For further reading:
In 1998, dCS invented the terms “Upsampling” and “Upsampler” to define a separate digital-to-digital converter unit used to convert low-resolution digital data to a higher resolution, higher sample rate data stream, to present a high-resolution DAC with better data and so replace part of the DAC’s oversampling function.
An Upsampler appears to make it easier for the DAC to carry out the conversion to analogue by taking over part of the processing load.
The two terms have been misused by many o…
The short answer is: we do.
dCS DACs oversample the data in several stages, the first stage being to either 24/176.4 or 24/192, the second stage oversamples to 24/352.8 or 24/384, and so on. Using a separate Upsampler unit (which uses the same digital hardware and the same process as the DAC oversampling) to upsample to 24/192 (for example) replaces the DAC’s first oversampling stage.
Sampling theory indicates that adding the Upsampler should make no difference at all, but most people can hear…
PCM is Pulse Code Modulation and it means that the analog signal is measured at some fixed rate – the sample frequency (e.g. 192,000 samples per second) – and each measurement has some bit depth (usually 16 or 24 bits).
CDs are 16bit / 44,100 Hz so the analog signal level was measured (or reproduced) based on 16 bit samples that were taken every 1/44,100th of a second.
DXD is a shorthand for high-rate / high-depth PCM and it corresponds to either 24 / 352,800 or 24 / 384,000. The reason for tw…
The end result is the DAC itself being fed by a very high-rate stream which makes it possible for subsequent processing to be done in such a way that filtering happens well outside the audible band.