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Hi,
I posted this here since this is the thematically closest component in the Twisted Pear portfolio.
I am thinking about building another Buffalo DAC and would like to make it capable of DSD playback. I assume a lot of people saw the announcement of the Benchmark Media DAC2 which is now also build around the ESS9018 DAC chip. However, what really caught my attention is the fact that this DAC enables DSD playback over any digital input with DOP streams.
There must be some kind of circuitry that parses the DOP flag in the PCM data and shifts the data into the right position as well as indicating the presence of a DSD stream so the ESS chip configuration can be changed to DSD.
Any ideas how to do this for a Buffalo III?
Cheers
Thomas
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All they are doing is processing the DOP (likely with something like a DSP or controller such as XMOS) and churning out DSD. There are a few USB interfaces that can do that (Amanero for example) easily. The B3 auto detects PCM/DSD when wired for it. Cheers! Russ Edited by user Sunday, August 18, 2013 2:54:08 AM(UTC)
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It is actually pretty simple to convert DoP from any PCM (even SPDIF) source to DSD using XMOS, but I think this is seriously over-hyped. :) Edited by user Sunday, August 18, 2013 3:00:13 AM(UTC)
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Well, I have not tried so I can't speak to the hype part. I have played with the Amanero but that is again USB only. I was hoping I could leverage my current multichannel setup with a Lynx AES16e. However, if I understand you correctly you think I could loop a XS1-L1 in the I2S signal and transform the bits as needed as well as using one of the GPIO pins to indicate DSD? Since that same processing needs to happen for the USB input anyhow I suppose you could either use the stream coming via the USB port or the one coming from the I2S input. While under no circumstance I would want to introduce any delay to your USB interface that sounds like an interesting firmware update for later? Cheers Thomas Edited by user Sunday, August 18, 2013 6:13:14 AM(UTC)
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No need for a firmware update or GPIO to indicate DSD, if you supply PCM or DSD the DAC will detect either, and play it correctly - right now :). I have been using it like that for years with modded SACD players. Doing DoP is something that would have to happen in front of the DAC. To do DoP well (no transients on format switch) requires a delay (unless you don't mind pops on transitions between PCM and DSD). Some folks do it without the aforementioned delay, but they also produce very nasty transition transients - Amanero included. :) Pick your poison. Edited by user Sunday, August 18, 2013 12:09:52 PM(UTC)
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Right. I was thinking to do the DOP detection and unmangling between the S/PDIF mux and the Buffalo III. "Looping" the Xmos in the I2S data path... That might of course increase I2S jitter but I am assuming you will take well care of that for the USB input anyhow.
The DOP web site has some guidance on how many samples to wait for to avoid the pops you are mentioning.
Cheers
Thomas
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It is the "samples to wait" that will cause the delay. And it is not exactly small. :)
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Well, they recommend Quote:4. Recommended implementation
While there is certainly more than one way to implement this solution on the receiver side, the authors found the following implementation to work reliably:
•In order to switch from PCM to DSD mode the receiver has to detect 32 consecutive DSD marker bytes on all channels used.
•In order to switch from DSD to PCM mode the receiver has to detect at least 1 single missing DSD marker byte in at least 1 channel.
This introduces an additional latency of around 180usec. If the USB buffers are accessible for reading while the USB microframe is still being received then no additional delay is necessary.
I guess it would be interesting to fiddle with a transition sequence. Since you control the content you can send whatever you want to the DAC. Maybe you can use 16 samples to dial the last PCM signal to 0 and then use the following 16 samples to slowly ramp up volume on the DSD samples. The DSD to PCM sounds more challenging but again one could try that in reverse. Cheers Thomas Edited by user Monday, August 19, 2013 5:59:34 PM(UTC)
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The only way to do it right is with a FIFO. :) So that you can give the DAC adequate time to react to changes (by say muting) This rerquires close control between the DoP device and the DAC. This is one reason I have been taking my time on my USB module. :)
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Sure a Fifo will give you full control over the sequence and if you can trigger a mute from the module to the DAC then even better. I probably should just wait for your module to come out.
Thanks for the explanations
Thomas
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