Is every bar on the marimba in tune?

What it measures

An ordinary tuner hears only the note. A marimba bar also rings at higher pitches at the same moment, and those overtones give the instrument its warm, round sound. Marimba Studio measures both.

• The note. The nearest note name, and the difference from it in cents (100 cents is one semitone).
• The overtones. The first and second overtone as a multiple of the fundamental, compared with the target for the instrument.
• A reference to hear. The keyboard at the top follows the instrument you choose: marimba, xylophone, vibraphone or plain bars. Tap a bar and it plays a generated reference tone for that instrument. After a recording you can listen to your strike and to the reference one after the other.

Everything runs in the browser. The sound is analysed on your device and is never uploaded.

Why the overtones matter

When a bar is struck it bends in several patterns at once. The slowest pattern is the fundamental and usually sets the note. Faster patterns add the overtones.

A plain straight bar has overtones at 2.76 and 5.40 times the fundamental, which sounds clangy. A marimba maker carves an arch under the bar. The thinner middle lowers the fundamental much more than the first overtone, and the cut is adjusted until the overtone is exactly four times higher. A 200 Hz bar then has overtones near 800 Hz and 2,000 Hz.

These are approximate targets. Makers and registers differ, so treat a small difference as a question for the music department, not as proof of a fault.

The cord runs through two points where the bar barely moves, called nodes, 22.4% of the length from each end. That lets the bar ring freely. A bar in tune on its fundamental can still have a mistuned overtone, and the second check is what reveals it.

Measure the school marimba

Start with a few bars, for example C3, E3, G3, C4, E4, G4, A4 and C5, depending on the range. If the setup works, record every bar including the sharps and flats.

1. Set up

   Use a quiet room. Hold or fix the phone steady about 30 to 60 cm above the bar and away from the frame. Switch off voice enhancement if the phone has it. Confirm the marked A4 of the instrument, usually 440 or 442 Hz, and set the same value in the tuner.

2. Record

   Open the tuner in its own browser tab and press Record. Strike one bar and let it ring. The note and its overtones appear while the bar is still sounding, and each strike gets its own result. For an original phone recording, use Analyse a recording instead; that works best with repeated strikes on a single bar.

   Strike near the centre for a clean pitch, and about a quarter of the length from one end to bring out the upper overtone. Leave 5 to 8 seconds between hits, and longer while low bars still ring.

3. Label and save

   Press Save this result for every bar you want to keep, then Download CSV. Note the make and model of the instrument, the A4 setting and the room temperature. Keep the original recordings.

4. Compare

   Read the main-note error and the overtone errors separately for each bar. Repeat under similar conditions, for example once a month, to see which bars drift.

Open the tuner

How the numbers are calculated

For a note n semitones from A4:

target = A4 × 2^n/12 Hz
note error = 1200 × log₂(measured Hz / target Hz) cents
overtone error = 1200 × log₂(measured ratio / target ratio) cents, where the measured ratio is overtone Hz / fundamental Hz

A positive value is sharp and a negative one is flat. The tuner takes a short piece of sound after the strike, applies a Hann window, zero-pads it and runs an FFT, then refines each peak by fitting a parabola through it. The full method is written out in the “How it works” section at the bottom of the tuner.

Where the project stands

• The analysis passes the automatic tests on synthetic bars at 44.1 and 48 kHz, including noise and mains hum.
• Live strike detection, the demo and the reference keyboards for each instrument work in software.
• Recording with a real microphone on the school instrument is still to be confirmed.
• The goal of 1 to 2 cents accuracy has been shown on synthetic signals only. It still has to be shown on real recordings: check single tones from a tone generator, then repeated strikes on the same bar.

Learn more

• How to Make a Marimba, Part 3: shaping and tuning bars (video).
• Finding marimba bar nodes: the salt test (video).
• Yamaha: marimba bar shapes and vibration patterns.
• University of Iowa marimba samples: real recordings to listen to. They are not built into the tuner.

Questions