Abstract

A synthesizer that distorts its upper partials while keeping a low fundamental clean cannot do so with a crossover: a nonlinearity fed with upper partials generates difference products that land below its input, back in the band the crossover was protecting, and a complementary crossover also alters the waveform's peak. This problem was researched and there seem to be some methods that can resolve this. This disclosure describes a method that uses a fact available only inside a synthesizer, that the instrument knows its own oscillator phase exactly, rather than having to estimate it. By keeping the signals within the machine itself and serving as a self-reference, the signal is split by weighting each partial's coefficient rather than by filtering, which reconstructs exactly and changes no phase; the upper part is distorted; and what the distortion put back into the protected band is then measured by synchronous detection against the instrument's own phase, averaged over a whole number of periods of the fundamental, and subtracted. The whole-period window has an exact null at every other harmonic, so the estimate settles in one window and neither hears its neighbors nor ripples. Measured over 1782 steady-state cases, the residual left in the protected band was 103.7 dB below the instrument's fundamental, against 8.7 dB for a 4th-order Linkwitz-Riley crossover on the same material; the split alone changed the waveform's peak by 2e-15 dB where the crossover changed it by up to 2.49 dB. Two conditions are necessary: one instance per voice, and silence for one window at the start of a note.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

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