Sine tones, sweeps, and pink noise
A sine you can sweep across the whole audible band, plus white, pink and brown noise, with the level in your hands. What you use to find a room resonance, check a speaker, or set a monitoring level.
Start low. A sine carries far more energy into your ears than music at the same meter reading. This starts at −24 dBFS and stops at −6. Turn your system down before you press play, then come up.
Sweep the band
White, pink, brown: why three noises
They differ in one thing — how the energy is spread across the spectrum — and that one thing changes what each is good for.
| Noise | Slope | Sounds like | What it is for |
|---|---|---|---|
| White | flat per hertz | a hiss, top-heavy | Electrical measurement, testing a chain end to end. |
| Pink | −3 dB per octave | even, like rain | Setting monitor levels, hearing what a room does. |
| Brown | −6 dB per octave | a waterfall | Masking, concentration, sleep. Not a measurement signal. |
White sounds harsh because of arithmetic, not because it is badly made: the octave from 10 to 20 kHz contains ten thousand hertz, the one from 100 to 200 contains a hundred. Equal energy per hertz therefore piles almost everything into the top. Pink corrects exactly that, which is why it sounds flat to us and why it is the reference for calibration.
What a sweep tells you about a room
Play a slow sweep at low level from 40 to 300 Hz and listen from your normal seat. Where a frequency jumps out, you have found a resonance — the room adding several decibels of its own. Move your head half a metre and it usually changes, which is the confirmation: it is the room, not the speaker.
These come from the distances between facing surfaces. Two walls 3.4 metres apart resonate near 50 Hz, and at every multiple above it. Knowing where yours are is worth more than any amount of correction applied blind — you cannot equalise away a room mode you have not located, and cutting the wrong band just makes everything thinner.
Use the logarithmic sweep. A linear one spends most of its twenty seconds above 10 kHz, where nothing you are looking for lives.
Frequently asked
What is pink noise for?
Setting a level, and judging a room. White noise puts the same energy in every hertz, so it sounds harsh and top-heavy — there are ten times more hertz in the top octave than in the one below it. Pink noise puts the same energy in every octave, which is how we hear, so it sounds flat and even. That is why it is the reference for calibrating monitors and for hearing what a room does to the sound.
How do I find a room resonance?
Sweep slowly, from about 40 to 300 Hz, at a low level, and listen from where you normally sit. A resonance announces itself: one narrow band suddenly jumps out, and it usually changes if you move your head. Note the frequency. Most rooms have two or three, set by the distances between facing walls — a 3.4-metre gap resonates around 50 Hz, and its multiples with it.
What does brown noise sound like?
Like a waterfall, or distant traffic. It rolls off 6 dB per octave — twice as steep as pink — so almost everything is in the low end. It is not a measurement signal: it is used for masking, for concentration and for sleep, because it has no detail for the ear to grab onto.
Can this damage my hearing or my speakers?
Yes, if you push it. A sine is the worst case: it has no peaks and troughs, so at the same meter reading it carries far more energy into your ears than music does — and a sustained low tone at high level can also cook a tweeter or bottom out a woofer. This tool starts at −24 dBFS and will not go above −6 dBFS. Start low, raise it slowly, and take the headphones off before you change source.
Is the frequency exact?
It is exactly what your browser's audio clock produces, which is accurate to well under a hertz — good enough for anything acoustic. The sweep is logarithmic by default, meaning it spends as long in each octave; a linear sweep spends most of its time in the top octave, where you learn the least.