INTRODUCTION
Not all periodic oscillations occur
within the range of audible frequencies, but this does not mean that you can not hear
them. For example, a violinists vibrato may take the form of
an oscillation at, say, 5Hz, while the growl produced by over-blowing a brass
instrument may occur at 18Hz. Even in isolation, you may hear a periodic waveform at
subsonic frequencies - for example, a clock oscillator with an output of 1Hz
will sound like a series of repeating clicks. (Strictly speaking, these have a high
bandwidth due to the transient nature of the waveform, and you would not hear a sine
wave at the same frequency, but that is not the point.)
Synthesisers have a class of oscillators -
Low Frequency Oscillators (LFOs) - that create these, and many other,
effects. They can add vibrato to a sound, produce growl, act as low frequency
clocks and, on some synthesisers, double as audio frequency oscillators.
IN USE
The RS80 is a flexible LFO with an extremely low minimum frequency (one cycle every
50 seconds) that allows you to create a variety of slowly varying modulations and
effects. Its maximum frequency lies in the middle of the audio range. The RS80
can, therefore, be used in three ways: as a low frequency modulator; as an audio
frequency modulator; and as a secondary sound source. It is therefore vital that,
just like a primary audio oscillator, the RS80 exhibits pitch
stability, waveform accuracy, and a lack of unwanted noise
and/or distortion.
The operation of an LFO may be divided into
three major categories: its frequency, its waveform, and its level.
FREQUENCY
The FREQUENCY knob has two ranges:
&127; HIGH
Turning the FREQUENCY control from its minimum to its maximum will cause the RS80
to produce its upper range of frequencies from 3Hz to 1,400Hz.
&127; LOW
Turning the FREQUENCY control from its minimum to its maximum will cause the RS80
to produce its lower range of frequencies from 0.02Hz to 5Hz. #
You may control the LFO rate by applying a
suitable CV to the LINEAR CV IN socket. This conforms to the Hz/Volt standard used by
Yamaha and most Korg monosynths. If you use it as a conventional oscillator you will
find that the it produces a different tone to the RS90, adding flexibility to the
synthesiser.
Waveforms
The RS80 generates four waveforms simultaneously. The first two of these are the sine
wave and the triangle wave, which are often used for imitating acoustic
characteristics such as vibrato and tremolo. The square wave is suitable for acoustic
effects such as trills, as well as for controlling many other aspects of the
synthesiser. Finally, there is the sawtooth wave, which can assume both rising- and
falling- shapes.
&127; SINE
This has no associated level control and, in normal use (i.e. with no oscillator sync
applied), it outputs a ±5V sine wave at the current LFO frequency.
&127; TRIANGLE
The level of the triangle wave is controlled using the associated LEVEL control, and has
a maximum output of ±5V.
&127; SQUARE WAVE
The level of the square wave is controlled using the associated LEVEL control, and has a
maximum output of ±5V.
&127; SAWTOOTH
The level of the sawtooth wave is controlled using the associated LEVEL control, and has
a maximum output of ±5V. The sawtooth waveform can be inverted from a rising
sawtooth to a falling sawtooth waveform by turning the LEVEL control from its fully
anticlockwise position through to its most clockwise position. No output will be
obtained when the knob is at its "12 o'clock" position.
Reset In
The RS80 offers a reset input ('sync') that allows you to re-initialise the LFO waveform
by applying a second waveform at the RESET input. This re-initialises the LFO
waveform every time a positive-going voltage is detected. If the reset signal is a
low-frequency periodic waveform, it will retrigger the RS80. If the reset signal is a
mid- or high-frequency period waveform, it will act as a 'sync' input, increasing
the harmonic complexity of the waveform generated by the RS80. If the reset signal is
aperiodic, more complex effects will occur.
Status LED
The status LED gives you a direct visual indication of the LFO frequency. |