PCM2707 -> I2S -> PCM1794 clocking query

[rja]

Probably a stupid question, but I'm unfamiliar with a lot of things, and am trying to learn . But there's a hell of a lot to take in... I'm about 3/4 done on the schematics, so I'm not that far off!

If I want to use different sample rates(for audio and DVD), then I need to use an ASRC, don't I? I can't just hook up the 2707 directly to the 1794? If The AD1896 is rather a lot of money from Farnell here in the UK - £20 or thereabouts. I don't mind buying it if I need it, but if I don't...

The card will be primarily used for audio, but I'd like to be able to watch films on the PC as well. I'm not keen on using software resampling, because the box may eventually be used on an xBox, modded with XBMC.

Cheers,

--Rich

[s_volkovoy]

Sure, you can. PCM 2706/2707 generates clock using internal PLL depending on semple ftequency(32/ 44.1/ 48) so you don't need any SRC.

[rja]

Oh wow! Excellent! I was expecting to hear that the answer was no - I'm chuffed to save some money .

Would I stand to gain anything by implementing the ASRC? I know it helps reduce jitter, but this first circuit isn't going to be terribly high-fidelity. It'll be IC's mounted on DIP adaptors, and then into veroboard. I figured it'll be good enough for experimenting, and once I work out exactly what I'll need, I'll design a PCB around my chosen components.

Cheers,

--Rich

[shyliang]

PCM2702+PCM1794,Good idea!
I just want to buil a USB DAC like that.

[rja]

The 2702 doesn't output i2s. You'll need the 2706 or 2707 if you want to connect the PCM1794 to a USB interface. It's a rather awkward package if you're wanting to prototype - I struggled to find an adapter board.

--Rich

[luzhu]

thanks

[shyliang]

OH!Thanks.
PCM2707 can output S/PDIF signal.
Then if I use this S/PDIF signal to connect to
the S/PDIF input PIN of DIR9001,
can it work?
Or I must set PCM2707 into I2S format?

[rja]

I'm far from being an authority on these things - it's just something I've looked into doing, and am part-way through building. Please listen to others before you base any decisions on my comments or advice.

But from what I've read, i2s is preferable over spdif because it carries less jitter. Going from the PCM2706/7 to the PCM1794/8 using i2s would be better in terms of having a lower component count, and lower cost, as well as reduced jitter. But if you wanted to keep your options open regarding future use, spdif isn't a bad idea - you would find it much easier to switch from using the PC as a source, to a CD player, for example.

How about basing your design around having one PCB for the DAC, and output stage, with the input being fed via i2s? You could then build a separate module for the interface - whether it be an spdif receiver, or a USB->i2s converter.

Mounting the two boards next to each other, and passing i2s from receiver PCB to DAC PCB over very short(<50mm) wires shouldn't hurt much, IMO. You could also go through an ASRC IC(SRC4192 or AD1896), to help reduce jitter and remove any issues regarding clock timing?

Good luck!

--Rich

[shyliang]

THANKS.
But I read the datasheet of PCM2707 and didn't find
what you said like "i2s is preferable over spdif because
it carries less jitter".
It do not mention any about jitter.

[rja]

http://en.wikipedia.org/wiki/I2S

The I2S bus separates clock and data signals, resulting in a very low jitter connection

http://www.tnt-audio.com/clinica/jitter1_e.html

Incoming SPDIF data link is affected by interface jitter in all its components: its transitions timing is perturbed by both transmitter, line induced and interfering noise jitter

It's worth reading up on, IMO.

--Rich