SYNCHRONIZATION AND RING MODULATION

The 6581 SID chip lets you create more complex harmonic structures through synchronization or ring modulation of two voices.

The process of synchronization is basically a logical ANDing of two wave forms. When either is zero, the output is zero. The following example uses this process to create an imitation of a mosquito:

EXAMPLE PROGRAM 9:

 10 S=54272
 20 FORL=0TO24:POKES+L,0:NEXT
 30 POKES+1,100
 40 POKES+5,219
 50 POKES+15,28
 60 POKES+24,15
 70 POKES+4,19
 80 FORT=1TO5000:NEXT
 90 POKES+4,18
 100 FORT=1TO1000:NEXT:POKES+24,0

LINE-BY-LINE EXPLANATION OF EXAMPLE PROGRAM 9:

Line(s)	Description
10	Set S to start of sound chip.
20	Clear sound chip registers.
30	Set high frequency voice 1.
40	Set Attack/Decay for voice 1 (A=13, D=11).
50	Set high frequency voice 3.
60	Set volume 15.
70	Set start triangle, sync waveform control for voice 1.
80	Timing loop.
90	Set stop triangle, sync waveform control for voice 1.
100	Wait, then turn off volume.

The synchronization feature is enabled (turned on) in line 70, where bits 0, 1, and 4 of register 4 are set. Bit 1 enables the syncing function between voice 1 and voice 3. Bits 0 and 4 have their usual functions of gating voice 1 and setting the triangular waveform.