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Sound 101
Volume Number:9
Issue Number:3
Column Tag:C Workshop

Related Info: Sound Manager

Sound 101

Evolution of the Mac voice

By Iggi Monahelis, Pleasanton, California

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

About the author

Iggi Monahelis is a programmer who bought his first Mac as soon as he could back in 1984. He is the principal designer and co-author of “Read My Lips”, the sound annotation utility for the Macintosh.


This is an introductory article, hence the name Sound 101, dealing with basic recording and playback of sounds on the Macintosh. It explains the required steps to be taken in order to digitize sounds using a microphone, in two different sound formats, and play them back. It is a good stepping stone for someone who has little or no knowledge of how to do these things in a program on the Macintosh. As a matter of fact, one can probably copy the routines given in the article, and use them in their own program without a lot of modifications.

Ancient History

The Macintosh has had the capability of producing sounds since day one. The famous introduction of the Macintosh back in 1984 used sound, in the form of digitized speech, to allow the Mac to introduce itself. Inside Macintosh back then had a chapter on the Sound Driver with just a few routines, literally StartSound, StopSound and SoundDone, that allowed the programmer to control the Sound Driver. The Sound Driver produced sound using three different sound synthesizers:

1) the four-tone synthesizer, used to make simple harmonic tones, with up to four “voices” producing sound simultaneously. Hence the name four-tone.

2) the square-wave synthesizer, used to produce sounds such as beeps.

3) the free-form synthesizer, used to produce complex sounds, music and speech.

You had to “describe” the sound to the Driver as a waveform, basically fill a buffer with a bunch of numbers, and tell the Sound Driver to start producing noise based on these numbers. Very primitive.

Middle Ages

With the introduction of the Macintosh II class of machines, the Sound Driver had graduated to the Sound Manager. It was indeed a graduation because several innovations had taken place:

1) The hardware now included a new sound chip which freed the machine’s processor from doing all the work.

2) The introduction of sound resources. Sound resources can “contain” any sound you can imagine, from a simple beep sound to digital recordings of CD’s. And because they are resources, in the Macintosh sense of the word, you can work with them using standard Resource Manager calls. To play a sound resource all you have to do is load it and pass the handle to the resource to the SndPlay routine.

3) The Sound Manager now has seven routines to allow you to work with sound.

To produce sound, commands are sent to a synthesizer, as was the case with the Sound Driver. The Sound Manager uses a queue to send these commands to a synthesizer, these queues are called channels. To make complex sounds, many sounds may need to be produced simultaneously. For this reason several synthesizers can have multiple channels.

The new Sound Manager uses three synthesizers to produce sound:

1) the wave-table synth, lets you supply a wave table that describes the sound. This lets you produce more complex sounds, also it lets you play multiple sounds simultaneously by opening several channels. It corresponds to the old four-tone synth with four channels open.

2) the note synth, used to produce simple sounds, such as a note. The note synth can produce only one note at a time. It compares to the old square-wave synth from the Sound Driver.

3) the sampled sound synth, used to play digitally recorded sounds. In this case instead of passing the note or a wave table describing the sound you want played, you pass a buffer that contains samples of the sound to be played. This synth compares to the old free-form synth from the Sound Driver.

Despite the innovations that came with the Mac II and the graduation of the Sound Driver to a Manager, it was still difficult to digitize sounds using System software. It was easy once you had a sound resource to play it and several programs, mostly shareware, were created to play sound resources. Farallon came out with the MacRecorder® sound digitizer which allowed you to digitize sounds using the software that came with it, but still you could not do that in your own program without writing a lot of code yourself.


With the introduction of the Macintosh IIsi and Macintosh LC, Apple for the first time included a built-in microphone with the Macintosh. System software versions 6.0.7 and later have a new and improved version of the Sound Manager. The Sound Manager chapter goes from 32 pages to 114 pages. This latest version introduces a whole slew of new features, some of which are:

1) There are now routines to record sounds using the built-in microphones, or any third party microphone with the appropriate driver for Macs that do not come with a microphone.

2) One can record either sound resources (‘snd ‘), or record directly to a file on disk in a format known as: Audio Interchange File Format (AIFF).

3) There are routines that allow for compressing and decompressing of sound data.

4) There are now routines that allow for the playing of sounds directly from disk. So one does not have to load all of the sound in memory in order to play it.

5) Customization galore. Besides the high-level routines for recording and playback there are low-level routines so that one could customize the way recording and playback is done.

Writing the program

It is always easier to start with a basic program, understand it, and then expand on it. The Sound 101 program is just such a program for learning the basics about recording and playing sounds. The program can record and play 'snd ' and AIFF sound files. It also allows for the selection of sound quality.

Here goes the code with explanations...

© 1992 Praxitel, Inc. and Iggi Monahelis

This is the “main” for the Sound 101 project.  It has the minimum stuff 
to get a mac
program going.  Basically, it does all the required mac initializations, 
sets up the menu
bar, and then gets and processes events.

#include “Sound101.h”

extern int  gDestroyChannel;
extern SndChannelPtr gSndChan;
extern short     gFRefNum;
extern long gQuality;



This is the main routine for the Sound 101 application, it does all the 
Mac initializations.
Then calls the EventLoop procedure to get and process events.

void main(void)
 InitGraf((Ptr) &thePort );

 EventLoop();    /* Do event processing until user quits */




Set up the menu bar for the Sound 101 application
void SetUpMenus(void)
 MenuHandle myMenu;
 myMenu = GetMenu(mApple);
 AddResMenu( myMenu, ‘DRVR’ );
 InsertMenu( myMenu, 0 );
 InsertMenu(GetMenu(mFile), 0) ;



Event handling for the Sound 101 application.
Get events forever, and handle them by calling DoEvent.
void EventLoop(void)

 do {
 gotEvent = WaitNextEvent(everyEvent, &event, 50, 0);
 if ( gotEvent ) {
 /* if we are done with the sound, dispose the sound 
    channel and close the sound file. */     
 if ( gDestroyChannel ) { 
 OSErr  myErr;
 if (gSndChan)
 myErr = SndDisposeChannel( gSndChan, TRUE);
 if (gFRefNum)
 myErr = FSClose(gFRefNum);
 /* make sure we do it only once! */
 gDestroyChannel = FALSE;
 gSndChan = 0;
 gFRefNum = 0;
 } while ( true ); /* loop forever */
} /*EventLoop*/



Determine the event type and dispatch accordingly
void DoEvent(EventRecord *event)
 short  part, err;
 char   key;

 switch ( event->what ) {
 case nullEvent:
 case mouseDown:
 part = FindWindow(event->where, &window);
 switch ( part ) {
 case inMenuBar:
 /* process a mouse menu command */
 case inSysWindow:
 /* let the system handle the mouseDown */
 SystemClick(event, window);
 case inContent:
 case inDrag:                
 case inGoAway:
 case inGrow:
 case inZoomIn:
 case inZoomOut:
 case keyDown:
 case autoKey:
 /* check for menukey equivalents */
 key = event->message & charCodeMask;
 if ( event->modifiers & cmdKey ) {
 /* Command key down */
 /* if command-period was pressed, set our global
    to clean up the sound channel and close the
    open sound file. */
 if ( key == ‘.’ )
 /* command period was pressed */
 gDestroyChannel = TRUE;
 case activateEvt:
 case updateEvt:
} /*DoEvent*/



Handles menu selections for the Sound 101 application
void DoMenuCommand(long menuResult)
 short  menuID, menuItem;
 short  itemHit, daRefNum;
 Str255 daName;

 menuID = HiWord(menuResult);
 menuItem = LoWord(menuResult);
 switch ( menuID ) {
 case mApple:
 switch ( menuItem ) {
 case iAbout: {  /* bring up the About box */
 OSErr  err;
 Rect   tempRect;
 aboutDlg = GetNewDialog(128, nil, (WindowPtr) -1);
 if ( aboutDlg ) {
 /* Open a dialog box */
 SelectWindow(aboutDlg);  /* Lets see it */
 while (TRUE) {
 ModalDialog(NULL, &itemHit);
 if ( itemHit == 1 )

 /* all non-About items in this menu are DAs */
 GetItem(GetMHandle(mApple), menuItem, daName);
 daRefNum = OpenDeskAcc(daName);
 case mFile:
 switch ( menuItem ) {
 case iPlaySound:
 case iRecordsndSound:
 case iRecordAIFFSound:
 case iQuality:
 case iQuit:
 /* unhighlight what MenuSelect (or MenuKey) hilited */



Quit the app
void Terminate(void)
 /* exit if no cancellation */
} /*Terminate*/

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