Скачать или смотреть Noise Modulation

Often, when attempting to eliminate background noise, using noise reduction hardware or plug-ins, noise modulation can occur.

It sounds like this. Essentially the background noise goes away in the gaps between the audio signals and then reappears when the audio returns.

Also known as "the halo of crud", noise modulation is often more objectionable than the noise itself, since the changing noise level will draw the listener's attention. So care needs to be taken, not to be too aggressive when attempting to eliminate noise.

Noise modulation can also occur in editing when cutting between wide shots and close ups, when the production dialog had been recorded using boom mics. In the wide shots, where the dialog may be more distant, any room tone (the background sound), will be proportionately louder. This will cause the background sounds to surge or "shift" on the cuts.

These shifts can be minimized by blanketing, actually adding more room tone in the close-ups, so that the background noise levels match. To totally eliminate any changes in the background noise, the production dialog can be replaced using ADR.