Appunti SOS - Part 2

For example, a sawtooth wave will provide the basis of most of the orchestra's brass and string sections, a square wave will synthesize woody sounds such as clarinets, while the thinner-sounding pulse waves provide the reedier tones of oboes and bassoons.

Moving away from the orchestra, you can use the same waveforms to synthesize modern instruments. A combination of sawtooth and pulse waves provides some remarkably accurate imitations of bass guitars and, suitably modified, a sawtooth will generate a range of timbres that you can play through effects units to sound just like a lead guitar. Of course, you have to play the sound like a guitar too, but that's another story. The important point is this: a synthesizer that offers just three waveforms provides you with the raw materials to imitate most of the instruments that you'll find played by an orchestra, a rock group, and the Viennese Oom-Pah Champions of 1898.

A perfect 'noise generator' produces all audio frequencies simultaneously, and this is close enough to provide a basis for many analogue 'drum' sounds that would be quite unobtainable using conventional waveforms (see Figure 7). Indeed, filtered noise is the basis of the most popular percussion sounds of the 1990s -- the Roland CR78, CR5000, TR808 and parts of the TR909 all generate their voices in this fashion.

the physical differences between drums and metallic percussion instruments mean you can't program convincing bells and gongs using a noise generator. Consequently, this is an area in which a basic synthesizer such as the Minimoog in figure 7 does not excel. But if you look at the patch sheets of a more complex synth such as an ARP Odyssey or ARP 2600 you will find lots of 'metallic' sounds. This is because they have a 'ring modulator' -- a circuit that produces the dense cluster of non-harmonic overtones that are characteristic of metal sheets. With suitably chosen filters and envelopes, these can provide startling imitations that are, once again, quite beyond the capabilities of a simple harmonic oscillator.

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