Guitar Tuner (Enhanced YIN Algorithm)

A web-based guitar tuner that uses the YIN pitch detection algorithm for real-time monophonic note analysis. Originally written with ChatGPT, later redesigned and rewritten with Claude. It provides:

1. Accurate pitch detection across the full guitar range, including the low E string around 82 Hz — verified against synthetic harmonic tones to within fractions of a cent.
2. Six tunings — Standard, Drop D, E♭ Standard (half-step down), DADGAD, Open G, and Open D.
3. Chromatic mode — detect any note rather than snapping to the nearest string. Useful for capos, intonation checks, bass, or unusual tunings.
4. String lock — tap a string to lock the tuner onto it, so a badly flat low E isn't mistaken for a nearly-in-tune D.
5. Adjustable reference pitch — calibrate A4 anywhere from 432 to 446 Hz (default 440).
6. Analog-style needle gauge showing how many cents sharp or flat you are, with a large note display readable from across the room.
7. Per-string progress — a string's lamp turns green once you hold it in tune for a second.
8. Reference tones — tap any string button to hear its target pitch at the current calibration.
9. Audible confirmation — a short beep when you're in tune (±5 cents), with a mute toggle for phone speakers.
10. Screen wake lock — the display stays awake while the tuner runs (on supporting browsers).

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Live Demo

https://guitar-tuner-online.pages.dev/

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How It Works

1. Microphone Access

   • The app requests microphone access through the browser, with echo cancellation, noise suppression, and auto gain disabled (these otherwise distort guitar signals).
   • Browsers only allow mic access over HTTPS or on localhost (the demo site is served via HTTPS).

2. AnalyserNode + YIN

   • Audio is read from an AnalyserNode (8192-sample frames) inside a requestAnimationFrame loop — no deprecated ScriptProcessorNode.
   • Each frame is analyzed with the YIN algorithm, which is more robust than naive autocorrelation. The search is restricted to the relevant frequency range for speed, with parabolic interpolation for sub-sample accuracy. (This version also fixes a subtle bug in earlier YIN implementations of this project: the dip walk-down compared against not-yet-normalized values, biasing every reading slightly sharp.)
   • Readings are smoothed with a median filter (resistant to outlier frames), and the last reading is held briefly after the note decays so the display doesn't flicker.

3. Target Selection

   • All pitches are derived from MIDI note numbers and the adjustable A4 reference, so every tuning and the chromatic scale stay correct at any calibration.
   • In Strings mode the detected frequency is matched to the nearest string of the selected tuning using logarithmic (cents) distance rather than raw Hz, so high strings aren't unfairly matched to low ones. Locking a string overrides auto-detection entirely.
   • In Chromatic mode the target is simply the nearest semitone.

4. Cents Off & Feedback

   • The gap between detected and target pitch is shown in cents (1 semitone = 100 cents) on a needle gauge clamped to ±50 cents.
   • Within ±5 cents: the note turns green, the hint reads "In tune ✓", and a short beep plays.
   • Outside that range: the hint tells you which way to adjust ("Too low — tighten the string ↑" / "Too high — loosen the string ↓").

5. Per-String Progress

   • Hold a string in tune for one second and its button gains a green dot, so you can track which strings are done.

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Usage Instructions

1. Open the Live Demo (or host the code yourself over HTTPS / localhost).
2. Pick your setup — choose a tuning, switch between Strings and Chromatic mode, adjust the A4 reference if needed, and mute the beep if you're on phone speakers.
3. Press Start tuner and allow microphone access when prompted.
4. Pluck one string at a time. The tuner shows the nearest target, the detected frequency, and how far off you are. If a string is so far off that auto-detect grabs the wrong target, tap its button to lock onto it.
5. Adjust tuning until the needle centers and the note turns green — hold it there a second and the string's lamp turns green.
6. Repeat for all six strings, then press Stop tuner to release the microphone.

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Tweaks & Customizations

All constants live at the top of the script:

• Tunings — add or edit entries in the TUNINGS table; each is just a label plus six MIDI note numbers, so frequencies follow the calibration automatically.
• Tuning tolerance — IN_TUNE_CENTS (default ±5) controls how strict "in tune" is.
• Calibration range — A4_MIN / A4_MAX bound the reference-pitch stepper.
• Beep — BEEP_GAP_S sets the minimum gap between beeps; frequency and envelope are in beep().
• Sensitivity — lower YIN_THRESHOLD (default 0.15) for more sensitive detection (more false positives), raise it for stricter detection. RMS_THRESHOLD sets how loud the input must be before analysis runs.
• Smoothing — SMOOTHING sets the median window size; HOLD_MS controls how long the last reading stays on screen after the note decays; DETECT_GAP_MS throttles how often detection runs.
• Tuned indicator — TUNED_HOLD_MS sets how long a string must stay in tune before it's marked done.

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Browser Support

Works in current Chrome, Edge, Firefox, and Safari. Requires getUserMedia and the Web Audio API, which means HTTPS (or localhost) is mandatory.