Audio garbled when using Multi plugin to record from 2+ USB soundcards on Raspberry Pi

[GitHub issues - opened <github@alsa-project.org>]

alsa-project/alsa-lib issue #472 was opened from TommyKaneko:

I have been trying to use the multi plugin to record multiple channels from mutliple soundcards on the Raspberry Pi.  The results are a garbled mess.

I have diagnosed the reasons as thus:
- current raspberry Pi OS uses alsa v1.2.8+rpt1
- the "fix" for the multi plugin was implemented in v1.2.9 : https://github.com/alsa-project/alsa-lib/commit/369df322577034ea872978d6470edbadf30d81a9

I am aware that the multi plugin was not meant to be used on multiple soundcards that are not in sync, however if the clock drifts over time, this is ok for my application.

I am here to seek advice on how I should go about creating a workaround.  The limitations are that I need to use cheap USB microphones (it is a weight issue).

Without going along the microcontroller route, I thought one way was to make an [external plugin](https://www.alsa-project.org/alsa-doc/alsa-lib/pcm_external_plugins.html), based on the newly patched pcm_multi plugin.  I am working on this, while climbing the steep learning curve.  Perhaps I can contribute an external plugin for the project...

In the meantime, does a developer have a better suggestion that I might have success with?  Or any tips if you are familiar with the pcm_multi plugin? @perexg ?

Issue URL     : https://github.com/alsa-project/alsa-lib/issues/472
Repository URL: https://github.com/alsa-project/alsa-lib