Chromatic Tuner

A tuner answers one question: how far is the note you are playing from the note it is supposed to be, and in which direction. This one answers it in cents — the hundredth-of-a-semitone unit that makes “slightly sharp” measurable — and shows both the detected frequency and the target it is being compared against.

#What the readings mean

The gauge covers ±50 cents, which is exactly half a semitone in each direction: any reading beyond that window is nearer to a different note, and the tool will have re-labelled it. A needle sitting up to about five cents off centre is within the range that experienced players normally accept while playing; ten cents is clearly audible against another instrument; twenty is a mistake.

The reference pitch selector sets which frequency counts as A4. A4 = 440 Hz is the ISO standard, but plenty of orchestras tune to 442 or 443, historically informed groups use 415 for baroque repertoire and 430 for classical, and some players simply prefer 432. Choosing the wrong reference makes every note read as flat or sharp by a constant amount, which is the most common cause of a tuner that “does not agree” with the ensemble.

#How the detection works

The tool takes the microphone signal, and on each frame estimates the fundamental frequency by autocorrelation: it slides the waveform against itself and finds the time offset where the signal best matches its own past, which is the period of the lowest strong partial. The period converts to frequency directly, and the frequency converts to a note name and a cents deviation against the reference. A median filter over the last few frames keeps the display steady without hiding real drift — move the smoothing control up if the needle is nervous, down if you want to see a fast wobble.

Two consequences of that method are worth knowing. First, it tracks the lowest periodic component, so on a chord or a pair of strings it will report somewhere between them rather than a clean single pitch — tune one string at a time. Second, a very short note (a plucked string in its first tenth of a second) has too little periodic information to read accurately; let the note ring.

#Tuning something, in order

Start with the instrument’s own reference point. On a guitar, tune the lowest string first and then work up, so each new string can be checked against the previous one as a fourth or a fifth. On a violin, tune the A first because it is the reference the other strings are heard against, then the D and G below it, then the E. On a wind instrument, play at the dynamic you will actually perform at — a note that reads perfectly in tune when forced sounds flat when played softly, and the difference is the player, not the tuner.

When you are close, stop watching the needle and listen for beating: the slow throb between your note and a reference is the physical difference in frequency, and hearing it is a skill that transfers to playing in an ensemble, where no display is available. Use the reference tones panel above to produce a steady pitch and tune against that by ear, then check the needle.

#What a browser tuner cannot do

It hears one microphone, in one room. It cannot separate two strings, so it gives an average when both are sounding; it cannot measure a note shorter than roughly twenty cycles; and a phone or laptop microphone with automatic gain and noise suppression enabled can distort the waveform enough to bias the reading by a few cents. If a note refuses to settle, the room is usually the problem — background noise, another player, an instrument’s own resonance — rather than the maths.