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PROGRAM:

NAME

Network Audio System - a portable, network-transparent audio system

SYNOPSIS

The Network Audio System service is a network-transparent system developed at Network
Computing Devices for playing, recording, and manipulating audio data over a network. It
uses the client/server model to separate application code from the software drivers needed
to control specific audio input and output devices.

DESCRIPTION

The Network Audio System service provides applications with the ability to send and
receive audio data such as voice, sound effects, and music in a network environment. A
audio server inside the desktop terminal or personal computer controls the various input
and output devices in response to messages sent from client programs running on other
hosts.

A variety of utility programs are provided that can be used to play or record audio using
shell scripts or command-line procedures. More ambitious applications can communicate
directly with the audio server using a C-language programming library.

The Network Audio System service supports a variety of the common formats used to store
sound data. Audio inputs and outputs can run at a any of a range of sampling rates. The
audio server automatically converts all data to the designed format or rate.

Streams of data from multiple inputs can be mixed together and directed to any attached
output device. Sounds that are used many times can be stored in the server so that they
do not need to be transmitted over the network each time they are played. Furthermore,
inputs can be hooked directly to outputs (for example, a CD player can be connected to a
set of speakers) so that data can be played without requiring any client intervention or
network traffic.

AUDIO SERVER NAMES

Each audio server has a name that is used by applications in establishing a connection.
The format of the name depends upon the type of network being used. In TCP/IP
environments, audio server names look like:

tcp/hostname:portnum

where hostname is the name or numeric IP address of the desktop machine to be contacted
and portnum is the port number on which the server is listening. If the ``tcp/'' prefix
is not given, 8000 is automatically added to portnum so that the audio server name is
compatible with the X Window System display name.

In DECnet environments, audio server names look like:

decnet/nodename::num

where nodename is the name or numeric DECnet address of the desktop machine to be
contacted and num is the DECnet task AUDIO$num. If the ``decnet/'' prefix is omitted, it
is automatically added so that the audio server name is compatible with the X Window
System display name.

Most audio utilities accept a command line argument -audio servername for specifying the
audio server to be contacted.

% auinfo -audio tcp/ncdunit:8000

If no server is specified on the command line, the AUDIOSERVER environment variable is
checked to see if a name has been stored there. Otherwise, the DISPLAY environment
variable used by X Window System applications is checked and the corresponding audio
server is used.

SAMPLE PROGRAMS

Several sample programs that use the Network Audio System service are provided by NCD:

auplay This program simply plays the files listed on its command line. It is typically
used from shell scripts, command-line procedures, or other programs that just need
to ``dump'' sound data to the audio server.

audemo This program allows the user to select and play pre-recorded sound files or to
record new sound files. It provides a simple control panel for dynamically
changing the volume while a sound is being played and for aborting a sound.

audial This program generates North American telephone touch tones correspond to a given
string. audial can also recognize touch tones and produce the corresponding
string.

autool This program is compatible with the Sun audiotool program and is typically used to
play prerecorded sound files. Unlike auplay it provides a graphical interface to
allow the user to replay or cancel the data.

auinfo This program lists information describing the capabilities of an audio server.

auctl This program can be used to change various device parameters.

auscope This program is an audio protocol filter that can be used to view the network
packets being sent between an application and an audio server.

aupanel This program provides an X-based window-oriented interface allowing the user to
adjust the attributes of the devices provided by the Network Audio System service.

auedit This program provides an X-based window-oriented interface allowing the user to
edit audio files.

auconvert
This program allows the user to perform various conversion operations on sound
files.

auphone This program provides an X-based window-oriented interface allowing two-way real
time voice communication between two audio servers.

aurecord
This program is used to record audio data from an audio server into a file.

auwave This program provides an X-based window-oriented interface demonstrating the use
of waveform elements.

AUDIO FILES

The audio programming library and utility programs can be used to read and write files in
any of the following file formats:

Sun/NeXT
These files typically have a '.au' or '.snd' extension. They are usually produced
by Sun or NeXT workstations.

Creative Labs
These files typically have a '.voc' extension. They are usually produced by by
Soundblaster audio cards on IBM PC compatible computers.

Microsoft WAVE
These files typically have a '.wav' extension. They are usually produced by IBM PC
compatible computers.

AIFF
These files typically have an '.aiff' or '.aif' extension. They are usually
produced by SGI workstations or Apple computers.

Amiga IFF/8SVX
These files typically have an '.iff' extension.

Due to the nature of the file formats, only the Sun/NeXT file format can be piped through
standard input and/or standard output. The convention for specifying standard input or
standard output is to use a hyphen ("-") as the file name.

PROGRAMMING

Application developers may create their own audio clients using the Network Audio System
programming library.

ENVIRONMENT VARIABLES

The following environment variables are used by Network Audio System programs:

AUDIOSERVER
This specifies the name of default audio server to contact if no name is
explicitly given on the command line.

DISPLAY This specifies the name of an X Window System display that should be assumed to
also have a corresponding Network Audio System server.

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