Antialiasing Oscillators in Subtractive Synthesis

Abstract

In this article, oscillator algorithms for digital subtractive synthesis were reviewed. The algorithms were divided into three categories: bandlimited, quasi-bandlimited, and alias-reducing methods. In the first category, the most interesting methods are in practice those that utilize wavetable techniques. The second category consists of methods that low-pass-filter the underlying continuous-time signal prior to sampling. The optimization of the previously introduced BLIT and BLEP methods were considered as a filter design problem. A new technique called the PolyBLEP method was introduced as a variation of the BLEP method that does not require a table lookup but is based on a closed-form formula. In the PolyBLEP algorithm, an integrated polynomial interpolation function is used for acquiring samples to correct the transition region of the waveform. In the third category, the DPW oscillator algorithm generates an approximate sawtooth waveform that has reduced aliasing. This recently proposed method is probably the simplest useful technique for this purpose, because only the trivial sawtooth is simpler, but it is practically useless due to its heavy aliasing. An alternative decimation filter was proposed for the DPW2X algorithm to suppress aliasing well in the frequency region where human hearing is most sensitive