Table Lookup Oscillators Using Generic Integrated Wavetables
Table lookup oscillators form a basic building block of most software synthesis systems. Several of the classical digital and analog synthesis techniques require their use. The classical table lookup oscillator [1, 2] is commonly discussed regarding its amplitude error, but another source of error is mostly disregarded, although it influences the sound quality to a much higher degree, especially when running the oscillators at elevated frequencies. This error is due to the aliasing effect that occurs when shifting (or resampling) the original lookup table at higher rates. One obstacle that has been encountered when trying to emulate classical analog synthesizers, is that the naive implementation of waveforms for subtractive synthesis generate the same aliasing frequencies. Over the years, several solutions for the problem of generating high quality band-limited waveforms for emulating classical analog synthesis have been proposed, solving the problem for specific waveforms. Never-the-less, the general question of how to manage aliasing behavior efficiently in general table lookup oscillators is still not resolved. This article reviews existing techniques for analog synthesis and tries to expand them for the general case.