Generate a frequency sweep
Download a WAV file holding a logarithmic sine sweep from 20 Hz to 20 kHz over 10 seconds. The sweep moves through the full audible range at a constant rate per octave.
Equal time per octave
A logarithmic sweep doubles frequency at a steady rate, so each octave gets the same slice of the file. From 20 Hz to 20 kHz is about ten octaves, and each one receives roughly a second.
A linear sweep works differently and worse for audio. It rises at a constant number of hertz per second, so the octave from 10 kHz to 20 kHz takes half the file while the octave from 20 Hz to 40 Hz passes in a few milliseconds. The low end is gone before a speaker has settled.
Measuring a system
Play the sweep through a system, record the result, and deconvolve the recording against the original. That yields the impulse response, and from it the frequency response and the decay behaviour of the room.
The method separates the linear response from distortion: harmonic products arrive ahead of the main response in the deconvolved result, so they can be measured or discarded rather than contaminating the curve.
What it suits
- Speaker and room response measurement.
- Checking a filter or crossover across the full band in one pass.
- Finding rattles and resonances, which announce themselves as the sweep passes through.
- Testing playback hardware for dropouts or band limits.
Edge fades
The file fades in and out over 10 ms. Starting a 20 Hz tone at full amplitude produces a step, and a step contains every frequency, which would put a broadband click at the head of a measurement.
Steady tones instead
For a single fixed frequency use the sine generator or the 440 Hz tuning tone. To set the sweep range, duration, or direction yourself, use the full Tone Generator.