Linux Sound Support
When it comes to playing music, there are several methods that can be used.
First, don't plan on digitizing a 60 minute music CD as a sound file and storing it on your hard disk. Some simple calculations show the size of the data involved:
60 minutes x 60 secs/minute x 44100 samples/second x 2 channels x 2 bytes/sample = more than 635 million bytes!
Small sound samples at low sampling rates are reasonable though:
10 seconds x 8000 samples/second x 1 channel x 1 byte/sample = 80 thousand bytes
A more compact method of storing music is MOD files. These originated with the Amiga computer, but MOD file editors and players are now available on other systems as well, including Linux. MOD files essentially store a bank of short samples (instruments), and sequencing information (musical notes). These files are of the order of 30K to 300K bytes in size and can represent several minutes of music (i.e. a complete song).
MIDI stands for Musical Instrument Digital Interface, and as the name suggests, is a standard hardware and software protocol for allowing electronic musical instruments to communicate. MIDI files describe songs in terms of keypress events, and can be played using either an internal FM synthesizer on the sound card, or external MIDI devices.
Another, less common, file format is Adagio files. Adagio is a music description language developed at Carnegie Mellon University. Programs to play Adagio files, and convert between Adagio and MIDI files are available.
We can't forget another important application for sound—games! Several graphical games supporting sound run under Linux, including Bdash and Xboing.
To make use of the sound support in the Linux kernel, applications are needed. Several of the important ones are Sox (a utility for converting sound files from one format to another and adding effects), and tracker (a MOD file player). Some graphical programs that run under X are available as well, including xmix (a sound mixer), xplay (a sound player/recorder), and xmp (a MIDI file player).
There are many others, including some interesting applications such as speech synthesis.
Now it's time for me to get up on my soapbox. Sound support in Linux is quite new, and application support is not as complete as for some other operating systems. I envision seeing a complete set of sound tools, that would provide a consistent, graphical user interface for all of the common sound functions. This would help bring Linux to the forefront of multimedia operating systems. Some of the tools that need to be developed are:
sound player/recorder tool
file conversion utility
MOD file player
MOD file editor
MIDI file player and sequencer
FM synthesizer patch editor
text to speech synthesizer (how about support for a /dev/speak device?)
an X window manager supporting sound
Many of these already exist in various forms, and just need more development to be more reliable and consistent. Any volunteers?
An interesting side note is that the author of the Linux sound drivers, Hannu Savolainen, is porting them to other Intel operating systems as well. The package has been dubbed VoxWare, and should make it easier to write sound applications that are portable across several operating systems.
The Linux Sound-HOWTO document provides more information on the topics discussed in this article and provides other references. Look for it on your local Linux archive site.
If you have access to the Internet, the following FAQs (Frequently Asked Question documents) are regularly posted to the usenet newsgroup news.announce as well as being archived at the site rtfm.mit.edu in the directory /pub/usenet/news.answers:
PCsoundcards/generic-faq (Generic PC Soundcard FAQ)
PCsoundcards/soundcard-faq (comp.sys.ibm.pc.soundcard FAQ)
PCsoundcards/gravis-ultrasound/faq (Gravis Ultrasound FAQ)
audio-fmts/part1,part2 (Audio file format descriptions)
These FAQs also list several product specific mailing lists and archive sites. The following Usenet news groups discuss sound and/or music related issues:
alt.binaries.sounds.misc (Digitized sounds and software)
alt.binaries.sounds.d (Discussion and follow-up group)
alt.binaries.multimedia (Multimedia sounds and software)
alt.sb.programmer (SoundBlaster programming topics)
comp.multimedia (Multimedia topics)
comp.music (Computer music theory and research)
If you have Internet mail access, then you can subscribe to the SOUND channel of the Linux Activists mailing list. To find out how to join the mailing list, send mail to email@example.com.
The Readme files included with the kernel sound driver source code contain useful information about the sound card drivers. These can typically be found in the directory /usr/src/linux/drivers/sound.
The Linux Software Map (LSM) is an invaluable reference for locating Linux software. Searching the LSM for keywords such as “sound” is a good way to identify applications related to sound hardware. The LSM can be found on various anonymous FTP sites, including sunsite.unc.edu in the file /pub/Linux/docs/LSM.gz.
Note that at the time this article was written, the sound driver was at version 2.4, and was included as part of the Linux kernel version 0.99 patch level 15 (and is probably ancient history by the time you read this).
Jeff Tranter (Jeff_Tranter@mitel.com) is a software designer for a high-tech telecommunications company in Kanata, Canada. He is the author of the Linux Sound HOWTO.
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