ADAU1701

I tried to play 20hz audio, the picture that comes out is something with a similar pulse, 10ms once

Hello,

It looks like your I2S input is not synchronized to the 1701's master clock. Since the 1701 has no ASRCs, incoming I2S can only come from a source operating from the same master clock as itself. For example this could be an extra codec to provide more ADC inputs, or the I2S output of another ADAU1701, where all the chips involved are clocked by a single 12.288 MHz. oscillator.

According to Dave Thib's post here, you can connect the incoming BCLK to the 1701's MCLK input, in effect having the incoming I2S drive the -1701. For example, at a 48K sample rate, the BCLK is 64 x Fs = 3.072 MHz. Ground both of the 1701's PLL Mode pins, then its PLL will derive the 50 MIPS core clock from this. With the I2S synchronized this way, it should work. Note that the 1701 is now dependent upon the I2S input, when this goes away the chip stops running. If your application involves an external (off-board) I2S input, I'd suggest choosing a DSP which includes ASRCs.

Best regards,

Bob