# What is a 'noise sweep'?

If you look around the internet, you can find the term noise sweep or white noise sweep all over the place and this is defined, but I can't find the basic definition of sweep anywhere. What does sweep refer to in the context in and of itself?

• White Noise sweeps are absolutely amazing to generate procedural wind sound effects if done the right way. I'm doing it in my custom C++ Engine and its absolutely beneficial for the game me and my team are building. We can dynamically change how wind sounds depending on the environment in the game. – Deepak Chennakkadan Mar 30 '15 at 5:15
• @DeepakChennakkadan: interesting, but what exactly are these “white noise sweeps” – I suspect, basically white noise run through a variable-frequency low pass or band pass filter? Definitely very useful, though I would rather call that “filter sweep”, not “noise sweep”. (Though I suppose it's a bit arbitrary.) – leftaroundabout Mar 30 '15 at 21:48

a sweep is usually sine waves at 20hz to 20khz played smoothly. I've only ever heard the term sine wave sweep, never white noise sweep fwiw.

• Okay, that does make sense. I guess i'm trying to figure out why the word 'sweep' is used. Is that because the sound "sweeps" across the full frequency spectrum over time? – dthree Mar 30 '15 at 6:12
• Thats what I've always assumed. It needs to be called something. Sweep is is probably used to differentiate between that and static sounds like white noise and pink noise or pure sine waves. – coaxmw Mar 30 '15 at 14:11

As said by coaxmw, sweep normally means a sine oscillator starting at 20 Hz and then smoothly “gliding” up through the entire audible spectrum.

Now, in principle you could also do this with other types of oscillators. E.g. dubstep music, as it were, uses lots of sawtooth sweeps. Band-filtered noise can also be considered an oscillator – “noise sweep” could refer to a sweep performed with such an oscillator.

However, none of this makes a lot of sense for the technical applications of sine sweeps. The reason to do such a sweep is generally, you want to investigate the transfer characteristic of some PA system. Assuming little nonlinear distortion, it's sufficient to know the transfer for all sine waves; any actual signal can then be constructed as superpositions of such sine waves. In particular, the superposition of all audible sine waves is, pretty much by definition, white noise. So, when people are talking about a “white noise sweep” what they mean is probably, white noise decomposed into a sine sweep.

I thought that people took a narrow bandpass filter starting at 20hz and sweeping up to 20K across white noise for the purpose of creating an impulse response - you play the sound through your speaker and record how the room reacts. I think sine wave sweeps can be used for that purpose too but I guess I thought a noise sweep was a distinct method of making the IR.