-----Original Message----- From: Miller Puckette [mailto:mpuckett@man104nfs.UCSD.EDU] Sent: Thursday, March 25, 1999 8:12 PM To: Guenter Geiger; pd-list@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 - 8bit. 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 for 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, therefor having 8 bit data for input and 16 bit data for output, or vice versa.
Obviously the OPL3SA3 doesnŽt work this way, as DMA0 and DMA1 both are (from a hardware point of view) 8bit DMAŽs. 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 the 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.
Guenter