masterclock slave mode i2s

Suggestions/requests/ideas for RuneAudio core features and functions

masterclock slave mode i2s

Postby monica2 » 18 Apr 2016, 19:21

I would like to use a music streamer based on one of these boards (Raspberrypi3, Odroid, BBB), I don’t really care which, provided that it does what I need. The board would need to be connected to the DAC chip directly via the i2s ports. There’s no crystal on the DAC board. The tricky part is that I want to by-pass the clock that comes with the streamer board, and use an external masterclock for both the dac and the streamer. In other words, I want to take time and frequency for both the dac and the streamer board from a low jitter external clock. So no re-clocking, but one clock for the whole system. From reading online, I don’t believe the raspberry can be put on slave mode, but apparently the Odroid C2 is more versatile for not coming with a clock on board.

Any suggestions?
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Re: masterclock slave mode i2s

Postby PeteB » 18 Apr 2016, 20:39

monica2 wrote:... I don’t believe the raspberry can be put on slave mode, but apparently the Odroid C2 is more versatile for not coming with a clock on board.

Any suggestions?

The HiFiBerry DAC+ Pro has its own "correct" clock (2 of them), and uses the Raspberry Pi2 I2S port, with the Pi 2 in slave mode, and the DAC+ Pro master mode. There is some discussion of that in the HiFiBerry Forum, and elsewhere online. The DAC+ Pro can also be used as a clock source and feed the I2S signal to an external DAC, IF you know what you are doing (it is not as simple as it sounds).

https://support.hifiberry.com/hc/en-us/articles/205711451-DAC-Pro-connect-external-I2S-DACs

So, I assume the Pi 2 can be used in slave mode by other devices too.

The Odroid C1 cannot be used in slave mode.

http://forum.odroid.com/viewtopic.php?f=116&t=19951

Not sure about the C2.

Edit:

It would be quite a feat to make this work correctly, so if you decide to go for it, please post a project report for the rest of us mere mortals... :D
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Re: masterclock slave mode i2s

Postby pistollero » 18 Apr 2016, 20:45

Yes... The market is missing that i2s board.....hope some of the suplier design one soon....
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Re: masterclock slave mode i2s

Postby PeteB » 18 Apr 2016, 21:07

pistollero wrote:Yes... The market is missing that i2s board.....hope some of the suplier design one soon....

For around $40, you can use the clocks and I2S header on the DAC+ Pro, without using the onboard DAC output. THAT is not so difficult, and others have done it.

Making 3 independent devices work together as the OP suggested, that would be a challenge! :mrgreen:
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Re: masterclock slave mode i2s

Postby pistollero » 18 Apr 2016, 21:24

PeteB wrote:
pistollero wrote:Yes... The market is missing that i2s board.....hope some of the suplier design one soon....

For around $40, you can use the clocks and I2S header on the DAC+ Pro, without using the onboard DAC output. THAT is not so difficult, and others have done it.

Making 3 independent devices work together as the OP suggested, that would be a challenge! :mrgreen:

I waiting for mine to arrive.....but it would be great a dedicated board with better clocks.....for that price
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Re: masterclock slave mode i2s

Postby monica2 » 18 Apr 2016, 23:20

If these devices were made with the mere purpose of outputting a pure i2s signal without any clock, and if they were prepared to take an external masterclock signal, then this would be no challenge at all...
The problem is that nobody seems to be doing it right, so the end user is stuck with the disgusting and ubiquitous USB crap, or with i2s signals that can't really be successfully used.
I believe someone will come up sooner or later with the right board. When that happens, it will be digital independence day.
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Re: masterclock slave mode i2s

Postby PeteB » 19 Apr 2016, 00:06

I believe that for a low-cost solution, you could use a Pi with a DIGI+ board, and then connect to something like this:

http://www.twistedpearaudio.com/digital/buffalose.aspx

If the above DAC is as good as some of the other products from the same source, it should work well with its own clock, and better with an external, calibrated source. That would basically be a proof of concept that it works.

Once some Linux code is ported to a Pi 3 or Odroid C2 to emulate a basic transport, you will have exactly what you asked for.

A Pi or Odroid as a source (or Intel-based Linux box), I2S to an external DAC, and a clock source of your choice (pretty much what others are already planning on, so you can probably find a discussion on diyaudio or a similar forum). Depending on the clock source, I think the total cost could be well under $1K, for something you can only find in a studio or a lab.
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Re: masterclock slave mode i2s

Postby monica2 » 19 Apr 2016, 00:21

I have played with more than one version of the buffalo dac and thought it always gave rather mediocre results. But following your suggestion though, regardless of the dac use, would not eliminate the problem, namely the clcok on the PI. I have tried that route and it doesn't take us anywhere, but to more or less the same results.

I know nothing about programming or coding these things, but I hope you're right. And I hope someone comes up with a solution soon.
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Re: masterclock slave mode i2s

Postby monica2 » 19 Apr 2016, 00:23

what discussion at diyaudio you mean specifically?
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Re: masterclock slave mode i2s

Postby PeteB » 19 Apr 2016, 03:26

I can't remember specific threads, sorry. Best do a search there, or just ask and someone will point you in the right direction.

I agree about the Pi clock, it is not really intended for this purpose.

The DAC+ Pro design shows that you do not need to use the Pi as a clock source, it will work fine as an I2S slave.

It looks like the Buffalo DAC can use an external source, so in that case, you would have your choice of clocks, too.

To me, the Pi and any one of the better I2S DACs sounds fine, for casual listening. The DAC chip uses an internal PLL to correct the clock, and I am ok with that. The bigger issue for me, is the SNR of anything connected to a Pi (and I assume to an Odroid C1 or C2). That is something I notice, especially with headphones.

Nevertheless, it seems like a fun project putting it all together. I wish you best of luck with it, and I hope you will post the results at some point! :)
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