Impulse Tone

Background

A pure tone extends over an infinite period of time and is characterized by a single frequency. An impulse is the opposite. It's an all zero waveform except there is an instant peak which produces all frequencies. There are no exact impulses just as there are no pure tones: the impulse will always extend over time, whereas the sine wave will always be limited in time.

This page provides you with a fairly good approximation of an impulse - the best one can get from a 44.1 kHz file (sound file courtesy from wavTones).

Applications

Impulses are used to detect phase inaccuracies in loudspeakers, a defect unlike other measured properties such as frequency response. Phase inaccuracies introduce frequency delays and are mainly the result of passive cross overs. Measuring the length of the impulse response is directly related to the time differences that exist between different frequencies.

The impulse tone is also used to characterize the acoustical properties of a room. Acoustic engineers often clap their hands to hear how the room responds back. The clap of the hands is a handy (no pun intended) approximation of an impulse and is sufficient to give the engineer an idea of whether the room sounds right. A proper investigation requires a test tone such as the impulse provided here.

By recording the response of a room to the impulse tone, one obtains the so-called "impulse response" of the room (actually, the combination of your loudspeaker and room). Reverberation time can be obtained by seeing how fast the impulse response waveform decays in time. Spectral characteristics of the room can be derived from the impulse response spectrogram.

Sound File

This file presents a -3 dbFS impulse, with a 1-sample width and a 44.1 kHz sample rate. Impulse duration is 0.0227 ms and its frequency response extends from 0 Hz to 22,050 Hz.

If you are hearing this sound file through loudspeakers and you are not located inside an anechoic room (!), it is likely that the sound you hear mostly comes from your room's response, not the impulse itself. Through headphones, your perception is influenced by your headphone's impulse response... and the impulse response of your own ears!

Related pages

Other Full Range Signals (20-20,000 Hz)

• Swept Sine Tone
• White Noise

External Links

• High Quality Online Impulse Generator