Sound stuff: Looking for bidirectionnal audio!

Sound stuff: Looking for bidirectionnal audio!

Post by James Hightow » Thu, 30 Mar 1995 16:33:14

: >I am currently trying to find a way of playing audio and recording in
: >simultaneously. A possible application could be a real time effect
: >processor, or a direct to disk multi track recorder.

: I am attempting this sort of thing by using brute force- using two sound cards.
: I hav a GUS and a SB16, which can apparently be used at the same time.  
: Haven't had much success yet though, as using the GUS (alone or with the SB)
: only kind of works, and then usually causes a total system crash from which I
: have to do a reset.  (then run e2fsck from floppy- yuch!)

I'm doing 16 bit 44.1khz bidirectionnal with a gus and sb16 with no problems.

My config: (cat /dev/sndstat)

> Config options: 35c0a

> Installed drivers:
> Type 1: OPL-2/OPL-3 FM
> Type 2: SoundBlaster
> Type 6: SoundBlaster16
> Type 7: SB16 MIDI
> Type 4: Gravis Ultrasound

> Card config:
> SoundBlaster at 0x220 irq 7 drq 1
> SoundBlaster16 at 0x220 irq 7 drq 5
> (SB16 MIDI at 0x330 irq 7 drq 0)
> Gravis Ultrasound at 0x240 irq 15 drq 6
> OPL-2/OPL-3 FM at 0x388 irq 0 drq 0

> PCM devices:
> 0: SoundBlaster 16 4.11
> 1: Gravis UltraSound

> Synth devices:
> 0: Gravis UltraSound 2.4 (1024k)
> 1: Yamaha OPL-3

> Midi devices:
> 0: Gravis UltraSound Midi

> MIDI Timers:
> 0: System Timer
> 1: OPL-3/GUS Timer

> 2 mixer(s) installed

Note that the GUS is at 0x240, and the sb is at drq 5.
Are you sure you have the SB and GUS on different dma channels?
They default to the same.

Also, I had to read and write from the same program -- just pipeing
srec to splay was a loss.

"It runs like x, where x is something unsavory"
                -- Prof. Romas Aleliunas, CS 435


1. Sound stuff: Looking for bidirectionnal audio!

These tasks are difficult to implement without special hardware and/or
operating system constructions. The real time effect processing requires
that the recorded sample is played back almost immediately after being
recorded (otherwise there is some disturbing delay).

The problem with D2D is the disk I/O. Recording CD quality sound requires
that the file system+disk I/O code is able to store continuously 176k of
data to a file without pauses longer than 0.3 sec. On my system this is
not possible (DX4/100+IDE disks+ext2fs). It may work with SCSI disks
and/or using raw disk partitions (no fs on them). Doing recording and
playback at the same time makes things still worse.

This limitation is there since at the time I started writing the sound
driver there was just the SB which was not able to work in duplex mode.
However since full duplex is the most requested feature, it's propably
the time to start implementing it.

It's likely that it leaves about 5% of CPU free. Interrupt processing is just
too time consuming to be done 44100 at times/sec.

The standard WSS interface doesn't support two DMA channels but some
cards may have a proprietary extension (SG NX Pro 16 is not one of them
AFAK). The ad1848.c is a generic driver that is intended to support all
AD1848/CS4248/CS4231 based cards such as WSS and GUS MAX. For this reason
there is preliminary support for dual DMA channel mode.

Hannu Savolainen

"Hackers don't use factory prebooted DOS."

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