether we're sending a PCM or DSD signal to be decoded by a Sigma-Delta DAC. With respect to PCM, a typical DAC applies multi-bit modulation for converting incoming data into a Sigma-Delta signal, and then that signal is processed by a following Low-Pass Filter stage. DSD decoding skips the Sigma-Delta conversion part of the process as the signal is directly decoded by the DAC, after which it is then processed by the Low-Pass Filter stage. The differences between the two processes are relatively minimal and somewhat akin to comparing 10 dimes with a 1-dollar bill and trying to determine which is better. In one case where you have a coin purse, 10 dimes is better. In the case where you have a wallet though, the dollar bill is preferable. In either case, you still have the exact same amount of currency. Likewise in the case of PCM vs. DSD, you still have the same amount of data being processed. It's simply a matter of how the decoding hardware (DAC) was constructed as to which format is preferable. Therefore, no matter how you view it DSD and PCM are nothing more than different ways of looking at the exact same thing. While there are differences, where and when the data is converted is of little practical importance with respect to the end result. In fact, during the recording process virtually all DSD recording are first converted into PCM for mixing, equalization and other "artistic" processing. Upon completion, the data is then converted back to DSD format and manufactured into discs of "so called" DSD recordings (SACD) for distribution to consumers. In addition, the majority of DSD recordings are actually converted from original PCM masters. One should note that most all such back-and-forth conversion is performed via software – not hardware. In similar fashion, during DSD playback from a PC both the uDAC3 and Icon DAC employ a computer-resident ASIO driver along with a special USB communications chip that is contained within the NuForce product. Together, each of these works in cooperation with the other for achieving real-time DSD to PCM conversion. One should also note that the interestingly enough, the DSD format was originally developed to facilitate conversion to the 44.1kHz CD standard. Hence, the PCM equivalent of a 2.8Mhz DSD file would be manifest as an 88.2kHz file at 20-bit resolution. Compared to a 24-bit PCM file, DSD delivers a dynamic range that is actually 24dB less. Similarly, a "double" 5.6Mhz DSD file is the equivalent of a PCM file recorded at 176.4kHz and 20-bit resolution.

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