5.5
Applications
Fig. 25 ORGAN ENVELOPE GENERATION
While many applications of the PSG in music generation are
apparent, for instance in the area of toys and games, other applica-
tions are possible even in the area of high accuracy sophisticated
musical instruments such as high-end electronic organs. With tone
frequencies generated from another source to meet the exacting
requirements of organ operation, the PSG can be used as a complex
envelope generator. The PSG is also effective for generating bass
notes and rhythms with percussion instruments, taking advantageof
the PSG’s high accuracy in producing low frequency notes. The
following paragraphs detail examples of these applications.
5.5.1 ORGAN ENVELOPE GENERATION
The envelope generation diagram shown in Fig. 25 illustrates how an
AY-3-8910 can be configured to produce envelopes for organ
voicing. All functions are controlled by a microcomputer.
The basis of this system consists of a master frequency generator
with a string of dividers. This produces all frequencies for the
keyboard. The microcomputer and the AY-3-8910 are actually used
to replace the usual components of voicing filters that would
ordinarily be used in an electronic organ.
The microcomputer shown is a Gl PIC 1650 controlled by inputsfrom
the keyboard keyer circuit and a control switch matrix. The keyer
inputs octave and key closure information to develop the envelope
amplitude and duration for the note to be played. The control switch
matrix can be used to control sustain and add other special effects.
The ROM shown connected to the AY-3-8910 is optional depending
on the amount of data necessary for the microcomputer.
The system shown here may also consist of multiple AY-3-8910’s all
controlled by a single microcomputer. It represents an economical
solution to developing voicing control with a minimum of compo-
nents.
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