Ghostly background noise after using Noise Reduction

I used the noise reduction tool to remove background noise from a video i shot using my iPad 4 with a shotgun mic. I did boost the volume levels in iMovie before exporting the audio file. The backgroung noise has gone but unfortunately has been replaced with a noise that I can only describe as ghosts having a party. I had a similar issue to a lesser extent with another video, (also filmed on the iPad but without boosting the volume in iMovie) but this one is very, very noticeable and I don’t know how to fix it. Any ideas?

Without hearing it, I can guess that it’s moving or changing noise. That just kills the Noise Reduction tool. Noise Reduction only works on sounds that never change over the course of the clip such as fan noise, air conditioning or microphone hum. It will not do crowd sounds, jet going over or other complex and ever-changing sounds. “Noise” is not “stuff I don’t like.” It actually has rules.

Open the clip before you did anything to it. Reduce the sound clip to mono (Tracks > Stereo Track to Mono), drag-select a 15 second portion with typical noises and File > Export Selected: WAV (Microsoft). Post it here.

Do Not post after Noise Reduction.

Scroll down from a forum text window > Upload Attachment.


Hi Koz

Many thanks for your reply. Excerpt of audio with background noise attached.


It sounds like wind noise, (not that kind :¬), resonating the building, rather than an electronic artifact …
''Kim'' before-after spectrogram.png
Chopping off all the frequencies below 230Hz with audacity’s equalizer will get rid of it ,
but consequently the result has no bass , but is still comprehensible …

Attached: plain noise reduction, volume boost.

We can’t do anything about “recording from the back of the auditorium” sound and that audience microphone feedback, oooOOOOOooooo, is permanent. As before, it’s moving/changing and that just kills a lot of the patching tools.


I know what that is. It took me a minute. When the sound engineer cranked the volume up so they could hear the question, the sensitivity went up enough to hear the jets throttling back on their way to the airport. That’s exactly what it sounds like when an international jet joins the approach pattern to LAX (still miles away) and SoCal Approach tells them what altitude and speed to use to mesh with the other landing jets.

You’re still stuck with it.


If it is a one-off noise , like an aircraft passing,
it’s feasible to chip-it-off in little-bits using Audacity’s “Spectral edit multi tool” …
Demo of Audacity ''Spectral edit multi tool'' .gif

But if it is wind-noise repeatedly occurring every few seconds, then it would take an age to remove all instances using that tool. [All instances could be removed in seconds using the equalizer, at the cost of losing bass ].