LINE-BY-LINE EXPLANATION OF EXAMPLE PROGRAM 1:

Line(s) Description
5 Set S to start of sound chip.
10 Clear all sound chip registers.
20 Set Attack/Decay for voice 1 (A=O,D=9).
Set Sustain/Release for voice 1 (S=O,R=O).
30 Set volume at maximum.
40 Read high frequency, low frequency, duration of note.
50 When high frequency less than zero, song is over.
60 Poke high and low frequency of voice 1.
70 Gate sawtooth waveform for voice 1.
80 Timing loop for duration of note.
90 Release sawtooth waveform for voice 1.
100 Return for next note.
110-180 Data for song: high frequency, low frequency, duration (number of counts) for each note.
190 Last note of song and negative Is signaling end of song.

VOLUME CONTROL

Chip register 24 contains the overall volume control. The volume can be set anywhere between 0 and 15. The other four bits are used for purposes we'll get into later. For now it is enough to know volume is 0 to 15. Look at line 30 to see how it's set in Example Program 1.

FREQUENCIES OF SOUND WAVES

Sound is created by the movement of air in waves. Think of throwing a stone into a pool and seeing the waves radiate outward. When similar waves are created in air, we hear it. If we measure the time between one peak of a wave and the next, we find the number of seconds for one cycle of the wave (n = number of seconds). The reciprocal of this number (1/n) gives you the cycles per second. Cycles per second are more commonly known as the frequency. The highness or lowness of a sound (pitch) is determined by the frequency of the sound waves produced.

The sound generator in your Commodore computer uses two locations to determine the frequency. Appendix E gives you the frequency values you need to reproduce a full eight octaves of musical notes. To create a

 This page has been created by Sami Rautiainen. Read the small print. Last updated February 10, 2002.