Open-source USB interface: Audio Widget

[realmadrid]

UnixMan

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Good luck

Juan

[bonalux]

Hi there, i've bought an AB1.1 and want to use the i2s output to drive a pair of PCM1704 (old stuff...i now). There is the possibility to put the AB1.1 in a 16bit i2s mode instead of a 24/32? PCM1704 utilize the sony right aligned standard and not i2s, putting out 16bit between LRCK changes could save me from adding any glue logic to align data. Obviously this will lower the BCK clock, but i have to ask, just in case anyone has a solution.

Also, in the latest firmware i've read that the output was upgraded to 32 bit output, from what release this change was implemented?

Thank you.

[borges]

The PCM1704 is a great part! Personally, I use a Xilinx Spartan3 as glue logic, but I see how that can be a little over the top....

The AVR32 PISO can supposedly be set up to do all sorts of weird things, including I2S. Unfortunately I'm no expert in using it.

Beware of one thing: The PCM1704 latches its SIPO registers at a given bit clock tick. So to reduce jitter you want to tap its bit clock directly from the XOs, not via the MCU. That might be a bit tricky here since the XOs are 22/24MHz while the MCU's PISO can only run up to 16MHz.

Børge

[bonalux]

Thank you Borge for the quick reply. I'm no expert in xilinx pieces nor AVR32 so i hope some software expert can point me in the right direction. Regarding PCM1704 it is supposed (from BB/TI) that it is a highly insensitive part to jitter, so the MCU clock can be enough? Don't know... Actually i have an AD1865 dac with a shifter and take i2s from hiface usb that runs pretty well, i've bought an AB1.1 because hiface it's incompatible (and by the word of producere newer will be) with linux, i hope AB1.1 is at the same level once fitted with dedicated PSU's.

If there is not such a possibility i will use a shifter, but to reduce the trial and error factor i need also to know what nr of bit the output of AB1.1 is.

Regards.

[bonalux]

Oppss.. forgot to mention that i want to use them without digital filter in pure NOS stile

[borges]

Every IC manufacturer on the planet states their chips are highly insensitive to jitter. It's like stating your ICs are black with metal pins.

The PCM1704 is a multi-bit converter. This means the time-current integral you get from jitter is dt*dI where dt is the error period and dI is the difference from one output sample to the next. The dt error only occurs once per audio sample, in your case 1/44100s. With 8x oversampled data it happens 8x as often but then again dI is probably smaller, too.

With modern delta-sigma architectures the clock signal is used for a lot more output updates, and the current steps are taller. But then again the errors may even out over time.

You may get a working unit using the clock from the MCU but for Hi-End aspirations I'd recommend trying to make the MCU act as bit clock slave.

Børge

[bonalux]

Thank you Borge, very useful information. I will try as you suggest clocking the unit with a divider directly from the XO.

[borges]

That or use 11.2896 / 12.288 MHz XOs directly. Then you can feed the DAC chip directly and bypass all the dividers to the MCU.

Here's a neat trick which works for the PCM1704 which doesn't need MCLK/WCLK=2^n: Use a 13.0548MHz clock. Divide by 34 for 48*2^n and by 37 for 44.1*2^n. You'll be within +-92ppm of the target frequency. I have a very few extra but they operate at 5V.

Børge

[Turbon]

Originally Posted by borges

Well, this is what the AB-1.12 is about. With it we (you:-) can prototype with other DAC chips and regulators.

Børge

When will this be available? Somewhere it was sais that we get the 1.12 and 1.13 boards in one kit...

Brgds

[Turbon]

Originally Posted by GeorgeBoudreau

oh.. I have a WM8741 single DAC card with I2C control bus at the 90% mark. I never took it any further as it needs a configuration system to work properly.

As this one:

H I F I D U I N O

Brgds