[mythtv-users] alsa upmixing to spdif

Nick Rout nick at rout.co.nz
Thu Jul 12 02:24:28 UTC 2007

All of my sound goes to a device called ALSA:spdif2 which feeds a DTS/AC3
THX certified amplifier/speaker setup. (yes I have 2 sound cards, the
operative one is a Xitel HiFiLink Pro (USB soundcard).

Anyway, 5.1 material plays fine, but 2 channel material gets upmixed by
the amplifier in a fashion that I do not like. I would like to try getting
alsa upmixing to work. I have had a look at thrwads like this
http://www.gossamer-threads.com/lists/mythtv/users/134552 and

I have a couple of questions:

1. The specific setups I have seen are for the situation where the
soundcard is directly feeding the speakers, rather than my situation where
the stream needs to be fed out the spdif port - will this work for me?

2. I can see what happens when such a setup is fed a 2.0 channel signal -
the left front is fed to the left rear, ditto right front/rear, left and
right mixed into centre and LFE. Sensible. However what happens when a 5.1
signal is fed into it? Obviously you don't want this mixing going on to a
stream that is apready 5.1. I want to have the same alsa device for all
output (otherwise I would have to set different player commands for
different video files).

3. It doesn't seem right to just send L+R to the LFE - is there any
possibility of a filter to just send below a certain frequency to this

Nick Rout

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