Most typically, these scales are usually 12-TET Western scales, with some quantizers providing a piano-style layout to indicate the available notes. With quantizers, the available 'numbers' are voltage levels set by the quantizer's scale. If a number, or in the case of synthesizers, a voltage level is between two selected numbers, it is either rounded up or down to the nearest whole number.
Quantizers can be thought of as rounding off voltages, the same way that a number with a decimal such as 2.75 can be rounded off to make a whole number such as 3. One of its applications is to make sequences of voltages sound more 'musical' than sequences of uncorrelated voltage levels. A quantizer is a module that takes control voltage signals and constrains them to a particular set of notes in a modular synthesizer.
