LFOs and os­cil­la­tor mod­u­la­tion

Future Music - - FEATURE -

What’s also great is that you’re not just re­stricted to us­ing a ded­i­cated LFO

A synth’s low-fre­quency os­cil­la­tor is es­sen­tially a ‘reg­u­lar’ in­audi­ble os­cil­la­tor that op­er­ates at low speeds, and is used to mod­u­late other pa­ram­e­ters – kind of like an ex­tra hand wig­gling a knob for you at the rate and shape you set. LFOs in the semi-mod­u­lar world are es­pe­cially useful, as sig­nals can be piped wher­ever you choose thanks to those patch­bays. Plug an LFO’s CV out­put straight into an os­cil­la­tor’s fre­quency/pitch in­put, and the LFO will wob­ble the pitch: in­stant vi­brato. Plumb an LFO out­put into am­pli­tude in­put and you’ll mod­u­late vol­ume for tremolo good­ness. Plus, mak­ing those phys­i­cal con­nec­tions your­self will help you plan out your mod­u­la­tion strat­egy and get to grips with what’s go­ing on from the start.

At­ten­u­a­tors are mas­sively help­ful when patch­ing LFO sig­nals: by plug­ging the LFO’s out­put into an at­ten­u­a­tor’s in­put, then the at­ten­u­a­tor’s out­put into the des­ti­na­tion of choice, you can use the at­ten­u­a­tor’s knob to tem­per the amount of LFO mod­u­la­tion, ef­fec­tively giv­ing you a ‘mod amount’ knob. And you can also mix mod­u­la­tion sig­nals to­gether for unique mod shapes.

What’s also great about the semi-mod­u­lar and mod­u­lar worlds is that you’re not just re­stricted to us­ing a ded­i­cated LFO; you can take any os­cil­la­tor sig­nal’s out­put and use it to mod­u­late any other sig­nal with a CV in­put. Some os­cil­la­tors can be tuned so low they be­come LFOs in them­selves, but the real fun starts when you mod­u­late other pa­ram­e­ters with os­cil­la­tors for au­dio-rate side­band ef­fects. Us­ing an au­dio-rate os­cil­la­tor to wob­ble the pitch of another au­di­ble os­cil­la­tor is rudi­men­tary FM syn­the­sis, but un­like the idio­syn­cratic FM-synth world of op­er­a­tors and car­ri­ers, your pur­pose­ful patch­ing will again guide your process – and you can mod­u­late pretty much any­thing us­ing an au­dio-rate source.

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