Music Theory Tools: Notes, Scales, Chords and Metronome

The Music Theory page gathers four panels behind a tab strip. Notes turns a note and octave into a frequency, period and wavelength and converts a typed Hz value to the nearest note in cents. Scales & Chords spells 14 scales, builds 20 chord qualities and names clicked notes. Circle of 5ths pairs each major key with its relative minor, key signature and diatonic triads. Metronome runs 30–300 BPM in four time signatures with tap tempo and note durations in milliseconds. Pitches use twelve-tone equal temperament with A4 = 440 Hz by default (MIDI 69; MIDI 60 is C4), and Reference A4 retunes the Notes grid between 415 and 466 Hz.

Updated 2026-10-01Reviewed by CalcX Editorial Team5 sources5 min read

How to use it

Pick a panel.The strip switches between Notes, Scales & Chords, Circle of 5ths and Metronome; each has its own address.
Notes.Choose a note and octave, or click a key to hear it. The cards read frequency, MIDI number, period and wavelength; Reference A4 retunes frequency, period and wavelength between 415 and 466 Hz, not the MIDI number or note names. A typed pitch under Frequency → note (cents off) returns the nearest note and its cents.
Scales & Chords.Choose a root and scale for the spelled notes, degrees and whole/half pattern; Play up sounds root to octave. The builder shows note names and lit keys; the identifier names two or more clicked keys.
Circle of 5ths.Click a wedge to select a key. The cards give its signature, relative minor, parallel minor and scale; the table lists seven diatonic triads, toggles major and natural minor and plays each row.
Metronome.Set BPM and a time signature (2/4, 3/4, 4/4, 6/8), then Start; Tap tempo averages recent taps and offers a rounded value to apply. The table converts note values to milliseconds.

Worked readouts

Every value below is what the page displays.

Set	Readout
Notes: A4, Reference 440	440 Hz, MIDI 69, period 2.2727 ms, wavelength 0.77955 m
Notes: C4	261.626 Hz, period 3.8223 ms, wavelength 1.311 m
Notes: C4 at Reference A4 432	256.869 Hz, period 3.893 ms, wavelength 1.3353 m
Notes: 446 under Frequency → note	A4 +23.4 cents; 480 Hz reads B4 -49.4 cents
Scales: D Major	D E F# G A B C#, pattern W-W-H-W-W-W-H
Chords: C Major 7th; A Minor	Cmaj7 = C3 E3 G3 B3; Am = A3 C4 E4
Chords: click C4 E4 G4 A4	C6 · Major 6th, then Am7 · Minor 7th
Circle: C major	signature no accidentals; relative Am · no accidentals; parallel Cm · 3♭ · Bb Eb Ab
Metronome: 120 BPM	quarter 500 ms, dotted quarter 750 ms, 16th 125 ms; 6/8 every 250 ms

Where the numbers come from

Every pitch is a MIDI note on the equal-tempered grid: frequency = A4 × 2^((MIDI − 69)/12), so a semitone is the twelfth root of two and a cent a hundredth of a semitone. A4 is 440 Hz by default; Reference A4 retunes the Notes panel from 415 to 466 Hz, moving frequency, period and wavelength while MIDI numbers stay fixed. Wavelength divides 343 m/s, the speed of sound in air near 20 °C; a quarter note lasts 60,000 ÷ BPM milliseconds.

Range and scope

The reference band is 415–466 Hz, and only the Notes panel follows it.: Every other panel always sounds at 440 Hz; the Reference A4 field clamps to the band.
BPM is clamped to 30–300.: A typed 20 runs at 30, and the duration table follows the clamped tempo; tap tempo averages the last eight taps and restarts after a gap over 2.5 seconds.
What it does not do.: It is not a listening tuner, a score or tab player, or a room-acoustics tool: no microphone, no imports. To tune from live sound use the microphone tuner in the Audio Lab; for room modes and reverberation, the Engineering Handbook acoustics panel.

The chord builder spells its own way

Pitch names follow a simple rule: the chord builder uses sharp spellings unless the root contains a flat, so C minor prints as Cm = C3 D#3 G3, not C E♭ G. The Scale panel spells the same pitches the other way — C natural minor reads C D Eb F G Ab Bb — and B♭ minor's v reads Fm [F G# C]. Write the spelling the key expects.

Where it helps

Tuning and ear training

Play a reference note, then type a pitch you hear under Frequency → note: A4 +23.4 cents is a quarter-semitone sharp. The octave table lists all twelve frequencies for the selected octave.

Writing and checking progressions

Build any of the 20 chord qualities, or click a voicing and read every name the identifier gives it — C6 and Am7 are the same four pitch classes. The circle adds the key's relative minor, parallel minor, signature and triads.

Practice room and recording

Tap the tempo and apply the rounded Detected 120 BPM, or set BPM directly. The duration table turns each note value into milliseconds for a click track or delay time; in 6/8 the fourth click is accented.

References

ISO, ISO 16:1975 — Acoustics: Standard tuning frequency (Standard musical pitch), iso.org （访问日期：2026-10-01）— A4 = 440 Hz.
Wikipedia, Scientific pitch notation （访问日期：2026-10-01）— C4 as middle C and the MIDI frequency formula.
Wikipedia, Equal temperament （访问日期：2026-10-01）— twelve equal semitones and the 100-cent semitone.
Wikipedia, Circle of fifths （访问日期：2026-10-01）— relative minors and the order of sharps and flats.
Wikipedia, Metronome （访问日期：2026-10-01）— beats per minute and accented beats.