Quick read: Three ambience parameters can share one tempo: delay time, reverb predelay, and modulation rate. Time-based values use milliseconds = 60000 ÷ BPM × note division; modulation uses BPM ÷ 60 ÷ beats-per-cycle for hertz. Give delay an audible division (dotted-eighth), predelay a tiny one (a 32nd note), and modulation a slow one (one cycle per bar). The surprise is that slower modulation sync sounds tighter, not looser. On Helix and Quad Cortex, delay and modulation take note values directly; predelay is usually a millisecond field, so compute and type it.
Two earlier pieces locked single ambience parameters to tempo: the one-tempo-grid delay put the delay on a dotted-eighth, and subtracting predelay from decay tuned the reverb tail to clear before the next chord. This is the version with a third block on the same grid: modulation. When the delay's repeats, the reverb's entry, and the modulation's sweep all come off one BPM, the ambient bed stops being three separate effects and starts moving like one connected space.
Two Formulas, Three Blocks
Everything here comes from two conversions. The first covers anything measured in time — delay, predelay:
Milliseconds = (60000 ÷ BPM) × note division
where a quarter note is 1, a dotted-eighth is 0.75, an eighth is 0.5, a 16th is 0.25, and a 32nd is 0.125.
Modulation is the odd one out, because it's a rate, not a time. An LFO is described in hertz — cycles per second — so it gets its own conversion:
Rate (Hz) = (BPM ÷ 60) ÷ beats per LFO cycle
One cycle per bar of 4/4 means four beats per cycle. One cycle per two bars means eight. The bigger the number of beats per cycle, the slower and more glacial the sweep.
That's the whole toolkit. Three blocks, two formulas, one tempo feeding all of them.
What Division Each Block Wants
Syncing isn't the same as picking the same note value for everything. Each block has a job, and the right division follows the job.
- Delay — an audible division. This is the one the listener consciously hears as rhythm. A dotted-eighth gives the off-grid pull that built U2's delay sound; a straight quarter gives a steady call-and-response. You want this one to be obvious.
- Predelay — the smallest division. Predelay is the gap before the reverb starts. Too long and it becomes a second echo; too short and the reverb smears into the pick attack. A 32nd note keeps the reverb sitting just behind the note, locked to the grid but felt as part of the note rather than separate from it.
- Modulation — a slow division. This is the bed underneath. One LFO cycle per bar, or per two bars, makes the chorus or tremolo breathe with the song. It should be felt, not counted.
A Worked Example at 84 BPM
Take a ballad at 84 BPM. Run every value through the two formulas and you get a complete, internally locked ambient rig:
| Block | Division | Formula | Value |
|---|---|---|---|
| Delay | Dotted-eighth | (60000 ÷ 84) × 0.75 | 536 ms |
| Reverb predelay | 32nd note | (60000 ÷ 84) × 0.125 | 89 ms |
| Modulation rate | One cycle / bar | (84 ÷ 60) ÷ 4 | 0.35 Hz |
Set the delay to 536 ms (or just choose "dotted-eighth" if the block syncs by note value), type 89 ms into the predelay field, and set the modulation to 0.35 Hz or to a per-bar note value. The reverb's decay you set by ear so the tail clears before the next chord change — that's the subtract-from-decay move from the companion post, and it's the one value here that's tuned to the arrangement rather than the grid.
For the chart-extraction crowd, here's the same three blocks at 120 BPM:
| Block | Division | Value at 120 BPM |
|---|---|---|
| Delay | Dotted-eighth | 375 ms |
| Reverb predelay | 32nd note | 63 ms |
| Modulation rate | One cycle / bar | 0.50 Hz |
The Part That Runs Against Instinct
The natural assumption is that to make modulation feel locked, you sync it fast — one cycle per beat, so the sweep audibly pulses with the song. In practice that does the opposite. A per-beat LFO at 84 BPM runs at 1.4 Hz, fast enough that the ear hears it as a distinct wobble sitting on top of the part, competing with the delay's rhythm for attention. Two rhythmic things, both demanding to be counted.
Slow it to one cycle per bar — 0.35 Hz — and the modulation drops below the threshold where you track it as rhythm. It becomes motion in the background, a slow tide under the notes. It's locked to the same grid, so it never drifts, but because it's slow it reads as the room breathing rather than a second metronome. The tighter-sounding setting is the slower one. That's the finding that surprises people who sync modulation for the first time: faster is louder, slower is tighter.
Setting It on Helix and Quad Cortex
Both platforms make two of the three blocks easy and leave one for the calculator.
- Delay: Set the time parameter to a tempo-synced note value (dotted-eighth) on either platform. With the global tempo set, the delay tracks any BPM automatically.
- Modulation: Most modulation blocks on both Helix and Quad Cortex let you set the rate to a tempo-synced note value rather than a fixed hertz figure. Pick the per-bar (or per-two-bar) value and it locks to tempo. If a particular block only offers hertz, run the second formula and type the number in.
- Predelay: This is the manual one. Reverb predelay is almost always a plain millisecond field on both platforms, so compute the 32nd-note value (89 ms at 84 BPM, 63 ms at 120) and enter it directly.
Set the global tempo once, derive the three values, and the entire ambient bed moves as a single organism — repeats, reverb, and sweep all pulsing off one number instead of three effects quietly disagreeing about where the beat is.
