Some synthesizers go beyond the simple ADSR envelopes. A perfect example is a type of envelope generator in which the actual envelope shape is defined in terms of pairs of numbers, with each pair consisting of a level (the amount of the envelope) and a rate (the speed or time of the slope) parameter, which determines exactly how quickly the envelope will reach that level, beginning with the previous level. Famous synthesizers that included rate/level envelope generators include the Yamaha DX7 and the Casio CZ-101.

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