Adjusts the time it takes for the volume to fall from the Sustain level to zero once the key is released. It can be used to create sounds that have a “fade-out” quality.
Most synthesisers can generate multiple envelopes. One envelope is always applied to the amplifier to shape the volume of each note played, as detailed above. Additional envelopes can be used to dynamically alter other sections of the synthesiser during the lifetime of each note. Bass Station II’s second Envelope Generator (Mod Env) can be used to modify the filter cut-off frequency, or the pulse width of the Oscillators’ Square Wave outputs.
Like the Envelope Generators, the LFO (Low Frequency Oscillator) section of a synthesiser is a Modulator. Instead of being a part of the sound synthesis itself, it is used to change (or modulate) other sections of the synthesiser. For example, the LFOs can be used to alter Oscillator pitch, or Filter cutoff frequency, as well as many other parameters.
Most musical instruments produce sounds that vary over time both in volume and in pitch and timbre. Sometimes these variations can be quite subtle, but still contribute greatly towards characterising the final sound.
Whereas an Envelope is used to control a one-off modulation over the lifetime of a single note, LFOs modulate by using a repeating cyclic waveform or pattern. As discussed earlier, Oscillators produce a constant waveform, which can take the shape of a repeating sine wave, triangle wave etc. LFOs produce waveforms in a similar way, but normally at a frequency which is too low to produce a sound the human ear could perceive directly. As with an Envelope, the waveforms generated by the LFOs may be fed to other parts of the synthesiser to create the desired changes over time – or ‘movements’ - to the sound.
Imagine this low frequency wave being applied to an Oscillator’s pitch. The result is the pitch of the Oscillator slowly rises and falls above and below its original pitch. This would simulate, for example, a violinist moving a finger up and down the string of the instrument whilst it is being bowed. This subtle up and down movement of pitch is referred to as the ‘Vibrato’ effect.
A waveshape often used for an LFO is a Triangle wave.
Alternatively, if the same LFO signal were to modulate the Filter cut-off frequency instead of the Oscillator pitch, a familiar wobbling effect known as ‘wah-wah’ would be the result.
A synthesiser can be broken down into five main sound generating or sound modifying (modulating) blocks:
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Oscillators that generate waveforms at a various pitches.
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A Mixer that mixes the outputs from the Oscillators together (and add Noise and other signals).
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Filters that remove certain harmonics, changing the character or timbre of the sound.
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An Amplifier controlled by an Envelope generator, which alters the volume of a sound over time when a note is played.
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LFOs and Envelopes that can be used to modulate any of the above.
Much of the enjoyment to be had with a synthesiser is with experimenting with the factory preset sounds (Patches) and creating new ones.
There is no substitute for ‘hands on‘ experience. Experiments with adjusting Bass Station II’s various controls will eventually lead to a fuller understanding of how the various synth sections alter and help shape new sounds.
Armed with the knowledge in this chapter, and an understanding of what is actually happening in the synth when tweaks to the knobs and switches are made, the process of creating new and exciting sounds will become easy.