Audio expert help

Patryk Rebisz wrote on 6/22/2006, 10:43 AM
I have a short interview recorded on the street with a crowd of people around. I do see definitive spikes in volume when the person is talking but still what would be your approach to clean up the audio -- get rid of some of the street sounds and crowd sound? If you could post your work flow in such situation i would really appreciate it.

Comments

busterkeaton wrote on 6/22/2006, 11:11 AM
I'm no audio expert, but the first thing I thought of is to try noise reduction on the background. You may need Sony Noise Reduction for this. It won't get all the noise, but it should get some. For example, if you have a highway behind you, it may get the continous whoosh of cars reduced, but it won't take out a car horn honking. As I think about this step, if I see that it worked, I would probably try EQ and compression first then do the noise reduction because, it most likely be most effective at the end of the audio chain.

I would definitely see if EQ'ing the track worked. The human voice does not contain very very low or very very high frequencies, so I would roll those off. I would try to find the frequencies of voice and boost those. In the track EQ tool, I take a small band of frequncy and do a sweep of the audio to find out which frequncies I need to boost and which I need to reduce. Set the gain to 15.0 and the Bandwidth to something like 0.3. Then in the graph, drag this back and forth as a loop of your audio plays, using this, you hopefully can find a frequency where you are getting just the voice or mainly the voice and then widen the bandwidth to something suitable and lower the gain as well. The goal would be that the voice is clear without sounding processed.

I would also try compression on the track. Compress it at 2:1 or 3:1. The Vegas defaults start the compression at about -15db. You may want to look at your levels and see what the noise of the background by itself is and adjust this number.
Spot|DSE wrote on 6/22/2006, 11:55 AM
You should probably start with a different mic. Can you let us know which mic you're using and how? Booming? On cam? stand mount? Lav?

*usually* this sort of problem comes down to equipment choice.
Earlier this week I was mic'ing inside a door-less airplane at 140kts, and needed to pick up less than loud conversation with clarity. It took quite a bit of testing to find the right combination, but I did it after 6 flights and 12 microphones.
Patryk Rebisz wrote on 6/22/2006, 12:59 PM
We were using shotgun mic mounted on top of the camera.
Requiem_ad wrote on 6/22/2006, 1:17 PM
the problem I find with compressors used for this situation is that they tend to bring up the noise floor (back ground noise) you can try one set to about 2:1 with a gate if you have one, with a slow release, the problems with gates are , used wrong they can make audio tracks sound chopped, thats why a slow release so the background sound fades out rather than cuts off, experment with it, you will find what you need, if you dont have some sony audio effects, try and find some freeware audio plugs, they are everywhere, anyway, I cant tell you what to set the threshold at depends on the loudness, maybe start around -40db try an attack around 300 ms with a release at around 1000ms, this is a relativly slow attack settings, may work for you
baysidebas wrote on 6/22/2006, 2:01 PM
If the desired audio is of higher level than the background you could use compression of the signal below the level of the background and expansion of the signal above that level. This is easily done in audio processing applications with "dynamic" amplitude controls. In CoolEdit (now Adobe Audition) you can actually manipulate a graphical depiction of the response to achieve the effect desired. This results in a much smoother sounding track than just gating the noise floor but you can combine both methods to suit your needs. The other suggestions are just as valid and may also be effective. It all depends on what your source material is actually like. Sometimes the audio engineer feels like a painter with a palette of methods and requires a deft hand at mixing them to get just the right "color."
michaejlt wrote on 6/22/2006, 2:07 PM
This tutorial demonstrates how to cancel or reduce the background noise in an audio file. This example is a soft guitar playing with fans running in the background. The fan noise is cancelled out using the noise filter in Adobe Audition 1.0

http://www.wrigleyvideo.com/videotutorial/tutdes_audition_noise.htm


Best Regards
busterkeaton wrote on 6/22/2006, 2:14 PM
Thanks Bayside,

I hadn't played much with the Graphic Dynamics tool in Sound Forge, but now I see how it works.