Ten Criteria for Evaluating Synthesis Techniques

A synthesis technique (Figure ib) is a strategy for generating sound samples based on some control information called parameters. Parameters generally change at a rate that is significantly slower than the audio sampling rate. Whereas sound samples are usually produced at a constant rate, parameter-setting messages are often sporadic and irregular. For example, in the familiar Yamaha DX7 synthesizer (Chowning and Bristow 1986), the synthesis technique is frequency modulation (FM) synthesis, which produces a steady stream of audio samples, whereas MIDI pitch-bend is a parameter that changes only when the performer moves the instrument's pitch wheel or foot pedal. For a historical summary of synthesis techniques, see, for example, Smith (1991). A processing technique (Figure la) is similar to a synthesis technique except that it includes an additional input of one or more audio sample streams at the audio sampling rate. An example of a common processing technique is reverberation. Here, the parameters are controls, such as the initial delay before the first reflections, the balance between the reverberant and dry signals, and the decay rate of the echoes. A wide variety of synthesis and processing techniques have been invented. The question may arise as to which technique is best. As it turns out, there is no simple answer. The best technique depends on the priorities of the user and the problem to be solved.