Need help removing hum

[Richard Crowley]

What did the audio levels look like during recording? We can tell from the audio clip that the limiter was engaged. But it sounds like the audio recording level was set too high, forcing the audio up against the limiter nearly all the time.

The limiter is provided as a safety measure to avoid clipping. It is NOT an "auto-level" feature that allows us to ignore setting proper recording levels.

[Greg Miller]

Richard,

I think you make a good point about excessive limiting. That is probably why the unwanted noise ramps up after the last spoken word. The limiter is releasing then, and gain is coming back up, bringing the noise level up with it.

[Rick Reineke]

"[/i]it sounds like the audio recording level was set too high, forcing the audio up against the limiter nearly all the time"[/i]
- Louder than normal PB levels as well.. Monitoring at very loud levels will produce all kinds of extraneous noise... and fry your ears into hearing things that really don't exist.
Calibrate your monitors to a known reference level and keep them there.

[Kathy Smith]

When I'm monitoring on headphones, and seeing the levels on the camera display, where should the level's fall?

[Rakesh Malik]

The audio levels should ideally bet between -12 and -18 dB, though you should also check peaks to make sure that you're not exceeding 0 dB for more than a transient.

If you're using a mic that isn't terribly sensitive, you might have to use a fair bit of gain to get to that level, in which case you're likely to end up with some noise from the preamp in the recording.

If the recorded noise if fairly mild (I haven't had a chance to listen to your audio sample yet), you might even be able to take care of it with little more than a carefully tuned multiband compressor.

[Battle Vaughan]

This sounds like ordinary "room tone" to me, something every mike will pick up if it is sensitive enough.

One of the first things I was taught, fwiw, was to always record 30 seconds of room tone when doing audio, for patching over excisions in the finished audio --- total silence in a room sounds unnatural, and would be noticed if you edited and just dropped out the total audio. It is also such a low level sound that I wouldn't be concerned about it.

It doesn't sound like a gear problem, just the natural sound of the environment.

[Rick Reineke]

"seeing the levels on the camera display, where should the level's fall?
I prefer peaks @ around -6.0dBFS, with a high quality limiter in place. But 12-18dBFS would be good, especially with 24 bit.

[Martijn Damen]

The audio sounds distorted a bit, like the input level on the transmitter was too high or the gain on the receiver. But nothing serious. It could sound a bit better with some high cut and some other tricks, but not much. Background sound and/or music would hide most imperfections I think.

[Richard Crowley]

Originally Posted by Kathy Smith

When I'm monitoring on headphones, and seeing the levels on the camera display, where should the level's fall?

Generally: As HIGH as you can manage without WITHOUT going OVER the limit (0dB Full Scale)
In practical terms it depends on WHAT you are recording, HOW you are recording it, and WHERE (under what conditions). It is not something easily boiled down into a general command. You get the FEEL for where the levels should be after practice with your gear and your program material.

Now with SOME gear, you can increase the record level to the point where it would be clipping, but the limiter is artificially reducing the record level to prevent clipping. This has the effect of squashing the dynamic range, and also pumping up the background noise in gaps between words, etc. That is what it sounds like happened to the audio in your example. Without the limiter, it would be terribly clipped and you would know instantly that the record level was too high.

It would probably be instructive to try recording some things just for practice WITHOUT the limiter engaged so that you can see what the dynamics actually are. And you can experiment to see how the signal-to-noise ratio is compromised when you record too low, and how the audio is clipped if you go too high. There is a "Goldilocks Zone" where the record level is "just right".

Of course, you must also apply some amount of judgement to allow some "headroom" for expected (and unexpected) audio level peaks. Again, you must develop a "feeling" for this based on what you are recording. A "talking head" lecture from someone who has delivered the same speech 100 times before may be pretty predictable and leveled-out. OTOH, a live performance of something really dynamic (and/or amateur performers) is almost guaranteed to have some significant peaks over the average audio levels. THIS is what the limiters are there to catch. The limiters are NOT intended to be used as an "auto-level" function. That would be like abandoning steering and depending on the guard-rails to keep you on the road. You would probably arrive at your destination, but your car will be pretty banged-up from riding up against the rails all the time.

[Rick Reineke]

"That would be ilike abandoning steering and depending on the guard-rails to keep you on the road."
- Good analogy Richard!

[Kathy Smith]

OK, thanks for all the help so far. Here is another person recorded in the same space with the same equipment. Does it this recording show the same problems as the other one I posted before? What can I do to improve this voice? Or should I leave it as is?
https://www.dropbox.com/s/i0npkqf1ds...Jack.aiff?dl=0

[Greg Miller]

Did you use some sort of noise gate on this? Or was it manually edited? For example between 8:02 and 8:38 seconds, after the word "ways" there seems to be a momentary dropout of the room tone around the breath noise. Then the room tone returns when the speech resumes.

For that matter, I feel as if the room tone (that predominant 120 Hz background noise) is pumping up and down in level throughout the duration of the file. Did you have any kind of AGC applied during recording (compression? limiting?) or applied in post?

[Kathy Smith]

Greg,

This is supposed to be "RAW" file but it is exported out of Final Cut without anything applied to it. The only thing that was set was peak limiter. I do hear that dropout so I am now wondering myself what it was caused by. I will go back to the recording again and double check to make sure there is nothing applied to the file when I export. I am exporting this out of cut sequence in Final Cut.

[Greg Miller]

There also seem to be some extremely brief drops around 4.61 and 4.70.

Exactly what all was in the recording chain, starting with the mic?

[Kathy Smith]

Microphone: Sanken COS-11D
Camera: Canon C100
Microphone was wired to the camera with XLR cable
Mic was clipped to his jacket on a right side, around 3-4inches down from his chin
I had peak limiter on.