OSCILLATORS
Phase / FM
BeatZille’s oscillators are capable of all kinds of ‘FM’ sounds by plugging an audio-frequency
source into the
phase
modulation input. ‘FM synthesis’ is a bit of a misnomer, as this technology
was actually based on phase modulation (see Wiki articles about
).
With its 4 oscillators and 4 filters, the full version of Bazille is capable of 8-operator FM. BeatZille’s
2 oscillators plus single filter give you 3-op FM – enough for many typical FM sounds.
Phase
The righthand knob adjusts the basic phase position i.e. where in its cycle the waveform will
start whenever a note is played. The range is usually 720° i.e. 2 cycles, but this is reduced to
360° when different waves are combined (the pitch drops an octave). The value of Phase is
irrelevant when the mode is set to
random,
as in the above image.
The oscillators in most analogue synths are free running i.e. the phase is never reset. Because
the oscillators in digital synths aren’t computed until a note is played (otherwise the CPU would
be busy computing inaudible sounds), the initial phase needs to be defined:
random
Resets the oscillator to a random phase each time a note is played.
...............
gate
Resets to the value of Phase each time a note is played so that all notes
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start with the same phase (assuming Phase isn’t being modulated).
catch
Each oscillator gets its phase from where the most recent voice left off – for
...................
a better ‘free running’ effect despite voice rotation (‘round robin’).
Phase modulation
(with mode selector)
The bipolar knob on the left adjusts the amount of phase modulation (or frequency modulation,
depending on the modes) from a signal connected to the socket. Connect another audio-rate
oscillator here for classic ‘FM’ sounds (both should be sine waves).
The first 3 options are for regular phase modulation with different depth ranges. As modulation
in these modes only affects
phase
, the overall pitch of the oscillator is preserved:
PM fine
for subtle phase modulation
...............
PM medium
for typical ‘FM’ uses, including self-modulation (‘operator feedback’)
........
PM coarse
for maximum phase modulation
..........
The next two options offer linear FM in two frequency ranges. With linear FM, modulation
adds
to the frequency – the overall pitch is only preserved if the modulating waveform is symmetrical:
lin 100Hz
linear FM, 0 to 100Hz
............
lin 1kHz
linear FM, 0 to 1000Hz
...............
The last two options offer relative FM. In this mode, modulation
multiplies
the frequency. Again,
the overall pitch is only preserved if the modulating waveform is symmetrical:
rel fine
relative FM: oscillator frequency * ( 1 +/- 0.5 * modulation)
.................
rel coarse
relative FM: oscillator frequency * ( 1 +/- 5 * modulation)
............
The linear and relative modes are unusual in that they offer ‘through-zero FM’. If a 100Hz
oscillator is linear frequency modulated with -1000Hz, it will run ‘backwards’ at 900Hz.
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