Create is the instrument. Everything it plays is pulled into the key detected over in Mix, so whatever you press is already in tune with the tracks you are mixing; with no tracks loaded it sits in C major.

If you cannot hear anything

Opened in a side panel rather than in its own tab, Ducker is running inside a frame, and a frame is not allowed to make a sound until somebody has clicked inside it. Sometimes it is not allowed at all, if the frame was never given permission to play audio in the first place. Worse, the sound engine can stay stuck in that blocked state for as long as the page is open, which looks exactly like a keyboard that has stopped working.

So the engine is built on your first click rather than when the page loads, and if it is still not running a moment later it is thrown away and built again on your next click. When even that fails, a bar appears at the bottom of the page with a button to try once more. If that does not work either, nothing on the page can fix it: open Ducker in its own tab and the sound comes back.

The transport

Every transport in Ducker is the same two buttons: a play, and its own pause beside it. The play button never turns into a pause. It goes green while its thing is running and red while it is parked, and the pause beside it stays greyed out until there is actually something to stop. That is true in the Sound Lab, on Record, on Transpose, on the Bridge Undertone and on the Master page, so once you know one of them you know all of them. The spacebar does the same as pressing play or pause.

Pause really does mean silence, not a fade with something still humming underneath it. Whatever was running stops: notes, echoes, reverb tails, a piece playing itself, the arrangement. Press play again and it starts cleanly from where you left it.

Sound Lab

Built so you do not need to know any synth jargon. Everything it plays comes from your tracks' key, so anything you press is already in tune with your music.

What the keys play: Chords gives you a whole chord per key, Notes a single note, Drums the kit, Risers and Hits the transition sounds. With Chords or Notes you also choose between Synth, Piano and Guitar.
Piano: A struck-string tone rather than a sample, and the same one the Circle of Fifths uses when you click a key on it. The knobs shape the synth, so they sit out while Piano is selected.
Why it does not decay in a straight line: A real note does not fade at one rate, and a single decay is most of what makes a synthesised string sound synthesised. The two or three strings of a unison start in phase and dump their energy into the bridge quickly, then drift out of phase and hand it back and forth between themselves for far longer. So a piano note falls away fast for a moment, bends, and then hangs on: measured here, a grand loses about 46 dB a second at first and around 19 dB a second after the knee. Your ear uses that bend to tell a piano from an organ with a decay on it. The upright, having two strings rather than three and a short frame, has a much shallower knee, which is part of why it sounds blunter.
Letting go of a key: A damper is a strip of felt landing on a moving string, not a mute button, so lifting a key does three things rather than one. The felt takes time to stop the string, and longer on a heavy bass string than a light treble one. What it cannot stop at all is the soundboard, which goes on ringing for a moment after the string has been silenced. And the top of a real piano has no dampers fitted, so those notes simply ring until they die on their own. All three are why a piano sounds like an instrument rather than a recording being cut off, so all three are here.
Concert grand, upright, bright: Three instruments, not one turned three ways. What separates real pianos is how sharp the partials go (short stiff strings are more inharmonic), which partial is loudest, how far apart the unison strings are tuned, and the body resonances. Grand is long, soft-hammered and even, with three strings barely apart. Upright is short and stiff: its second partial is louder than its fundamental, which is what "boxy" means, with a hard mid resonance and the top rolled off. Bright is a hard hammer with the lid up and the unisons wide enough to shimmer.
Guitar: A plucked string built the same way the pianos are, so a guitar chord and a piano chord sit at the same level and in the same room. The one thing it does differently is the strum: a chord rolls out note by note rather than landing all at once, because that is what a hand does. As with the pianos, the synth knobs sit out while a guitar is selected.
Steel acoustic, nylon, electric: Three instruments rather than one with the tone turned three ways. Nylon has almost nothing above the fourth partial and a fat air resonance under 100 Hz, which is why a classical guitar sounds round and close. Steel strings are stiffer, so their partials go sharp, and the dreadnought body adds a presence peak: that is the jangle. The electric has no box at all, so it rings roughly three times longer than the other two, with the speaker rolling off everything above 5 kHz and just enough amp to thicken it.
Where the string is picked: The single most audible thing missing from most synthesised guitars. Where a string is set going decides which partials it gets at all: pluck it a sixth of the way along and there is no sixth partial, because that point is a node of it. That comb of missing partials is why picking by the bridge sounds nasal and picking over the soundhole sounds round. Each guitar here is picked where its player would pick it, so the steel has a hole in its spectrum around the sixth partial, the nylon around the fourth, and the electric is picked so close to the bridge that its first notch falls above anything the model carries, which is exactly why it reads as flat and bright.
What else makes the two acoustics sound like wood: Their upper partials die away far faster than the fundamental, which is most of what separates wood from metal. They have four or five box resonances rather than one generic peak. The body answers the pluck with a short low thud of its own, quite separate from anything the string is doing, which is the air inside the instrument being pushed. And every note starts a fraction sharp and settles, because a string set going hard is momentarily under more tension than it will be a moment later. The noise at the front of all three is a pick rather than a hammer, so it is far shorter and much brighter than any of the pianos.
Drums: Twelve pieces laid across the keyboard in playing order, kick through crash, with the names printed on the keys and the computer key that fires each one printed above.
Shaping the kit: With Drums selected, Sound controls swaps the synth over for the kit. Depth tunes every drum up or down in semitones, and twelve down really is an octave down. Ring is how long the head is left to sound, from dead to boomy. Room opens or closes the top of the whole kit. Snap is how hard the stick lands, which is mostly the beater click and the wire crack.
Hold to sustain: Turn it on and the kick, snare, rim and toms stop being one-shots: they decay to a floor and stay there for as long as the key is down, then damp when you let go. Not a drum kit any more, but exactly what you want when you are building a bed out of a floor tom. A held drum recorded onto the timeline remembers how long you held it.
Kits: Four different instruments, not one instrument at four sizes. Each kit builds its kick and snare a different way and then plays through its own bus. Jazz is a felt beater and a brushed snare, mostly wires and swish, with the cymbals carrying the time. Funk is a clicky tuned kick and a gated crack of a snare through a driven bus. Rock is a long pitched kick and a fat snare with a room tail behind it, saturated. Orchestral is a timpani and a field drum: dark, slow, no dirt at all, the snare a rattle of grains rather than one hit. Pick one in the drum machine and it applies to the pads too.
Wah and slide: Both belong to the built-in pieces rather than to the keyboard, but they are what makes those two parts sound like themselves. A wah is a narrow resonant band rocking up and down across the strings, which is why it sounds like a vowel rather than like a tone control being turned, and why some of the dry signal always has to get past it. A slide arrives from below rather than starting in tune: the note bends up into place over about a sixth of a second, which is the whole sound of a bottleneck.
Arpeggiator: Rolls one note at a time for as long as you hold a key, following your track's detected tempo. In Chords it walks the chord under your finger; in Notes it walks that note through its fifth, octave and twelfth, which is how you get an ostinato out of a single key. It works on a voice you have taken from Play along too, so you can arpeggiate any of the pieces.
The board: One panel rather than a Beginner and a Pro mode, grouped the way a synth is: two oscillators, a filter, an envelope with its shape drawn beside the knobs, an LFO, and the space section. Every control has a plain-English readout under it. There is a full walk-through of each one in Every control on the synth below.
Pitch and mod wheels: Under your left hand, where they are on a real keyboard. Pitch bends whatever is sounding by up to two semitones and springs back when you let go; mod opens a vibrato and stays where you leave it. Both reach notes that are already playing.
Character and shaping: Pick a character first: warm pad, bright pluck, dreamy keys, glassy bells, Deep bass (an almost pure sub, round and clean) or Giallo bass (the Goblin Suspiria register: a fat saw at 65 Hz with a sub underneath it, a low resonant filter that snaps open on every note, and a slap of tape echo). The knobs then shape it in plain terms: Tone is how much top end, Body how thick, Bite how resonant, Attack how quickly it arrives, Tail how long it rings, Movement how much it wobbles, Space how much room it sits in, Length how long risers and hits last, Register how high or low.
Transition sounds: Pick Risers or Hits and every key fires one tuned to that note. Hold a riser key and it keeps climbing, sustains as long as you hold it, then cuts off hard the moment you release, so you can time it to a drop. Hits are one-shots. Tonal is built from your key, airy is noise-based, and Full is the finished article: a noise sweep, a detuned chord climbing an octave, a sub carrying the weight underneath, a shimmer on top, and a tremolo that accelerates from a slow pulse to a flutter as it goes. It occupies the whole band rather than one corner of it, so it works on its own instead of needing three stacked. The Full hit is the matching landing: a swell arriving just before the impact, a chord, a noise crash and a sub drop.
Playing it yourself: Use the letter keys printed on the keyboard. With only notes in key on, each letter is one step up the scale rather than a chromatic semitone, so you cannot land on a wrong note.
Record: Keeps what you played as the notes themselves rather than as a recording of them, so the exported file is played back fresh and comes out cleaner than what you heard live.

Every control on the synth

Beginner and Pro used to be the same synth twice, which meant learning the app before learning the instrument. There is one board now, grouped the way a synth panel actually is, and every parameter is a knob with a plain-English readout under it. Here is what each one does.

Oscillator 1 · Wave: The raw shape the note starts as. Saw is bright and buzzy and is the basis of most synth strings, brass and basses; square is hollow and woody; triangle is soft with a little edge; sine is a pure tone with nothing above the fundamental.
Oscillator 1 · Octave: Moves the whole instrument up or down by octaves without changing anything else. Two down for a bass part, one or two up for a lead that has to sit over a mix.
Oscillator 1 · Voices: How many copies of the oscillator play at once, each detuned slightly against the others. One voice is clean and thin; seven is the classic supersaw. More voices cost nothing but thickness.
Oscillator 1 · Spread: How far apart those copies are tuned. A little makes the sound wide and alive; a lot makes it seasick and out of tune, which is sometimes exactly what you want.
Oscillator 2 · Wave: A second oscillator with its own shape, or Off to run on one. Two different shapes layered is where most of a patch's character comes from.
Oscillator 2 · Pitch: How far oscillator 2 sits from oscillator 1, in semitones. Minus twelve adds an octave underneath for weight; plus seven adds a fifth for a hollow, organ-like tone; plus nineteen adds shimmer.
Oscillator 2 · Blend: The balance between the two oscillators. All the way down is oscillator 1 on its own; halfway is both equally.
Oscillator 2 · Glide: How long the pitch takes to slide from one note to the next instead of jumping. Off for anything rhythmic; a hundred milliseconds or so for a lead that slurs between notes.
Filter · Type: Which part of the sound the filter keeps. Low pass keeps the body and removes the top, which is the everyday choice. High pass keeps the top and removes the body, which is how you make something sit above a busy mix. Band pass keeps a slice in the middle and throws away both ends.
Filter · Cutoff: Where the filter starts working. On a low pass, turning it down makes the sound darker and further away; turning it up makes it brighter and closer. It is the single most-used control on any synth.
Filter · Resonance: How much the filter emphasises the frequencies right at the cutoff. A little adds focus and character; a lot makes it whistle and squelch, and is what makes an acid bass sound like an acid bass.
Filter · Env amount: How far the envelope pushes the cutoff each time you press a key. Positive means the filter snaps open on the attack and falls back, which is what makes a note sound plucked. Negative closes it instead.
Filter · Drive: How hard the signal is pushed before the filter. Clean at zero; warmer and thicker in the middle; broken and buzzing at the top. Drive adds harmonics, so it also makes a sound brighter.
Envelope · Attack: How long the note takes to reach full volume. Instant for plucks, drums and anything rhythmic; slow for pads that swell in.
Envelope · Decay: How long it takes to fall from full volume down to the sustain level once the attack is over.
Envelope · Sustain: The level the note holds at for as long as the key is down. At zero the note always dies after the decay, however long you hold it, which is a pluck. At a hundred it holds at full volume, which is an organ.
Envelope · Release: How long the note takes to fade once you let go. Short is tight and rhythmic; long leaves a tail that overlaps the next note.
Envelope · FX length: Only live for Risers and Hits: how long the transition sound takes to climb or ring. It sits out for the ordinary voices.
The envelope picture: The four envelope knobs drawn as the shape they make. The dotted horizontal line is the sustain level and the vertical one is where you let go of the key, so you can see what each knob is doing rather than holding four numbers in your head.
Motion · LFO goes to: What the slow oscillator wobbles. Filter is the classic sweep; pitch is vibrato; volume is tremolo.
Motion · Rate: How fast that wobble is, from a slow drift under a pad to a flutter fast enough to be part of the tone.
Motion · Depth: How far it wobbles. Zero switches the LFO off entirely.
Space · Reverb: How much of the sound is fed into a room. Dry is the raw synth; hall puts it at the back of a big space.
Space · Delay: The gap between the echoes, in milliseconds. Short gaps thicken a sound; long ones read as separate repeats.
Space · Feedback: How much of each echo is fed back in to make the next one. Low gives a slap; high gives a trail that runs for bars.
Space · Echo: How loud the echoes are against the dry sound.
Hovering a dial: Rest on any knob for a moment and it tells you what it does, which is the same list as this one but where you are working rather than over here.
Pitch wheel: Bends everything currently sounding by up to two semitones and springs back to centre the moment you let go, exactly like the wheel on a hardware synth. It reaches notes that are already playing, not just the next one.
Mod wheel: Opens a vibrato onto whatever is sounding and stays where you leave it. It is independent of the LFO section, so you can add movement by hand over a patch that has none.
Only notes in key: Dims the keys that would clash with your tracks' key and snaps your computer keyboard to the scale, so each letter is one step up rather than a chromatic semitone. Turn it off for the full chromatic keyboard.

Play along

Five short pieces that play themselves and light the pads as they go. While one plays the pads become that piece's own keyboard: sixteen chromatic steps from its home note, so the tune walks visibly across the grid. Add to timeline drops it into Record as one track per part, where you can mute a part and play it yourself.

Use its sound keeps a piece's voice on the keyboard after it stops: the same character, the same tempo, and the pads laid over the register that part actually lives in, so you can wander off from it rather than only play along with it. A piece with more than one voice offers each separately: Giallo hands you either the music-box lead up top or the bass underneath it, tuned to its own octave. Back to your key above the pads puts them back on your own tracks' scale.

Für Elise is Beethoven's, out of copyright and here as written. The other three are original patterns written in the style of the records they name rather than transcriptions of them. A melody is the part of a song copyright actually protects, and transposing one or changing a note in it does not make it a different melody, so those are ours. Almost everything else about how a record sounds is not the protected part: the tempo, the key, the groove, the instruments, the chord vamp, how much space is left between the parts. Those are copied as closely as they can be heard.

Baggy stomp is 1990 Madchester, and it is a stomp rather than a shuffle: straight sixteenths, the weight carried by the kick and a low tom figure instead of by the hats, shaker where a hat would be, an upright stabbing rather than vamping, a bass riff that never lets up, and a wah guitar scratching muted sixteenths on the offbeats. That scratching is the part you hear as "the guitar" long before you hear any notes in it.

Record

A small multitrack. Hit Record, it counts in a bar, and everything you play from there lands as a clip on whichever track is armed, at the point on the timeline where you started. Press Record again to keep it. Add a track and go again to stack the next part on top.

Tracks and clips: Each track has its own fader, arm button, mute and solo, exactly like a channel over on Master. Clips show their notes as little ticks, positioned by pitch, so you can read a part at a glance. Drag a clip along its lane to move it, snapping to whatever quantise is set to, and double-click one to remove it.
Mute and solo: M takes one track out. S does the opposite: it takes everything else out, so you can hear one part on its own without touching the others. Solo more than one and you hear that group. Mute always wins on the track it is set on, and both apply to the export as well as to playback, so what you hear is what you get.
Changing what a track plays: The dropdown under each track's name is the instrument it is playing. Change it and the notes stay exactly where they are, played by something else: a part recorded on a synth becomes a piano or a guitar, and a drum part moves to a different kit. This is how you try an idea four ways without playing it four times.
Why it stays smooth: A part on the timeline is a fixed list of notes that will sound the same every time it plays, so it is worked out once, quietly in the background, and after that it plays as a single piece of audio however often it repeats. That matters more than it sounds: one grand piano note is over forty separate pieces of machinery, a piano note rings for four or five seconds, and at eighth notes that is fifteen of them overlapping at once. Four parts came to eight thousand, all built in one go at the start of every pass, and putting them together turned out to take longer than playing them did. That is what made the sound break up, the playhead drift and the export never arrive. Now the work depends on how many different parts there are rather than on how long the song is or how many times it goes round, and a part still being prepared plays note by note in the meantime, so nothing ever waits.
Zoom and moving about: + and − stretch the timeline out and bring it back, with 0 to fit the window again; there are buttons above the timeline for the same thing. A stretched timeline scrolls sideways and follows the playhead while it runs. ← and → move the playhead a beat at a time, or a whole bar with Shift held; ↑ and ↓ jump between clip edges, and Home and End go to the two ends.
Snap: With Snap on, a part you drag pulls onto whichever is nearest: a bar line, the edge of another clip, or the playhead. That covers the three things you actually want: on the beat, butted up against what is already there, or lined up with where you are working. It only pulls when you are genuinely close, and the distance is measured on screen rather than in bars, so zooming in gives you finer control instead of a stickier grid. Turn it off and parts go exactly where you drop them.
Playing along with a part: Click a clip, or a track's name, and the keyboard picks up that part's sound: the same piano, the same guitar, the same synth character it was played with, down to the settings saved on the clip rather than a stock preset. Click a beat and you get its kit on the pads. So adding to something you have already put down, an octave lower or in another key or whatever you fancy, costs one click and then playing. The Keyboard follows tick on the record bar turns it off if you would rather the keyboard stayed exactly where you set it.; Selecting a part also shows you what it is made of: every key it uses is marked, and the pads move to the register that part actually lives in so a bass line marks pads rather than marking nothing off the bottom of the keyboard. Press play and those keys light in time as the part goes past, the same way Play along lights them. It is the quickest way to see what you played, and to find the notes again so you can add to them.
Moving a part to another key: Drag a clip up or down and it changes pitch without moving in time at all. Every note shifts by the same number of semitones, so the shape of the part is kept exactly. Eleven pixels is a semitone, twelve semitones is an octave, and the badge on the clip shows where you are as you drag. Sideways still means move, and which of the two you get is decided by whichever way your hand goes first, so neither can happen by accident. Drums do not move, because there is no such thing as a snare drum a fifth higher. Undo puts it back.
Put it on the beat: What you actually played is kept alongside whatever the quantise setting did to it, so nothing is lost by recording loosely and this button always has the performance to work from. Click the clip you want and press it: every note moves to the nearest step of the song's grid, the clip moves to the nearest bar line, and its length rounds out to whole bars so it loops cleanly. The grid is the song's rather than the clip's, which matters whenever a take started somewhere other than on a bar. Undo puts it back if you preferred it loose.
Why it has its own grid: The quantise setting on the record bar is for capture: a sixteenth by default, so a take does not drift while you play it. A sixteenth is far too fine to rescue playing that is genuinely loose, though, because it moves each note to the nearest sixteenth, and once you are more than half a sixteenth out that is the wrong one. Eight notes meant for the beat can end up sitting on eight offbeats, every one of them legitimately on the grid. So this button has its own grid, an eighth by default, and it works from what you played rather than from the already-snapped copy. Choose a quarter for something very loose and a sixteenth for something you played tightly and only want tidied.
When it cannot know what you meant: Snapping can only move a note to the nearest step, so if a note is more than half a step out there is no way to tell which step it was aiming for. When that happens it says so rather than reporting a clean success, and suggests undoing and trying a coarser grid. A part that Ducker wrote itself, or one loaded from Play along, was written on the grid to begin with and will tell you there is nothing to tighten.
BPM: The tempo box moves the whole arrangement, not just the grid. Everything already down is stretched or compressed by the same amount, so the parts stay lined up with each other and with the bars. Loading a piece from Play along sets the tempo to that piece's, and takes whatever is already on the timeline with it.
Cut, trim and duplicate: Click a clip to select it. Cut splits it in two at the playhead. Trim ◂ and Trim ▸ pull the front or the end back to the playhead, or grab a clip's edge and drag it. Trimming narrows the clip's window rather than deleting anything, so dragging the edge back out brings the notes straight back. Duplicate lays a copy in immediately after, which is how you turn one bar into eight. With a clip selected, Delete removes it, Shift+D duplicates and Shift+X cuts.
Build from what you played: The two buttons above the timeline treat your last take as a sketch rather than a performance, so you do not have to be able to play the thing you can hear. Make a beat reads where you hit and roughly how high: low taps become kicks, high ones become hats, everything between becomes a snare. It snaps all of that onto the grid at your tempo, then fills in what a drummer would have added anyway, a backbeat on two and four and a steady eighth-note hat underneath, so four rough taps come out as a two-bar groove.; Build a song around it does the melodic half. It pulls the notes you played into your tracks' key, works out which chord fits each bar from the notes that actually fall in it, and then writes the parts around it: a bass line, a pad and a beat. Everything lands at the same point on the timeline and runs the same length, so it plays as one thing. Your original take stays exactly as you played it on its own track.; There are five arrangements rather than one, and they are different bands rather than the same band with the volume moved: a ballad on brushes with one bass note a bar, boom bap with ghost notes before the snare and a bass that leaves gaps, rock on driving eighths, four to the floor with a kick on every beat and an octave bass under offbeat stabs, and a cinematic one on toms with no cymbals at all. Each has its own kit, its own drum pattern, its own bass figure and its own pad shape.
Choosing what it sounds like: The Sound like box beside the buttons decides which of those you get, so wanting four to the floor is a matter of asking for it. Left on Fits what you played it reads the tempo and hands you the one that belongs there, and Make a beat goes on reading your own taps. Name a style and both buttons give you that style whatever the tempo, which means Make a beat lays the groove down in that style's kit, over as many bars as you played, rather than working from where you hit. Surprise me is still a lottery, but a narrow one: it picks among the two or three styles that suit your tempo, and never the same one twice running.; Neither button invents a tune. They take the shape you gave them and finish the job, which means the more deliberate your rough take, the more it will sound like the thing in your head. Change the BPM before you build and everything comes out at that tempo.
Undo: Every change to the timeline can be taken back: recording, moving, trimming, looping, cutting, duplicating, deleting, adding a track, dropping in a piece, and anything the build buttons wrote. Use the Undo and Redo buttons or Cmd+Z and Cmd+Shift+Z (Ctrl on Windows). It goes back sixty steps, so you can experiment without being careful.
Looping a clip: Drag a clip's right edge out past the end of its material and it repeats rather than stretching, with a hairline where each pass begins and a ×N on the label. Loop in the toolbar doubles it: 2, 4, 8, then back to 1. This is how two bars of drums become a whole track. It is not the same as the arpeggiator: an arpeggiator rolls the notes of one key you are holding and stops when you let go, so it never leaves that key's harmony; a looped clip is a part that plays itself while you record something else over it.
Moving around: Click anywhere on the ruler or an empty lane to put the playhead there; if it was playing, it carries on from the new spot. ↓ and ↑ step forward and back through every clip edge in the arrangement, the way arrow keys walk edit points in a video timeline, and Home and End jump to the two ends. The |◀ button next to Record goes back to the start.
Each clip keeps its own sound: A clip stores the voice it was played with, so changing the character, the kit or the knobs afterwards shapes only what you record next. Anything already down stays exactly as it was.
Quantise: 1/16 by default, which nudges every note onto the nearest sixteenth so a take lands in time even if your timing does not. Free keeps exactly what you played.
Loop: On by default, so the arrangement runs round while you work out the next part. It switches itself off while you are recording, so a take can run as long as you like.
Exporting: Plays every unmuted track back fresh into the file, so it comes out cleaner than the live version and lands at a safe level. Each part is worked out once and added in wherever it appears, so a song that loops eight times costs no more than the same two bars once. It saves a plain WAV wherever it is allowed to, which needs no encoder and so arrives in seconds; only somewhere that refuses a WAV does it fall back to a compressed file, and that one has to be recorded in real time.

Sound Lab

Oscillator 1

Oscillator 2

Filter

Envelope

Motion

Space

Arpeggiator

Record

Your two tracks

Track A

Track B

Circle of Fifths

Transpose

Bridge Undertone

DUCKER

Sound Lab

Oscillator 1

Oscillator 2

Filter

Envelope

Motion

Space

Arpeggiator

Record

Your two tracks

Track A

Track B

Circle of Fifths

Transpose

Bridge Undertone