Polyrhythm
simulator.

Explore the rhythms in your music.

Choose a music file or try the synthetic 3:4 example. The browser looks for repeating attacks in four frequency ranges, then suggests a tempo, drum parts and up to four repeating rhythm layers. Uneven patterns retain their rests on a subdivision grid. After upload, Track & detection and Rhythm & layers share one workspace. Switch views without losing playback, your loop or edits. The playback buttons, original/rhythm blend and MIDI action stay within reach while you work. Press Sound on to hear the recording and rhythm voices together.

Analysis uses up to 32 seconds at a time. You can choose another passage, correct the tempo, move the rhythm grid and adjust each layer’s timing. Drag the In and Out handles over the waveform to choose an exact loop, or drag the selection to move it. Snap edges to beats or detected attacks, or choose Free. Zoom into the waveform for close edits. The visible grid uses four beats per bar; select an attack and press Align beat here to shift the grid without changing the recording. Undo alignment restores the previous grid. Turning the loop off lets the original recording play through.

This is an experimental estimate, not instrument separation or a complete transcription. The downbeat and half-time or double-time interpretation can be ambiguous. The kick, snare and hi-hat assignments are editable suggestions based on the attacks’ spectral balance. A full mix can contain similar-sounding instruments, and changing tempos or fills may need manual correction. In the full Sound Lab, linking switches the four views to analysis of the actual output mix, including the recording. This is separate from the beat-detection estimates.

Files stay on your device, with no server upload. The current limit is 20 MB and five minutes to keep memory use bounded on phones. Analysis runs in a background worker; audio is optional and pauses when you leave the experiment.

Choose which attacks count.

Raise Attack threshold to exclude weaker detections. Pink bars show the attacks that survive; grey bars show those being rejected. The waveform previews the same selection. Apply detection rebuilds the rhythm layers using this threshold while preserving your loop and grid alignment. This replaces the current layers, so finish detection before making detailed edits.

Export drum MIDI.

Export MIDI saves the current rhythm with its tempo, note timings, drum assignments and velocities. With a track loaded, use MIDI in the shared control bar to open the export options from either view. Your selected loop is the default; you can choose one four-quarter-note cycle instead. Each active layer becomes a named track using General MIDI percussion notes. Muted layers are omitted. Import the file into a DAW and choose a drum instrument there. The MIDI file contains notes, not the uploaded music, kit samples or recorded clips; your DAW’s drum sounds can differ.

Start with a groove.

Compact groove boxes group twenty presets by Rock / metal, Cyberpunk and 808. Each loads the drum assignments, tempo, timing and accents. Song-inspired studies include We Will Rock You, Enter Sandman, Bleed, the Amen break, Planet Rock, Sexual Healing, Clear and Voodoo Ray. They are short reductions or style studies, not full-song transcriptions. About this groove explains each one.

Each polygon connects the actual note positions around the cycle. Equal timing makes regular shapes; uneven timing makes irregular shapes. The coloured bands around them divide time into equal slots. Filled segments contain hits and outlined segments are rests. The wider band belongs to the selected layer. Tap its segments or the larger step buttons to edit the pattern. A note sounds when the steady clock enters its segment. Select a layer to highlight it, then tap a step to add or remove a note. The matching step buttons follow the same clock as the circular view. Quieter hits pulse more softly. Changing the grid preserves existing notes; grids that cannot represent them exactly are unavailable. Even hits redistributes the notes equally.

Make your own kit.

Switch to Drum kit and assign any layer to a kick, snare, hi-hat, cymbal, tom or percussion sound. Rock / metal, 808 and cyberpunk presets use recorded drum samples while keeping your rhythms. The hybrid kits respond to velocity with changes in level and timbre, and the 808 uses recordings from the original hardware. Up to twelve layers share the same transport. Sample sources and licences.

Press Record on a layer to make a sound of your own. Allow the microphone, wait for 3, 2, 1, then capture up to four seconds. Stop early if you like. Hear previews the sound; each beat retriggers it. You can replace or delete a clip, and switch between it and a drum part. Clips stay in browser memory unless you choose Save session to include them in a local file. Reopen that file to continue another time.

Give each hit a pitch.

The pitched sequencer uses the same cycle as the drum layers. Select a layer and make it melodic, or add a pitched layer. Draw notes in the piano roll, drag them in pitch and time, or pull their right edges to change length. Notes at the same time make chords. Note snapping includes eighths, sixteenths, thirty-seconds and eighth-note triplets. The Synth view gives each layer a sine, triangle, sawtooth or square oscillator and its own attack, decay, sustain and release envelope. Note length determines when release begins. Keyboard arrows and the selected-note controls provide another way to edit. Pitches use equal temperament with A4 at 440 Hz; this interface calls MIDI note 60 C4.

DAW Mode brings the note editor, rhythm geometry, layer mixer and four measured audio views into one window. On phones, Sequence, Layers and Audio views share the same transport behind three view buttons. MIDI includes the pitched notes and durations on melodic channels, with percussion on channel 10. MIDI carries notes, not synthesizer sounds or recorded clips. Export WAV to capture the whole mix instead, including drums, synths, recorded clips and the original-track blend. The stereo 48 kHz, 16-bit file is cut to one cycle or your selected loop, up to 60 seconds. It renders locally on your device.

Keep a musical sketch.

Session saves the editable notes, layer names, kit choices, synth settings and recorded clips to a file on your device. The name and saved-file status are shared between the rhythm section, pitch section and DAW Mode. An amber dot marks unsaved edits; undoing back to the saved version clears it. Open that file to continue later. Original music files and their source loops are not included; reopening creates a standalone instrument session. Nothing is uploaded. Undo and redo cover layer and note edits, settings and recorded clips, with up to sixty recent states. Playback, original-track trimming and file selection are outside that edit history.

In DAW Mode, a compact layer rail sits beside one focused editor. Rename or duplicate a layer, compare actual onset times in the shared bar, and use mute or solo to hear relationships. The timing grid includes each layer’s offset. Click an empty drum lane to add a hit. Select a hit to inspect its beat and velocity, preview it, snap it to the grid or delete it. Drag horizontally for timing and vertically for velocity; hold Shift for unsnapped timing. Removing a hit leaves the others at their existing times. The larger selected-layer step grid provides another way to edit. Pitched lanes open the piano roll.

Draw adds notes; Select lets you drag a box around a phrase. Shift-click adds or removes notes from the selection. Move or resize the selected group together, preserving its internal spacing and pitch intervals. Note tools can act on any selection or all notes. The piano keys audition pitches without adding notes. Scale guides highlight major, natural minor and minor-pentatonic pitches without changing the music. Fit scale and Quantise are explicit edits. Quantise moves note starts to the chosen subdivision while preserving lengths; group transposition preserves intervals at the MIDI range limits. Pull a velocity pin to adjust the selected notes together while keeping their accent differences. Numeric pitch, beat and length inspect the last selected note. Keyboard arrows move the selection; Shift with up or down moves an octave. Ctrl or Command A selects all and D duplicates where space permits.

Six original synth starting sounds and four short note patterns are included. DAW Mode also has its own groove browser: drum patterns can be replaced while your synth layers stay intact, with an option to keep the current tempo. Renaming layers leaves playback uninterrupted. Waveform and filter edits update sounding synth voices; velocity and envelope changes apply to subsequent triggers. The optional second-order low-pass filter has a logarithmic cutoff control and linear Q resonance. Its graph shows the digital filter’s magnitude response at the displayed sample rate, not the entire instrument’s spectrum. The four audio plots show the actual combined output instead. The same synth, envelope and filter implementation is used for playback and WAV rendering.

What is a polyrhythm?

A polyrhythm combines contrasting rhythmic divisions at the same time. In 3 against 2, one layer plays three evenly spaced beats while another plays two in the same duration. Both meet again at the start of the next cycle.

Here, each shape represents hits per shared cycle. A dot plays once and a line has two endpoints. With even spacing, three hits form an equilateral triangle and four form a square. Four uneven hits still form a four-sided polygon, but it need not be a square. The surrounding time segments show the spaces between the notes. Adding sides adds beats. The ratios describe divisions, not time signatures. A 2:4 pattern is a simple subdivision rather than the contrasting relationship of 3:4.

Try three against four.

1. Set two layers to three and four beats, then press Play.
2. Switch Sound on to hear the two percussion voices.
3. Follow the triangle and square. Listen for the point where their beats coincide.
4. Slow the tempo, then add a fifth-beat layer.