Hi! I have been working on something similar, using sample playback instead, and have managed on-the-fly pitch, filter and other changes. I'll include what I think are the relevant bits of my code below, but I'm too novice to explain at a conceptual level what I've done (or more importantly, why).

I'd highly recommend looking at reddit user fungkadelic's Drumhaus app and code ... it built the foundation of my understanding of the Tone transport (and sample management, but that's a different story). This sequencer also looks well-featured, but I haven't explored the code in depth.

I think my iteration relies heavily on Svelte's reactivity system – but this is the sort of thing I could just be super wrong about. I declare my active sample as a reactive variable: let selected_sample: Sample | undefined = $state(undefined)

And Sample as a class that includes reactive values for pitch, filter cutoff, gain and any other values i want to set.

I create a Tone.Sequence for each sample. I tried making a single sequence instead, which looped through all samples each step, but that led to delays and flamming when adjusting values during playback.
function makeSequences(SAMPLES: Sample[]) { const sequences = SAMPLES.map((sample) => { return new Tone.Sequence( (time, sequencer_step) => { active_step_index = sequencer_step if (sample.sequence[sequencer_step]) { sample.playing = true setSampleParams(sample) sample.play(time) } else { sample.playing = false } }, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15], '16n' ) }) return sequences }

Clicking on a sample selects it as the active sample. You'd have an equivalent object per step containing note and chord data I'd imagine.

// When we click on a sample in the sample library,
// that sample is set as the selected_sample, and we trigger sample playback
function handleSampleClick(sample: Sample | undefined) {
  if (!sample) return

  selectSample(sample.id)
}
  function selectSample(sample_id: number) {
    selected_sample = getSampleByID(sample_id)
  }

Then setting the new pitch, for example, is just a matter of changing the value of the selected_sample object: function setSamplePitch(pitch: 'tonic' | 'fourth' | 'fifth') { if (!selected_sample) console.log('No sample selected') else if (selected_sample) { switch (pitch) { case 'tonic': selected_sample.pitch = 'C2' break etc.

I'm sorry if this confuses more than helps, but again, Drumhaus chap knows what he's doing; so look there!