FW: Audio drivers again?

Guenter Geiger guenter.geiger at psp-vie.be.philips.com
Fri Mar 26 13:27:43 CET 1999

> -----Original Message-----
> From: Miller Puckette [mailto:mpuckett at man104nfs.UCSD.EDU]
> Sent: Thursday, March 25, 1999 8:12 PM
> To: Guenter Geiger; pd-list at iem.mhsg.ac.at
> Subject: Re: FW: Audio drivers again?

> To answer some of Guenter's specific questions:
> OSS (at least as it's delivered in RedHat 5.2) doesn't work in full
> duplex with my opl3sa3 card.
> My high noise floor problem in OSS didn't go away when I
> tried switching
> DMA channels.  Guenter's remarks that both channels are 8 bit
> conflicts
> with comments in the INSTALL documentation for the ALSA
> distribution, but
> anyway switching the channels didn't help.

What I meant saying there was, that they both have the same transfer width -
What the soundcard is doing with 8bit is another problem.

The Soundblaster for example uses an 8bit DMA for 8bit data and an 16 bit DMA
16 bit data (this is e.g. DMA1 (8bit) and DMA5 (16bit)).
Now, to trick the SB16 into full duplex, the driver just uses both channels,
having 8 bit data for input and 16 bit data for output, or vice versa.

Obviously the OPL3SA3 doesn´t work this way, as DMA0 and DMA1 both are
(from a hardware point of view) 8bit DMA´s. The soundcard puts 2 bytes
together for 16 bit.

Getting myself free from the "evil claws" of my company now, I will hack away on
OSS driver for my card (the SB PCI128), probably getting it to *really* support
4 output
channels and some other things I need for pd.

> In ALSA 0.2 I got a 25 dB noise floor, roughly the same as in
> NT, and in
> 0.3 I got 40 dB in the left channel, 25 in the right.

It starts getting funny :). We have to distinguish not only
between soundcards, but also between soundcard channels now.


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