User Manual

11
the vibration in the sound.
Different instruments playing the same pitch sound different, like
an oboe and a violin playing A440. That’s because musical sounds
generally have many frequency components. They're called harmonics,
or overtones, or partials. The harmonics of a pitched musical sound
are related to the pitch we hear, called the fundamental, by simple
relationships, 1X (fundamental, or rst harmonic) 2X(2nd harmonic), 3X
(3rd harmonic), 4X (4
th
harmonic), 5X (5
th
harmonic), 6X (6
th
harmonic),
and so on. These relationships dene what we call the harmonic series.
The presence and strength of different harmonics is what gives a sound
its characteristic tone color, or timbre. We can represent a musical sound
as a waveform. The waveform is a time graph of the actual shape of the
Figure 11: a basic waveform graph
vibration. See Figure 11.
The waveform of a single
harmonic is called a sine
wave. It is the simplest type
of periodic vibration there
is. If you listen to a 500 Hz
sine wave, you hear a pitch
nearly an octave above
middle C, with a mellow, muted quality, like a ute or a whistle. A 100
Hz sine wave also sounds mellow and muted, but its pitch is more than
an octave below middle C.
VCOs
The heart of the FreqBox is a Voltage Controlled Oscillator, or VCO.
The FreqBox VCO is a descendant of the same oscillators used in the
Moog Voyager and Little Phatty® synthesizers. An oscillator is a type
of circuit that vibrates electronically such that the changes in voltage
(electrical potential) can be used as a sound source. An oscillator circuit
doesn’t produce sound until it is changed from an electrical signal to
a mechanical signal, usually by the means of loudspeakers. The sound
made by an analog oscillator circuit is most often a very simple signal
because it has very simple vibrations.
The "voltage controlled" part of a VCO refers to the fact that in this
circuit a control voltage (CV) determines the frequency of the oscillator.
A steady CV will result in a steady pitch, while a changing CV will cause
a change in frequency. The FreqBox has a front panel Frequency control
changing that generates a voltage that increases as the control is turned
clockwise. This causes the frequency of the FreqBox VCO to rise.