8bit audio "retrofier"

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?

Did you search the forum for "mod player" (search field on top of this page).

Or google "mod player site:arduino.cc"

Here's one. Leo..

That's a really cool project but nothing similar to what I want to do. I need the convert two separate analog audio channels to digital values, add them together to create a mono stream and convert it back to analog audio.

Yea, I think arduino could make this. There is no reason to sample 2 channels, than add as you can make addition in the analog domain than sample only one channel. Common arduino with AtMega328 IC doesn't have a DAC (DUE board has), so you need an external one, like MCP4912 or MCP4725. Start your research, sure you can find a lot of projects with sample code using "arduino +dac+..." search pattern. LInk you posted seems O"K, arduino could sample input up to 76 kHz.

kamelryttarn: Is this article useful for my application?

As your link shows, it is possible to do modestly high rate sampling with an Atmega328-based Arduino, but it's not clear how one would do two channels. Some microcontrollers have a scan mode where the ADCis configured for continuous sampling and the input multiplexer sequentially selects a different input with each conversion, but I don't know that the Atmega328 has such a mode.

One can change the ADC prescaler to get faster single conversion rates at the expense of ADC resolution so it may still be possible to implement your concept with single conversion and switching the ADC source pin in software.

A Teensy 3.6 can do proper stereo digitizing. It is unfortunately way too much HiFi for your purposes.

You know you can do an analog sum with two resistors? You don't need to convert to digital to simply add 2 channels. Just two 1K resistors will feed two channels into one.