Audio out with an FTDI UART cable
This encodes audio as either PDM (using a first order sigma-delta stage), 32-bits PWM or 64-bits PWM and sends it as binary data to a UART including standard start and stopbits.
This probably works with many UART cables, not just FTDI.
The program requires raw audio samples in a suitable samplerate to work.
The sample rate is calculated like this:
baudrate / 10 * 8 / output_bits_per_sample
For PDM and 64-bits PWM, this gives:
baudrate / 10 * 8 / 64
Example: 3MBaud = 3000000 / 10 * 8 / 64 = 37500
For 32-bits PWM:
baudrate / 10 * 8 / 32
The following prepares a .wav file into a suitable raw file to be used at 3MBaud in PDM mode.
sox input.wav --bits 16 --channels 1 --encoding signed-integer --rate 37500 output.raw make uart-sound && ./uart-sound output.raw /dev/ttyUSB0 3000000 0