Commodore 128 Programmer's Reference Manual page 347

SOUND AND MUSIC ON THE COMMODORE 128 337
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A parameter that is not specified will retain its predefined or currently redefined
value. Pulse width applies to the width of the variable pulse waveform (wf = 2) only.
The Commodore 128 has initialized the following ten envelopes:
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f—
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i
r
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' ENVELOPE
ENVELOPE
ENVELOPE
ENVELOPE
ENVELOPE
ENVELOPE
ENVELOPE
ENVELOPE
ENVELOPE
ENVELOPE
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o,
1,
2,
3,
4,
5,
6,
7,
8,
9,
A
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12,
0,
o,
9,
o,
0,
0,
8,
0,
D
9,
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0,
5,
4,
9,
9,
9,
9,
9,
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0,
12,
15,
5,
4,
2,
o,
9,
4,
o,
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o,
o,
o,
o,
o,
1,
o,
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1,
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wf
2,
1
0
3
0
1
2,
2,
2,
0
pw
1536
512
2048
512
instrument
piano
accordion
calliope
drum
flute
guitar
harpsichord
organ
trumpet
xylophone
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FILTER
Define sound (SID chip) filter parameters
FILTER [freq], [,lp] [,bp] [,hp] [,res]
where:
freq Filter cut-off frequency (0-2047)
lp Low-pass filter on (1), off (0)
bp Band-pass filter on (1), off (0)
hp High-pass filter on (1), off (0)
res Resonance (0-15)
Unspecified parameters result in no change to the current value.
You can use more than one type of filter at a time. For example, both low-pass
and high-pass filters can be used together to produce a notch-(or band-reject) filter
response. For the filter to have an audible effect, at least one type of filter must be
selected and at least one voice must be routed through the filter.