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SEM family: the OB-8's Page 2 LFO functions #9

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opened 2026-10-12 02:40:06 +00:00 by bcox · 1 comment
bcox commented 2026-10-12 02:40:06 +00:00
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The OB-X8 carries the OB-8's "Page 2" functions for its LFO, none of which mini-SEM has. As recalled, with no manual read:

  • A delay and a fade-in on the LFO's depth.
  • The LFO's rate following the keyboard.
  • Phase offsets between the voices' LFOs (90 and 180 degrees), for spreading pulse-width modulation across the voices.
  • A quantized LFO, moving in steps.

Read the OB-X8's manual first: this list is from memory and is the part of the OB-X8 I am least sure of.

Notes for whoever takes it up:

  • engine/modulation_generator.h, the Korgs' and the Juno's, already has a delay and a fade; instruments/sem/lfo.h has neither.
  • Each sound now has two LFOs (lfo.* and lfo2.*), and lfo.per_voice arranges both. Decide which of these functions each LFO gets.
  • With lfo.per_voice on, each voice's LFO already starts at its own place in the cycle; the hardware's phase switch is a different, fixed spread.
  • Related: #8, LFO shapes.
The OB-X8 carries the OB-8's "Page 2" functions for its LFO, none of which mini-SEM has. As recalled, with no manual read: - A delay and a fade-in on the LFO's depth. - The LFO's rate following the keyboard. - Phase offsets between the voices' LFOs (90 and 180 degrees), for spreading pulse-width modulation across the voices. - A quantized LFO, moving in steps. Read the OB-X8's manual first: this list is from memory and is the part of the OB-X8 I am least sure of. Notes for whoever takes it up: - `engine/modulation_generator.h`, the Korgs' and the Juno's, already has a delay and a fade; `instruments/sem/lfo.h` has neither. - Each sound now has two LFOs (`lfo.*` and `lfo2.*`), and `lfo.per_voice` arranges both. Decide which of these functions each LFO gets. - With `lfo.per_voice` on, each voice's LFO already starts at its own place in the cycle; the hardware's phase switch is a different, fixed spread. - Related: #8, LFO shapes.
bcox commented 2026-10-15 01:13:04 +00:00
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Three of these are in, in 05e6833 and 49f192f, for both of each sound's LFOs in mini-SEM:

  • lfo.delay and lfo.fade (and lfo2.), 0 to 10 s each: after a voice is given a key, legato or not, the patch's LFO depths are silent for the delay and then come in over the fade, in a straight line. The lever and pressure are heard at once.
  • lfo.track (and lfo2.), 0 to 1: LFO TRACK, the rate following the key about middle C, 1 an octave to the octave. With lfo.per_voice off the one LFO follows the latest key struck.

Where they come from: the OB-8's owner's manual (first edition, November 1982), which has all of these on its Page 2. The OB-X8 was only recalled as carrying them, and no OB-X8 manual has been read, so this ticket is retitled for the OB-8.

Still open here, from the OB-8's Page 2:

  • A delay and attack for each of the two LFO depths apart (here one of each for all of an LFO's depths).
  • Quantize: the LFO moving in steps.
  • Phase: 90 or 180 degrees between the two halves' voices.
  • The triggered waveform and its trigger point.
  • Invert, for each depth.
  • LFO ENV MOD: the rate under an envelope.
Three of these are in, in 05e6833 and 49f192f, for both of each sound's LFOs in mini-SEM: - `lfo.delay` and `lfo.fade` (and `lfo2.`), 0 to 10 s each: after a voice is given a key, legato or not, the patch's LFO depths are silent for the delay and then come in over the fade, in a straight line. The lever and pressure are heard at once. - `lfo.track` (and `lfo2.`), 0 to 1: LFO TRACK, the rate following the key about middle C, 1 an octave to the octave. With `lfo.per_voice` off the one LFO follows the latest key struck. **Where they come from:** the OB-8's owner's manual (first edition, November 1982), which has all of these on its Page 2. The OB-X8 was only recalled as carrying them, and no OB-X8 manual has been read, so this ticket is retitled for the OB-8. **Still open here**, from the OB-8's Page 2: - A delay and attack for each of the two LFO depths apart (here one of each for all of an LFO's depths). - Quantize: the LFO moving in steps. - Phase: 90 or 180 degrees between the two halves' voices. - The triggered waveform and its trigger point. - Invert, for each depth. - LFO ENV MOD: the rate under an envelope.
bcox changed title from SEM family: the OB-X8's Page 2 LFO functions to SEM family: the OB-8's Page 2 LFO functions 2026-10-15 01:13:04 +00:00
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