Analogue sound systems represent sound waves as a time varying electrical signal. The voltage of the signal represents the value of the sound wave.
Analogue sound uses analogue electronics to process sound.
Sound sources include microphones, audio tape, and analogue synth sources such as oscillators. These create electrical signals that represent the sound. Many modular synths use a dual power supply (that is, a three power rails, 0V, 12V and -12V). The signal usually operates between about +/- 10V.
Analogue procession modules, such as filters, envelope generators, etc operate on the sound signal. They usually use additional analogue control signals, for example a voltage controlled filter applies filtering to an analogue sound signal based on the value of an analogue control signal.
The final output signal will be sent to an amplifier and speakers for live output, or to some kind of recording device for stored output. This could an an analogue tape device, but it is more likely to be digitised and processed by a DAW (Digital Audio Workstation) or similar.
There are several advantages to analogue sound, specifically in terms of sound synthesis.
Firstly, analogue synths have imperfections - much like traditional physical instruments. Tuning isn't accurate to six decimal places, waveforms are often slightly distorted, a certain amount of noise is present. Within limits, these imperfections can make the sound more appealing to the ear.
Secondly, analogue synths have a physical interface to play with - actual knobs, switches and patch cables. Many people find this sort of interface more intuitive to experiment with, and find that they can do more with it, even if those same effects are also available from a digital synth.
Finally, you can build your own analogue synth modules, it is great fun, and you end up with something physical that you have created. You can write your own modules for a digital synth too, but some people find that less satisfying.
But there is also a little bit of hype around. Analogue synths are fashionable, and original vintage synths are expensive - because they are rare, not necessarily because of how fantastic they are.
Analogue sound has a few disadvantages. The imperfections mentioned earlier (such as tuning errors, distortion or noise) are only ok in very small amounts. If they become excessive, it can be a problem. Nobody wants to listen to a synth that is totally out of tune, or puts out a background hiss.
Analogue synths can get quite expensive because each module adds extra hardware costs. Compared to an open source software synth, where you use need a PC and possibly a sound card, but after that you can add as many software modules as you like at no additional cost.
There are certain things that are difficult to do in analogue. Complex sequencing and complex envelopes, for example, are better done by a digital computer.
Sometimes a hybrid approach can be best, using analogue modules where it makes sense, but using an Arduino or Raspberry Pi board to handle complex control tasks, managing sampled data, storing the final sound digitally and so on.
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