Detune, Beating and Stereo Width

In the lesson on notes and frequencies, you learned to tune a sound to the nearest cent. Here we do exactly the opposite: we're going to detune sounds on purpose. It's one of the secrets behind enveloping pads, leads that fill the whole stereo field, and supersaws. But it's also one of the most common causes of basses that wobble and chords that sound slightly out of tune.

Two close frequencies beat

Let's start with the simplest experiment. The first button plays a sine wave at 440 hertz. The second plays two sine waves at the same time, at 440 and 441 hertz, the third at 440 and 443 hertz, and the last at 440 and 450 hertz. Listen closely to the volume of the sound, more than its pitch.

As soon as there are two sounds, the volume starts to wobble: it swells, fades, then swells again. This is called beating. The two vibrations are sometimes in phase, and they add up, and sometimes opposed, and they almost cancel out. The number of beats per second is simply the difference between the two frequencies: one per second for 440 and 441 hertz, three for 440 and 443, ten for 440 and 450.

You probably noticed that the last example beat so fast it started to buzz. When the beats get even faster, the ear can no longer follow them as a wobble and hears them as roughness. And if you move the two sounds even farther apart, up to a semitone, you end up hearing two distinct notes rubbing against each other: that's the minor second, seen up close.

The same detune doesn't beat the same everywhere

Synths set detune in cents, and that makes sense, since a cent is the same gap to the ear in every register. But beating depends on the gap in hertz. So the same detune produces slow beats in the low end and fast beats up high. The following table gives the number of beats per second between two voices a few cents apart.

Look at the first column. On an A1, two voices 10 cents apart beat only about once every three seconds. In practice, your 808 or your sub doesn't sound any wider: its volume rises and falls slowly, and one note can seem weaker than the one before, depending on when the beat lands. That's why people generally avoid detuning basses and the sub.

Detune, unison and supersaw

On a synth, the detune knob detunes one oscillator against another, usually by a few cents. The unison setting goes further: it stacks several copies of the same voice, each one slightly detuned, and often spreads them from left to right across the stereo field. You then choose the number of voices, the amount of detune and the stereo width.

Why does this widen the sound? Because the beats don't land at the same moment on the left and on the right. Each ear receives a slightly different mix that keeps changing, and your brain interprets that difference as a wide sound that surrounds you, rather than a point in the center. Listen to a single sawtooth, then three and five sawtooths detuned around the same A.

Here everything plays in the center, but you can already hear the sound thicken at each step, like a small string section. A stack of detuned sawtooths, often five to nine, has a name in producer slang: the supersaw. It's the basis of a lot of wide leads and pads in electronic music. The last button, though, goes too far: the sound no longer seems wide, it seems out of tune.

Chorus, a detune that moves

A chorus gets a similar result with an effect instead of extra voices. It copies the sound, delays the copy by a few milliseconds, and keeps varying that delay with an LFO, that is, a very slow oscillator that moves a setting. When the delay gets longer, the copy plays back very slightly slower, and so a little lower; when it gets shorter, the copy is a little higher. You get a copy that gently drifts out of tune and back in, and that beats against the original.

The advantage of chorus is that it works on any sound, even a guitar or a recorded vocal. Its usual controls are the LFO speed, often called rate, the amount of variation, called depth, and the mix with the original sound. A slow rate and moderate depth give a full, discreet sound; a fast rate and a lot of depth give an unstable vibrato that can quickly sound out of tune.

How far should you detune?

There's no magic number, but there are landmarks. With a few cents of gap, the sound widens without any audible out-of-tuneness. Between about 10 and 20 cents, the effect becomes obvious, and that's often supersaw territory. Beyond twenty cents or so, many ears start to hear several slightly out-of-tune notes rather than one wide note, especially when the sound is on its own or playing chords.

There are two reasons for this. First, the beats get so fast that they turn into roughness, as in the example at 440 and 450 hertz. Second, your ear no longer knows which pitch to settle on, and the note seems off compared with the bass and the other instruments, which are in tune. On a chord, every note is detuned, the clashes add up, and the chord can turn muddy. So a lead playing on its own can take more detune than a pad playing four notes.

In this loop, if you had to add unison, you'd put it on the chords rather than on the bass. The site plays a simple sound here; rebuild the same loop in your DAW, with a real unison setting, and compare.

As you've heard, the ear is very sensitive to small gaps between frequencies. In the next lesson, we'll see that the twelve rows of your piano roll are themselves a compromise, very slightly out of tune compared with natural intervals.