Tone Generator
Play a pure tone at any frequency to test speakers, hearing and tuning — with a clear warning about volume and hearing damage.
Start at a low volume to protect your hearing.
Above half the sample rate you get a different tone entirely
Digital audio can only represent frequencies below half the sample rate — the Nyquist limit, which is 22,050 Hz at the usual 44,100 samples per second. Ask for anything above it and the tone does not go silent or distort. It folds back and comes out as a completely different, audible pitch:
| You ask for | Sample rate | You hear |
|---|---|---|
| 21,000 Hz | 44,100 | 21,000 Hz — unchanged |
| 25,000 Hz | 44,100 | 19,100 Hz |
| 30,000 Hz | 44,100 | 14,100 Hz |
| 50,000 Hz | 48,000 | 2,000 Hz |
This is not an approximation or a rounding artefact. Sampling a 30 kHz sine and a 14.1 kHz sine at 44,100 Hz gives values that agree to within two parts in a trillion — at the sample instants the two signals are the same signal, so nothing downstream can recover which one was meant.
That matters here because a tone generator is the one tool people deliberately push to the top of the range, usually to find the limit of their hearing. Any reading above the Nyquist frequency measures the software rather than the ear — so if a "25 kHz" setting is plainly audible, that is aliasing, not remarkable hearing. This generator stops below the limit for exactly that reason.
Why bass is harder to tune by ear
Two tones close together produce beats — a slow pulsing at exactly the difference between their frequencies. It is the most precise tool an ear has, because you are counting a rate rather than judging a pitch:
| Two tones | Beat rate | One beat every |
|---|---|---|
| 440 and 441 Hz | 1 Hz | 1.00 s |
| 440 and 444 Hz | 4 Hz | 0.25 s |
| 440 and 450 Hz | 10 Hz | 0.10 s |
Here is the part that catches people out. A cent is a ratio, so the same musical error is a different number of hertz at different pitches — and the beat you are listening for gets slower as you go down:
| Note | Frequency | One cent sharp is | One beat every |
|---|---|---|---|
| A4 | 440 Hz | 0.2542 Hz | 3.9 s |
| A3 | 220 Hz | 0.1271 Hz | 7.9 s |
| A2 | 110 Hz | 0.0636 Hz | 15.7 s |
| A1 | 55 Hz | 0.0318 Hz | 31.5 s |
Every octave down doubles the beat period, exactly. One cent sharp at A4 beats every 3.9 seconds; the same one cent at A2 takes 15.7 seconds — four times longer for an error that is musically identical.
So bass instruments are not harder to tune because low pitches are vague. They are harder because the evidence arrives four times more slowly, and most people give up on a beat before it has completed a cycle. The practical trick is to tune the octave above and drop down, or simply to wait longer than feels reasonable — around fifteen seconds per judgement at the bottom of a bass.
How to use
- Set the frequency and waveform.
- Start at a low volume and raise it carefully.
- Never start a high-frequency tone at high volume.
- Use headphones for hearing-related tests, speakers for equipment.
Frequently asked questions
What is a pure tone?
A sine wave at a single frequency, with no harmonics. Almost no real sound is pure — instruments and voices produce a fundamental plus a series of overtones, and it is those overtones that make a violin and a flute sound different at the same pitch.
What frequency is which note?
A above middle C is conventionally 440 hertz, and each octave doubles the frequency, so the A an octave up is 880. The relationship is exponential rather than linear, which is why equal steps in pitch are equal ratios in frequency.
Can this damage my speakers?
Yes, if you are careless. A sustained loud tone puts far more continuous energy into a driver than music does, and low frequencies at high volume can damage small speakers and tweeters quickly. Start quiet, and do not leave a loud tone running.
Can it damage my hearing?
Also yes. A sustained pure tone is fatiguing and potentially harmful at volume, and high frequencies are particularly unpleasant. The rule is to start at a low volume and raise it slowly — never the reverse, especially with headphones on.
What are the other waveforms for?
A square wave contains only odd harmonics and sounds hollow and buzzy; a sawtooth contains all harmonics and sounds bright and harsh; a triangle sits between. They are the basic building blocks of subtractive synthesis, which is why synthesisers offer exactly these.
What can I use this for?
Checking whether a speaker or channel is working, finding rattles and resonances in a room, tuning an instrument against a reference, and testing the frequency response of equipment. It is a genuinely useful diagnostic tool for anything audio.
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