What we tested in the current converter
We generated a 22,050 Hz mono WAV with a C-major triad for 1.5 seconds, 0.5 seconds of silence, and an F-major triad for 1.5 seconds. Each chord was made from three sine tones at equal source level. No video, performer, title, channel name, or copyrighted recording was used.
| Generated chord | Expected pitches | Detected chord starts | Result |
|---|---|---|---|
| C major | C4, E4, G4 | 0.023 s for all three notes | All expected pitches found |
| F major | F4, A4, C5 | 1.985–1.998 s | All expected pitches found |
The browser exported a 117-byte MIDI file with eight note events and no console errors. Six events matched the two intended triads. The F-major chord also produced short A4 and C5 fragments starting at 3.286 seconds, each lasting 0.185 seconds.
What “polyphonic” means here
A monophonic line has one pitch at a time. A polyphonic passage can contain several simultaneous pitches, as in a chord. MIDI represents those pitches as separate note events whose time ranges overlap. In this test, the three notes of each intended chord began within 0.013 seconds of one another, so a MIDI editor displays them as a chord rather than a sequence.
Why chord transcription can add or miss notes
A recording contains frequencies, not labeled keys. Harmonics from one note can overlap another note's fundamental frequency. Reverb can keep energy ringing after a release, and several instruments can mask one another. The model must infer which pitches begin and end, so a clean triad is easier than a full mix and even a clean test can create short edge fragments.
How to review a converted chord
- Open the MIDI in a piano roll. Notes that start together should line up vertically.
- Compare the lowest and highest expected pitches. Missing outer notes can change the chord inversion or identity.
- Inspect chord releases. Very short notes immediately after a chord may be tail fragments rather than intentional notes.
- Edit only after listening. A visually unusual note can still belong to a suspension, melody, or inner voice.
What this test does and does not prove
It verifies that the current local-file converter can output overlapping notes and captured both generated triads in this run. It does not establish an accuracy percentage, prove that every chord voicing will be complete, or show that a dense song can be separated into instruments.
If a draft contains short unwanted events, use the extra-note cleanup test. For mixed recordings, read the track-separation boundary. If the notes are present but the sound is wrong, see the instrument and playback guide.