Hi,
The code above seems wrong to me.
As I understand it, a cpal buffer size correspond to an alsa period size.
So the alsa buffer size should be: nperiods * cpal_buffer_size.

While it is currently cpal_buffer_size / 4 and I suppose that nperiods == 4.

I think that better defaults for cpal would be a nperiods == 2.

Cheers,
Alex