I just discovered the Urd, with its USB Audio output that can feed a USB DAC. Having designed a number of USB devices and hosts, I am familiar with the USB Audio mode where the destination can control the rate of data from the source, and I wonder if there is any combination of Urd + USB DAC that uses this feature.
With USB Audio, if the source happens to be running a little faster or slower than the destination, a low-bandwidth communications channel on the bus allows the USB Host to reduce or increase the number of audio samples in future buffers to keep the source in sync with the destination. This avoids real-time sample rate conversion, and also avoid complicated PLL systems to match the rate of the DAC to the media. Ideally, the USB DAC would run from a high-quality local sample clock, without any PLL circuits to slave to an external clock.
For this USB Audio feature to work, a USB DAC Device would need to implement this mode. There are three audio modes, I recall, so there's no guarantee that a USB Audio Device DAC would necessarily use the best mode. In addition, the Schiit Urd as USB Host would also need to implement this mode, and in particular would need to slow down the CD transport motor, or speed it up, in order to adjust the rate of audio data flow to match the DAC clock.
Does anyone have any idea whether all of the pieces are place for this to work?
Brian
by the way, the quote came from this thread https://www.diyaudio.com/community/threads/solid-cd-player-for-700.410272/#post-7628351
Why not ask Schitt Audio about their DACs? You'd like to think their DACs would interface as you want and they certainly know what you're looking for. I have owned Gungnir, Bifrost, and Modi and all were great for their niche.
I thought the topic might have already been discussed here, and someone might have a pointer.
Last time I asked a question on schiit.com, the AI went in circles until finally answering. I figured DIYaudio might be more direct.
Plus, this thread is an invitation to discuss the Urd in a thread of its own, as motosapien was also hoping to find.
Last time I asked a question on schiit.com, the AI went in circles until finally answering. I figured DIYaudio might be more direct.
Plus, this thread is an invitation to discuss the Urd in a thread of its own, as motosapien was also hoping to find.
IMO you will have to ask the manufacturer. If the CD drive used is https://www.suos-hifi.com/_files/ugd/a83b4d_9d41cf6de34d490f821ceeb49614e25b.pdf (likely as StreamUnlimited tray loader is used too https://www.suos-hifi.com/_files/ugd/a83b4d_f1e63b71ff8a416c94f0f542041d62af.pdf ), then it may have a way to control the reading speed via external audio MCLK input. Since the device author says that they developed all their MCU firmware to be UAC2 compliant (they actually had to code both UAC2 host and device) and most UAC2 DACs run in asynchronous mode only, they had to handle the feedback somehow. Either asynchronously resampling the fixed incoming rate from the CD drive, or actually controlling the CD drive speed. Actually the same issue applies with their UAC2 device emulation for the two USB inputs - likely they have to handle the async feedback somehow too.
Quite an advanced MCU programming, IMO.
Quite an advanced MCU programming, IMO.