PTB error: audio device has 4 output channels but stereo audio provided

Hi

I’m trying to run a PsychoPy experiment using an external sound card (USB audio interface) connected to a speaker, but I keep encountering the following error when using the PTB audio backend:

PTB-ERROR: Audio device 1 has 4 output channels, but provided matrix has non-matching number of 2 columns.

From what I understand, this indicates a mismatch between the number of output channels exposed by the device (4) and the audio data being provided (stereo, 2 channels).

What I’ve tried so far:

Forcing stereo output in code:

from psychopy import prefs
prefs.hardware[‘audioChannels’] = 2

The experiment runs in blocks, with each block using a different audio file, specified via a conditions file.

Any guidance with this would be greatly appreciated!

Thank you very much.