What is a wavetable?
Most synth oscillators repeat one wave shape over and over at the pitch of the note: a saw wave at 220 Hz is the same little ramp, drawn 220 times a second. One repeat of the shape is called a single cycle. Its shape decides which harmonics the note has, which is most of what you hear as its tone.
A wavetable is a list of single cycles stored one after another. Each one is called a frame. The oscillator plays one frame at a time, and a control called position decides which. The frames are usually arranged so that each one is a small change from the one before, so sliding the position from the first frame to the last sounds like one tone turning into another while the note keeps playing.
It works like a flip-book: each page is a still drawing, and flicking through the pages in order makes the drawing move. The frames are the pages, and the position is your thumb.
Wolfgang Palm built the idea into his PPG Wave synthesisers in the early 1980s, and Waldorf carried it on in hardware after that. Today most people meet it in software: Xfer Records' Serum, Matt Tytel's Vital, Ableton Live's Wavetable instrument and Native Instruments' Massive all have wavetable oscillators.
Reading the lab
The lab above is a small wavetable synth with one oscillator and four tables, which you pick with the buttons at the top. Play it from the on-screen keyboard, from your computer keyboard (the row from A to ; plays the white notes) or with Play riff, which loops a two-bar line in A minor at 120 BPM.
The big screen draws the whole table. Every grey line is a frame, with frame 1 at the front and frame 64 at the back, in the same kind of tilted stack you'll see in Serum or Vital. The dashed amber line is where the Position knob sits. The pink line is the frame the oscillator is reading right now, and while a note plays it moves on its own whenever the envelope or the LFO pushes it. Under the stack, a lane shows how the position travels over one note.
Every time you change something, the lab renders an A at 220 Hz through the same oscillator code you hear, and the two smaller screens and the Right now panel are measured from that note. The oscilloscope shows one cycle of it, and the harmonics screen gives each of its first 64 harmonics a bar. Where the note starts on one frame and moves to another, the start is drawn faintly behind.
How a wavetable oscillator works
Inside the synth, each frame is a short list of numbers that describes one cycle of a waveform. Serum and Vital both use 2,048 numbers per frame, and so does this lab. To play a note, the oscillator reads through the frame from start to end and loops back, once per cycle, so at 220 Hz it goes round 220 times a second.
The speed it reads at depends on the pitch. At a sample rate of 44.1 kHz, a 220 Hz note has to get through 2,048 × 220 = 450,560 frame points every second with only 44,100 output samples to do it in, so each output sample jumps about 10.2 points along the frame. Most jumps land between two stored points, and the oscillator works out a value in between them. Play an octave higher and every jump doubles, to about 20.4 points.
The position works the same way across frames. With 64 frames, 0% is frame 1 and 100% is frame 64, so each frame is a step of about 1.6% on the knob. At 50% it plays a blend of frames 32 and 33. Blending is what makes a slow sweep sound smooth; without it you'd hear the tone jump from one frame to the next.
Wavetable position
Every wavetable synth has a position control, even if the name changes: Serum labels it WT POS, and other synths call it position, frame or index. It usually runs from the first frame to the last, either as a percentage or as a frame number.
Start with the Basic shapes table in the lab. It holds four waves you might know from oscillators and waveforms: a sine at frame 1, a triangle at frame 22, a square at frame 43 and a saw at frame 64. The frames in between are crossfades, so frame 11 is about half sine and half triangle.
Turn the position up and the tone gets brighter in stages, as the frames pick up more harmonics. The level stays about the same, because every frame in the lab is scaled to the same peak height, so what you hear changing is the mix of harmonics.
The frames between the classic shapes are worth a listen too. Halfway between the square and the saw, the even harmonics are at half the strength they have in a saw, while the odd ones are a blend of both. That puts each even harmonic about 10 dB below its odd neighbours. A saw has them level and a square has none, so the blend has a hollowness that sits between the two.
What's inside a wavetable
A table can hold any set of single cycles, so the useful question is how its frames are ordered. A good table changes a little from frame to frame in a direction you can hear, like darker to brighter or one vowel to another, because then the position becomes a single knob that moves the tone along that line.
Harmonic tables
Some tables are built straight from harmonics. In the lab's Harmonic stack table, frame 1 is a sine, frame 2 adds the 2nd harmonic at half the level, frame 3 adds the 3rd at a third of the level, and so on until frame 64 holds the first 64 harmonics of a saw. Moving the position up adds harmonics one at a time, which makes this table a good place to hear what each one adds.
The Sweep table works differently. Every frame keeps a quiet bed of all the harmonics, and a group of loud ones sits on top of it, climbing from the 1st harmonic at frame 1 to the 40th at frame 64. On the harmonics screen you can watch the peak travel. It sounds close to a filter with plenty of resonance being swept, and it's one way a wavetable can do a filter's job.
Pulse width
A pulse wave is a square that spends less time up than down. At 50% width it's a square, and as the width shrinks it sounds thinner and more nasal. Analogue synths such as the Roland Juno-106 let an LFO move the width, which is called pulse width modulation and gives a slowly shifting, chorus-like tone. In a wavetable each width can be a frame, so moving the position does the same thing. The lab's Pulse table goes from 50% wide at frame 1 to 3% wide at frame 64.
The level drops as the pulse narrows, because there's less wave there. A 3% pulse has its first dozen or so harmonics at nearly the same level, but each of them is quiet.
Tables made from recordings
Serum and Vital can import an audio file and cut it into frames, one cycle each, in the order they happen in the recording. A sung vowel that slides from "ah" to "ee" becomes a table whose position slides the same way, so a synth note can open and close like a mouth. The steadier the pitch of the recording, the smoother the table, because each frame has to be one complete cycle to loop without a click.
Moving the position with envelopes and LFOs
A wavetable that sits on one frame is a fixed wave with an unusual shape. The sound people mean when they talk about wavetable synths comes from the position moving while a note plays, and that's done with modulation: you connect an envelope, an LFO or another control to the position, and it turns the knob for you. In Serum and Vital you drag the envelope or LFO onto the knob you want it to move.
With an envelope
An envelope moves the position the same way on every note. In the lab, the Env amount knob sets how far it pushes, and Env time sets how long it takes to come back to wherever the Position knob is. Say Position is at 14% and Env amount is +60%: each note starts at 74% and slides back to 14% over the envelope time.
On the Harmonic stack table that's a note that starts with about 47 harmonics and ends with 10, the way a plucked string loses its bright overtones as it rings. A subtractive synth gets the same effect with a filter envelope, and the ADSR envelopes lesson covers how envelope stages work in general.
A negative amount works the other way round, so each note starts lower in the table and rises to the Position knob. Long envelope times of two to four seconds give pads a tone that keeps developing while you hold the chord.
With an LFO
An LFO swings the position up and down over and over. Rate sets how many swings happen each second and depth sets how far each one goes. In the lab, a depth of 60% means 30% either side of the Position knob, so with Position at 40% it covers 10% to 70%. At 0.5 Hz each full swing takes two seconds, which spreads the movement across several notes of the riff.
Rates under about 1 Hz give slow drifts that suit pads and chords. Rates locked to the tempo, like one swing per 1/8 note at 120 BPM (4 Hz), turn the movement into rhythm, and that's how plenty of the growling basses in dubstep and drum and bass are made. The LFO lesson goes into rates, shapes and tempo sync.
Wavetable vs subtractive synthesis
Subtractive synthesis starts with a bright wave, usually a saw or a square, and takes harmonics away with a filter. Everything above the cutoff gets turned down, so a subtractive synth can make a sound darker, and beyond adding resonance it can do little to the balance below the cutoff.
A wavetable changes the wave itself, so a frame can have any balance of harmonics at all: a loud 7th harmonic with a quiet 3rd, a gap in the middle, or the shape of a vowel. The Sweep table in the lab keeps the low harmonics quiet while the loud ones climb, which a low-pass filter can't do. Most wavetable synths also have a filter after the oscillator, so you can sweep the table for movement and use the filter to tame the top.
The subtractive vs FM vs wavetable comparison puts the three side by side.
Wavetable synths: Serum, Vital and others
In Serum, made by Xfer Records, the main oscillators each have a WT POS knob. Its wavetable editor lets you draw frames or build them from harmonics, and its warp menu bends, mirrors or syncs each frame as it plays.
Vital, by Matt Tytel, works in a similar way and has a free version. It uses the same 2,048-sample frames as Serum, and it can build a table from an audio file or even from typed text, which it turns into speech and slices into frames.
If you use Ableton Live, its Wavetable instrument has two oscillators with a position control on each and a library of tables sorted by category. Native Instruments' Massive and Massive X use wavetable oscillators too, and on hardware, Waldorf's synths go back to the Microwave, which used PPG's tables.
Whichever you use, the Position knob in the lab is the same control as WT POS in Serum or the position knob on an oscillator in Wavetable.
Aliasing and wavetables
Digital audio can only hold frequencies up to half its sample rate, which is 22.05 kHz at 44.1 kHz. Anything above that folds back down as a new, out-of-tune tone. That's called aliasing, and it sounds like a metallic whine that moves the wrong way when you bend the pitch.
A bright frame can hold hundreds of harmonics. Play it at A3, 220 Hz, and the 100th harmonic is at 22 kHz, right at the limit for 44.1 kHz audio; play it an octave higher and half of those 100 harmonics are over the line. Good wavetable synths deal with this by keeping several copies of each table with the top harmonics removed, and picking the right copy for each note. The lab keeps it simple: its frames have at most 64 harmonics and its keyboard stops at E4, where the 64th harmonic is at 21.1 kHz. The aliasing and oversampling lesson lets you hear it happen.
How to make a wavetable pluck, step by step
This works in Serum, Vital, Ableton's Wavetable or any synth that lets you modulate the position, and it's what steps 4 and 5 in the lab do.
- Pick a table that goes from dark to brightA harmonic table, or one that runs from a sine to a saw, makes the movement easy to hear. Exotic tables can wait until you know what the position is doing.
- Set the position for the end of the noteMove it to the frame you want each note to settle on. Lower in a dark-to-bright table means a rounder end.
- Connect an envelope to the positionUse a second envelope, so the amp envelope stays free. Set its attack to 0, its sustain to 0 and its decay to 200 to 400 ms.
- Set the amountStart around +50% and listen to the first few milliseconds of each note. More amount gives a brighter, harder pluck.
- Shape the amp envelope to matchA short decay with a low sustain makes it a pluck; a high sustain keeps the note going after the brightness has gone.
- Play it across the keyboardBright frames can alias on high notes, so check the top of your range and back the amount off if it starts to sound harsh.
Starting settings for moving the position
These are places to begin with a table that runs from dark to bright. The amounts are shares of the whole table.
| Sound | What moves it | Amount | Time or rate |
|---|---|---|---|
| Pluck | Envelope, sustain at 0 | +40 – 70% | 150 – 400 ms decay |
| Pad | Slow LFO, or a long envelope | 20 – 40% | 0.05 – 0.3 Hz, or 2 – 4 s |
| Growl bass | Tempo-synced LFO | 30 – 60% | 1/8 or 1/16 note |
| Lead | Short envelope, plus a little LFO | +20 – 30% | 300 – 600 ms, 4 – 6 Hz |
| Evolving drone | Two slow LFOs at unrelated rates | 30 – 50% each | 0.03 – 0.2 Hz |
Common wavetable mistakes
Leaving the position still
Load an interesting table, park the position and you've got a static wave with an odd shape, which a sampler could play just as well. Even a small, slow LFO on the position makes a held note sound alive.
Sweeping the whole table on every note
Going from the first frame to the last usually means passing through several unrelated tones, and each note ends up sounding like a different patch. A sweep across a quarter or a third of a well-ordered table is often enough.
Judging frames by their level
Frames with fewer harmonics, or narrow pulses, can come out quieter than their neighbours, and a frame that's a decibel louder will tend to sound better simply because it's louder. Listen at the same level before deciding one part of a table beats another.
Forgetting the top of the keyboard
A bright frame that sounds fine on a bass note can alias on a lead an octave or two up. If high notes sound brittle or slightly out of tune, move the position down the table for those notes or put a low-pass filter after the oscillator.
Train your ears
The quiz under the lab plays the riff with hidden settings and asks whether the position is still, swung by an LFO or swept by an envelope on each note. The controls are covered and every round is level matched. Listen inside each note: an envelope does the same thing at the start of every note, while an LFO carries on across them and catches each note at a different point. Eight rounds take a few minutes, and your best score is kept in your browser.
Questions people ask
What's the difference between wavetable and subtractive synthesis?
A subtractive synth starts from a bright wave and removes harmonics with a filter. A wavetable synth changes the wave itself by moving through a table of frames, so it can add harmonics, take them away or rearrange them. Most wavetable synths have filters as well, so you can use both.
What does WT POS mean in Serum?
It's the wavetable position: the knob that picks which frame of the current table the oscillator plays. Modulating it with an envelope or an LFO is how you make a Serum patch move as it plays.
How many frames does a wavetable have?
It depends on the table. Serum and Vital store each frame as 2,048 samples and allow up to 256 frames in a table, while plenty of tables use far fewer and let the synth blend between them. The tables in the lab on this page have 64.
Can I make a wavetable from my own sample?
Yes. Serum and Vital both let you drag an audio file onto the wavetable display and cut it into frames. Sustained sounds with a clear pitch, like a held vowel or a single synth note, give the smoothest tables.
Is wavetable synthesis the same as sampling?
No. A sampler plays back a whole recording, so a sample gets shorter as you play it higher. A wavetable oscillator repeats single cycles, so a note lasts as long as you hold the key at any pitch, and its tone moves only when the position does.
Is Vital free?
Vital has a free version with the full synth engine. The paid versions add more presets and wavetables, and Pro lifts the daily limit on making tables from text.