Raspberry Pi ideas … recommended ADC/DACs?

[Stuart Longland]

Hi all,

Silly question, what's a recommended sample rate and bit depth to look
for in a ADC or DAC? I've just got my Raspberry Pi going this
afternoon, and I'm considering how I go about setting up audio.

The Pi has an audio output, but sadly they didn't see it fit to include
an audio *input*.

USB is a possibility, but apparently the Rpi has difficulty running more
than one USB audio device at a time.

One is just enough, I can use a CD4066 to multiplex this, I lose
software-VOX capability unless I include the necessary VOX hardware, but
probably not a big loss.

Two other options:
1. Use a discrete ADC chip connected via I²S
2. Use the ADC channels of a microcontroller, acting as a companion chip

That leads me to what I should look for. 16bit 48kHz would be ideal,
but a STM32F103 provides a 12-bit ADC and DAC on-board and IIRC, capable
of decent sample rates.

AVR chips aren't as good, but they can still do 10-bit samples, and can
possibly do respectable sample rates.

What does FreeDV require in terms of sample rates and bit depths?
--
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
...it's backed up on a tape somewhere.

[Steve]

The codec2 software interface is built around PCM Sign+15-bits maximum at 8 kHz.  I think Sign+11 bits would work well in the floating point algorithms.

Back in the old days they made 8-bit ulaw to 12-bit linear chips, and it was good enough for telephones :-)