Sound synthesis refers to the creation of interesting sounds using artificial means. The word artificial is referring to the creation of the sound by man. In a sense, sound synthesis has been going on for a long time, and what are considered by many today to be natural instruments are in fact examples of sound synthesis.
Most people consider synthetic sounds to be those produced through the use of electronic devices, and as digital sound synthesis grew of the these techniques, such will be referred to as synthetic sounds. Special sound effects are an important matter associated with sound synthesis because almost all synthesis methods use some sort of wave form as a base and modify it to create the desired sound.
A brief history of sound synthesis methods
One of the earliest devices used in sound synthesis was the tape recorder. The first use of the tape recorder apart from recording was to splice different pieces of composition together. Another early use of the tape recorder was to change the pitch and speed of a recorded piece. This was done by changing the playback speed of the recorded music, although such changes also affected the duration of the recording. After the tape recorder, the next major step in sound synthesis was the use of analog circuits, such as oscillators, op-amps, resistors, capacitors, inductors, and filters to create sounds. One early idea behind many analog synthesis methods was to take a source signal, either a recorded sound or one generated using oscillators, and to filter this signal, perhaps providing a feedback loop to control the generated signal. A variety of filters and envelopes were used to eliminate unwanted harmonics, and to modify the relative amplitudes. The adaptation of digital technology to sound synthesis was the next big step. Digital methods offered advantages over analog methods because of several factors.
Some general points about good synthesis methods
The best methods of synthesis are generally based on tried and true principles. A good synthesizer must have facilities to do what it was designed for. When using a synthesizer in a performance situation, real time control facilities should be paramount.
Sound synthesis methods
Of the many techniques developed for sound synthesis, an important one is FM or frequency modulation. This is because it allows for the generation of a wide variety of sounds, using a small number of parameters. After a suitable starting signal or FM has been generated filters and envelopes are used to take away the unwanted components of a sound while synthesizing sound. The frequency content determines what a synthesis sound will sound like.
An early idea was to take white noise, and filter out all of the unwanted components until only the desired components remain. This method of subtractive sound synthesis proved difficult to do because of limitations of filters.
A much better approach is to generate a sound with the desired components already present, as well as some unwanted components, and to use filters to remove only the unwanted components, as well as to adjust the relative frequency content. The final step in getting realistic sounds using synthesis is to simulate some special effects.
One of the most basic effects is reverberation. Reverberation can be created by adding a time delayed version of the original signal to itself. The relative magnitudes of how the two are mixed determine the amount of reverberation is present.
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