How to learn the basics of additive synthesis | …

Sound Synthesis Theory/Modulation Synthesis - …

A piece of music composed with fast and slow granular synthesis.

Additive synthesis is a method of sound creation based on adding sine waves of different frequencies to create more complex sounds. Each sine wave typically changes amplitude over time to create evolving sounds.

Additive synthesis: spectral envelope Up: Examples Previous: Transfer functions for amplitude Contents Index Additive synthesis: Risset's bell

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The peak amplitude of a waveform for a particular spectrum depends on the phases of its harmonic components, and lower peak amplitudes give better signal-to-noise ratios. Most previous work on peak amplitude reduction has only considered individual spectra, but applications such as wavetable synthesis require multiple wavetables. A recent study compared various phase selection methods for multiple wavetable synthesis and found that genetic algorithm (GA) optimization gave peak amplitude results 10–25% lower than other methods. Various phase selection methods are compared with regard to group additive synthesis, a special case of multiple wavetable synthesis, where each wavetable contains a distinct subset of the harmonics. The results show that GA and simulated annealing optimization are consistently good, and usually outperform random phase selection, Schroeder’s method, van den Bos’s method, and Pumplin’s method with one or two wavetables. The GA runs several times faster than simulated annealing and strikes the best balance between efficiency and effectiveness. With three or more wavetables, the random, van den Bos, Pumplin, GA, and simulated annealing methods give about the same results. Group additive synthesis peak factors are up to 30% worse than their wavetable synthesis counterparts, unless wavetable matching and peak-factor optimization are integrated. While multiple wavetable synthesis allows lower peak factors and relative spectral errors than group additive synthesis, group additive synthesis has the advantage that it allows better and more intuitive control than multiple wavetable synthesis. The GA and simulated annealing low-peak methods help get the best performance out of both multiple wavetable synthesis and group additive synthesis.

Example of harmonic additive synthesis in which each harmonic has a time-dependent amplitude. The fundamental frequency is 440 Hz.

As demonstrated by software such as , it is possible to analyse the frequencycomponents of a recorded sound and then resynthesize arepresentation of the sound using additive techniques. Bycalculating the frequency and amplitude weighting of discretepartials in the frequency domain (typically using a ), an additive resynthesis system canconstruct an equally weighted sinusoid at the same frequency foreach partial.

In additive synthesis, the sound is constructed from partials – single sine waves firing in parallel, changing amplitude and even frequency over time.