Linux puskom-ProLiant-DL385-Gen10 5.4.0-150-generic #167~18.04.1-Ubuntu SMP Wed May 24 00:51:42 UTC 2023 x86_64

//usr/share/doc/libasound2-plugins/upmix.txt

 UPMIX PLUGIN
============

The upmix plugin is an easy-to-use plugin for upmixing to 4 or
6-channel stream.  The number of channels to be expanded is determined
by the slave PCM or explicitly via channel option.  For example, the
following PCM defines upmixing to 5.1 from 1-6 channels input:

	pcm.upmix51 {
		type upmix
		slave.pcm "surround51"
	}

You can use this PCM as a default one by defining below:

	pcm.!default "plug:upmix51"

The upmix plugin copies left and right channels to rear left and right
with a certain delay.  The delay size can be specified by "delay" PCM
option in msec.  For example, to set 10ms delay in the above case:

	pcm.upmix51 {
		type upmix
		slave.pcm "surround51"
		delay 10
	}

As default, 15ms delay is used.

The channel option specifies the number of channels of output.  Either
4 or 6 channels are supported.  When 0 is passed, the plugin tries 4
or 6 channels appropriately suitable for the slave pcm.  The channel
option is useful if the slave PCM has no strict input condition (like
plug or route plugin).

	pcm.myupmix {
		type upmix
		slave.pcm "something"
		channels 6
	}

The center and LFE channels are the average of sum of left and right
signals.

The accepted format is currently only S16.