Tempo Map Builder

Mouse

• Click an empty spot on the graph to create a tempo node at that bar and BPM — keep the button held to drag it straight away.
• Drag a node to change its bar (horizontal) and its BPM (vertical). The readouts update live while you drag.
• Click a node, or a row in the node list, to select it for precise editing.

Touch

• Tap empty graph space to add a node; press and drag a node to move it. Node grab zones are much larger than the drawn dot, so you do not have to be accurate.
• Page scrolling is suppressed over the graph so drags never turn into scrolls.

Keyboard

• Space start / stop playback (works anywhere in the widget except inside a text or slider field). During the Follow the curve challenge Space is your tap instead.
• Tab steps onto each node in turn. With a node focused:
• ↑ / ↓ nudge its BPM by 1 (hold Shift for 5).
• ← / → move it one bar earlier / later.
• J cycles the segment leaving that node through Ramp → Ease in → Ease out → S-curve → Jump.
• Delete or Backspace removes the node (the bar 1 node is pinned and cannot be removed).
• Arrow keys are never hijacked while a number field or slider has focus.

Segment shapes

• Every node carries the shape of the segment leaving it. Whatever the shape, the tempo is read beat by beat: the beat starting at position p lasts 60 / B(p) seconds, and those durations are added up. That is why a curve is not the same as its average tempo.
• Ramp (straight slope) — linear. B = B0 + (B1 − B0) × u, where u goes 0 → 1 across the segment. The plain accelerando or ritardando.
• Ease in (flat, then falling away) — B0 + (B1 − B0) × u². The tempo barely moves at first and does most of its travelling at the end. This is the honest shape of a real closing ritardando: hold the tempo, then broaden hard into the last bar.
• Ease out (steep, then levelling) — B0 + (B1 − B0) × u(2 − u). Most of the change happens immediately, then it settles. Use it for a sudden lift that then cruises, or for a cedendo that gives way at once.
• S-curve (smoothstep) — B0 + (B1 − B0) × u²(3 − 2u). Gentle at both ends, quickest in the middle. The most natural-sounding tempo change of the four; a conductor's default gesture.
• Jump (dashed, flat then vertical) — the tempo holds steady, then switches instantly at the next node. Your sudden Meno mosso or Doppio movimento.
• After the last node the tempo is held flat to the end of the piece (dotted grey tail). The node at bar 1 is pinned: its BPM is editable, its bar is not.

Presets

• Rit. into final chord — 16 bars at 96, dead steady until bar 13, then an ease-in ritardando down to 52 for the last chord.
• Accelerando build — 24 bars. Four bars in tempo, then a long ease-in climb from 88 to 152 that keeps gathering; the kind of build that sits under a rising string line.
• Rubato phrase — 8 bars. Push forward off the downbeat (ease out to 90), pull back through the middle with an S-curve to 66, then give the time back and settle at 72. Time stolen, time repaid.
• Train accelerando — 32 bars of 2/4. A locomotive from 42 to 176: ease-in from standstill, a straight ramp once it has traction, then ease-out as it reaches line speed.
• Film cue with hits — 20 bars plus three pinned hit points, so you can see the hit-point report working straight away.

Hit points

• Pin a bar to a target time — bar 9 must land at 15.0 s — and the widget reports where that bar actually lands under the current curve and by how much you are out. Markers appear on the graph, green when you are inside 0.10 s.
• Fit map on a hit-point row scales every node's BPM by exactly the ratio it needs. Because every beat lasts 60 / BPM, scaling all tempos by k divides the whole map's duration by k — so the fit is exact apart from rounding BPMs to whole numbers. It moves the shape of the curve not at all, only its height.
• Fitting one hit point moves all the others, exactly as it does in a real session. Fit the latest one first, then adjust individual nodes to rescue the earlier ones.

Follow the curve (challenge)

• Press Follow the curve. You get a one-bar count-in on a woodier click, then the map plays and you tap every beat on the big pad (or with Space).
• Guide sets the difficulty: Every beat clicks all the way through; Downbeats only gives you bar 1 and nothing else; Silent gives you the count-in and then leaves you alone to carry the accelerando or ritardando by feel.
• Each tap is marked on the graph, hugging the tempo curve: a tick above the line means you were early (rushing), below means late (dragging). Longer tick, bigger miss.
• Scoring removes your average offset first, so a consistent 40 ms lag does not cost you — what is graded is whether you tracked the change. Missed beats score zero, so tap all the way to the end.
• The report tells you your average offset, your steadiness, your worst moment, and which gesture you rushed or dragged: “you rushed the ritardando in bars 13–16”. Editing is locked while the challenge runs so the target cannot move under you.

Readouts

• Map length is the true integrated duration, not bars × average tempo. Tempo range is the lowest and highest BPM the curve actually reaches.
• Every node row shows how long its segment lasts in seconds, and the selected-node hint gives the same figure for the segment you are editing. Drag a node and all of it updates live.

Tips

• Hear the difference between the shapes: load Rit. into final chord, play it, then set the bar-13 segment to Ramp and play it again. Same endpoints, same bars, different length and a very different gesture.
• A classic ritardando is only the last 2–4 bars: put a node where the slowing starts and another at the final bar, set Ease in, and drop the BPM by roughly a third.
• To audition one gesture in isolation, drop Total bars down so playback covers just that stretch — the map length readout tells you exactly how long it takes.