On Tue, 3 Apr 2018, Chris Chronopoulos wrote:
unfortunately the original question has still not been addressed: can this (or other similar) interfaces be run on ALSA drivers at 384 kHz? this i can concede to, and i should clarify that what i'm really interested in is the high sample rate USB to PCM (I2S) interface. there are dedicated parts that accomplish this for much less than $100, which is why i'm interested in users' alsa experiences at this sample rate.
If you want 16 outputs, then I would think you also want ALSA to see a much lower sample rate in any case. That is, 16 (or 8 per channel) from whatever app to ALSA 16 ports at 48K. Then your custom alsa driver will access the buffers of those ports and basically rearange the data into a second buffer than gets sent via USB to your device. Most USB devices can handle a buffer size of 128 which is the same speed/latency as 384k with a buffer size of 1024.
I am not sure of that is clear, 384k at the alsa end would need to have a buffer size of 1024 for the same stability and latency as a 48k device with buffer size 128. I think pretty much any usb device can run at 48k with buffer at 128. With the custom driver between alsa and USB, the alsa buffer size would be 8 times smaller and the sample rate would also be 8 times smaller than at the USB end. I would tend to go with the maximum buffer size the device will handle because it is output only and so latency is unlikely to be noticable.
If you really want to do your conversion before alsa, I do not see any reason you could not. However, you do need to remember that whatever buffersize you are used to will not mean the same thing. That is, if you have trouble with a 48k device at 128 buffer size, you will have the same problem with a 384k device at 1024 buffer size.
Alsa does not determine the buffer size, the application connecting to alsa does, within the limits of the driver.
-- Len Ovens www.ovenwerks.net
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