Note Frequencies: Tuning Kicks and Samples

In the previous lesson, you saw that a note is first of all a fundamental, a precise frequency. For melodic instruments, you almost never need to know that number: you play a row, and it's in tune. Low sounds are a different story. A kick, an 808 or a bass sample often comes with its own pitch, which doesn't necessarily fall in your key. To tune them, you need to be able to read frequencies.

A starting point: A at 440 hertz

The whole scale starts from a single reference. The note A4, the A just above middle C, vibrates at 440 hertz. It's the most widespread tuning reference today, and it's your DAW's default. After that, two rules are enough: going up an octave doubles the frequency, and going up a semitone multiplies it by about 1.0595.

Let's go down from A4. One octave lower, A3 vibrates at 220 hertz, then A2 at 110 hertz, A1 at 55 hertz and A0 at 27.5 hertz, which is the lowest key on a piano. Listen to these four A's as sine waves: it's the same note, and yet the last one feels more like pressure than sound.

On ordinary headphones or small speakers, the A at 27.5 hertz may be almost inaudible. That's normal: many playback systems reproduce the extreme low end poorly. Remember the zones of the spectrum we saw at the start of the course: the sub sits roughly between 20 and 60 hertz, and the fundamentals of most 808s fall in it or just above it.

The table of low notes

Here are the frequencies of the three octaves used most for basses. There's no need to learn them by heart, but keep a few landmarks in mind: E1 around 41 hertz, A1 at 55 hertz, C2 around 65 hertz. Notice too that from one column to the next, on the same line, the frequency doubles: that's the octave.

One detail matters a lot in the low end: the gap between two neighboring notes is tiny in hertz. Between E1 and F1, there are only about 2.5 hertz. Between E3 and F3, there are almost 10, for the same semitone. That's why an error of a few hertz, which wouldn't matter in the midrange, can make an 808 sound completely off.

The cent, the unit of fine-tuning

Between two rows of the piano roll, there's nothing. Yet a sound can easily fall between them: a sample recorded on an out-of-tune instrument, a loop that's been sped up slightly, a kick whose maker didn't think about the key. To measure these small gaps, each semitone is divided into a hundred equal parts, called cents. So an octave has 1,200 cents.

The useful thing about the cent is that it doesn't depend on the register. Ten cents are the same gap to the ear on an A1 as on an A4, whereas in hertz, that's about 0.3 hertz in the first case and 2.5 hertz in the second. Listen to an A, then the same A followed by a version raised by 10 cents, then by 50 cents, that is, a quarter tone.

Ten cents are barely noticeable when the two sounds follow each other. Fifty cents sound clearly out of tune: the second sound no longer belongs to any row. Keep an order of magnitude in mind: when two sounds play at the same time, just a few cents are enough to make them clash, as you'll hear in the lesson on detuning.

Tuning a kick, an 808 or a sample

The method is always the same, in three steps. First, you find the frequency of the sound's fundamental. Next, you look up the nearest note in the table and the gap in cents. Finally, you correct it with the sampler's pitch controls: semitones for the note, and the fine-tune control, in cents, for the rest.

Let's take an example. A kick has a fundamental around 50 hertz once its attack is over. The nearest note is G1, at 49 hertz, and the gap is about 35 cents sharp. If your track is in G minor, lower the fine-tune by 35 cents, and your kick will land on the tonic. If it's in G sharp minor, it's simpler to go up about 65 cents to reach G♯1, at 51.9 hertz.

To find the fundamental, you have two tools. A tuner shows the note name and the gap in cents directly: play the sound on its own, ideally a held note, and read it. A spectrum analyzer draws all the frequencies present; the fundamental is usually the first big peak from the left, and the harmonics appear at two, three, four times its frequency.

In the next lesson, we'll see what happens when you change the pitch of a whole sample: why it speeds up, and how to stop it from doing so.