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B.3 ALGORITHMS

APPENDIX B: THE FM TONE SYNTHESIS > B.3 ALGORITHMS · PDF p. 107 · OS 1.12

B.3 ALGORITHMS — figure 1
PDF p. 107
B.3 ALGORITHMS — figure 2
PDF p. 107

An algorithm is a set routing, or combination, of the operators. Routing the modulation in different ways gives you several different methods of applying modulation and naturally different results.

Carrier Envelope Modulator Feedback Feedback Modulator Envelope output

Carrier Direct output

Output Algorithm Modulation Level Pictured above is a 2 operator algorithm, which is FM synthesis in its most basic form. The Digitone II has four operators available which can be routed in many different ways. Different algorithms dramatically changes the characteristics of the output - for example stacking four operators can lead to very complex timbres.

The Digitone II has eight different algorithms where the four operators are routed in different ways. For more information, please see “A.2.1 FM TONE” on page 89. Each algorithm has two carrier outputs (X and Y) that come from two different operators depending on what algorithm you chose. It is possible to use the MIX parameter to mix between these outputs so that you can cross-fade between two separate timbres. For more information, please see “A.2.1 FM TONE” on page 89.

The lines going to X and Y indicate the output from a carrier. There are two different ways a carrier output is sent to the X/Y outputs: 1. Its amplitude is unaffected by the operator envelope (dotted line). 2. Its amplitude is affected by the operator envelope (filled line). The sound from the X/Y outputs is then routed via the overdrive to the filters.

B.4 FM RATIOS

Frequency modulation is applied in multipliers of the principal frequency to retain the sounds tonality. These multipliers are known as ratios. Each operator group’s ratio is a multiplier of the input pitch (note value). The higher the ratio, the higher the pitch frequency. For example, when applying modulation with a ratio of 1:2 (carrier:modulator), the carrier output resembles a square wave. A ratio of 1:1 sounds like a sawtooth, and odd numbers can be used for various metallic or other “natural” sounds. In Digitone II, the FM ratios for the different operator groups works like this: