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Swept Sine (Full Spectrum)
Background
These audio files scan all audible frequencies from 20Hz to 20kHz in a 20s time span. When the time scale is logarithmic, sweeping between 20Hz and 40Hz (one octave) or from 10kHz to 20kHz (one octave) will take the same time. When the time scale is linear, sweeping from 20Hz to 40Hz will be much faster, and equal to the time taken to sweep from 10kHz to 10.02kHz (which only represents a 3-cent pitch interval!).A log sweep is characterized by a pink-like spectrum, a linear sweep by a white-like spectrum.
Applications
Sine sweeps are used as reference tones to check frequency response or the adverse effects of room modes. Compared to pink noise or white noise, sine sweeps produce frequencies with a much higher energy, as they dedicate the fully available dynamic to play one frequency at a time, not simultaneous frequencies like noise.This gives sine sweeps a better immunity against room ambience and background noises. Sine sweeps are particularly useful to determine resonant frequencies.
Usage
When checking by ear, the sound should evolve smoothly from the lowest frequency to the highest. No strong frequency dips or peaks should be present. Please note that due to the increased sensitivity of our ears in some area of the audio spectrum, some frequency ranges - particularly in the upper medium - may be perceived louder than they actually are (the so-called Fletcher-Munson effect). For this test, don't pay attention to this phenomenon, but rather to strong and localized frequency dips or peaks. When checking by ear, use the logarithmic version, as our ears are more or less working logarithmically. In combination with a audio spectrum analyzer, "peak hold" is necessary to measure the full frequency scale in a single session. Assuming the spectrum analyzer performs its analysis across the log-frequency scale, perfect systems will exhibit a flat response to the logarithmic swept sine stimulus. When using a linear FFT analyzer, please refer to the linear version instead.
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