The clock between 52840 USB Audio and I2S will be out of sync after few seconds

[OPQ]

Hi,

I try sdk 17.02 nRF52840 usb audio demo,I want to achieve 48KHz stereo music play by a I2S DAC.

I finished adding DAC for I2S to play the sound data of USB Audio ,and it works well most time, but I found that about every few seconds ,I can hear a noise frame ,I think the cause was that the clock between 52840 USB Audio and I2S were out of sync .

So I wonder how to avoid this noise issue?

Thanks.

[Kenneth]

It looks like you are experiencing underflow/overflow of data coming in from USB vs. what is sent on I2S. 

To overcome underflow/overflow then interpolating/discarding samples would be the solution. Interpolating/discarding samples can introduce distortion in audio, but are depended on the clock offset between peers and buffer size.

[OPQ]

Asynchronous usb audio would be help, Is there any reference on nRF52840 that related to asynchronous usb audio?

[Kenneth]

Ideally you would want to adjust the audio PLL clock to avoid underflow or overflow, this could be done in run-time by monitoring the available buffers. This is not possible on the nRF52-series, but should be doable on the nRF53-series.

Kenneth