Future Retro XS - Manual (Page 21)

ANALOG CONTROLS
FREQUENCY +/-: This control allows Oscillator B’s frequency to be offset approximately –9 to +9
semitones from Oscillator A. When this control is set to its mid position marked with a “0”, Oscillator B
should be in tune with Oscillator A (as long as nothing is selected to modulate the frequency of either
oscillator). Rotating this control counter clockwise of the “0” mark will decrease Oscillator B’s
frequency. Rotating this control clockwise of the “0” mark will increase Oscillator B’s frequency. You
can use this control to create everything from slight oscillator detuning for that “phat” chorus/flanging
sound, or also to create chord intervals between each oscillator.
WAVE B: This control selects which waveshape will be used for Oscillator B. As you can see Oscillator
B generates four waveshapes being the sine, triangle, sawtooth, and square/pulse waveforms.
A SINE wave (the one that looks like an S turned sideways) is the most basic waveform, having only a
fundamental frequency and no additional harmonics. Sine waves sound very thin and are pure in sound.
A TRIANGLE waveform contains a fundamental frequency and all odd harmonics (3rd, 5th, 7th, and so
on) of that frequency. This causes it to sound slightly fuller than a sine wave.
The SAWTOOTH waveform is one of the most complex shapes, which contains a fundamental
frequency and all harmonics of that frequency. Sawtooth waves are very full sounding and have a
unique raspy quality to them.
A SQUARE wave also contains a fundamental frequency and all odd harmonics of that frequency; the
difference between it and a triangle waveform is that the harmonics are more pronounced in the square
wave, giving it a somewhat hollow yet fuller sound than the triangle. In the XS, the duty cycle of this
square wave can also be varied to create what is known as a square/pulse waveform. The width of this
pulse alters the harmonic content of the waveform, and this is determined by the PWM control.
Consider the true square wave whose pulse is 1/2 the period of the waveform. We know that the 2nd
harmonic and its multiples have been eliminated leaving only the odd harmonics. Let’s say the pulse
width is changed to 1/3 the period, which then eliminates the 3rd harmonic and its multiples such as the
6th, 9th, and 12th harmonics. A pulse width of 1/4 the period would then eliminate the 4th, 8th, and 12th
harmonics.
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