First of all I would appreciate if we could leave this thread free of comments about why I would like to do this or that 16bits or higher gives better sound. I know it does. High quality audio is NOT the goal here.
I have a Raspberry Pi running Retropie that is used for retro (Commodore 64) gaming and some old school MOD/chipmusic. I would like to have true 8bit mono audio output. Sending the digital audio from the Raspberry to a home made sound card sounds like way too much work so I was thinking about re-digitizing the analog audio with two separate 8bit analog-to-digital converts (limiting the input to 7bits), binary sum the two channels and then convert the digital stream with a 8bit DAC.
It would be nice with a sample rate of about 22kHz but anything between 11-20kHz would be acceptable. Can the Arduino UNO do this with the internal ADC or do I need external converters?
I was thinking about using a fixed voltage reference of a suitable value and trimpotentiometers for each channel so that I can adjust the maximum analog output of each channel to generate an AD-value of 127
Is this article useful for my application?