Filter-based alias reduction for digital classical waveform synthesis

The classical waveforms used in the subtractive sound synthesis have rich spectral content, which causes their sampled digital implementations to suffer from aliasing distortion. Several antialiasing waveform synthesis algorithms have been suggested, and they either remove the aliasing completely or reduce it greatly. A new approach to alias reduction is proposed where the remaining aliased components are suppressed by applying digital highpass and/or comb filtering to the output of an antialiasing algorithm. Applicable filter designs for this novel postprocessing approach are discussed and evaluated with respect to the alias reduction performance using noise-to-mask ratio (NMR). The NMR can be reduced by 10 dB at high fundamental frequencies with a computationally efficient highpass filter. The NMR can be further reduced by using a combination of an IIR comb filter and a DC blocking filter, which provides the best alias reduction performance at high fundamental frequencies.