[Fpga-synth] Stereo Audio Interface

[Andrew Barrow]

Hey guys,

I have lurked on the list... I do FPGA stuff for an audio company and also
mess with analog synths. Both interests have however remained pretty
separate.

Anyway, look closely at your available DACs and ADCs or codecs. There are
some that have a PLL and run without master clocks--this would get you to
four lines. In fact, the Alesis ones (Wavefront Semi now) I think will run
with only LRCK and audio in and out--their master and bitclks are both
PLL-derived from the frame.

I have also successfully used a standalone PLL (it was an ICS502 maybe..
.can't quite remember) to generate mclk from the bitclk, but it was a case
where a 256Fs mclk was acceptable (I think the chip I mention is only a 4X
multiplier). If you need 512Fs you can probably find some other chip to do
it.

If you can find one or the other of the dac or adc with a PLL it will
probably also output the mclk so you don't need BOTH to have a PLL.


Cheers,
Andrew


On Thu, Aug 7, 2008 at 3:08 PM, Eric Brombaugh <ebrombaugh1 at cox.net> wrote:

> Nicholas Gregorich wrote:
>
>> Eric Brombaugh wrote:
>>
>>> I've designed a little I2S stereo audio codec board that will plug into
>>>
>>
>> Hopefully this isn't too picky but doesn't codec imply ADC and DAC?
>> It did initially confuse me.
>>
>
> Never too picky for engineers! :)
>
> You're right - I was sloppy in describing the part as a codec. It's
> actually just an audio DAC. Sorry for any confusion.
>
>>
>>  > Not greedy at all - it's a nice goal to have. Unfortunately, a combined
>>  > ADC/DAC codec requires at a minimum 5 I/O signals (mclk, sclk, lrclk,
>>  > di, do) and there are only 4 signals available on the Digilent 6-pin
>>  > connectors.
>>
>> Could a small CPLD be used make 5 signals fit on 4 pins? Maybe deriving
>> the lrclk from the sclk? I think there are CPLDs in the $1 range.
>>
>
> Interesting idea. I'd probably start by muxing the SCLK and LRCLK onto one
> line using the MCLK and some synchronization bits. Any suggestions for a
> cheap CPLD that runs off of 3.3V and doesn't take up too much real-estate?
> I've done some stuff with Xilinx XC95 parts, but they're more like $5 - more
> expensive than the DAC I'm using now.
>
>  Unfortunately I don't own a S3E or S3A board so I won't be participating
>> in the project.
>>
>
> What do you use?
>
> Eric
>
>
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