Synth Waveforms Explained: Sine, Triangle, Saw, Square, Pulse

Each synth waveform sounds different because it carries a different set of harmonics, the quieter overtones stacked above the note you play. A sine has none and sounds pure, a triangle adds a few faint odd ones and sounds soft, a sawtooth has every harmonic and sounds bright and buzzy, a square has only the odd ones and sounds hollow, and a pulse is a lopsided square that gets thinner and more nasal as it narrows. Pick by how much brightness you want to start with, because a filter can take harmonics away but has nothing to remove if they were never there.

Types of synth waveforms at a glance

An oscillator repeats one shape over and over, from dozens to thousands of times a second, and that repeating shape is its waveform. The speed sets the pitch: A4, the A above middle C, repeats 440 times a second (440 Hz). The shape sets the tone.

Any shape other than a sine can be broken down into a stack of sine waves at whole-number multiples of the note. First comes the fundamental, then the 2nd harmonic at twice the frequency, the 3rd at three times, and so on. Play A2 (110 Hz) on a sawtooth and it contains 110, 220, 330, 440 Hz and upward. A square at the same pitch skips the even ones: 110, 330, 550, 770 Hz. Your ear hears the whole stack as one note with a color, and that color comes from which harmonics are present and how loud each one is.

The fading rate is the part to remember. In a sawtooth or square, the nth harmonic sits at 1/n of the fundamental’s level, so the 9th harmonic is still a ninth as loud. In a triangle it falls at 1/n squared, so the 9th is down to 1/81 and the top end is close to silent. That is why a triangle and a square, with harmonics at exactly the same frequencies, sound so far apart.

To hear the difference, hold A3 on any synth with a wave selector, step through the shapes, then sweep the filter on each one and listen to how much there is to take away. In Gelato Synth, the Shape slider on the Osc A page morphs from sine through triangle, saw and square to pulse on one held note, while a live oscilloscope draws the wave you are hearing.

Sine and triangle waves: the soft shapes

What does a sine wave sound like?

A sine wave is a smooth, rolling curve, and it is the only sound with no harmonics at all. At A4 it sounds like a hearing-test beep. An octave or two higher it becomes a soft whistle, and down around C1 (about 33 Hz) it is a deep hum you feel more than hear. Nothing in it is bright, so on its own it sounds plain.

That plainness is what makes it useful:

• Sub bass. A sine an octave below your main bass adds weight without mud, since it has no overtones to clash with anything else. It is also the heart of the long, booming 808-style bass.
• Whistles and pure leads. Add a gentle vibrato (an LFO on pitch at about 5 Hz) and a little glide, and a sine becomes a whistle or a theremin-like line.
• The FM building block. FM synths such as Yamaha’s DX7 make bells, electric pianos and basses by letting one sine wave wobble the pitch of another very fast. FM synthesis explained walks through the ratios.

Two practical warnings. A low-pass filter has nothing to take away from a sine, so sweeping the cutoff only turns it down. And phone and laptop speakers barely reproduce the low end, so a sine sub at C1 can vanish completely. Check it on headphones, or add a little drive, which creates harmonics a small speaker can play.

What does a triangle wave sound like?

A triangle wave looks like a row of sharp peaks: straight lines rising and falling at the same angle. It carries only odd harmonics (3rd, 5th, 7th and up), and they drop off so quickly that it sounds like a sine with a little more edge. Think of a soft flute or an ocarina.

Use a triangle when a sine is too dull and a saw too bright, for soft leads or a mellow bass under acoustic guitar. The Nintendo Entertainment System (NES) had a triangle channel with no volume control, and its music usually gave that channel the bass part, so a triangle bass in short, bouncy notes sounds instantly retro.

What does a sawtooth wave sound like, and what is it used for?

A sawtooth ramps up in a straight line, then drops straight back down, like the teeth of a saw blade. Some synths draw it ramping down and jumping up instead, and the two sound identical. It is the only basic shape that contains every harmonic, each one at 1/n of the fundamental, so it sounds the fullest and buzziest. Played raw, it has a brassy rasp with a lot going on above the note.

That density is why the sawtooth sits under so many classic sounds:

• Strings. A bow’s stick-slip grip drives a violin string in a sawtooth-like motion, so a saw with a 200 to 300 ms attack and the filter about half closed is a good start for synth strings.
• Brass. A filter envelope that sweeps open over 50 to 100 ms on each note, then settles partway back, gives a saw the “bwah” of synth brass.
• Supersaw leads. Roland built the supersaw into its JP-8000, released in the late 1990s: seven saws detuned against each other, the sound that came to define trance.
• Reese and acid bass. Two saws a few cents apart give the growling, phasing Reese bass. One saw through a resonant filter with a short envelope is the start of an acid line.
• Plucks and pads. A short filter envelope makes a pluck; long attack and release times make a pad.

The saw is also the best shape for learning a filter, because it gives the filter the most to remove. Sweep the cutoff of a raw saw from fully open to nearly closed and you hear it go from brassy to muffled to a dark hum. Synth filters explained covers cutoff and resonance step by step.

Square wave vs pulse: what pulse width modulation does

A square wave jumps between two levels and spends exactly half its time at each: flat top, flat bottom, vertical edges. That even split cancels every even harmonic, leaving the 1st, 3rd, 5th and up at the same 1/n levels as a saw. Play C2 and a saw’s first overtone is C3, an octave up; a square’s first is G3, an octave and a fifth up. The missing evens give it a hollow, woody sound, close to a clarinet in its low register, which also leans on odd harmonics. It is a classic bass wave and the sound of early game consoles.

A pulse wave is a square with the balance changed. The share of each cycle spent at the top is the pulse width, also called the duty cycle. As the width moves away from 50%, a different set of harmonics drops out: the pulse loses every harmonic whose number is a multiple of 1 divided by the width, so a 25% pulse loses the 4th, 8th, 12th and so on.

A narrow pulse lead sounds like an 8-bit game because the NES pulse channels offered 12.5%, 25% and 50%. Two quirks help when you turn the knob. A 25% pulse and a 75% pulse sound the same, since one is the other flipped upside down. And at 0% or 100% the wave flattens into a straight line and goes silent, so many synths stop the width control short of the ends.

Pulse width modulation (PWM) means letting something move the width while you play, usually an LFO. As the width sweeps, harmonics fade in and out continuously, and one oscillator starts to sound like two slightly out of tune with each other. That chorus-like shimmer is the classic sound of analog string pads.

To try it, pick a pulse wave, route an LFO to pulse width, set the rate between 0.3 and 1 Hz, and set the depth so the width swings between about 50% and 15%. Hold a C major chord (C, E, G) with a slow attack and some reverb. Push the rate to 4 or 5 Hz for a nervous, wobbly version. You can also let an envelope drive the width, so each note starts hollow and thins out as it fades.

Sawtooth vs square: which waveform to pick

Put a saw and a square on the same note and the saw sounds fuller. The square sounds hollow, as if the middle has been scooped out, because its even harmonics are gone. Both give a filter plenty to work on, so pick by the part you are writing:

A few rules of thumb:

• When unsure, start with a saw. It has the most harmonics, so a filter can take it almost anywhere darker. Going the other way, from a sine to something bright, takes drive or FM.
• Layer to get both. Roland’s SH-101 can mix a square one octave below its saw as a sub oscillator, and that saw with a square under it is a classic analog bass. How to make a synth bass has full recipes.
• Leave room in the mix. A raw saw fills most of the frequency range, so in a busy track, set the cutoff lower than sounds right when the part plays alone, especially under a vocal.