[PlanetCCRMA] new KDE update, pulseaudio fails

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Fri Apr 22 16:59:31 PDT 2011

On 04/22/2011 04:37 PM, Craig Bourne wrote:
> Sorry about posting to the wrong group-- I'll try to keep that
> straight in future.
> re:  I would try to use "left", "right" first and point them to the
> channels where stereo output should come out. Then use the others (you
> can - and I do that for RME cards - repeat them if there are not
> enough distinct names)
> I have no clue as to how to "point them to the channels where stereo
> output should come out".
> I am not (at least until a much later production step for current
> work) using 7.1 or even 5.1 channel output. For now output is directed
> to a 2.1 channel speaker setup with Left, Right and Sub-woofer. Mono
> would suffice for much of the work I do so this defined channel name
> might perhaps also be relevant.
> so, one alternative channel map that your tip and the documentation
> suggests, to my still limited understanding is:
> left, right, subwoofer, mono, aux0, aux1, aux2, aux3, aux4, aux5,
> aux6, aux7,  aux8, aux9, aux10, aux11, aux12, aux13, aux14, aux15,
> aux16, aux17, aux18, aux19, aux20, aux21, aux22

auX goes from aux1 to aux15. "aux16" will fail so this will not be 
parsed correctly.

> another (which assumes that only the listed aux channels are defined

That is correct, you can only use the names that pulseaudio defines 
(which reflect "common" configurations).

> and that something else is to be repeated (but still reflects my
> ignorance of the technique "point them to" anything):

I know this is confusing. PA finds a card with no mapping and does not 
know where to send "left" and right" (which will be what most software 
plays through). Most cards have defined mappings (and most have only two 
channels!) and PA knows what to do. You are telling PA specifically 
which output channel of your card is "left" and which is "right". If 
"left" is found many times (like below) then PA will send to all those 
output channels whatever is send to "left". Same for surround channels.

> left, right, left, right, left, right, left, right, subwoofer, mono,
> mono, aux0, aux1, aux2, aux3, aux4, aux5, aux6, aux7, aux8, aux9,
> aux10, aux11, aux12, aux13, aux14, aux15

This may work...

> Does either of these make sense in terms of what you were trying to tell me?

The second one does.

> Also completely opaque to me is this from the documentation's
> definition of channel map "(Default depends on the number of channels
> and the driver)". Given that the definition itself contains a numbered
> list of aux channels, this could perhaps refer only to the number of
> aux channels or it could mean something more general about a
> configuration of a channel map by default if the user does not specify
> one (this. however,  seems unlikely as pulseaudio is evidently not
> creating a default and that is why I am tinkering with this file).

Correct, pulseaudio does not find a usable channel map for your 
particular card and alsa does not provide any usable information to PA, 
so PA can't use the card. If you tell it explicitly then it will know 
what to do with so many channels :-)

This makes sense to a point because there is no universal sensible 
mapping of channels for a card like the RME. You could assume that 
everybody would have stereo monitoring attached to the first two 
channels but that may be false in some case, and pulseaudio could be 
sending audio to the "wrong" channel (ie: one that has nothing attached 
to it). Or you may want in a studio environment that _no_ channels from 
PA get routed to that card (ie: you don't want a system "new email" 
sound to appear in the middle of your perfect recording take).

-- Fernando

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