Making Music
  Computer Music Software and Hardware

Smooth Operator

Tech terms Zero-crossing point The point at which a waveform crosses the central line where it will have zero volume. Cyclical A repetitive waveform such as square or pulse wave. Fourier analysis The process of analysing a waveform and breaking it down into its sine wave components. Continuous model In PM, a bowed or blown instrument model such as a violin or trumpet where energy is continuously generated. The sound continues for as long as the energy is applied. Impulse model In PM, a plucked or struck instrument model such as a plucked string or vibraphone where the energy is applied in one 'impulse' and the sound dies away naturally.

FM synthesis needs a few other elements, too, including an envelope and VCA (this is often a part of the envelope) and this combination is known as an Operator. Different FM synthesisers had different numbers of Operators. The DX7 had six, the DX9 had four (it actually had six but two were deliberately disabled to reduce its functionality) while some prototype instruments had eight. Yamaha also produced FM chips with limited functionality which were the PC soundcard standard for many years.

Operators could be linked in various combinations known as Algorithms which define how many Carriers and Modulators there are, and how the are connected. A six-Carrier Algorithm, for example, would be the FM equivalent of Additive synthesis. Other Algorithms could include two or three Modulator/Carrier pairs, two Modulators modulating one Carrier, one Modulator modulating two Carriers, and so on.

One of the major difficulties in programming FM is that there seems to be no simple or intuitive correlation between the Modulator and Carrier settings. If you alter a low pass filter in an analogue synth you know what's going to happen - FM is not predictable in this way. Although the original FM was based on sine waves, to complicate matters even further, it's possible to use any kind of waveform.

FM synthesis never really left the music field and keeps popping up on plug-in synthesiser cards and soft synth emulations including Native Instrument's FM7. But it's still the back end of a donkey to program!

Waveshaping

Waveshaping can produce sounds that seem related to FM but it's a different process. It adds controlled distortion to a waveform to change its shape. Consider a sine wave, for example, and think about changing its shape and you'll realise that any other shape will include additional harmonics (think about a sawtooth or triangle wave). Waveshaping, therefore, creates complex sounds from simple waveforms. Casio used Waveshaping in its range of CZ synthesisers as an 'alternative' to FM and called it Phase Distortion.

Granular synthesis

Many forms of synthesis were developed by academics and Granular synthesis is one. The foundations were laid by the composer Iannis Xenakis in the 1950s although it wasn't until the 1970s that academics began to see how it might be implemented on a computer.

The process involves playing a rapid succession of very short sounds called grains, typically around 35ms long. This corresponds to the timing resolution we can discern with our ears which is between 10ms and 50ms. Audio events that are closer than this tend to be heard as one sound, similar to the way that individual stills in a film blur into an action movie when played quickly through a projector. A grain can be any sound segment from a synthesised waveform to a sample.

Three common methods of synthesis include Sequential which simply involves playing one grain after another; Scatter which uses several grain generators so grains might overlap and play simultaneously; and Granular Sampling which involves extracting a grain from a sample and repeating it, or extracting many grains and playing them in random or predetermined order.

Envelopes play an essential part in the process as the amplitude of the grains must be controlled to avoid clicks and glitches as they play. You're probably familiar with the glitches that occur if a sample hasn't been looped correctly at zero-crossing points. Imagine that on a microscopic scale!

Granular synthesis sounds are typically described as 'shimmering' and generally have a lot of tonal movement - ideal for new age and ambient music. There are no commercial hardware Granular synthesisers but the process is ideal for software synthesis and there are a few programs such as Chaosynth, Granulab and GrainWave that allow you to explore its possibilities. Reaktor also has a Granular module.

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