of Microprocessors

752
MUSICAL ApPLICATIONS OF MICROPROCESSORS
1.0
86 ~SOUND
~FILE
'--,--,..-----'
1.0
Instrument Definition Statements
SET FUNCLENGTH = 8K
INS 0 GENFM; {P5=DUR, P6=AMP, P7=PITCH}
OSC BI P6 P5 F2 D; (AMP ENVELOPE)
OSC B2 1 P5 F3 D; {DEV ENVELOPE}
OSC B3 1 P5 F4 D; {MOD FREQ ENVELOPEl
OSC B5 B2 B3 Fl D; {MODULATION OSCILLATOR}
ADN B6 B5 P7;
OSC 87 81 86 Fl D; (CARRIER OSCILLATOR)
OUT B7;
END;
Fig. 19-17. Generalized FM instrument
Other unit generators, some of which are diagrammed in Fig. 19-16,
use similar statement formats. The FLT generator, for example, is a
generalized second-order digital filter (see Chapter 14). It has a signal input
and output, both of which are I/O blocks, and five coefficients, which can be
any kind of variable or constant. Thus, the filter characteristics can be
specified as constants, parameters in note statements, or by other signals via
the I/O blocks. Also, since arithmetic expressions are allowed in any of the
coefficient fields, the FLT statement may be set up for control in familiar
terms such as center frequency and Q factor. FLT also requires four temporary
values for the internal delays, which can be set to any specific initial value or
allowed to default to zero. SNDFILE is not really a generator at all; it instead
reads samples from an existing sound file. The various parameters include an
amplitude factor, an increment for the read pointer (which should be 1.0 to
read every sample), and starting and ending positions in the file. If more
samples are read than exist between start and end positions, the pointer
wraps around to the beginning as if the file was a huge waveform table. The