Eliminating elevator hum in post

EA_Cru_2002

EA_Cru_2002

Active member
I just filmed a short film entitled "Elevation." A big portion of the film plays inside an elevator. Because we shot on location, and because there would be no way I could convincingly do ADR as these scenes were dialog heavy, I just shot with audio on location. Unfortunately, the elevator gave off the typical HUM elevators do. Is there a way I can get rid of this in post? I heard of some plug ins. I use Final Cut Pro HD. I'm not a real audio guru so is there an easy solution to this and if so, specifically what would I need to do? Thanks guys.
 
I would first mess with your EQ. I usually find that the hums are more of a low end issue (so turn down your low end of the EQ), and hiss/static tends to be in the high end (turn down the high end of the EQ). Great thing about this is MOST speaking voices are in the mid range anyway, so you're not effecting them as badly.
 
Man, in my zombie short I discovered the well, but I was very pleased: I cut the frequencies under 400KHz (low cut filter) and cut the frequencies higher than 7KHz. Man, my sound was soo much cleaner... It wasn't an elevator though, but I think the principle still aplies after a little bit of tweaking...
 
I will try this A.S.A.P.! Thanks for the advice. Before I started filmmaking, whenever I used to hear George Lucas say film is 50% sound, I thought he was overexaggerating. He wasn't. It just isn't as noticeable, but it's just as important as the visuals. And it's cheap sound, more than cheap visuals, that give an amatuer project away.
 
personally i would first try to understand what's the frequency of the noise, using the spectral view of cool edit (i takes a little bit of experience, but not too hard) on a part of recorded audio without dialog. and i would eliminate it with a notch filter in NLE software.

if you can't do that because you don't have skills / software, try to apply a denoiser (premiere) filter which may fix it automatically (play around with the paramters).

as a last option, try to apply a highpass filter starting with a cut freq at about 500Hz. if it fixes it, try to lower the cut frequency as much as u can still having the hum removed. if the dialogue is affected by the filter in an acceptable way, keep that.

Anyway, if you can post a sample somewhere (including a part without dialogue), i can try to detect the bad freq for you.

Andrea
 
don't use a filter. use a muliband EQ

waves Q10 is well known for fixing location problems.

just make a notch in the EQ - pick a very small portion of frequency

and start sweeping - run the notch across all frequencies untill the problem is located.


and not to sound like a dick or anything, but go to audio sites to find out about audio.

look up Bob Katz .................... Audio is very complicated
 
on second thought, ignore that post. sorry.


if you have the noise alone then select a portion of it, invert its phase and loop it over your parts you want to fix.

in theory the two noise tracks will be exact opposites and will cancel each other out. This is how noise removal programs work.

It doesn't always work, but nothing does.
sorry again, i'll stop now
 
Hum consists of the fundamental (mains frequency, 60 Hz in North America, 50 Hz most other places) and a series of integer harmonics (2x, 3x, 4x, 5x ...). If you notch only the fundamental, there will still be considerable energy in the harmonic spectrum. Luckily, the bandwidth is usually narrow (high Q) so you can use a few parametric filters (perhaps 4 or 5 bands would be enough) and really attack it. The easiest method would be to analyze the structure of the hum (using a DAW or similar) and then go about building your filters to attack the problem. I have successfully attacked similar problems and been able to realize reductions of nearly 40 dB (100 to 1).
 
there is no way your going to get rid of all the harmonics without ****ing up what your trying to save. If your going to cut out frequencies, all you can do is find your favorite compromise between hum and clean material.
 
taubkin said:
Man, in my zombie short I discovered the well, but I was very pleased: I cut the frequencies under 400KHz (low cut filter) and cut the frequencies higher than 7KHz. Man, my sound was soo much cleaner... It wasn't an elevator though, but I think the principle still aplies after a little bit of tweaking...
Click to expand...


Holy crap. That's a lot of frequencies to cut. You are really cutting into the vocal frequency repsonse with that. I would think doing that would make your dialogue sound really mid-rangish, almost telephone like.

-Dave
 
Do you think trying to find the frequency and then bringing it down with the parametic eq function in FCP would be enough? I know, as many of you said so, there are better, more elaborate options available but I'm the type that says, if it works fine, then it's fine. If viewers are so concerned about the hum that it detracts from the movie, chances are my movie sucks anyway and getting perfect elevator sound won't save it anyway. As it is, the hum isn't so bad to take away from the film so I'm not super worried about having it absolutely perfect. I'm just looking for a way to minimize it, not take it away, as it is realistic that an elevator would have some humming properties.
 
davey:

Actually, you can easily eliminate hum as it's harmonic structure is very well understood. A band reject filter with a Q of 20, at the second harmonic of (North American mains), the width (-3 dB FH / FL) of the notch is only 6 Hz wide. This won't "f- up" the project at all. As I stated, I have done this many times before and if done properly it really works well.

EA Cru 2002:

If you want to email me a short (10 second) segment, I will process it and send it back for you to evaluate yourself. Then, no speculation will be necessary as you can make your own determination.
 
Dave_Fisk said:
Holy crap. That's a lot of frequencies to cut. You are really cutting into the vocal frequency repsonse with that. I would think doing that would make your dialogue sound really mid-rangish, almost telephone like.

-Dave
Click to expand...

I might have the numbers completely wrong, or I might have a poor sounding dialog track. I am a little far from my editing station, and I have a terrible ear for those things. Thank god I'm not an audio editor, and this was just my zombie flick...

I am probably wrong on the 400Hz, though, it's almost the fundamental A... It can certainly be 150Hz and 17Kz, but I will only know it after I come back home... It did sound much better than the noisy track though, and I didn't feel the voice of my character changed that much...

But thanks for noticing!
 
khmuse :

If you try to remove all the elevator hum and it's harmonics you will **** up what your trying to save.

common you KNOW that SOME of that hum is in the vocal range. Try to remove it all and your audio will sound un-natural. Just do the best you can.
 
Thanks for the offer khmuse but I unfortunately it's a little hard for me to get a file from my editing computer to a computer hooked up to the internet (trust me, it's a weird circumstance). :embarasse

Anyway, I think I'll just do some trial and error with this. So far I'm treading that line between eliminating the hum and getting the dialouge to sound okay. This whole experience making this film has been a huge learning lesson for me as since I had to do a lot of the film myself, I had to learn a lot of technical skills I didn't beforehand like color correction, audio filtering, etc. Best film course I ever had.

P.S. I just found out my film got accepted into the Hawaii International Film Festival (I'm from Hawaii). I sent them a rough cut of the film with the big hum and they accepted it. Now I'm trying to fine tune it so it sounds halfway decent in a theater.
 
davey said:
on second thought, ignore that post. sorry.


if you have the noise alone then select a portion of it, invert its phase and loop it over your parts you want to fix.

in theory the two noise tracks will be exact opposites and will cancel each other out. This is how noise removal programs work.

It doesn't always work, but nothing does.
sorry again, i'll stop now
Click to expand...

If you try this you may run into trouble at edits. If the noise from take A and the noise from take B don't exactly match (which it won't) then as soon as there is an edit, your 180 out of phase noise will no longer be 180 out, and if its not out of phase at all you are incresing your noise. Have fun.

I use Waves plug in's I wish I has some cool guerilla way to do this besides eq. Notch and high pass filters.
 
How do you find Waves stuff?

I love how clean there stuff sounds, but the compressors sound a little odd to me..
 
davey said:
How do you find Waves stuff?

I love how clean there stuff sounds, but the compressors sound a little odd to me..
Click to expand...

I use the Waves plug ins all the time. The noise reduction (X-noise) is pretty good, user friendly, but takes some finesse to get optimal results. Does a decent job at cleaning up noisy wireless mics, if you have good levels. The better the noise print you can give it, the more accurate it is at taking it out, room tone serves multiples purposes. The "click" removal is more for restoration type work and I have not found many uses for it. X-Crackle on the other hand is quite handy.

More later sorry, gotta run.
 
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