Re: [LAU] Jack users - how many channels do you want with PA module-jackdbus-detect?

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To: Mac <ussndmac@...>
Cc: <linux-audio-user@...>
Date: Thursday, February 28, 2013 - 10:31 pm

On Thu, February 28, 2013 4:25 am, Mac wrote:

Pulse audio thinks in stereo, not channels.

Pulseaudio is designed to work with the standard desktop audio setup:
-left and right input or mic input (mic is normally mono on L/R)
- 2 to 8 outputs labeled:
5)spdif out, normally stereo (ASE3/spdif are stereo standards)
but may be encoded as surround.

A stereo signal that is converted to a 4.1, 5.1, 7.1, may have a left and
right channel that is different than the original stereo signal. So unless
you are using a pulse/jack bridge to do surround sound output, you need a
stereo line from pulse to jack to get the same two channels that went in.
Personally I have not noticed the difference, but then an MP3 is not
quality audio, it already sounds "off" (the kind of off milk left out

Jackd, is a multi-channel setup. Any one channel is on it's own and not
connected to any other except for being in sample sync.

So any audio coming from Pulse has to be expected to having been dealt
with as stereo, that is, if there is some effect on one side, it will be
on the other as well. (or if there are more than two channels they will
have been all effected together as well) Any audio going to Pulse, must be
expected to be effected together on their way to whatever app is capturing
that audio via pulse.

The PA-jack bridge is not only a bridge between audio servers, but a
bridge between two different paradigms. A channel paradigm on the jack
side and a stereo/surround paradigm on the pulse side. A bridge between
the desktop and pro-audio. In this case, the best way for pulse to see
jack is as a stereo sound card with no controls. The only time more
channels should be granted to Pulse is if the desktop is using jack as a
surround device for playback to a firewire device. Any other device does
not need jack at all and can playback surround directly to the audio
device on it's own.

If we are creating a surround recording in jack, we don't need pulse at
all and can do all our surround processing in jack.

No matter what pulse defaults to in channel numbers, it will always allow
configuring to as many channels as the device supports if the default is
not what the user wants.

Len Ovens

Linux-audio-user mailing list

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Re: [LAU] Jack users - how many channels do you want with PA..., Len Ovens, (Thu Feb 28, 10:31 pm)