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APPENDIX A: THE DIGITONE FM SYNTHESIS
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C which always works like a carrier, is limited mostly to integers since it is generally used for carrying the
base note of the sound. For more information, please see “11.3.2 RATIO C” on page 40.
A
has a more extensive number of ratio values to allow for more inharmonic relationships. For more informa-
tion, please see “11.3.3 RATIO A” on page 40.
B (B1 and B2) controls both operators at the same time. The minimum value for B1 and B2 is .25. As you
turn the encoder, B2 increases until it reaches the max (16). It then starts over from .25 and B1 increases to
the next value (0.5). This revolving behavior continues until both operators reach the maximum value. This
parameter behavior is similar to the movement of the hands on a watch. For more information, please see
“11.3.4 RATIO B” on page 40.
A.5 THE OPERATOR ENVELOPES
If you modulate one oscillator directly with another it creates very harsh harmonics, so you need to limit the
modulation level to control the amount of modulation. In Digitone you use an envelope and a LEVEL param-
eter control to attenuate the amount of how much the modulator affects the carrier. The envelopes also
give the possibility to control the modulation over time. A piano for example, when first struck, the timbre is
sharp but quickly fades to a softer tone. Envelopes and modulation level are vital elements in FM synthesis
and are the tools that you use to shape the sounds you want to achieve.
The Digitone FM engine has two operator envelopes that are designed to be practical and easy to use. One
envelope is for operator group A, and one is for group B (B1 and B2).
The envelopes are essentially expanded AD (Attack Decay) envelopes, but with an added adjustable end
level (the amplitude level the sound reaches at the end of the decay stage). Normally, an AD envelope al-
ways ends at zero level, but with FM you often want to retain some modulation after a short pluck or fade in
for example. For more information, please see “11.4 SYN 2 PAGE 1” on page 40.
Please note that operator envelope B controls the output from both B1 and B2.
The envelopes can be either triggered or gated - making it either an ADE (Attack Decay End) or an ASDE
(Attack Sustain Decay End) envelope. The sustain phase does not have an envelope level. It is instead the
LEV parameter that sets the sustain level. The note length defines the length of the sustain phase. For more
information, please see “11.5.2 ATRG” on page 42.
Trigged ( ATRG / BTRG ON)
Attack End level Decay
Note on
Gated ( ATRG / BTRG OFF)
Attack Decay End level Sustain
Note on Note off