Tuner

Why it exists

Because a one-euro tuner tells you whether the note is right, not how wrong it is. Here the offset is written in cents, which is the unit you actually think in: five cents you cannot hear, twenty you can, and fifty is a quarter tone.

No app, no account. It is a page.

On listening

The audio stays in the browser. It is not recorded, it is not sent anywhere, and the microphone stops when you press Stop or leave the page — your operating system’s indicator confirms that better than any sentence written here.

The three filters a browser usually applies to speech are deliberately switched off: echo cancellation removes exactly the sustained sound of a vibrating string, and automatic gain control chases the level and deforms the very thing being measured.

On the method

The frequency is not estimated from the bins of a Fourier transform. At 8192 samples a bin is almost six hertz wide, and there are barely two of them between the low E and F of a bass: the E would sit in the same bin for a good twenty cents. Here the period of the wave is measured instead, and at those frequencies it lasts more than a thousand samples — a long thing measured rather than a short one.

The method is McLeod’s, with parabolic interpolation of the peak. Above all it is what keeps the octave right: on a low string the second harmonic is often stronger than the fundamental, and a tuner that takes the tallest peak reads a note above the one you are playing.

On the tunings

Ten, and ten they stay. Seven for the six-string guitar — standard, drop D, half step down, drop C, DADGAD, open G and open D — and three for the bass, in four and five strings. Under each one there are a couple of songs that use it, because the name “open G” says less than Start Me Up.

If your instrument is not on the list there is chromatic mode, which ignores the tuning and simply gives you the nearest tempered note.

On the reference

A4 moves between 432 and 446 Hz, as in the note-to-frequency tool. It is there for playing along with a piano tuned elsewhere, with an old recording, or with an orchestra that sits at 442. The standard is still 440.

On the audio input

If you have more than one microphone — the laptop’s, a sound card, an interface with the guitar plugged in — the menu lists them and you can pick. The names appear after you allow access the first time: before that the browser keeps them hidden, because the list of devices attached to a machine identifies it almost as well as a cookie.

Changing input while the tuner is on closes the previous stream and opens the new one: that is what turns off the recording light on the device you are no longer using.

On the reference note

The «Listen» button plays the string you are aiming at, at exactly the pitch the tuner is waiting for. It is there for tuning by ear — still the best way to tune a guitar to itself — and for hearing where you should end up before you turn the peg.

The frequency is the same one the needle compares against, not one worked out separately: were they two different sums, the day one of them forgot the reference A the tool would play one note and demand another.

Change string while it plays and the note slides across instead of starting again. Change the reference A and it moves too: the opposite would be absurd.

Why they do not go together

The reference note and the microphone never come on together, and turning one on turns the other off. This is not a technical limitation: a speaker holding an E while the analyser listens to the room makes a tuner that measures itself, and says “in tune” with the guitar leaning against the wall.

With headphones there would be no problem, but the browser cannot tell whether you are wearing them.