XERXES INSTRUCTION MANUAL
REV 0.7
Page
4
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OSCILLATOR 1 AND 2
Oscillators are electronic circuits that generate the audio waveforms for the synthesizer. Xerxes contains
a total of 16 digitally controlled analog oscillators, two of which are used for each note. These two
oscillators can have different waveform shapes, and they can also be combined in various ways thru
cross modulation, providing a large number of possible waveforms. Certain modulation combinations
can also cause self-resonance, when additional high resonant frequencies are generated within a single
waveform cycle via electronic feedback in the circuit. Oscillator self-resonance, created purely in analog
hardware, is one of the unique features responsible for the special sound of this instrument.
OCTAVE
Selects the octave in feet
(16’, 8’, 4’, 2’, 1’)
, which transposes the keyboard up or
down in octaves. The smaller the number the higher the pitch on the keyboard.
TRANSPOSE
Transposes the oscillator pitch from -7 (down) to +7 (up) in semitone steps, allowing
for quick interval changes between the oscillators. A setting of 0 is neutral and does
not transpose the pitch.
WAVEFORM
Selects the oscillator waveform. Each waveform has a different timbre, which
depends on the harmonic content in the waveform:
•
Triangle
wave contains very few odd harmonics, containing a very pure sound
with few overtones.
•
Sawtooth
wave contains all the integer harmonics (both even and odd), making it
useful for producing tones that are very rich in overtones.
•
Square
wave only contains odd harmonics. It can produce flute-like sounds with
certain oscillator frequency combinations.
•
Pulse
wave contains harmonics that are dependent on the selected pulse width.
Pulse width can be controlled with the Pulse Width knob, and it can also change
at audio rates when Pulse Width Modulation (PWM) is enabled. Pulse amplitude
can vary at audio rates when Pulse Amplitude Modulation (PAM) is enabled.
OSC x PWM
Selects Pulse Width Cross-Modulation, where the pulse width of the current oscillator
is modulated by the waveform amplitude of the other oscillator. If this button is
pressed, Pulse waveform is automatically selected. PWM can produce very rapid
change in overtones that depends on the frequency and waveform settings on the
other oscillator. In this modulation setting the pulse width can still be adjusted using
the Pulse Width knob. LFO can also automatically vary the pulse width when selected.
