I've got two Lolin32 boards. I'm transmitting audio via Bluetooth to the first one, transferring it to the second one via I2S, and sending it to a speaker via Bluetooth again. The signal comes out as very noisy and I'm assuming the noise is introduced by the I2S connection. I've tried connecting the two boards with a breadboard and soldered cables directly onto the boards but the signal barely gets better either way. I've tried using the optional master clock line (MCLK) too but the signal somehow gets way noisier that way. The board that receives the I2S signal and sends it via Bluetooth outputs a lot of ´BT_APPL: btc_media_aa_prep_sbc_2_send underflow´ warnings. The incoming/outgoing Bluetooth and the I2S work with 44.1kHz. The pins I'm using for MCLK/BLCK/WS/DATA are 0/4/5/18 (out) and 0/26/33/32 (in). I've tried switching the master/slave roles for both boards. When the second board is the master, the Bluetooth warnings stop but the output sounds the same.
Is there anything I can physically do with the connection to eliminate the noise? Or do you think it is software related?