Oscilloscope

Y–T is the waveform Amplitude up, time across. Timebase sets how much time is on screen, in the 1–2–5 steps a scope has always stepped in.

X–Y plots one channel against the other Time is thrown away. Two tones of the same frequency draw a line, an ellipse or a circle depending only on the angle between them; simple ratios close into figures.

One input has no second axis — so lag makes one A single instrument down a single input gives two identical channels, and identical channels draw a diagonal line and nothing else, whatever the preset. Lag X–Y, on the Bench under Picture → Vertical, plots the signal against itself a moment earlier instead. A held note becomes a closed loop whose shape is its harmonic content, and it moves when you move.

This is a phase portrait, not a Lissajous figure: the second axis is the same signal, so what you are reading is how the sound changes over that moment rather than how two sounds relate. Auto sets the delay to a quarter of a period, which is what makes a pure tone a circle, and it locks slowly on purpose — chasing the pitch would hold the circle round through vibrato and hide the very thing worth seeing. Locked slowly, vibrato makes the loop turn.

Heard is how much of the delayed copy reaches the right speaker, when the speakers are on the shaped side. Heard, a signal plus itself a moment later is a comb filter that tracks the pitch. In headphones it cuts deepest at half, and in a room at full. It starts at 20%, which is mostly width, and stops at 50% — the top of the slider is the setting where, in headphones, the right ear loses some of a note's harmonics entirely. That is allowed on purpose; it is where the effect is strongest.

AC coupling, and where its corner sits Under Vertical, per lane. It blocks what is not moving, so a converter with a DC offset does not push the trace off the screen — a one-pole high pass, the same one a bench scope puts in front of its input. The corner is where it starts taking things away: at ten hertz, which is where a scope usually sits, a slow drift goes and the signal does not; down at one hertz almost nothing is removed quickly, which is what you want when the drift IS the signal; up at twenty it thins the bottom of a bass note as well.

The corner is worth knowing about because the numbers under the trace are about the coupled signal, not the raw one. At ten hertz that moves a peak reading by a per cent or two, and rather more on anything near the corner; at one hertz an asymmetric signal — a half-wave rectified tone, say — can read a third higher, because a pole that slow has not finished taking the offset out within the window. That is what AC coupling at one hertz means rather than a fault, and the readout names the corner while it is on so the numbers say which signal they are about.

The same corner reaches the speakers when they are on the shaped side, from one set of numbers: the screen and the speakers cannot disagree about what AC coupling is.

Spect is a spectrogram Frequency up, time running right to left, level as ink. Hover it and it names the frequency and the note under the pointer.

Zoom magnifies, and the wheel works In Y–T it shows a slice of the capture stretched, centred on the trigger — the record is unchanged, so the measurements still read all of it. In X–Y it scales the figure; on the spectrogram it closes in the frequency band.

A filter, on two taps Under Filter. It reshapes the trace, which is the point of having one here: a low pass rounds a square's corners toward a sine, a notch carves a harmonic out of the picture, a resonant sweep draws its own ringing. Screen reads and Speakers get are separate switches, so the filter can be an instrument for looking while what you hear is untouched, or both, or the other way round. Resonance is nought for gentle and a hundred for extreme, and at nought a low pass is maximally flat. It runs on the samples rather than in the audio graph, so it reaches the test tone too — which is arithmetic and has no audio graph at all. Point a source at the cutoff and it sweeps.

The voice: a second oscillator inside it Under Oscillator, on the Shape tab. A second oscillator runs at Ratio times the note, and FM swings the voice's phase with it: pure at nought, then brighter, then bells and clangour. A 3:2 ratio sounds harmonic for the same reason a 3:2 figure closes. Ring multiplies by it instead and takes the note away. Sync runs a saw or square faster than the note and restarts it every note cycle, so the pitch holds while the tone tears; put an LFO or the envelope on it for the classic sweep. Sub adds a square or sine an octave or two down, and Unison stacks detuned copies so the figure thickens and shimmers. FM and Sync can take sources. With a split, it is the layer being edited, so the two halves of the keyboard can be two different voices. Nothing gets louder: copies and the sub are mixed, not piled up.

Shaping: drive, fold and crush, in every note Under Shaping, on the Shape tab. Drive pushes the wave into a soft ceiling, so a sine rounds towards a square; the reading is how much the quiet parts are lifted. Fold bends the wave back on itself each time it would pass full scale: the peaks fold into the wave, and in X–Y the figure grows petals. Put an LFO on it and they open and close. Crush takes the wave down to a few levels and Rate holds each sample, for the steps and the folding-back of a lo-fi sampler. It is done to each note on its own, before its envelope, so a chord stays a chord rather than turning to mud, and a note keeps its colour as it dies away. Behind the ⋯, four times oversampling is cleaner for a hard drive on a high note, and costs twice as much, so a big chord gives it up first; see The voice budget.

The voice filter: one in every note Under Voice filter, on the Shape tab. A low, band or high pass or a notch in each note, after its shaping and before its level. Key track makes the cutoff follow the note, so a high note is not duller than a low one. Envelope sweeps the cutoff up or down by that many octaves with the filter's own envelope, whose four are behind the ⋯: a note that opens bright and closes, or a resonant wah, per note. The cutoff can take a source. The Filter on the Picture tab is a different thing: it filters the whole trace, for looking.

The voice budget: what a big chord gives up Every copy, every shaped note and every filter costs the computer something, and sixteen notes with everything turned up would cost more than it has — the sound would break up. So the page keeps a budget, and when a chord would go over it gives things up in the order they are missed least: first the four times oversampling for twice, then unison copies, then notes still fading after you let go, and only then held notes you cannot see — the inner voices of a chord, before any drawn one, and never the last note. A note given up fades out rather than clicking and stays silent until you lift its key. The readout says voice budget: and what it took, and the copies come back when you play the next chord or change what you asked for. No preset gets near it with eight notes on each layer; it is for patches built with everything on, and chords struck over long releases.

The plane: what folds the picture folds the sound Under Plane, on the Effects tab, for the generator and for a microphone, a line input or a file. Mirror folds the figure onto one half of itself, X onto its right or Y onto its top, and to the ear that is full-wave rectification, the octave-up pedal: a mirrored sine is its octave, every harmonic even. Radial is what happens at the circle: Clip rounds the loud parts off towards it, keeping every point's direction, so it is a clipper that does not bend the stereo image; Fold reflects them back in, a wavefolder on both channels at once. The radius can take a source. Twist turns each point by an angle in proportion to its distance from the middle, so the loud parts swirl and the quiet ones stay put — a stereo rotation that depends on level, and it can take a source too. Kaleidoscope folds the figure into a wedge of its own reflections. Snap puts both channels on a grid: a bitcrusher, and pixels. Behind the ⋯, Scale X and Scale Y are balance and width, and Shear leaks one channel into the other. All of it acts on what is drawn and on what is heard, and in poly on the chord you hear as well as the notes that are drawn.

With two layers playing, Layers at the top of the section chooses. Together is one plane for both. A or B gives layer B a plane of its own, starting as a copy of A's, and says which layer's the controls are showing — the same choice as Edit A and B on the Play tab. B's has a Turn of its own, which can take a source like the screen's rotation can — an oscillator on it spins B alone — and while it does the screen's X–Y rotation turns layer A only, so one figure can stand still while the other turns. The picture does not move when you leave Together, but the sound does: each layer is now bent on its own, and a mirror on two chords apart is not a mirror on the two together, which also makes their difference tones. B's own is its delay and chorus too: Delay and chorus has the same Layers row, the same switch, and with B's shown its controls are B's, so one layer can echo while the other stays dry, or each at its own time. Only the oversampling stays one for both.

The bending ones run at twice the sample rate, so that what they add above half the rate is filtered away rather than folded back as notes that are nowhere in the key. At 4 kHz the clip's worst stray tone is 27 dB down at once, 55 at twice and 108 at four times. The fold and the snap are rougher at any rate, which is their character. Behind the section's ⋯ you can choose once or four times. While any of them is on, the picture and sound are 0.7 ms later; scale and shear cost nothing. A mirrored wave sits above zero, and AC coupling takes that off what you hear.

On a microphone, a line input or a file the plane works on what comes in, before anything draws it or plays it: what you see is what a monitored line input sends to the speakers. A mono input becomes two lanes while an effect is on, because what the effect makes of it is a pair. A rack's stems and a band split do not get it: their lanes are not one stereo pair. The line under the section's title says which it is doing.

Delay and chorus: echoes you can see Under Delay and chorus, on the Effects tab, after the plane, and on a live input or a file as well as the generator. Echo is how loud the repeats are, nought for off; Time is free, or Sync sets it to a note value of the tempo and it follows the tempo when that moves. Feedback brings each repeat back again, and stops at 0.9 so it always dies away. Ping-pong sends each repeat to the other side, so on the screen the ghost figures alternate between the figure and its mirror image across the diagonal. Chorus is a short delay whose time swings, one side on a sine and the other on its cosine, so the figure breathes and turns; with Feedback behind the ⋯ it is a flanger. Echo and Time can take a source: on the echo, a pedal or a wheel brings repeats in from none, and the delay keeps listening while it is at nought, so what comes back is what you just played; on the time, a source stretches it an octave either way, and the repeats bend in pitch as it moves, like tape. Neither feedback can take one: a loop inside a loop is how a patch runs away. With two layers playing, the section's Layers row gives layer B an echo and a chorus of its own, with its plane — one switch for both — and a source on the echo reaches each layer through that layer's own fade.

The picture as a score Tick Play the picture, under Score on the Picture tab, and a playhead crosses the screen at the tempo, playing what it passes. Low on the screen is low in pitch, in the page's key, over the octaves you choose; the brightest points in each column are the notes, up to four at once, and the brighter the harder. Draw a figure and it plays itself; turn it and the melody inverts. A long persistence is a score that lingers. The notes are heard in the generator's voice while it is heard, and never drawn, so the score cannot play itself into what it is reading. The playhead is on the page's bar, so its first column is always a downbeat and Stop under Key and tempo silences it; see below.

The arpeggiator Arp, in the Keyboard section, plays a held chord a note at a time at the tempo: up, down, up and back, in the order you played it, or at random, from a crotchet to a semiquaver triplet, over one to three octaves. In the dyad each step pairs your lowest note with the next, so the figure steps through the shapes of the chord's intervals in time. Every note is struck afresh, and the first waits a moment for the rest of the chord. Letting go stops it; switching it off with keys down gives the generator the whole chord. Its notes go out through MIDI out.

Thresholds, and Pluck Threshold, among the Signal sources, is a moment made from any other source: choose what it watches and a level on the Sources tab, and it fires each time that source rises through the level. It strikes things, not sliders: the harmonograph's Swing again, a solid's Kick, or Pluck, a note of the pitch set under Score, played in the generator's voice and sent out as MIDI. An onset can pluck too, so every hit can play a note.

MIDI out Under Settings, MIDI, choose a port and a channel, and the score's notes and the crossings' go out to it. With a synth on Local Off the picture plays it, and its line outs coming back in close the loop through a real instrument. At most forty notes a second; every note is ended when the scope stops, the page is hidden, or the port changes; the readout says sending while they go.

Your input, into the generator Under Input into the generator, on the Effects tab: your microphone or line input fed into the generator itself. FM speeds and slows the trace with your waveform, so a figure is drawn faster and slower within every cycle you play. Ride scales the figure by it, so the sound rides on its outline. Clock traces the figure at your pitch instead of its own, so a held note holds it still; on a waveform, the generator plays at your pitch, locked to each of your cycles, and a fifth or an octave above it if the interval says so. When you stop, it goes back to its own. It works on the test tone while Hear the generator is ticked, and the line under the title says when it is not reaching it.

From can be A second generator instead: a figure of its own, traced at its own rate, drawn beside the first on lanes three and four and needing no device. The same three modes carry it into the first — slowly, a figure pulled faster and slower as you watch; at audio rates, FM between two generators, the sidebands on the spectrogram. It is heard only in what it does to the first, it works whether or not the generator is heard, and a split or layered keyboard takes its lanes while it plays.

Persistence is the phosphor How slowly the screen forgets. Off for a waveform; long or infinite for X–Y, where the figure is built up a pass at a time.

Record makes a clip to share Record, along the top, starts a clip of the screen and what it sounds like; press it again to stop. The clip waits under Clip beside it, to watch, save as a video file or discard. The sound is what the speakers play, and your input too when it is drawn but not heard — so a clip of you playing has you in it. If a microphone can hear the speakers, what they play is in the clip twice; headphones avoid that. A silent generator stays silent: tick Hear the generator first. The panes beside the screen are not in the clip, and a clip stops by itself at three minutes.

The photocell: the picture moving the controls Photocell, above the screen, puts a light sensor on it — drag the reticle onto the picture, or give it focus and move it a cell at a time with the arrow keys. How bright the phosphor is under it becomes a source, Photocell, which can be put on a control like an LFO: park it on the edge of a figure and it pulses as the beam sweeps past, drop it inside a solid and it reads how dense it is. Point it at rotation or zoom and the figure moves itself — and moves what the photocell sees, which is the loop. It fills with its own reading, so you can see what it is seeing. The presets under Pictures and sounds → The picture plays itself are sixteen of these loops set up and running — the last with nine sources and no hands — and Playing live → Played with the picture puts your hands on top of five more. A loop needs its reticle on the trace of the figure at rest: in the dark it reads nought, nought moves nothing, and nothing ever lights it.

It can reach any control, the filter and the generator included, so the picture can be heard as well as seen. Three things keep that loop from running away. It moves a control at most half as far as another source could, and every source reading the picture on one control shares that half between them — three of them on the cutoff move it no further than one. Its reading can change no faster than two full swings a second, so it cannot flip back and forth every frame. And the limiter is still last, so a loop that finds a resonance is caught rather than heard at full scale. Persistence is its memory: long persistence makes it slow and smooth, short makes it twitchy. Over a spectrogram it reads nothing, because no beam draws one. Clear, beside Panes, wipes the screen and what the photocell sees, and leaves persistence as it was set.

What the picture says, and what the loop is doing With the photocell on, five more sources read the whole picture rather than one point, under the same rules. Roundness is one for a circle and nought for a line — and one for a square too, because it sees how spread a figure is, not its corners. Coverage is how much of the screen is lit. Change is how much the picture moved since the last frame. Novelty is how far the picture is from anything it showed in the last fifteen seconds: nought when it keeps coming back, high when it has gone somewhere new. Direction is which way round the beam travels, plus or minus. Boredom climbs slowly while the picture neither moves nor goes anywhere new, and drains once it does: put it on something that shakes the figure and a loop that has settled will, after a few seconds, nudge itself out again. It reaches less than the others and can never climb faster than a quarter a second.

The readout says what the loop is doing: settled when nothing moves, cycling when it keeps coming back to where it has been, wandering when it moves and does not repeat, running away when the screen fills or the limiter is working hard to hold the sound down. The interesting setups are the wandering ones: two sources crossed onto two controls — say Roundness on the lag, with lag X–Y on, and Novelty on rotation — and persistence long enough to give it memory.

The beam has a brightness On a cathode-ray tube the spot's brightness is how long it dwelt on a spot, which means it goes as one over its speed. The trace turns bright where it slows to turn around and faint through the fast sweeps — which is most of why a real scope does not look like a plot. A circle comes out perfectly even, because a circle traced at a steady rate really does have constant speed.

Where it applies Settings → Beam. On for X–Y, and off for the waveform by default: dimming the steep edge of a square wave fights the measuring that Y–T is for. Off / subtle / moderate / high widens both the range of tone and how much speed it takes to cross it. On a very long timebase the waveform falls back to a flat trace, because past two samples a pixel the screen is showing each column's range rather than a path, and a range has no speed.

Panes What sits down the right-hand side. Turn them all off and the trace takes the whole width.

Scope, the Bench and Settings Scope is for watching and playing: the screen has the window, and the strip along the top keeps the trigger, the timebase, the zoom and persistence. The Bench is where everything is tuned: the controls take the middle of the window and the screen sits beside them, still running, so you can watch a figure answer with your hand on the control. On a wide window the Bench stops at the width three columns need rather than spreading them apart. Settings opens from either and holds what you set once and leave — MIDI, Audio, Presets and Beam. Every section lives in one of the two places and nowhere else.

The Bench is six tabs, by task: Play (the source, the keyboard, the generator), Picture (the lanes, the display, the vertical scale, the trigger, the trace filter), Shape (the drawbars, the voice's oscillator, shaping and filter), Effects (the plane, the delay and chorus), Sources and Measure. Each section's title carries ⋯, and behind it is that section's explanation and the handful of settings reached for rarely. The source chips stay beside the screen on every tab, so a chip can be dragged onto a control wherever it is.

Press / to find any control by name — it knows a few other words for things, so adsr finds the envelope and lfo the oscillators — and choosing a result takes you to it, opening whatever it is behind. B switches between Scope and the Bench, and the view and the tab are remembered.

The Sources tab One family of sources at a time. Down the left, the families: In use, every source that is on something now, then the oscillators, the signal's level and envelope, what the sound is doing, your hands on the keyboard, the controllers you have moved, the picture itself and your macros, each with how many it has. A family with nothing in it now is quieter, and says how to get something when you choose it. In the middle, the chosen family's sources, each with a meter of what it is doing right now and an arrow counting where it goes, so you can see at a glance which band is moving or which knob is up. On the right, the chosen source: what it is, every control it is on with its own depth and a cross to take it off, and Add a destination to put it on another. An oscillator's shape and rate are there, and a controller can be renamed or forgotten there. The tab opens on In use when anything is patched. Choosing a source also makes every control it is on, on every tab, draw its sweep.

Fade, under the families, is for when modulation should not arrive or leave all at once. In eases it in, Out eases it away, and In and out does both. Under it is the fade's envelope: a wait, the attack, a decay to the level it holds at, the hold, and the release. Drag the end of each stretch sideways for its time; drag the corner where the decay meets the hold up and down for the level held, so a strike can burst and then settle; drag the middle of a slope towards where it is going to make it quick to start, or away to make it slow (or use the arrow keys on a handle). Restart runs the envelope again on every note you strike, and Loop sends the attack and decay round again for as long as a note is held. A dot rides the envelope with the last fade to begin; its height is the level now. With the keyboard split or layered, A and B choose which layer's envelope you are drawing, and the other shows faint behind it: each layer's sound follows its own, and a note struck in a split restarts only its own layer's. The picture's controls follow layer A's. The whole envelope acts on notes; patching or taking off a routing uses its attack and release. It acts on a routing you patch or take off, and on every step the keyboard's sources take: with velocity on the drive, a note starts the drive where it rests and brings it up to how hard you struck, and under Out a release lets it back down slowly. The pedal and the notes' count, spread, melody and inner voices ease the same way; oscillators, the picture, the envelope and knobs are not eased, because they already move as they should. With any of them on, loading a preset glides its sliders from where they were, so the picture morphs into the new one instead of jumping; its menus and switches still change at once. A depth you drag answers your hand straight away, and a slider you touch during a glide is left where you put it. The fade is kept in this browser and is not part of a setup code, so loading a preset does not turn it off.

Macros: one knob, many controls Four knobs of your own, under Macros on the Measure tab. Each is a source like an oscillator, except that nothing moves it but you: touch one and it is chosen, then Add a destination as many times as you like, and that one knob moves them all, each by its own depth. Type over its name to call it what it does; the name is what every control it is on shows, and a setup code keeps it.

Morph, under them, slides between two sounds. Press A to store every slider, change the sound, press B, and the fader goes between them — the pitch by octaves, everything else in a straight line. Menus and switches are not morphed: a shape or a mode stays as you left it. A slider you move by hand keeps its place until the fader moves again. The fader is a control like any other, so a macro or an oscillator on it moves the whole sound at once. Loading a preset clears it.

Hearing: what you play, as sources The Hearing family reads the sound itself, from a microphone, a line input, a file or the generator. Pitch is the note, nought at middle C and one two octaves up, from a held key if there is one and otherwise from the sound; it holds when you stop. Brightness is where the energy sits, low for a dark tone and high for a bright one. Bass, Low mid, High mid and Treble are how loud each band is, at the band split's crossovers. Width is how alike the two channels are, one for mono. Flux jumps on each new note or hit and stays low on a held one. None of them can jump: a new note glides there in an eighth of a second an octave. Pointed back at the generator they are hearing, they are a loop, and held to the picture's reach like the photocell.

Onset is different: a moment, not a value. It fires once when a note or a hit begins, never on a release, and never faster than twelve times a second, and it can only strike things: the harmonograph's Swing again and a solid's Kick. To have your playing strike the generator, put your input and the generator in a rack and the trigger on your input's lane; an onset that would hear the generator it strikes is refused, since every strike would be the next onset.

The bands can spin a solid about each of its axes: Spin X, Y and Z are destinations, so put Bass on one and Treble on another and the low end and the top turn it different ways. And the drawings answer back, under Picture while they play: the harmonograph's Swing and Pendulum, and a solid's Tilt, Turn, Roll and Facing - so the way a solid is turned can open a filter, or the pendulum can be an oscillator locked to the drawing.

Key, tempo and the quantiser The Key and tempo section, on the Measure tab, is one key, one scale and one tempo for the whole page. Quantise the generator's pitch takes the pitch, after everything patched onto it, to the nearest note of the key, so a slow oscillator or the photocell on the frequency plays a melody in D dorian rather than a siren. A key you play outside the scale is moved too, and a note exactly between two goes down. It waits a tenth of a semitone past half-way before it steps, and never steps more than forty times a second, so a pitch resting between two notes does not flicker. Glide, behind the section's ⋯, slides between steps. The harmonograph and the figures are not quantised.

An oscillator's Sync locks its rate to the tempo in note values, from four bars to a semiquaver, with triplets. Tap sets the tempo from the last four taps and starts the locked oscillators on the beat you tapped. A keyboard or sequencer sending MIDI clock sets the tempo while it runs, and hands it back half a second after it stops. Its Start restarts the locked oscillators, and Continue does not.

Bar says where the page is in the music, in fours: 3.2 is the third bar's second beat. The score's playhead reads its columns from it, so switched on mid-bar it joins where the bar is, and its first column always lands on a downbeat. Stop holds the bar and silences the score; Start puts the bar back to the one and restarts the locked oscillators with it, so a synced sweep and the score begin together. While it runs, a tap is the one as well as the tempo. A device's Start, Stop and Continue work the bar the same way - Start on the device's first tick, as MIDI says it should - and while its clock runs the bar counts its ticks, so it keeps the device's place and not only its tempo. If the clock stops without a Stop, the bar carries on from where the clock would have had it. Two things do not follow the bar: the arpeggiator, which starts from your hands, because a first note held back to the next step would feel like lag; and a song position from the device, which is not read, so a Continue from the middle of a song carries on from wherever this page's bar stood.

Crossings: the picture as a rhythm Crossings, on the Effects tab, puts a line across each axis of the X–Y screen and plays a plucked note each time the beam crosses one going up. The X line is crossed once for every cycle of the X channel, wherever the figure is, and the Y line once for every cycle of Y. So the interval on the screen is the rhythm you hear: a just fifth plays three against two exactly, and a tempered one drifts slowly out of step and back. Each line has its note, C4 and G4 to start, with a decay and a level behind the section's ⋯. The lines flash when they fire.

It is a rhythm only when the drawing is slow: the harmonograph, or a figure traced a few times a second. At audio pitch the notes are limited to twenty-five a second and buzz. The notes are heard and not drawn, and only with Hear the generator on. The count beside the switch shows the lines firing either way. The lines follow the generator's own beam, not a microphone's, and are not drawn while the figure is rotated.