- Is the volume control analogue or digital? I've read that if the volume control is digital the signal must be converted to PCM.
One cannot change volume on a 1-bit data stream, be it PCM or DSD/PDM. It is the 1-bit format which is the issue, not PDM or PCM.
The DirectStream converts incoming data to 28.22MHz at 30 bits (calling this 10x DSD is a bit confusing; the sampling rate is 10 times that of standard DSD, but referring to DSD implies a 1-bit architecture.)
The 30 bit data stream allows for volume changes. After the volume change, the data is down converted and noise shaped to 2x DSD 1-bit and the FPGA output goes to the low pass filter for conversion to analog. The output is transformer coupled (like most tube amps).
As a side note, the DirectStream oversamples 10x DSD rates as this allows integer conversions (no numbers to the right of the decimal point) for both sample rate families of 44.1 base rate and 48 base rate. Integer conversion provides for simpler math and no rounding errors. This is why there is no loss of resolution. It is a very cool design.