LFO (Low Frequency Oscillator) opcodes are part of the Modulation category of opcodes. They are used to create effects such as pitch vibrato (when modulating pitch), tremolo (when modulating volume) and filter wobble (when modulating filter cutoff)
LFOs are triggered by note-on events for the specified region, which means there are no free-running LFOs in the SFZ spec. If a free-running LFO is needed, for example to apply one slow pitch vibrato wave to a series of rapidly plucked oud notes, that will need to use an external modulation source outside the SFZ player - in other words, perhaps in a DAW that the SFZ player is being used in as a plugin.
SFZ 1 LFOs
3 LFO destinations in SFZ 1 standard:
- amplfo (amplitude)
- fillfo (filter)
- pitchlfo (pitch)
Assignable LFOs (SFZ 2)
Much like the Flex EG, these newer LFO can target almost any tone-defining parameter:
Assignable LFO Destinations
These destinations are added as a suffix to ‘lfoN_’. For example, lfo01_pitch=100 makes LFO 01 affect pitch with a max depth of 100 cents, and lfo03_freq_lfo01_oncc117=1.3 would make LFO 03 add up to 1.3 Hertz to the frequency of LFO 01, with the amount modulated by MIDI CC 117.