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In Analog Music Synthesizers, keyboard tuning was done at the highest octave, either with a single master oscillator frequency, or possibly one for each of the 12 notes. All lower octaves were easily generated by frequency division by two, which can be done simply by clocking each of 12 binary counters. These produce square waves, which can be converted first to triangle waves and then sine waves by low pass filters which change the wave shape by reducing harmonics.