An alternative to VCOs in creating basic signal waveforms, commonly used in electric organs and pianos but less frequently in synthesizers. The basic top-octave division setup uses a set of 12 oscillators (which may or may not be voltage controlled), one for each note in the chromatic scale, and in the highest octave that the instrument is capable of playing. Octave dividers are then used to create the chromatic scales for each of the lower octaves; each time that one of the top octave notes is divided by 2 (halving its frequency), it creates that note one octave lower. This is distinct from a divide-down architecture, which uses a single ultrasonic master oscillator.
The main problem with top-octave division is the twelve individual oscillator circuits; if common techniques like vibrato and portamento are to be implemented, twelve copies of the necessary circuitry are required. This makes the synth more complex to design and expensive to build. Additionally, control of the frequency of individual notes is not possible without effecting the frequency of the same note in other octaves. The technique is not very amenable to voice allocation, and so tends to be used mostly with instruments that are fully polyphonic (such as string synthesizers) and have limited timbral controls.