Hello! I am currently making a guitar pedal with the Bela and I want to change the audio in/out from stereo to mono. What would be a good way to do this?

I found this stereo to mono circuit:
https://brashleraudio.files.wordpress.com/2012/08/screenhunter_02-aug-27-19-35.gif?w=584&h=187
Should I use something like this? and what resistors would be best with the Bela?

Or is it possible to just use the left pin and ground of the audio in/out and do no conversion?

Thanks,

Bram

You don't need that. Depending on what you want to achieve, you can:
- just use on channel
- you can sum the two input signals in the digital domain (equivalent to the circuit you linked), and then output the same signals to both output channels

If for some reason you want to have mono when the cable is plugged only into the Left (mono) jack, but stereo if both cables are present, you can do this with the style of jack that grounds the sleeve to the ring when a cable is inserted.

You put a resistor in series with both outputs (say, 1k), then connect a resistor between right sleeve and tip, then connect the sleeve through a resistor to the left tip.

If the right channel jack is unplugged, then there is a path between right tip to right sleeve to left tip. The combination of resistors from both ends should be equal to get 50% R/L mix at the output.

Then if you plug a cable into the right jack, the junction between the two tips gets shorted to ground when the plug shorts ring to sleeve. Both outputs are at 1/2 volume, but not mixing together since the mixing junction is grounded.

As for the way I do it, I process the left and right channels independently so I have 2 series mono processing chains. Then I use channel 1 for pre-distortion effects (wah, EQ, compressor) and channel 2 for time-based effects (delay, phase, flange, reverb, etc). Then I have a pre-processing loop and a send/return loop for distortion pedals.

2 years later

bumping an old thread.
i have to say i don't fully follow ryjobil's explanation, but here's what i came up with using switched jacks.
i absolutely DO want the options of summing stereo to mono.
what this should do is:
- for stereo (dual mono?), use mono cables in both L and R output jacks
- for summed mono, use a mono cable in L output jack
- for stereo over a single cable, use a TRS cable in R output jack.

if for some reason you only plug a single mono cable into the R output, the left is pulled to ground through the resistor. only question i have is what the value of the resistors should be.. will 1K work?

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