Filtering out motor noise
 

I was curious if motor noise picked up from a camera (or refrigerator, etc) can be effectively dealt with in post?

Surely the whine one hears in cameras like Canon's HV20 is not in normal voice range. I've fiddled around with the filters in FCP but never seem to get anywhere without also altering the tone/texture of all the sound.

It'd be nice to know if anyone has had success in this area.

best,
elmer

Elmer,

assuming you have Final Cut Studio, I suggest you try this in Soundtrack Pro. A combination of its noise reduction (based on a noise print that you define on a small section of audio that contains only the noise) and some EQ filters can often help. The downside is that doing this leaves some artifacts behind that can sound pretty nasty. You can also use Soundtrack Pro to display the frequency spectrum, which will confirm (or not) your theory that the whine one hears in cameras like Canon's HV20 is not in normal voice range.

I have had reasonable success in some cases, and yet was stuck in others. There really isn't a substitute for recording clean audio during aquisition.

- Martin

Hey Martin,

Have you got an examples lying around of what you've had to fix in the past?

What would be really handy is a sample of something that is fixable and something else that is beyond repair... Also some notes on how it was fixed would be greatly appreciated!

I'm finding it hard to gauge what can be fixed and what can't... I'm not sure whether it's my lack of knowledge that prevents fixing a scene, or whether the audio is actually just so badly captured that it's beyond repair... An actual "real life" sample would be much appreciated!

Thanks!

Chris!

Chris,

unfortunately, I am out of the country for another week so I don't have access to my files at home.

I've had fairly usable results filtering out hiss introduced by pre-amps, as well as a variety of sounds that are repetetive in nature, such as windnoise you'd get from placing a mic under a ceiling fan or the humming of an electrical transformer. It helps if the noise is limited to a small range of frequencies, because then you can use equalizers to filter out just those frequencies.

In general, though, I find it difficult to predict how much a recording can be cleaned up - well, at least with my methods and knowledge. Sometimes I am surprised how clean I get can a file, and then at other times I start a seemingly simple clean-up project and just don't find a recipe for success.

Of course, nothing beats a recording that's clean to start with! :-)

- Martin

If it's a repetitive noise, such as 60 Hz hum, the most effective way to get rid of it is to sample a noise-only segment, invert it, loop it and add it to the original in just the right amount. If there was any automatic or manual gain adjustment during recording, it will take some time to match that. You can then use a noise reduction program to get rid of the residual.

By adding the compliment of the noise, you don't step on the original recording at all. Noise Reduction programs, on the other hand, work by filtering certain frequencies. They tend to change the tone of your sound a bit, so tread lightly.

Here's a piece we shot that had as much 60 Hz hum and buzz as we had signal - in the part that has no music or sound effects! (About 1:15) Noise reduction programs totally ruined the dialog. We did the inversion trick, added a little noise reduction and went with it. http://colonelcrush.com/movie/index/00030401 You can hear some moments when we didn't track the auto-gain function properly. Oh well...

Interesting approach, I would have never thought that you can loop noise since it is random. I did want to try & record with two external, closely-matching mikes: one for the audio, the other one pointing at 180 degrees & recording noise. I would then invert the noise channel & add it to the audio, to get the noise-canceling effect. Since I don't have a mike pair, it may be a while before I actually try it...

P.S. Sorry, I just re-read your message :( Indeed, the 60Hz hum is anything but random, maybe that's why it worked?

Hi Roman,

Yes, the non-random nature of the 60Hz hum was the key. It could also work with motor noise (as the original poster asked), if the noise is cyclic and stable. Fortunately for us, 60Hz power noise is super stable.

You're also right that you can't use the cancellation technique for random noise, like from an HVAC blower, traffic, wind, etc.

I like using Sony Noise Reduction in combination with Sound Forge, and have rescued many a clip using them.

SoundSoap 2 performs similarly, and is a stand alone app. It allows review of of the noise removed.

Also, the new Adobe Soundbooth has a great graphic based tool for getting rid of continuous and random noise.

I found SoundSoap 2 to be very useful if only slight noise reduction is required. My camera has AGC that cannot be turned off, and all recordings done with an external mike have serious hum on quiet parts. I created noise presets for SSoap2 in Sound Forge, and use them on all of my tracks.

BTW, SSoap2 works as a plugin in Vegas, not just as a stand-alone. There's also a Pro version, but I'm not using it, both because of price & complexity. Of course, for those who know what they're doing & have a budget for audio, there's always Waves Z-noise which is probably one of the best noise reduction plugins.

The best I've found is the Sony NR plugin.

You can download the trial version of Sond Forge 9 which includes the NR plug in. You can use it for 15 or 30 days, something like that and see if it does the trick for you.

I've dorked around with so many free/low cost NR solutions, but shelling out the money for the Sony version was the only cure I found. It works great for that type of noise with very little artifacting.

Is there a Sony NR equivalent for Mac?

Yes. Soundtrack Pro (part of Final Cut Studio) includes NR.

Soundtrack Pro doesn't seem to have as much "power" as Sony NR.

I've used Soundtrack Pro for NR in the past, but have never been overly happy with the results...

I'm playing around with Sony NR now - it seems to have a lot more control.

not even close by half.... Try them side by side, you'll quickly grasp the diff.
Bias Inc SoundSoap Pro is very close. Soundtrack isn't remotely there by comparison.
IMO, SoundForge Noise Reduction is the best in class, without spending a bundle.
WAVES XNoise is very, very good too, and runs on Mac.
Cedar, NoNoise...both very good.
All the good ones are more difficult to operate than what Soundtrack comes with, or the cheap version of Soap, but the difficulty makes up for the quality of output.

Last night, I tried the Sony NR plugin on a really old (10yrs+) footage with lots of tape hiss. Very impressive. Compared to non-pro SoundSoap2, it did a much better job, even without too much tweaking. I just sampled the noise portion, and let the plugin do the rest.

For me, whatever NR I apply is typically only half of the job. I find that most of the noisy footage I have to work with also has fairly low signal, so I normally follow the NR in the chain by the Wave Hammer compressor to boost the volume.