I am working with a ADZS-BF548-EZLITE revision 1.4 and I have written a program to play wav files read from an SD card. Unfortunately, the output was very noisy and there were pops in the background. With a few tests - using the Audio_Loopback example and programs derived of it -, I could identify two different problems:
(1) There are periodic pops in the output when I use a sample rate of 22050 Hz. The number of pops per second is constant. It does not change with neither the size of the buffers used to communicate with the device drivers, nor the size of the SPORT audio frame, nor the processor clock. Using any other sample rate, audio output works well.
(2) The USB debug agent seems to interfere with audio output. When I call printf to print various debug messages to the console in VDSP, there is a probability of approximately 1 in 4 of getting severe distortion in the audio output.
While I can easily ignore (2), (1) is a major problem, because 22050 Hz is the sample rate we're using for speech processing.
Now I'm stuck. It would be great if someone could point out what's wrong or what I should test to track it down.