Sound Through the PC-Speaker

Linux supports most of the popular sound cards. If you don't have a sound card, you can still get a degree of sound support from the humble speaker that came with your PC. In this article, I will discuss one way of obtaining sound output without a sound card.

PC-Speaker is a driver for the modest sound output device that comes standard with most (perhaps all?) IBM PC clones. It is installed as part of the kernel or as a loadable module; either way, the kernel needs to be changed. PC-Speaker comes with a small set of programs to use with it—I have compiled these programs on my system without trouble.

The driver comes as a patch file, which must be applied to the Linux source directory (/usr/src/linux). When make<\!s>config is run after applying the patch, it will ask whether you want PC-Speaker support—answer “yes”. Give the commands:

make depend; make clean; make zImage

and your new kernel will be ready. The patches to the source include some header files for /usr/include/sys, which are necessary to make the utilities that accompany the driver.

The driver supports the following devices :

I have /dev/pcsp only defined on my machine:

crw--w--w-      1 root  root    13,     3 Aug 27 20:25  /dev/pcsp

The program pcsel sets options for PC-Speaker and is used to configure the /dev/pcsp device at system startup and to test new devices. You can also assign an output device to /dev/pcsp using the pcsel program. The supported output devices are:

Listing 1. Help Output from pcsel

Specifying the help option on the pcsel command line:

$ pcsel -help

gives you a listing of all the pcsel options and what they mean. With no options specified, pcsel reports the actual output-device and its parameters in this way:

$ pcsel
PCSP driver version 1.0
Actual PCSP output device: PC-Speaker
Volume : 100 %, real samplerate : 18356 Hz
Maximum Samplerate is 51877 Hz
16bit Stereo Emulation enabled

These two programs, vplay and vrec, can be used for recording and playing the following types of files:

Both programs accept the same options, which can be listed by specifying the help option:

vplay --help

The output of this command is shown in Listing 2.

Okay, confession time—the main reason I had for adding this driver to my kernel was to have sound effects in Doom. Here is another trivial example of what you can do with PC-Speaker. I have a directory of .wav and .au files. This shell script, called from my .profile file, plays one of these audio files at random each time I log in.

#!/bin/sh
# random-sound.sh: play a random file from the
# sounds directory
export count="`ls sounds/*|wc -l|sed s/ //`"
export count=`expr $count + 0'
(1>/dev/null 2>&1 vplay `echo sounds/*| \
awk BEGIN{srand()}{x=1+int(rand()*number)
print $x} number=$count') &

The latest version of PC-Speaker can be found at ftp://ftp.informatik.hu-berlin.de/, in the directory /pub/os/linux/hu-sound/pcsnd* (where * represents the latest version number).