RS40 Noise Generator / Sample & Hold / Clock is really three
separate ‘sub-modules’ that you can patch together to help generate
classic Sample & Hold effects. But effects are far from the only
uses for the sub-modules, and they can be patched into other RS
Integrator modules for an even wider range of effects.
Not all audio frequency oscillations exhibit this repetitious nature, and the most common of these 'aperiodic' waves is called "white noise". But why "white" and why "noise"? Let's explain each in turn…
A signal is perceived as noisy if it is random. Described another way, pure noise contains no discernible frequencies or tones.
But some noises may be described as rumbles, hisses, or even shrieks. In each of these cases, the waveform itself is random, but the signal only contains a narrow band of frequencies. Audible noise may, therefore, be "coloured" in exactly the same way that visible light is. If lower frequencies predominate, the noise has a deep, rumbling character, and it is called 'pink' or 'red' depending upon its exact nature. If high frequencies predominate the noise is called 'blue'. But if all frequencies are present in each amplitudes, the noise is 'white'. This is exactly analogous to light, where the presence of all the visible frequencies at equal amplitudes is perceived by the eye as the colour 'white'.
White Noise is, therefore, a signal that contains all the audio frequencies in equal amounts, but which manifests no recognisable pitches or tones. Another definition is this: a white noise signal is one in which the probability of a frequency being present is equal to the probability of any other frequency being present.
Many natural sounds display noisy characteristics - the crashing of waves and the howl of a strong wind are prime examples of these - and it would be impossible to synthesise such sounds without a noise generator. Many musical instruments also generate noise, although the amplitude of this part of the signal is generally low, and its colour is largely dependent upon the instrument. But if you start with white noise you can filter it to produce all other 'colours' of noise. You can also use resonant filters to accentuate certain frequencies, and modulate the noise amplitude to create such things as chiffs or wind and wave effects.
IN USE Some synthesisers offer 'noise' as an option on the main audio oscillators. This has a significant drawback: if your oscillators are acting as noise generators they are not outputting conventional waveforms. This can be very limiting and, for this reason, the Integrator's noise generator is provided on a separate module.
Unlike a standard oscillator, the Noise Generator requires no controls for its waveform or its frequency. There is, therefore, just one control and one output. There is no input.
Sample And Hold
Sample & Hold (S&H) circuits provide many of the most recognisable 'synthesiser' sounds by making modules such as oscillators and filters 'step' between values, thus creating rapidly varying patterns of pitch or timbre. They do so like this…
The S&H circuit produces stepped voltages by 'sampling', and then 'holding' the instantaneous value of any signal presented at its input. This signal could be a CV, an external signal such as the music from a CD or the sound of an instrument being played. Most commonly, however, a noise source is used because this creates a number of musically pleasing 'random' effects.
The circuit samples the incoming signal voltage when it is told to do so by an external trigger, usually provided by some form of clock or other triggering pulse. The voltage thus measured will then be held and presented to the output until the next trigger is received, at which time a further sample will be made, and the voltage at the output assumes its new value.
When the S&H output is presented to an oscillator's CV input it causes the pitch of the oscillator to follow the instantaneous amplitude of the signal presented to the S&H input. If directed to a filter, the S&H value determines the cutoff frequency of the filter, and therefore affects the brightness or timbre of any signal passing through that filter. Of course, the S&H circuit's output can be directed to all other modules, and can be used to modify any of the CVs or signals within the synthesiser.
For example, a sawtooth with a trailing edge produces a pronounced 'click' compared to a sawtooth with a leading edge. Furthermore, sawtooth waves will often trigger the S&H more frequently than a pulse wave of the same frequency. It has even been observed that different waveforms presented at the clock input will lead to different ranges of voltages being produced by the S&H circuit itself. You should use the RS80 LFO to experiment with these effects.
Putting It All Together
Unlike some other synthesisers with S&H modules, the three sub-modules in the Integrator are not pre-connected "behind the scenes". (If they were, the "one shot" button would not work.)
This means that you must patch sources into both the EXT SRC IN and EXT CLK IN sockets. The simplest and most obvious sources for these purposes are the noise generator and the clock, so now you should:
patch from the
NOISE OUT to the EXT SRC IN
At this point, the S&H OUT socket will be producing a random stepped CV in the range ±10v. You can now direct this to the input of your choice. The most common destinations are the audio oscillators and the filters. To apply S&H to either of these, patch the S&H OUT to either the CV-IN VARY on the RS90 VCO or the CV-IN VARY of the RS100 VCF. If you then increase the associated LEVEL control on the destination module the RS Integrator will, all other things being patched appropriately, produce a randomly stepped pitch or randomly stepped brightness effect.