Free online tool
Tone Generator: Online Frequency Generator, 1 Hz to 20 kHz
Free online tone generator: sine, square, sawtooth and triangle waves from 1 Hz to 20 kHz, with note names, volume, balance, sweep and binaural beats.
Hearing safety. Start with your device volume low and raise it slowly. Loud sound, especially through headphones or at high pitch, can damage hearing. Stop the tone if it is uncomfortable.
The sweep plays at the waveform, volume and balance set below. Sweeping to 20 Hz or 20 kHz passes through the whole range of human hearing, so keep the volume low.
Left ear: the frequency above. Right ear: that frequency plus the beat. Headphones are required; the effect does not work on speakers. This is just two tones a few hertz apart, with no health or mood claims.
The volume is high. Lower it if the sound is uncomfortable.
Square and sawtooth waves contain many harmonics and sound harsher than a sine at the same level. Sounds below about 40 Hz are hard to hear on laptop and phone speakers; do not turn the volume up to compensate.
About the Tone Generator
A tone generator plays a steady sound at a frequency you choose, so you can hear a single pitch, check a tuning, or test speakers. This free online tone generator makes sine, square, sawtooth and triangle waves from 1 Hz to 20 kHz, with note names, volume, balance, frequency sweep and binaural beats. It runs in your web browser with no sign-up, and nothing you enter is uploaded.
Use it as a sine tone generator for pure pitches, a frequency generator for test tones, or a Hz generator when you already know the number. It also works as an audio frequency generator for checking which speaker or headphone channel is which.
How to use the online tone generator
- Set your device volume low, then press ▶ Play. The tool starts quietly at 20%, so raise the volume slowly.
- Choose the frequency with the Frequency slider (log scale, 1 Hz to 20 kHz), by typing a value in Hz, or by typing a note name such as A4 or C#5. The nearest note and its offset in cents appear. A4 is 440 Hz unless you change A4 reference (Hz).
- Pick a waveform. Sine gives the pure tone; Square, Sawtooth and Triangle add harmonics.
- Use Balance to send the tone to the left or right speaker only, for example to check which channel is which.
- Switch to Sweep to glide from Start (Hz) to End (Hz) over Duration (s), with Curve set to Logarithmic or Linear. Or switch to Binaural beat to play two tones a few hertz apart, one in each ear. Use headphones for that mode.
The preset buttons (50, 100, C4, A4 440, 1 kHz, 5 kHz, 10 kHz, 15 kHz, 20 kHz) jump straight to common values, and −8ve, −1, +1 and +8ve move an octave or a semitone from the current frequency.
Start with a sine wave when you want a pure tone or need to match a pitch, because it contains only the frequency you choose. To tune by ear, set the A4 reference (Hz) to match your instrument, then watch the cents readout. A value near 0 means the frequency is close to the nearest note.
What is frequency, and how is it measured?#
Frequency is the number of vibrations per second, measured in hertz (Hz). A tone at 440 Hz vibrates 440 times each second. The Hz box and the Frequency slider both set this number directly, and a higher number gives a higher-sounding pitch.
How does frequency relate to pitch, and why is the slider logarithmic?#
Pitch is how we hear frequency. Doubling the frequency raises the pitch by one octave, so equal steps in pitch are equal ratios of frequency, not equal differences in hertz. That is why the Frequency slider is logarithmic: the same distance on the slider is always the same musical interval. In equal temperament, each semitone multiplies the frequency by 2^(1/12), about 1.05946. The note frequency calculator lists the frequency of every piano key.
What is the difference between sine, square, sawtooth and triangle waves?#
All four waves repeat at the frequency you choose. They differ in shape, and so in their harmonics, which are multiples of the fundamental. A sine wave has none. A triangle has odd harmonics falling off as 1/n², a square has odd harmonics falling off as 1/n, and a sawtooth has all harmonics falling off as 1/n. More harmonics at the same level sound brighter and harsher. The browser’s oscillators use band-limited versions of these shapes so that high notes do not produce aliasing.
What is 440 Hz and what is A4?#
A4, the A above middle C, is the standard tuning reference at 440 Hz. Other notes follow from f = 440 × 2^((n − 69) / 12), where n is the MIDI note number. A3 is therefore 220 Hz and A5 is 880 Hz. Change A4 reference (Hz) to hear other tunings between 400 and 480 Hz.
What are cents?#
A cent is one hundredth of an equal-tempered semitone, so there are 1200 cents in an octave. The readout shows how far the current frequency sits above (+) or below (−) the nearest note.
How does a frequency sweep work: linear or logarithmic?#
A sweep glides from Start (Hz) to End (Hz) over Duration (s). A linear sweep changes the frequency by the same number of hertz each second, so most of its time is spent at high pitches. A logarithmic sweep changes it by the same ratio each second, so each octave takes equal time, which matches how pitch is heard. A sweep from 20 Hz to 20 kHz covers about ten octaves.
What is a binaural beat?#
When two tones a few hertz apart play one in each ear through headphones, many listeners hear a slow pulsing at the difference frequency. The effect happens in perception, not as a sound in the room. Beat (Hz) sets that difference. The tool plays the two tones and makes no claim about health or mood benefits.