Bergen Sound Server & Library, Version 0.4.1

by Dave Pape (pape@evl.uic.edu)

Introduction

As with VSS, there are two basic parts to Bergen -- the client library (libbergen) and the server (snerd). There are also some basic client programs -- bergenPlay, bergenReset, bergenKill, and bergenDemo.

The library, server, client programs, and complete source code are here in bergen0_4_1.tar.gz. They are also available (at EVL) in ~pape, in my lib/ and include/ directories.

Change Log

Version 0.4.1

Modified Linux version of snerd to reduce the latency between when a play command is received and when the sound is heard, by telling the audio driver to use a smaller buffer of sound fragments.

Version 0.4

Added Linux support.

Added a duration() function to the bergenSample class.

Added a "gain" command to the main snerd program, which allows one to set an overall gain factor for the sound.

Corrected a bug in the SampleFile class. Samples will stop correctly when they reach the end of the file; previously, an explicit "stop" command had to be sent by the client, or the sound could not be played again.

Added port number option to snerd and to bergenServer class, to override the default port (5900).

Version 0.1

snerd now handles varying sample rates, channels, and sample sizes in sound files, and accepts an "-srate" command line option.

bergenServer now has a reset() function.

Known Bugs

• The UDP code does not convert the port number to network-byte-order on Intel machines. Since the server and the clients use the same code, this problem is not apparent as long as both are run on the same type of machine. But, a client on an SGI cannot communicate with a server on an Intel PC, or vice versa (except by fudging the port number via BERGEN_PORT; i.e. if snerd is started with the default port of 5900, then on the client do "setenv BERGEN_PORT 3095" [5900 = 0x170c; 3095 = 0x0c17]).
  To be fixed in version 0.5. (Note that fixing it will break existing Linux clients.)

Library Interface

#include <unistd.h>
#include "bergenServer.h"
#include "bergenSample.h"


main(int argc,char **argv)
{
 bergenServer * server = new bergenServer;
 bergenSample * sound = new bergenSample("sound.aiff",server);
 sound->setLoop(1);
 sound->play();
 sleep(1);
 sound->setAmplitude(0.25);
 sleep(1);
 delete server;
}

bergenServer class

#include "bergenServer.h"

bergenServer::bergenServer(char *host=NULL,int port=0)

The constructor will make a UDP network connection to the snerd server program, sending it a "ping" message to verify the connection. The argument host, if given, is the name or IP address of the machine which snerd is running on; if it is not given, the value of the environment variable BERGEN_SERVER is used; if this variable is not set, the connection is made to the local machine. The argument port is the port number that the server is listening to; if it is not given (or is 0), the value of the environment variable BERGEN_PORT is used; if this variable is not set, the default port of 5900 is used.

bergenServer::~bergenServer(void)

The destructor will automatically delete all sounds which are in its list of bergenSound objects (maintained by addSound() and removeSound).

void bergenServer::setDirectory(char *dir)

Sets the default directory for sound objects. bergenSample objects will use this directory if their sample file name does not include a path.

char * bergenServer::directory(void)

Returns the default directory name set by setDirectory().

void bergenServer::reset(void)

Re-initializes the connection to the server program, and re-creates all the sound objects (that it manages) on the server. This can be used to reset things if snerd crashes & is restarted, or if it is started after the bergenServer object is created.

void bergenServer::sendMessage(char *msg)

Sends the given text string to the server program. This is mostly for internal use, by the bergenSound classes.

int bergenServer::receiveMessage(char *msg,int size)

Gets the next message sent by the server program. This is mostly for internal use, by the bergenSound classes.

void bergenServer::addSound(bergenSound *sound)

Adds a sound to the server object's list. This is used internally, by the bergenSound class, and should not be called by applications.

void bergenServer::removeSound(bergenSound *sound)

Removes a sound from the server object's list. This is used internally, by the bergenSound class, and should not be called by applications.

bergenSound class

#include "bergenSound.h"

bergenSound::bergenSound(bergenServer *server)

The constructor must be given a pointer to a server object; it will tell the server object to add this sound to its list of sounds.

bergenSound::~bergenSound(void)

The destructor does an automatic kill before the sound object is removed.

int bergenSound::handle(void)

Returns the handle which the server program has assigned to this sound object; this is used in all messages to the server program which control the sound.

bergenServer * bergenSound::server(void)

Returns the pointer to the server object which was given when the object was created.

void bergenSound::setAmplitude(float amp)

Sets the sound's current amplitude; sends a message to the server program to accomplish this.

void bergenSound::play(void)

Sends a message to the server program to start playing the sound.

void bergenSound::stop(void)

Sends a message to the server program to stop playing the sound. The next time a play command is issued, the sound will start again from the beginning.

void bergenSound::pause(void)

Sends a message to the server program to pause the sound. The next time a play command is issued, the sound will resume from the point at which it was paused.

void bergenSound::kill(void)

Sends a message to the server program to remove the sound, and tells the server object to remove this sound from its list. The sound object should not be used after kill() is called; this is meant to be called from the destructor, and should not generally be used directly by applications.

bergenSample class

#include "bergenSample.h"

bergenSample::bergenSample(char *filename,bergenServer *server)

The constructor must be given the name of the sample file which the sound will play, in addition to the server object pointer.

void bergenSample::setLoop(int loop)

Sets the sound's looping flag -- if it is true (non-zero), the sound will loop continuously when it is played.

float bergenSample::duration(void)

Returns the total playing time of the sample file, in seconds. If the server failed to find the sample file, this will return 0. Note that this function requires sending a message to the server and waiting for the response, so it is potentially slow.

bergenTone class

#include "bergenTone.h"

bergenTone::bergenTone(void)

Creates the tone sound object.

bergenTone::setFrequency(float freq)

Sets the frequency of the sound to be freq cycles per second. The default frequency is 1000 Hz.

bergenWhiteNoise class

#include "bergenWhiteNoise.h"

bergenWhiteNoise::bergenWhiteNoise(void)

Creates the white-noise sound object.

snerd

Start snerd on your audio machine before running any client programs. It has two commmand line options:

• -srate rate - sets the output sample rate. The rate should be one that is supported by your sound hardware. e.g.:

  		snerd -srate 22050
  

  The default sample rate is 32000.
• -udpport port_number - sets the UDP/IP port number that snerd will listen to for commands from clients. e.g.:

  		snerd -udpport 9000
  

  The default port number is 5900.

snerd uses the SGI audiofile library to read sample files; this means that it can play samples in any format supported by that library (AIFF, AIFC, WAVE, etc.) It accepts 8- or 16-bit, 2's-complement or unsigned files of any sample rate. It will automatically resample the data to 16-bits, 2's-complement at the selected output rate. The resampling method is very crude; input files with a low sampling rate may sound very bad if snerd is running at a much higher output rate. For best results, use 16-bit, 2's-complement sound files and run snerd at the same sample rate as that of the files. Files can have any number of channels, but only the first channel will be played.