of Microprocessors

DIGITAL HARDWARE 627
A Hybrid Voice Module
Figure 17-23 is a block diagram of a hybrid voice module that is
practical for an individual to build. Very little is present that has not been
discussed in detail previ:msly. The most interesting feature is a "floatingpoint"
method of specifying the frequency parameter. The method allows a
frequency resolution of better than 1 cent throughout the audio range with a
single 15-bit parameter. The idea is to use the most significant 3 bits of the
parameter to specify an octave and 12 additional bits to specify a frequency
within the octave.
The frequency and waveform generator utilizes variable-sampIe-rate
techniques to minimize the size and resolution required in the waveform
memory. Waveforms as coarse as 4-bit resolution and 16 steps have been
successfully used in similar generators, and while a wide variety of timbres
POST
DIVIDER
MODE
CONTROL
WORD
WRITE NEW
WAVEFORMS
ADDR DATA WRITE
WAVEFORM
LOOKUP
ADDRESS
+512
JITTER
FILTER
+4
SYMMETRY
AND
9 TABLE-
SPLITTING
LOGIC
12-BIT
ACCUMULATOR
DIVIDER
10-BIT
4-WAY
MUXED
DAC
1----------4~IFo
1----------4~IQ
MODE
SELECT
~~~~~~tCY 12
WORD
10
VALUE
ADDRESS
VCA
PRESCALER
+2 N
15N:58
AUDIO
OUTPUT
Fig. 17-23. Hybrid voice module