What you can do with an audio signal generator
An audio signal generator produces clean, predictable signals so you can hear (or measure) what your equipment does with them. Because you know exactly what goes in, anything else you hear — a buzz, a rattle, a missing channel, a dip in the bass — comes from your speakers, headphones, cables or room. This page gives you the three classic test signals:
- Steady tones at any frequency from 1 Hz up to about 20 kHz, as sine, square, triangle or sawtooth waves.
- Frequency sweeps that glide from one frequency to another over a set time.
- Noise: white noise and pink noise.
Everything plays live in your browser, and any signal can be saved as a WAV file so you can use it in a DAW, on a phone, on a USB stick in a car stereo or on a test bench.
Testing speakers and headphones
Channel check. Use the Left / right check preset (or set the output to Left, Right or Alternate). The tone should come only from the side shown. If it comes from the wrong side, a cable or speaker is swapped; if it comes from both, the device may be mixing to mono.
Rattles and buzzes. Play the 20 Hz–20 kHz sweep at a moderate level. As the sweep passes through the low frequencies, listen for rattling panels, loose screws or a buzzing grille. Note the frequency shown on the oscilloscope when it happens.
Bass extension. Small speakers and laptop speakers can't reproduce very low tones. Step a sine wave down from 100 Hz (50 Hz, 40 Hz, 30 Hz…) to find where the sound fades out. Don't turn the volume up to compensate — that is how woofers get damaged.
Hum. The 50 Hz and 60 Hz presets reproduce mains hum (50 Hz in Europe, Africa, most of Asia and Australia; 60 Hz in North America and parts of South America and Asia). They are useful for recognising hum in recordings or checking a hum filter.
Frequency sweeps: logarithmic vs linear
A logarithmic sweep spends the same time on every octave: as long going from 20 to 40 Hz as from 10 to 20 kHz. That matches how we hear and how speakers are measured, so it's the right choice for almost all audio tests. A linear sweep changes by the same number of hertz each second, so it races through the bass and spends most of its time in the treble — useful for some electronics tests, but not for listening.
Longer sweeps (20–30 seconds) give you more time to hear what happens at each frequency. For a downloadable sweep file, the file length equals the sweep duration.
Pink noise vs white noise
White noise has the same energy at every frequency. Because each octave up contains twice as many frequencies, it sounds very bright and hissy. Pink noise falls by 3 dB per octave so that every octave has the same energy. That matches our hearing, and it's the standard signal for:
- checking whether two speakers sound the same,
- setting up the levels of a surround or multi-speaker system,
- rough room tests with a measurement app or a sound level meter.
Understanding the level (dBFS)
The level control is in dBFS — decibels relative to digital full scale. 0 dBFS is the highest level a digital signal can reach; −6 dBFS is about half the amplitude; −20 dBFS is a common reference for calibration. The level shown is the peak level: a sine wave at −20 dBFS peaks at exactly 10% of full scale, and downloaded files are normalised to the level you set.
What you actually hear also depends on your system volume, amplifier and speakers, so dBFS is not the same as the sound pressure level (dB SPL) a sound level meter shows. To calibrate, play the 1 kHz reference at −20 dBFS and adjust your system until the meter or your mixer reads the value you need.
Safe listening
Test tones are more tiring and more dangerous than music because all their energy sits at one frequency.
- Start with the level low (−30 to −24 dBFS) and your system volume low, then turn up slowly.
- Be especially careful with headphones and with high frequencies — tones above 8–10 kHz can be loud before they sound loud, and you may not hear the top end at all as you get older.
- Square and sawtooth waves contain strong high harmonics and can damage tweeters at high volume.
- Stop if you feel discomfort or hear ringing afterwards.
Downloading test signals as WAV
Below the player, Download as WAV renders the current signal — tone, noise or sweep, with its level and channel settings — into a 16-bit stereo WAV file at 44.1 or 48 kHz. Short fades at the start and end avoid clicks. The file name describes the signal (for example sine-1000Hz-10s--20dBFS.wav), so you can build a small library of test files. If you need MP3 or another format, convert the WAV with the audio converter.