Tone Generator (Frequency Generator)

About the Tone Generator (Frequency Generator)

Play a pure sine tone — or a square, triangle or sawtooth wave — at any frequency from 1 Hz to 22 kHz, as far as your device can play. Sweep smoothly between two frequencies, mix two tones, send a different tone to each ear, sound the DTMF tones of a phone keypad, or pick a musical note with your own A4 tuning and see the frequency chart of every note.

The sound is generated in your browser, starts quietly and fades in, so a tone never blasts out at full level. A live oscilloscope shows the waveform, and every signal can be saved as a WAV file at 44.1, 48 or 96 kHz in 16-bit, 24-bit or 32-bit float, with the same band-limited waveforms you hear.

Common uses

• Checking speakers, headphones and subwoofers with steady tones and sweeps (rattles show up as buzzing at certain frequencies).
• Finding the frequency of a hum or whine by matching it by ear.
• Tuning an instrument to a reference note at A4 = 440, 442 or 432 Hz.
• Testing phone systems and IVR menus that react to keypad tones.
• Physics and music lessons on frequency, pitch, octaves, harmonics and beats.
• Making test signals for audio software: a WAV of an exact frequency, level and length.

The four waveforms

• Sine: a single frequency with no harmonics — the purest tone.
• Square: the odd harmonics (3, 5, 7 …) at 1/n of the fundamental’s level; bright and hollow.
• Triangle: the odd harmonics at 1/n², alternating in sign; softer than a square.
• Sawtooth: every harmonic at 1/n; the brightest, buzzy sound.

These are the Fourier series the W3C Web Audio API defines for its oscillator types. Only harmonics below half the sample rate are produced (the waves are band-limited), so a high square wave does not fold back into unrelated, out-of-tune frequencies. Each wave is scaled so its peak is the set level.

Sweeps: linear and logarithmic

A linear sweep changes the frequency by the same number of hertz every second: f(t) = f₀ + (f₁ − f₀) · t / T. A logarithmic sweep spends equal time on every octave: f(t) = f₀ · (f₁ / f₀)^(t / T). Because we hear pitch in octaves, a logarithmic sweep sounds even, while a linear one seems to race through the bass and crawl through the treble. Sweeps can play once, repeat from the start, or go up and down.

Notes and tuning

Notes use twelve-tone equal temperament: f = A4 × 2^((n − 69) / 12), where n is the MIDI note number (A4 = 69, middle C = C4 = 60). ISO 16:1975 sets A4 at 440 Hz; many orchestras tune slightly higher (442 Hz), and baroque ensembles often use 415 Hz. One semitone is 100 cents, and the cents between two frequencies are 1200 × log₂(f / f_ref) — the page shows how far any frequency is from the nearest note.

DTMF keypad frequencies (ITU-T Q.23)

Each key sends two sine tones at once: one from its row and one from its column.

• Row 1 (1 2 3 A): 697 Hz · row 2 (4 5 6 B): 770 Hz · row 3 (7 8 9 C): 852 Hz · row 4 (* 0 # D): 941 Hz
• Column 1 (1 4 7 *): 1209 Hz · column 2 (2 5 8 0): 1336 Hz · column 3 (3 6 9 #): 1477 Hz · column 4 (A B C D): 1633 Hz

The A–D keys exist in the standard but are missing from ordinary phones. When dialling a number, each key sounds for the set tone time with a pause between keys (100 ms each by default).

Two tones, beats and left/right tones

Two tones close in frequency beat: the level rises and falls |f₁ − f₂| times per second (440 and 441 Hz beat once a second). Two standard intermodulation test signals are built in: SMPTE (60 Hz and 7 kHz, levels 4 : 1) and CCIF (19 and 20 kHz, equal levels). Left / right plays a different sine tone in each ear; with headphones many listeners hear a slow beating at the difference frequency, called a binaural beat. This page makes no claims about health, sleep or concentration effects.

Limitations

• Your device sets the upper limit: just under half its audio sample rate (22 kHz on most devices). Speakers, headphones and your hearing usually stop well before that, and small speakers play little below 100 Hz.
• The levels are relative to your device’s full scale, not calibrated sound pressure, so this is not a hearing test.
• Bluetooth speakers and headphones add a delay and may apply their own processing.
• If you hear nothing on an iPhone or iPad, check the side switch and the volume, then press Play again.
• WAV files can be up to 10 minutes long; loop them in your player for longer.

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