How the detector works, in plain words
- It cuts the audio into short frames of about a third of a second.
- For each frame it measures how much energy sits on each of the 12 note names (C, C#, D and so on), ignoring octave. This is a chromagram.
- It compares that pattern with templates for every root and chord type: for example C major lights up C, E and G.
- It chooses the best chord per frame, but prefers to keep the previous chord unless the evidence is strong, which removes flicker (a Viterbi smoothing step).
- It estimates the tempo, snaps chord changes to the nearest beat, drops chords that last less than a beat, and merges repeats.
That is why it does well on sustained harmony (guitar strums, piano chords, pads) and worse on a mix where drums and vocals blur the picture.
When to trust it, and when to check
| Situation | Trust level | What to do |
|---|---|---|
| Clear acoustic guitar or piano | High for main chords | Spot-check the 7th chords |
| Full band mix | Medium | Confirm the key, then check chord changes by ear |
| Short loop or sample (2 to 8 bars) | Medium to high | Chords repeat, so one fix applies throughout |
| A chord shown as sus or dim | Low to medium | Often a triad with passing notes; try the plain triad |
| Recording out of tune with standard | Low | Transpose by one semitone and listen |
No chord detector is perfect. The honest way to use one is as a fast first pass that gets you most of the chart, then fix the rest by ear.
What it will not detect
- Live microphone input: this tool analyses a file you drop in. Record first, then analyse.
- 9th, 11th, 13th, added-note and slash chords. They are simplified to the closest of the seven supported types.
- Individual voicings, inversions or which strings to play.
- Lyrics or sections like verse and chorus.
Use cases beyond learning a song
| You are | Use it to |
|---|---|
| A producer with a sample | Find the key and chords so you can play along or write a counter-melody |
| A teacher | Check a student's recording against the chart |
| A songwriter | Capture the changes of a rough demo you recorded on your phone |
| A DJ | Check the key and chord feel before mixing; see also the BPM finder |
Frequently asked questions
What is a chord detector?
A tool that listens to audio and names the chords over time. This one matches the notes it hears to seven chord types and lays the result out as a timeline with the key and tempo.
Can it detect chords live from my microphone?
No. It analyses an audio file. Record a clip with any app, then drop the file in.
Is the audio uploaded?
No. All processing happens in your browser. Only the page itself is downloaded.
Which chords does it recognise?
Major, minor, dominant 7th, minor 7th, sus2, sus4 and diminished, for all twelve roots.
How accurate is it?
Approximate: best on a single harmonic instrument, weaker on busy mixes and rich jazz chords. Use it for a fast first pass and confirm by ear.
Does it work on any genre?
It works best on harmony-driven music such as pop, rock, folk and worship. Rap, spoken word and drum-only tracks have little harmony to detect.
Why does the chord change slightly after the beat?
The detector looks at windows of about a third of a second, then snaps changes to the tempo grid. A sloppy or tempo-drifting recording will show changes a little early or late.