Marimba, C2 to C7. Scroll across and tap a bar to hear its reference tone.
Press Record and strike one bar at a time. The note and its overtones appear while the bar rings.
Settings
Compare the last strike
| Component | Reference Hz | Recorded Hz | Difference (cents) |
|---|
Each difference is 1200 × log2(recorded Hz / reference Hz). The overtone ratios above show how the bar is tuned relative to its own fundamental.
Spectrum of the last strike
Dashed lines mark the target overtones. Dots mark the peaks the tuner measured.
Strikes in this recording
Saved measurements
If a bar reads out of tune
Check the measurement first
- If every bar is off by about the same amount, the instrument is tuned to a different reference. A4 = 440 Hz and A4 = 442 Hz are 8 cents apart. Change the reference pitch in Settings until the middle bars read close to 0.
- The lowest bars a few cents flat and the highest a few cents sharp is often deliberate. Yamaha, for one, stretches the tuning of its bars the way a piano is tuned.
- Bars and resonators are tuned for a room at about 23 °C. In a warmer room the bars go flat and the resonators go sharp; in a colder room it is the other way round. Let the instrument stand in the room before you judge it.
- Let the previous bar die away, or damp it with your hand, before you strike the next one. A low bar that is still ringing can be louder than the bar you have just struck, and the tuner may then name the old bar again.
- Strike three times, a little away from the middle of the bar. If the spread (±) is as large as the error, measure again. An overtone that is “not found” usually means the bar was struck exactly in the middle, or it is a high bar whose overtone dies away too quickly to measure. Neither is a fault.
How far is too far
| Reading | The note | An overtone |
|---|---|---|
| Within 5 cents | In tune. Leave the bar alone. | In tune. |
| 5 to 15 cents | You can hear it when another instrument holds the same note. Write it down and measure again on another day. | It changes the colour of the sound more than the pitch. Write it down. |
| More than 15 cents | Out of tune. The bar needs retuning. | The bar sounds dull or sour next to its neighbours. Have it corrected together with the note. |
| 50 cents or more, or a short, dead sound | Look for a crack, a bar hung in the wrong place, a bar touching a post or its neighbour, or a worn cord. A cracked bar cannot be retuned and has to be replaced. | |
These bands are the working guide of this tuner. Makers do not publish one common tolerance.
How a bar is retuned
Material can be taken off a bar but never put back, so a tuner removes a little, measures, and repeats.
- The note is too high. Material is removed from the underside in the middle of the arch. This lowers the note more than the overtones.
- The note is too low. A little is removed from the underside at the very ends, outside the cord holes. This raises the note and the overtones together. The bar is not shortened, and nothing is removed at the holes, where it rests. Only small corrections are possible, so a bar that is far too low is usually replaced.
- An overtone is too high. Material is removed from the arch about a quarter of the way in from each end. This lowers the overtone and hardly moves the note.
- An overtone is too low. The whole bar is raised at the ends, and then the note is brought back down in the middle.
- A wooden bar is sealed again afterwards, because moisture changes its pitch.
Do not sand the bars of a school instrument yourself. Save your results, download the table and give it to whoever looks after the instrument. The bars then go to the maker or to a workshop that retunes tuned percussion.
By instrument
- Marimba. The overtones should sit at 4 and, on the low bars, 10 times the note. Wooden bars drift with age and moisture. In the top octave the overtones fade too fast to measure, so judge those bars by the note alone. On the lowest bars hold the microphone close to the middle of the bar, because small microphones hear little below 100 Hz.
- Xylophone. Most are tuned with the overtone at 3 times the note, some at 4. If every bar says “not found”, choose Vibraphone, which looks for 4. Retuning works as on a marimba.
- Vibraphone. The overtone should sit at 4 times the note. Aluminium does not take up moisture, so these bars hold their tuning much better than wood. A bar that reads wrong is usually dented, bent or not the original one, and is reground by a workshop or replaced. If a bar reads in tune but sounds weak, look at the resonator under it, not at the bar.
- Plain bar. There is nothing to retune: 2.76 and 5.40 follow from the physics of an even bar. If yours reads differently, it is not even along its length, or it is held away from its nodes, which lie 22.4% of the length from each end.
- Note only. Any steady tone is compared with the equal-tempered scale. Overtones are not checked.
Sources: Yamaha, care for mallet instruments and the tuning of percussion instruments; Mechanical Music Digest, the construction and tuning of vibrating bars; Percussion Clinic Adelaide, building a marimba.
How it works
- Recording. The microphone signal is used as it arrives, at the sample rate of the device. Echo cancellation, noise suppression and automatic gain are switched off, because they change the sound. A gentle filter removes any constant offset and rumble below 40 Hz.
- Finding strikes. While recording, the tuner follows the loudness in steps of 10 ms and keeps a running estimate of the room noise. A strike begins when the loudness jumps by more than half within a few hundredths of a second and is at least four times the room noise. The first reading appears about a tenth of a second later and is refined while the bar rings, for up to 1.5 s or until the sound has died away. With an instrument chosen, a sound is listed only if it rings like a struck bar: it starts suddenly, dies away, keeps its pitch, and has no row of harmonics at 2, 3, 5 or 6 times the note, which is the mark of a voice and of string and wind instruments. Note only measures any steady tone. In an uploaded recording, a strike is a peak of the loudness that rises by at least 20% of the loudest one, with strikes at least 0.3 s apart.
- Hann window. Each piece of sound, N samples long, is faded in and out by multiplying sample n by w(n) = 0.5 × (1 − cos(2πn / (N − 1))) Without this, the sharp cut at the two edges would add false frequencies to the spectrum.
- Fourier transform. The windowed piece is padded with zeros to a power of two, at least 4 times its length, and transformed with an FFT. Bin k stands for the frequency k × fs / N, where fs is the sample rate and N the padded length. Levels are given in decibels below the strongest bin above 60 Hz: level = 20 × log10(|X(k)| / max |X|)
- Peaks. A peak is a local maximum that stands at least 15 dB above the lowest point between it and any taller peak, and is no lower than −70 dB. Of two peaks closer than 15 Hz, only the taller one is kept.
- Between the bins. A parabola is fitted through the peak bin k and its two neighbours, whose levels are a, b and c. Its top lies at k + ½ × (a − c) / (a − 2b + c) which gives the frequency to a small fraction of a bin.
- The note. The fundamental f1 is the strongest peak above 60 Hz, unless a clear peak sits at a half, a third or a quarter of that frequency, or at another target ratio below it. That lower peak is then the fundamental, as long as it is no more than 20 dB weaker and is not mains hum at 50 or 60 Hz. A small microphone hears little of a low bar’s note and much more of its overtones. So below 200 Hz the tuner also accepts a weak peak as the note when the bar’s overtones sit where that note would put them, and if there is no peak at all it says so instead of naming an overtone. If you type the bar’s note, the tuner takes the strongest peak within 8% of it instead.
- Note name and cents. The note is n semitones from A4, and 100 cents make one semitone: n = round(12 × log2(f1 / A4)) target = A4 × 2n/12 error = 1200 × log2(f1 / target) cents
- Overtones. For each target ratio t, the strongest peak between 0.8 × t × f1 and 1.2 × t × f1 is taken. Its ratio r = f / f1 is shown with its error, 1200 × log2(r / t) cents. A peak counts only if it stands well above the noise around it. An overtone that fades long before the fundamental is read from the start of the strike.
- Several strikes. Live mode shows each strike on its own. For an uploaded recording of one bar, the results are averaged over the strikes, and the spread (±) is their standard deviation, which shows how repeatable the measurement is.
Where the targets come from: a plain bar with free ends has overtones at 2.76 and 5.40 times its fundamental. These numbers are the squares of the roots of cos x × cosh x = 1, divided by the square of the first root. Makers carve an arch under a marimba bar, which lowers the fundamental much more than the first overtone, and stop when the ratio reaches 4.