playing 4 channels

playing 4 channels

[Helmut Obertanner]

How can i tell my soundcard to play 1 stereochannel on Frontspeakers
and another stereochannel on rearspeakers ??
I can set my soundcard to 4 channelmode -> o.k.
I write samples in the following order to the soundbuffer:

LF,RF,LR,RR

but i get L-FRONT and R-FRONT on rear output too, and LR and RR are lost in 
space.
how could i solve this ?

regards, Helmut
http://funkyou.x4u.de 


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Re: playing 4 channels

[Takashi Iwai]

At Thu, 10 Oct 2002 16:20:31 +0200,
Helmut Obertanner wrote:
> 
> How can i tell my soundcard to play 1 stereochannel on Frontspeakers
> and another stereochannel on rearspeakers ??

what sound card?  i cannot tell you otherwise ;)

> I can set my soundcard to 4 channelmode -> o.k.
> I write samples in the following order to the soundbuffer:
> 
> LF,RF,LR,RR
> 
> but i get L-FRONT and R-FRONT on rear output too, and LR and RR are lost in 
> space.
> how could i solve this ?

this depends on the card, but in general, you can choose the route via
the pcm name.  for example, on sb live, you can play two stereo-wav
files separately to front and rear speakers like:

	% aplay -Dfront foo.wav
	% aplay -Drear bar.wav

but the chip can mix up the different streams, so the rear signals may
be contaminated from front on a certain mixer set up.


Takashi


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Re: playing 4 channels

[Takashi Iwai]

At Thu, 10 Oct 2002 20:12:12 +0200,
Helmut Obertanner wrote:
> 
> Am Donnerstag, 10. Oktober 2002 17:14 schrieben Sie:
> > At Thu, 10 Oct 2002 16:20:31 +0200,
> >
> > Helmut Obertanner wrote:
> > > How can i tell my soundcard to play 1 stereochannel on Frontspeakers
> > > and another stereochannel on rearspeakers ??
> >
> > what sound card?  i cannot tell you otherwise ;)
> >
> 
> I currently have a CMedia 8738(Model37),

oh, you had bad luck.  the rear output of this chip model is _always_
on the loudest level.  it seems like there is no mixer control for
it.  so the incoming stream must be attenuated in advance.

please read alsa-kernel/Documentation/CMIPCI.txt for more details.


Takashi


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Re: playing 4 channels

[Takashi Iwai]

Hi Helmut,

At Fri, 11 Oct 2002 11:53:42 +0200,
Helmut Obertanner wrote:
> 
> how is that with other cards, is the mastervolume also respoonnsible for the 
> rearchannels ???

it depends.  the later models of cmipci support 4/6 channels playback
via one DMA, i.e. interleaved output.  in this case, the output volume
is controlled by a master volume.

in the case of SB live, the rear output has different codec without
volume controls, but the emu10k1 dsp itself can attenuate the signals
inside.

most of other sound chips use AC97 for the rear volume controls.
some use the secondary codec, and some use a 4/6 channel-capable
codec.  in both cases, the "Surround" volume element will be there.

 
> another problem:
> in another thread i want to record, (for the realtime vocoder / FX on 
> microphone)
> 
> opening the device fails with: device busy.
> i use another pcm_handle for capture.
> 
> is it impossible to record while playing ?
> or what i'm doing wrong...

the rear output uses the ADC as the secondary DAC.  so, you cannot use
ADC together with 4 channel outputs.  (again, the later models use
only one DAC for interleaved 4/6 mode, and it's no problem.)


ciao,

Takashi


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