22. Sound Files
@sf{Debian}: `alsa-base'
@sf{WWW}: http://www.alsa-project.org/
This chapter covers the basic control of audio on Linux-based systems,
including how to adjust the audio mixer and how to play and record sound
files using basic tools. You can also play and record audio with
snd (see section
Editing Sound Files) and many other
sound applications.
In order to have sound working on your system, you need to have a sound
driver installed and configured for your sound card. There are two free
sound drivers that are popularly used on Linux-based systems. The
standard Open Sound System driver ("OSS/Free") by 4Front Technologies
is currently part of the Linux kernel and is what comes as default with
most Linux distributions. The Advanced Linux Sound Architecture
("ALSA") is another free driver that is becoming popular with
musicians who use Linux.
NOTE: Most systems come configured so that you must be the
superuser to be able to use sound devices, including audio CDs. If this
is the case on your system, ask your administrator to give you access to
these devices, typically by adding you to the audio group
(see section Groups and How to Work in Them).
22.1 Sound File Formats
The following table lists common audio file formats and their
traditional file name extensions. You can also use file to
determine a file's format (see section Determining File Type and Format).
| FILE EXTENSION |
SOUND FORMAT
|
.aiff |
Apple Macintosh audio file.
|
.au |
Sun Microsystems audio file (8000 Hz, u-law compression).
|
.cdda or .cdr |
Both are names for the audio compact disc format, used for burning
audio CD-Rs and CD-RWs (44.1 KHz raw stereo).
|
.gsm |
Global System for Mobile Communications (GSM) speech file format,
used in some voice-mail applications.
|
.midi or .mid |
The standard extensions for MIDI files.
|
.mod |
MOD file.
|
.mp3 |
MPEG II, Level 3 file.
|
.ogg |
Ogg Vorbis file.
|
.ra |
RealAudio file.
|
.raw |
Raw audio data.
|
.sf |
IRCAM SoundFile format, used by some music composition software,
such as CSound and MiXViews.
|
.voc |
SoundBlaster VOC file.
|
.wav |
Microsoft RIFF format ("WAV").
|
22.2 Adjusting the Audio Controls
A mixer program is used to adjust various audio settings, such as
volume and recording levels, and is also used for turning on or muting
the microphone or other input device. You must use a mixer to adjust
your audio settings before you play or record sound.
ALSA's default mixer is called amixer, and the following recipes
assume its use. There are other mixers, and some of them are easier to
use than amixer. If you want a graphical mixer, install the
aumix package, or see the end of this chapter for others.
22.2.1 Listing the Current Audio Settings
To list all audio input and output devices and their settings, type
amixer with no options.
Your sound card's components are organized in groups, from the Master
group containing the master left and right volume settings to the
individual groups for audio compact discs and digital sound
files. (These groups have nothing to do with the file access groups
described in Groups and How to Work in Them.)
-
To peruse the current mixer settings, type:
The following table describes some of the important sound groups that
amixer lists.
| SOUND GROUP |
DESCRIPTION
|
Master |
The master volume settings.
|
PCM |
Digital audio for playing sound files; the first channel is group
PCM,0 and the second is PCM,1.
|
CD |
The audio compact disc player (a cable must be connected from the
CD-ROM drive to the sound card).
|
Synth |
The synthesizer device for MIDI.
|
Line |
The sound input device (the jack on the back of the soundcard is
usually labeled LINE IN).
|
MIC |
The microphone device (the jack on the back of the soundcard is
usually labeled MIC).
|
To list the settings for only one group, use the `get' option
followed by the name of the group you want to list. Group names are case
sensitive--so giving MIC specifies the microphone group, while
Mic and mic are not valid groups.
-
To output the microphone settings, type:
-
To output the second PCM settings, type:
22.2.2 Changing the Volume Level
To change a mixer setting, give the amixer `set' command as
an option, followed by both the group and setting to change as
arguments. To change the volume level for a device, give either a
numeric value or a percentage for the volume level.
-
To set the master volume to 75 percent, type:
| | $ amixer set Master 75% RET
|
-
To set the PCM volume to 30, type:
22.2.3 Muting an Audio Device
The special `mute' and `unmute' arguments are used for muting
the volume of a given device. Before you can record something, you must
unmute the input device you want to record from. Remember to also mute
the microphone after you have finished recording, to avoid feedback when
you turn up your speakers.
-
To unmute the microphone and turn it on for recording, type:
| | $ amixer set MIC unmute capture RET
|
-
To mute the microphone, type:
| | $ amixer set MIC mute RET
|
-
To unmute the master volume and set it to 80 percent volume, type:
| | $ amixer set Master 80% unmute RET
|
22.2.4 Selecting an Audio Recording Source
To select a device for recording, use set followed by the name of
the device and the `capture' argument, which designates the
specified group as the one to capture sound from for recording.
-
To select the
LINE IN jack as the recording source, type:
| | $ amixer set Line capture RET
|
-
To select the microphone jack as the recording source, type:
| | $ amixer set MIC capture RET
|
NOTE: You can have only one group selected for capture at a
time, and when you select a group as an input source for recording, you
are simply turning the microphone or other input on; recording does not
occur until you use a recording tool.
22.3 Playing a Sound File
@sf{Debian}: `sox'
@sf{WWW}: http://home.sprynet.com/~cbagwell/sox.html
The
play tool distributed with
sox (a sound file
translation tool) can recognize and play many audio formats, including
WAV, VOC, AU, AIFF, and SND format files, as well as audio CD-format
files and various raw binary files; just about the only common audio
formats it can't handle are MP3 and MIDI files, which are discussed in
the sections to follow.
-
To play the file `pentastar.aiff', type:
| | $ play pentastar.aiff RET
|
NOTE: Before you begin playing sound, make sure you've set the
master and PCM volume levels with the mixer (see section Adjusting the Audio Controls). The most common reason for no sound
being produced when you try to play sound is not having the volume
turned up!
ALSA comes with aplay, a tool for playing sound files that is
similar to play, but does not recognize as many formats.
22.3.1 Playing an MP3 File
@sf{Debian}: `mpg321'
@sf{WWW}: http://freshmeat.net/projects/mpg321/
To play an MP3 file, give its name as an argument to
mpg321.
-
To play the MP3 file `september-wind.mp3', type:
| | $ mpg321 september-wind.mp3 RET
|
To buffer the audio, useful for when the system is running many
processes or otherwise has a lot of activity, give a buffer size, in
kilobytes, as an argument to the `-b' option. The default is 0 (no
buffer); if you need this option, use a size of at least 1024KB (which
is 1MB), or about six seconds of MP3 audio.
You can also use mpg321 to play "streaming" MP3 audio from the
Web; just give the URL of the MP3 stream as an argument.
-
To play the MP3 stream at http://example.net/broadcast/live.mp3,
type:
| | $ mpg321 http://example.net/broadcast/live.mp3 RET
|
-
To play the MP3 stream at http://example.net/broadcast/live.mp3
with a 2MB audio buffer, type:
| | $ mpg213 -b 2048 http://example.net/broadcast/live.mp3 RET
|
NOTE: The mpg321 tool is a free software replacement of
mpg123, another command-line MP3 player that is not free software.
But there are a great many other MP3 players available; some of them are
listed in Other Sound File Tools.
22.3.2 Playing a MIDI File
@sf{Debian}: `playmidi'
@sf{WWW}: http://playmidi.openprojects.net/
The
playmidi tool is for playing MIDI files; give the name of the
MIDI file to play as an argument.
-
To play the MIDI file `copa-cabana.mid', type:
| | $ playmidi copa-cabana.mid RET
|
If you have a non-MIDI sound card, you can still play MIDI files by
giving the `-f' option, which sends the MIDI output to the FM
synthesizer on the sound card, which in turn plays it using FM patches
that come with the playmidi distribution.
-
To play the MIDI file `copa-cabana.mid' on a non-MIDI sound card,
type:
| | $ playmidi -f copa-cabana.mid RET
|
22.4 Recording a Sound File
@sf{Debian}: `sox'
@sf{WWW}: http://home.sprynet.com/~cbagwell/sox.html
To record sound, first select an input device as a source for
recording. Sound cards may have
MIC and
LINE IN jacks, as
well as connections to the CD-ROM drive, all of which are sound inputs
that can be recording sources. When you select a device for capture,
your recording will come from this source.
Recording occurs from the currently active input, if any, which must be
set with the mixer; unmute it and set its volume level before you begin
recording. (Be sure to turn the volume on your speakers all the way off,
or you'll get feedback.)
To record audio to a file, use the rec tool. It can write many
audio file formats, either to a format you specify with the `-t'
option, or by determining the format to use based on the file name
extension you give the output file (see section Sound File Formats). Type C-c to stop recording.
Give the name of the sound file to record as an argument; if a
`.wav' file is specified, it records a simple monaural,
low-fidelity sound sample by default.
-
To record a simple WAV sample from the microphone and save it to a file
called `hello.wav', type:
This command begins an 8,000 Hz, monaural 8-bit WAV recording to the
file `hello.wav', and keeps recording until you interrupt it with
C-c. While the default is to make a low-fidelity recording--8,000
Hz, monaural 8-bit samples--you can specify that a high-fidelity
recording be made. (But remember that high-fidelity recordings take up
much more disk space.)
To make a stereo recording, use the `-c' option to specify the
number of channels, giving 2 as the argument. To make a 16-bit
recording, give `w' ("wide") as the argument to the `-s'
("sample size") option.
Set the recording sample rate by giving the samples per second to use as
an argument to the `-r' option. For CD-quality audio at 44,100Hz,
use `-r 44100'.
Finally, to record a file in a particular format, either give the name
of the format as an argument to the `-f' option, or use the
traditional file name extension for that format in the output file name
(see section Sound File Formats).
-
To make a high-fidelity recording from the microphone and save it to a
WAV-format file called `goodbye.wav', type:
| | $ rec -s w -c 2 -r 44100 goodbye.wav RET
|
-
To make a sound recording in the CD audio format, and write the output
to a file called `goodbye.cdr', type:
NOTE: When you're not recording sound, keep the inputs muted
(see section Muting an Audio Device); this way, you can
have a microphone plugged in without having feedback when playing
sounds. Also, make sure the volume levels are not set too high or too
low when recording; getting the right level for your microphone or other
input device may take some initial adjustment.
Like play, rec is part of the sox toolkit.
22.5 Other Sound File Tools
There are many mixer, playback, and recording tools available. The
following table lists some of them, giving their Debian package name and
URL, where available.
| TOOL |
DESCRIPTION
|
aumix |
A simple, visual audio mixer tool that can be used in X or in the
console--use this if you are too frustrated by amixer.
{@sf{Debian}}: `aumix'
|
freeamp |
A popular audio sound file player for X, the Free Audio Music
Player can play MP3 and Ogg Vorbis formats, and its graphical appearance
can be changed with "themes."
{@sf{Debian}}: `freeamp'
{@sf{WWW}}: http://www.freeamp.org/
|
maplay |
An MP3 player.
{@sf{Debian}}: `maplay'
|
mp3asm |
Use this tool to cut and paste MP3 frames and fix broken MP3
files.
{@sf{Debian}}: `mp3asm'
{@sf{WWW}}: http://packages.debian.org/stable/sound/mp3asm.html
|
xmms |
Inspired by Winamp, XMMS is a popular, comprehensive audio player
for X that features an array of plug-ins, support for many sound formats
(including MP3 and Ogg Vorbis), and "skins" to change its look and
feel; it can use FreeAmp themes as well--see previous listing for
freeamp.
{@sf{Debian}}: `xmms'
{@sf{WWW}}: http://www.xmms.org/
|
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