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Chapter 13
Sound Effects
234 Fastgraph User's Guide
Overview
In the realm of the IBM PC and PS/2 family of systems, a sound is
defined by its frequency, duration, and volume. The frequency of a sound is
measured in units called Hertz. While the PC and PS/2 can produce sounds
ranging from 18 to more than one million Hertz, the average human can hear
sounds between 20 and about 20,000 Hertz. The length of a sound, called its
duration, is expressed in clock ticks; there are either 18.2 of 72.8 clock
ticks per second, depending on the method used to produce the sound.
Finally, the volume determines the loudness of the sound. As we'll see in
this chapter, we can control a sound's volume only on the PCjr and Tandy 1000
systems.
Fastgraph contains several different methods for producing sound
effects. These include single tones, a series of tones expressed
numerically, or a series of tones expressed as musical notes. The sound
effects may be discrete, continuous, or performed at the same time as other
activity. The sound-related routines are independent of the other parts of
Fastgraph and do not require any initialization routines be called.
Sound Sources
All members of the PC and PS/2 families can produce sounds using the
8253-5 programmable timer chip and the internal speaker. This method is
limited to producing single sounds of given frequencies and durations,
although we can combine these sounds to create interesting audio effects or
play music. When we use this technique, we have no control over the sound
volume. In fact, sound volumes often vary slightly on different systems
because the physical properties of the speaker and its housing are not always
the same.
The PCjr and Tandy 1000 systems have an additional, more powerful chip
for producing sounds. This is the Texas Instruments SN76496A sound chip,
called the TI sound chip for short. The TI sound chip has three independent
voice channels for producing pure tones, and a fourth channel for generating
periodic or white noise. Each voice channel has a separate volume control
that allows us to control the loudness of the sound it emits.
Synchronous Sound
A sound effect is said to be synchronous if it is produced while no
other activity is being performed. In other words, a program makes a
synchronous sound by starting the sound, waiting for a specified duration,
and then stopping the sound. The program must wait for the sound to complete
before doing anything else. As long as the duration is relatively short, the
fact that the sound is synchronous has little or no effect on the program's
execution speed. Fastgraph includes routines for producing synchronous sound
using either the 8253-5 programmable timer or the TI sound chip.
The fg_sound routine uses the programmable timer to produce a sound of a
given frequency and duration. The frequency, defined by the first argument,
is expressed in Hertz and must be an integer value between 18 and 32,767.
The second argument defines the duration and is expressed in clock ticks;
there are 18.2 clock ticks per second. If the duration is zero or negative,
the sound will continue until it is stopped with the fg_quiet routine.
Chapter 13: Sound Effects 235
Example 13-1 uses the fg_sound routine to create different sound
effects, pausing for one second between each. It first produces three
distinct sounds of 20, 100, and 1,000 Hertz. Each of these sounds lasts for
approximately 1/6 of a second (three clock ticks). The program then makes a
warbling noise by quickly alternating sounds of similar frequencies.
Finally, the program creates a sliding tone of increasing frequencies between
100 and 500 Hertz. Each tone in this sequence lasts for two clock ticks, so
it takes about 4.5 seconds to play the entire sequence. In all cases,
example 13-1 displays an identifying message just before each sound.
Example 13-1.
#include <fastgraf.h>
#include <stdio.h>
void main(void);
void main()
{
int freq;
printf("20 Hz tone...\n");
fg_sound(20,3);
fg_waitfor(18);
printf("100 Hz tone...\n");
fg_sound(100,3);
fg_waitfor(18);
printf("1000 Hz tone...\n");
fg_sound(1000,3);
fg_waitfor(18);
printf("warble...\n");
fg_sound(400,1);
fg_sound(410,1);
fg_sound(400,1);
fg_sound(410,1);
fg_waitfor(18);
printf("sliding tone from 100 to 500 Hz...\n");
for (freq = 100; freq <= 500; freq+=10)
fg_sound(freq,2);
}
The fg_voice routine is analogous to the fg_sound routine, but it uses
the TI sound chip rather than the programmable timer to create sound. For
this reason, the fg_voice routine can only be used on the PCjr or Tandy 1000
systems. The TI sound chip allows us to control the volume of a sound, and
it also offers four distinct voice channels. Thus, fg_voice requires two
additional arguments besides frequency and duration to define the voice
channel and sound volume.
The first argument to fg_voice defines the voice channel, as shown
below.
236 Fastgraph User's Guide
value meaning
1 voice channel #1
2 voice channel #2
3 voice channel #3
4 voice channel #4, periodic noise
5 voice channel #4, white noise
If we use voice channels 1, 2, or 3, the second argument defines the sound
frequency in Hertz, between 18 and 32,767. If we use voice channel 4,
however, the second argument instead is a value that represents a specific
frequency, as shown in this table.
value frequency
0 512 Hertz
1 1024 Hertz
2 2048 Hertz
The third argument defines the sound volume. It must be between 0 and 15,
where 0 is silent and 15 is loudest. The fourth argument defines the sound
duration in clock ticks. As with the fg_sound routine, there are 18.2 clock
ticks per second, and if the duration is zero or negative, the sound will
continue until stopped with the fg_quiet routine.
Example 13-2 uses the fg_voice routine to create different sound effects
using the TI sound chip. As in example 13-1, there is a pause of one second
between each. The program first calls the fg_testmode routine to be sure it
is running on a PCjr or Tandy 1000 system (video mode 9 is only available on
these systems). If so, the program uses voice channel #4 to produce a 2,048
Hertz periodic noise, followed by white noise of the same frequency. Both
sounds are emitted at the maximum volume level (15) and last for about 1/6 of
a second each (three clock ticks). After these noises, example 13-2 produces
a 500 Hertz tone of increasing volume. In all cases, the program displays an
identifying message just before each sound.
Example 13-2.
#include <fastgraf.h>
#include <stdio.h>
#include <stdlib.h>
void main(void);
void main()
{
int volume;
if (fg_testmode(9,0) == 0) {
Chapter 13: Sound Effects 237
printf("This program requires a PCjr or ");
printf("a Tandy 1000 system.\n");
exit(1);
}
printf("2048 Hz periodic noise...\n");
fg_voice(4,2,15,3);
fg_waitfor(18);
printf("2048 Hz white noise...\n");
fg_voice(5,2,15,3);
fg_waitfor(18);
printf("500 Hz tone of increasing volume...\n");
for (volume = 1; volume <= 15; volume++) {
fg_voice(1,500,volume,0);
fg_waitfor(4);
}
fg_quiet();
}
Note how example 13-2 uses a duration of zero (continuous sound) and the
fg_waitfor routine to specify the duration for each volume level the 500
Hertz tone sequence. This causes the transition between changes in volume to
blend better with each other. The fg_quiet routine, which stops continuous
sound started with the fg_sound or fg_voice routines, ends the sound after
the final volume level.
The fg_sound and fg_voice routines each produce a single sound. We've
seen how to combine sounds to produce sound effects, but still the individual
sounds are defined numerically -- that is, by a certain frequency and
duration. It is often easier to create sounds from musical notes, and for
this reason Fastgraph includes a routine fg_music that produces such sounds.
The fg_music routine uses the programmable timer to produce synchronous
sound; it does not support the TI sound chip.
The fg_music routine has a single argument called the music string,
passed by reference as a byte array or character string. The music string is
simply a variable-length sequence of music commands, followed by a dollar-
sign ($) terminator. Music commands are summarized in the following table.
command meaning
A thru G Play the specified note in the current
octave.
# May be appended to a note character (A
through G) to make that note sharp.
. May be appended to a note character (A
through G) or a sharp (#) to extend that note
by half its normal length. Multiple dots may
be used, and each will again extend the note
by half as much as the previous extension.
238 Fastgraph User's Guide
Ln Set the length of subsequent notes and
pauses. The value of n is an integer between
1 and 64, where 1 indicates a whole note, 2 a
half note, 4 a quarter note, and so forth.
If no L command is present, L4 is assumed.
On Set the octave for subsequent notes. The
value of n may be an integer between 0 and 6
to set a specific octave. It also can be a
plus (+) or minus (-) character to increment
or decrement the current octave number.
Octave 4 contains middle C, and if no O
command is present, O4 is assumed.
P Pause (rest) for the duration specified by
the most recent L command.
Sn Set the amount of silence between notes. The
value of n is an integer between 0 and 2. If
n is 0, each note plays for the full period
set by the L command (music legato). If n is
1, each note plays for 7/8 the period set by
the L command (music normal). If n is 2,
each note plays for 3/4 the period set by the
L command (music staccato). If no S command
is present, S1 is assumed.
Tn Set the tempo of the music (the number of
quarter notes per minute). The value of n is
an integer between 32 and 255. If no T
command is present, T120 is assumed.
The fg_music routine ignores any other characters in the music string. It
also ignores command values outside the allowable range, such as T20 or O8.
Example 13-3 illustrates some uses of the fg_music routine. The program
plays the first few bars of "Mary Had a Little Lamb", followed by the musical
scale (including sharps) in two octaves, and finally the introduction to
Beethoven's Fifth Symphony. There is a pause of one second between each
piece of music, and the program displays the titles before playing the music.
Blank characters appear in the music strings to help make them more readable.
Example 13-3.
#include <fastgraf.h>
#include <stdio.h>
void main(void);
void main()
{
printf("Mary Had a Little Lamb...\n");
fg_music("T150 L8 EDCDEEE P DDD P EGG P EDCDEEE L16 P L8 EDDEDC$");
fg_waitfor(18);
printf("up the scale in two octaves...\n");
fg_music("L16 CC#DD#EFF#GG#AA#B O+ CC#DD#EFF#GG#AA#B$");
Chapter 13: Sound Effects 239
fg_waitfor(18);
printf("Beethoven's Fifth Symphony...\n");
fg_music("T180 O2 L2 P L8 P GGG L2 D# L24 P L8 P FFF L2 D$");
}
Asynchronous Sound
Sounds made concurrently with other activity in a program are said to be
asynchronous. Fastgraph's routines that produce asynchronous sound just
start the sound and then immediately return control to the calling program.
The sounds will automatically stop when the end of the sequence is reached,
and you also can suspend or stop it on demand before that time. None of
Fastgraph's asynchronous sound routines have any effect if there is already
asynchronous sound in progress. In addition, the asynchronous sound routines
temporarily disable the synchronous sound routines (fg_sound, fg_voice, and
fg_music) while asynchronous sound is in progress.
To expand the range of sound effects and to play fast-tempo music,
Fastgraph temporarily quadruples the clock tick interrupt rate from 18.2 to
72.8 ticks per second while producing asynchronous sound. Because many disk
controllers rely on the 18.2 tick per second clock rate to synchronize disk
accesses, your programs should not perform any disk operations when
asynchronous sound is in progress.
The fg_sounds routine is the asynchronous version of the fg_sound
routine. It uses the programmable timer to play a sequence of tones
simultaneous to other operations. This routine expects as its first argument
a variable-length integer array, passed by reference, containing pairs of
frequency and duration values. As with the fg_sound routine, each frequency
is expressed in Hertz and must be between 18 and 32,767. The durations are
also measured in clock ticks, but because the interrupt rate is quadrupled,
there are 72.8 instead of 18.2 ticks per second.
The format of the frequency and duration array passed to fg_sounds is
shown below.
[0] frequency of sound 1
[1] duration of sound 1
[2] frequency of sound 2
[3] duration of sound 2
.
.
.
[2n-2] frequency of sound n
[2n-1] duration of sound n
[2n] terminator (0)
240 Fastgraph User's Guide
Note that a null character (that is, a zero byte) terminates the array. The
second argument passed to fg_sounds is an integer value indicating the number
of times to cycle through the frequency and duration array. If this value is
negative, the sounds will continue until stopped with the fg_hush or
fg_hushnext routines.
Example 13-4 uses the fg_sounds routine to play the 100 to 500 Hertz
sliding tone sequence of example 13-1. To prove the sounds are being made
concurrently with other operations, messages are displayed while the sequence
is playing. This is controlled by the Fastgraph routine fg_playing, which
returns a value of 1 if asynchronous sounds are in progress, and 0 if not.
Note how the duration must be specified as 8 clock ticks (instead of 2 as in
example 13-1) to compensate for the quadrupled clock tick interrupt rate.
Example 13-4.
#include <fastgraf.h>
#include <stdio.h>
void main(void);
void main()
{
int i;
int freq;
int sound_array[83];
i = 0;
for (freq = 100; freq <= 500; freq+=10) {
sound_array[i++] = freq;
sound_array[i++] = 8;
}
sound_array[i] = 0;
fg_sounds(sound_array,1);
while(fg_playing())
printf("Still playing...\n");
}
Just as the fg_sounds routine is analogous to the fg_sound routine,
there is a Fastgraph routine fg_voices that is similar to the fg_voice
routine. That is, fg_voices uses the TI sound chip to play an asynchronous
sequence of tones. Its arguments are the same as those of the fg_sounds
routine, but the structure of the sound array is different. Its structure
is:
[0] channel # of sound 1
[1] frequency of sound 1
[2] volume of sound 1
[3] duration of sound 1
Chapter 13: Sound Effects 241
[4n-4] channel # of sound n
[4n-3] frequency of sound n
[4n-2] volume of sound n
[4n-1] duration of sound n
[4n] terminator (0)
The channel numbers, frequencies, volumes, and durations must be in the same
ranges as discussed in the description of the fg_voice routine, except the
durations are quadrupled because of the accelerated clock tick interrupt
rate. Again, note that a null character (that is, a zero byte) terminates
the array.
Example 13-5 uses the fg_voices routine to play the 500 Hertz tone
sequence of increasing volume introduced in example 13-2. As in example
13-4, the program displays messages while the tone sequence is playing to
demonstrate the sounds are being made concurrently with other operations.
Note how the duration is now 16 clock ticks (instead of 4 as in example 13-2)
because of the quadrupled clock tick interrupt rate.
Example 13-5.
#include <fastgraf.h>
#include <stdio.h>
void main(void);
void main()
{
int voice_array[61];
int i;
int volume;
if (fg_testmode(9,0) == 0) {
printf("This program requires a PCjr or ");
printf("a Tandy 1000 system.\n");
exit(1);
}
i = 0;
for (volume = 1; volume <= 15; volume++) {
voice_array[i++] = 1; /* use channel 1 */
voice_array[i++] = 500; /* 500 Hz frequency */
voice_array[i++] = volume; /* variable volume */
voice_array[i++] = 16; /* duration */
}
voice_array[i] = 0;
fg_voices(voice_array,1);
242 Fastgraph User's Guide
while(fg_playing())
printf("Still playing...\n");
}
There is also an asynchronous version of the fg_music routine. It is
called fg_musicb, and it uses the same format music string as the fg_music
routine does. However, the fg_musicb routine has a second argument that
specifies the number of times to cycle through the music string. If this
value is negative, the music will play repetitively until you stop it with
the fg_hush or fg_hushnext routine.
Example 13-6 plays the same three pieces of music as example 13-3, but
it does so concurrently with other operations. As the music plays, the
program continuously displays the title of each piece. Note how we can take
advantage of the repetition in the music string for the "up the scale"
sequence by playing the sequence twice.
Example 13-6.
#include <fastgraf.h>
#include <stdio.h>
void main(void);
void main()
{
fg_musicb("T150 L8 EDCDEEE P DDD P EGG P EDCDEEE L16 P L8 EDDEDC$",1);
while (fg_playing())
printf("Mary Had a Little Lamb...\n");
fg_waitfor(18);
fg_musicb("L16 CC#DD#EFF#GG#AA#B O+$",2);
while (fg_playing())
printf("up the scale in two octaves...\n");
fg_waitfor(18);
fg_musicb("T180 O2 L2 P L8 P GGG L2 D# L24 P L8 P FFF L2 D$",1);
while (fg_playing())
printf("Beethoven's Fifth Symphony...\n");
}
The next example demonstrates the effects of the Fastgraph routines
fg_hush and fg_hushnext, which stop sounds started with the fg_sounds,
fg_voices, or fg_musicb routines. The fg_hush routine immediately stops
asynchronous sound, whereas the fg_hushnext routine does so when the current
cycle finishes. Neither routine has any arguments, and neither routine has
any effect if no asynchronous sound is in progress. Furthermore, note that
fg_hushnext has no effect unless the asynchronous sound is continuous.
Example 13-7 runs in any text or graphics video mode. It displays
rectangles in up to 16 colors while playing continuous asynchronous music.
The program periodically checks for keystrokes with the fg_intkey routine,
and it continues to play the music while there is no keyboard activity. If
you press the Escape key, the program uses fg_hush to stop the music
immediately; this causes an exit from the while loop. If you press any other
Chapter 13: Sound Effects 243
key, the program uses fg_hushnext to stop the music as soon as the current
repetition finishes. Once it does, the program exits the while loop because
fg_playing will return a value of zero.
Example 13-7.
#include <fastgraf.h>
void main(void);
#define ESC 27
void main()
{
int color;
int old_mode;
unsigned char key, aux;
old_mode = fg_getmode();
fg_setmode(fg_automode());
color = 0;
fg_musicb("O4 L16 CC#DD#EFF#GG#AA#B O+ CC#DD#EFF#GG#AA#B$",-1);
while (fg_playing())
{
color = (color + 1) & 15;
fg_setcolor(color);
fg_rect(0,fg_getmaxx(),0,fg_getmaxy());
fg_waitfor(4);
fg_intkey(&key,&aux);
if (key == ESC)
fg_hush();
else if (key+aux != 0)
fg_hushnext();
}
fg_setmode(old_mode);
fg_reset();
}
Example 13-7 also demonstrates an important side-effect of the fg_musicb
routine when playing continuous music. Any length, octave, silence, or tempo
values changed within the string are not reset to their original values at
the beginning of each repetition. If we did not include the O4 command at
the beginning of the string, the later O+ command would cause the music to
play in octaves 4 and 5 during the first repetition, 5 and 6 during the
second repetition, and octave 6 for all subsequent repetitions (because you
cannot increase the octave number above 6).
The final two routines relating to asynchronous sound are fg_resume and
fg_suspend. The fg_suspend routine suspends music previously started by
fg_musicb, while fg_resume restarts the music from the point where it was
suspended. Example 13-8 plays the first few bars of "Mary Had a Little
Lamb". If you press any key while the song is playing, it stops. Then,
after another keystroke, the music resumes and continues until finished.
244 Fastgraph User's Guide
Example 13-8.
#include <fastgraf.h>
#include <stdio.h>
void main(void);
void main()
{
fg_musicb("T150 L8 EDCDEEE P DDD P EGG P EDCDEEE L16 P L8 EDDEDC$",1);
fg_waitkey();
fg_suspend();
printf("Music suspended. Press any key to resume.\n");
fg_waitkey();
fg_resume();
printf("Music resumed.\n");
while (fg_playing());
printf("Music finished.\n");
}
The fg_suspend routine has no effect if there is no asynchronous music in
progress. Similarly, fg_resume has no effect if there is no suspended music.
If you call fg_suspend and then need to cancel the music or exit to DOS
instead of restarting the music, call fg_hush instead of fg_resume.
Summary of Sound Routines
This section summarizes the functional descriptions of the Fastgraph
routines presented in this chapter. More detailed information about these
routines, including their arguments and return values, may be found in the
Fastgraph Reference Manual.
FG_HUSH immediately stops asynchronous sound started with the fg_sounds,
fg_voices, or fg_musicb routines.
FG_HUSHNEXT is similar to fg_hush, but it does not stop the asynchronous
sound until the current repetition finishes.
FG_MUSIC uses the programmable timer to play a sequence of musical
tones.
FG_MUSICB is the asynchronous version of the fg_music routine. It uses
the programmable timer to play a sequence of musical tones, concurrent with
other activity.
FG_PLAYING determines whether or not there is any asynchronous sound in
progress.
FG_QUIET stops continuous synchronous sound started with the fg_sound or
fg_voice routines.
FG_RESUME restarts asynchronous music previously suspended by
fg_suspend.
Chapter 13: Sound Effects 245
FG_SOUND produces a tone of a specified frequency and duration using the
programmable timer.
FG_SOUNDS is the asynchronous version of the fg_sound routine. It can
play a series of tones of specified frequencies and durations, concurrent
with other activity.
FG_SUSPEND suspends asynchronous music previously started by fg_musicb.
FG_VOICE produces a tone of a specified frequency, duration, and volume
using one of the TI sound chip's four voice channels.
FG_VOICES is the asynchronous version of the fg_voice routine. It can
play a series of tones of specified frequencies, durations, and volumes,
concurrent with other activity.
246 Fastgraph User's Guide
