[mythtv-users] Analog multi-channel sound, optimal configuration 0.24?

Terjesen Jens Peder Jens.Peder.Terjesen at devoteam.com
Fri Dec 3 11:51:35 UTC 2010

Jean-Yves Avenard wrote:


On 3 December 2010 21:13, Terjesen Jens Peder
<Jens.Peder.Terjesen at devoteam.com> wrote:
> I have it up and running with the MythTV box connected to the receiver with 3 minijack to RCA cables (front, center, surround and LFE).
> I first tried the onboard soundcard which worked but didn't give very great sound.
> Yesterday I installed an old unused Creative Soundblaster Audigy 2 which I had lying around and it was a significant improvement.
> What is the best configuration in MythTV for this setup?

scan for channels, then select the soundblaster one.
I have disabled the onboard sound in BIOS and I did scan for channels/sound devices, then selected ALSA:surround (and then some DEV=... or something) so it should be the Soundblaster card.

> I have selected ALSA:surround51 as sound device.
> At the moment I do not have a Subwoofer and have said so in the setup in the receiver which I think then will mix the LFE channel to the front speakers.
> Would it be better to use ALSA:surround50? Would alsa or MythTV do this mixing instead then?

won't make a difference

surround40, surround41 surround50 surround51 are all aliases to the same device.

so surround40 will report 6 channels, just like surround51

> When running speakertest with 6 channels it displayed LFE but the played sound said "center rear".

there is nothing internally really to differentiate say surround41 to surround50

> Is this normal or an indication that the channels are mixed up?
> Also when the cable for LFE was connected to the Subwoofer input on the receiver there was no sound, I had to pluf it into the Center input to hear the sound.

on my machine, LFE and center are on the same jack output, maybe you
just inversed those ?

if you do not have an LFE device, the best result you will get is by
setting a custom alsa pcm and mix the LFE though the front and left
Yes LFE and center is on the same jack on mine too and with the correct RCA connected to the center input speakertest said "center".
With the RCA plug from the same jack that in my opinion must be LFE was connected to the center input it said "center rear". From the same jack there is a third RCA plug, and when running speakertest with 8 channels it said "left side" when connected to the center input.

So to sum up:
Jack 1 gives left front and right front, with correct sound from speakertest.
Jack 2 gives center, LFE and left side, with correct sound from center and left side.
Jack 3 gives left back, right back and right side, with correct sound from speakertest.
I guess that one easy way to test if LFE comes through to the speakers is to disconnect all but the LFE cable and then play a DVD and see if I hear anything?

Do you have any pointers on how to set up alsa to mix the LFE to the front speakers?

> Is it probable that the frequency of the sound from speakertest is too high for the sound to be mixed to the front speakers by the receiver? Or is this an indication that the LFE is not mixed to the front speakers at all by the receiver? Is there an easy way to send a low frequency to the receiver to test this?

you can usually set the threshold for the frequency cut out on your amplifier
I will have another look in the setup menues on the receiver, but it is quite old and not really very high spec so not sure it is possible.

> I guess that I should select upmix of stereo to surround if I want sound from all speakers all the time?

the upmixer is really stereo to 5.0
OK, good to know.

Thank you for your good answers.


More information about the mythtv-users mailing list