Modal duo — a duophonic modal synthesizer

Modal duo is a patch derived from my Zebu factory patch ‘Modalate This.’ Both are modal synthesizer patches, but Modal duo is duophonic, as opposed to monophonic, and controlled by MIDI, as opposed to CV. To free up CPU for the second voice, the number of partials was reduced from ten to six, which somewhat limits the complexity and depth of the sound.

Modal synthesis is… (I’m just going to grab a quote) “Modal analysis is a common approach to investigating the vibrations of a sounding object. A mode is a particular pattern of vibration (similar to a standing-wave pattern on a string) that manifests itself as a resonance in an audio spectrum.” ( So, the basic idea is that a bunch of resonances from pinged filters (partials) add up to create a timbre. The resonant structure of modal synthesis makes it useful for replicating struck or plucked sounds; it excels at tuned percussion, like gamelan, marimba, or bells. (This patch in particular makes me think of the soundtrack to Akira.)

There is an excitation impulse — here, either a noise burst or sawtooth oscillator — that hits the resonant filters, creating different frequencies which interact with and interfere with one another as standing waves.

The resonances are summed and then passed into a stereo spread and finally a hall reverb to give a sense of space to the sound.

The default MIDI channel is 1. Audio is produced in stereo.


In the top left-hand corner are the controls for the excitation impulse. You can use either noise or sawtooth or blend between them, using the impulse mix control. The noise can be passed through an aliaser (controlled by the “noise fidelity” control), which will produce more granularized noise and change its content. The sawtooth can be tuned; frequencies around A0 work best, but different frequencies will result in trills and changes in timbre, depending on the envelope employed. The sawtooth can also be set to track the pitch; when this option is enabled, the frequency control acts as an offset.

Below, there are controls for the envelope. Very short envelopes will ‘ping’ the filters; longer envelopes will produce sounds which interact more with the filters themselves.

Below the envelope controls are controls for the reverb — decay and mix. And beneath these is a range control for the pitch-bend. (I generally don’t use this to pitch-bend notes, so much as I use it to slowly change the pitch of a note I repeatedly played.)

On the right hand side are the controls for the resonant filters. The ‘resonance-decay’ control governs the resonance of the filter; below .5000 or so, the filters won’t have much affect, but as you increase the value they ring out longer. Values of ~.7-.8 are useful for wooden percussion; .9 for metal percussion and 1.000 for bells.

Beneath the resonance-decay control is a ‘filter transpose’ control, which determines how the filters track the keyboard.

Along the right-hand side are controls for the partial frequencies. Honestly, I just adjust these until something sounds good — modal analysis is pretty complex, but your ears work well for finding interesting sounds. Different impulses will react to different partials uh… differently. (I am good at words.)

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