FormatConverter discards 2nd channel when going from 2 to 1 channels

[quantamrhino]

macOS Version(s) Used to Build

macOS 13 Ventura

Xcode Version(s)

Xcode 14

Description

Using formatConverter.Options as follows:

options.format = .caf
options.sampleRate = 48000
options.bitDepth = 16
options.channels = 1 // mono.

if I have a stereo file with 1 channel (left), this converts it to a mono file correctly.
But a stereo file with 1 channel (right) converts it to an empty file.
is this expected behavior - to discard the second channel?

If so, how does one convert a 1-channel stereo file to a mono file (with the non empty channel) as the first channel? (effectively flatten it).

Crash Logs, Screenshots or Other Attachments (if applicable)

No response

[NickCulbertson]

It sounds like it is just grabbing the first channel (left) and making it into a mono file. I wouldn't think that is the expected behavior, but it would take some digging to find where this is occurring and how to mix the two channels. If you want to make a minimal GitHub example I can take a look.

I think there is a Stereo Limiter AudioKit node that could be used to make an incoming stream Mono.