AVB-DC at < 48kHz?

[akp]

Hello

I believe that 1722 supports sample rate(s) lower than 48kHz, which is what the AVB DC works at natively.

In order to better achieve the channel counts I want, I would like to use a lower sampling rate (the audio bandwidth of my application is on the order of 4kHz). I am pretty sure 32kHz is supported by AM824 for instance but I don't know if any lower sampling rates are supported.

Is this true? If not I guess I will have to revert to 48kHz.

I have updated my code to generate a 32kHz LRCLK and that is output correctly when I set default_sample_rate to 32000 in main.xc. To get the 32kHz clock required a change to the function update_media_clock_divide() found in media_clock_server.xc. When the default_sample_rate is less than something like 38150Hz there is an integer overflow in that function.

That was the easy part.

Now I need to update some descriptors so the Apple computer knows that the board runs a 32kHz fs rather than 48kHz... any pointers of the places I need to change and how I would change them? I have updated aem_descriptors.h.in to say 32000 rather than 48000 in desc_audio_unit_0[] (lines 117 and 121 of the file) but I doubt that is enough.

I may well need to change the packetization to put 4 samples per 8kHz beat rather than 6 but that doesn't sound like it would be too hard.

[Andy]

OS X currently supports AVB sample rates that are integer multiples of 48 kHz only.

[akp]

Good to know. I won't be wasting any time on 32kHz then...

[steeley]

I would be interested to know if you get this working - I guess you could use 24k.
I'm looking to use 96k.

TIA
Ian.

[akp]

Hi Ian,

I am pretty sure Mac OSX supports 96k. It won't do 24k. I think it can do 48, 96, and 192k. But I have only used 48k. My development doesn't require much audio bandwidth.

Cheers
Adam