DSD data rates

dac

#1

If this has been asked before, please re-direct me.

The DirectStream DAC is limited to 2x DSD and Bridge II to 1x. Are there any technical reasons that higher data rates are not available? If this is possible are there any plans to implement 4x or even 8x?


#2

Been wondering this myself. I have DSD 128 (2x DSD) files on my USB drive and they do not play in the front USB input on the DMP. I have Bridge 2 on my DS Dac. Would the USB thumb drive play the DSD 128 file on that? I also have DSD 256 files and they don’t play either. My Oppo UDP 205 is capable of playing them no problem. So why can’t the DMP and DSD play them?


#3

The current DS software supports DSD64 and DSD128. The Bridge II supports DSD64. The DMP supports DSD64 and under some circumstances DSD128 (different versions of the software do DSD128 a little better or a little worse.)

The Bridge II will never support DSD128. I doubt, (but don’t know for sure) that the DMP will ever support DSD256.

The DS hardware could support DSD256, but that’s not trivial. The FPGA is essentially DSD256 inside, but getting DSD256 to the DS would take new USB code in the DS, new USB drivers for Windows, MAC and Linux or I2S. Many I2S sources can’t do DSD256, but that out of PS Audio’s hands.

PS Audio wants to support DSD256 where it’s possible, but I don’t have any idea when it might happen.


#4

Thanks Ted, that’s just what I wanted to know. Also thanks for the great work on Snowmass.


#5

Version 3 of the USB Audio Device Class specification (September 2016) finally includes explicit support for DSD as an encoding format. But who knows how long we’ll have to wait before major operating system vendors and USB chipset makers implement that.

Until that time we’re stuck with version 2, which doesn’t explicitly support DSD. We have to use DoP, packing 16 bits of DSD inside 24 bits of what the USB system thinks is PCM. To support DSD256 this way would require the equivalent of 705.6kHz 24-bit PCM sample rate support from the USB ecosystem. The limitation in most platforms/devices using UAC2 is 384kHz sample rate.

Hence Ted’s comment about needing custom USB device code and custom drivers to get past DSD128 for now. I2S is the alternate pathway to get native DSD256 into the DAC but where do you source that I2S signal from?

(Re the Bridge, some time ago I heard that the I2S lines from the Bridge to the FPGA have only been qualified for the equivalent of 192kHz PCM or DSD64 as DoP. They may not be physically capable of carrying a higher data rate than that.)