Subject:audio forensics

Posted by: TomBaker

Date:7/17/2002 11:38:36 AM

Help! I have sf 6 and just about every plug in know to man.
a client wants me to clean up some micro cass phone recordings (legally done in Texas) in which the other party is not very audible. There is lots of hiss of course. any tips? Like which noise reduction mode?

Subject:RE: audio forensics

Reply by: Rednroll

Date:7/17/2002 9:44:48 PM

Try each of them seperately on a small section and see what works best. Sound Forge has UNDO.

Subject:RE: audio forensics

Reply by: Ted_H

Date:7/18/2002 10:20:02 AM

Yes, trial and error is your best approach when using Noise Reduction. It's not as simple as saying the noise is of this type, so use this setting. The different modes may have a completely different effect on different types of noise. Start out by capturing your noise print, then select the whole file and preview it. While you preview the file, change the modes and adjust the "Noise Bias" and "Reduce Noise by" sliders until you find something that works. Also, the Noise Reduction manual contains LOTS of useful information. I read through it when I first started working here, and it really helped me to have a better understanding of how Noise Reduction works. In case you don't have it already, the Noise Reduction manual is located here:

http://www.sonicfoundry.com/download/step1.asp?CatID=12

Ted

Subject:RE: audio forensics

Reply by: Weka

Date:7/18/2002 2:18:05 PM

I had to do exactly this recently for a local lawyer. First I eq'ed everything below about 200hz and over about 4000. I then used the SF NR Vinyl tool. In this case it worked spectacularly well at increasing intelligibility. I then normalized and took a sample of the remaining noise in the NR programme, applied this and brick-walled the ass out of it. The improvements were stunning. The content of the recording has left me scarred for life. I'm too thin skinned for forensics.

Subject:RE: audio forensics

Reply by: Rednroll

Date:7/18/2002 4:12:13 PM

"I then normalized and took a sample of the remaining noise in the NR programme, applied this and brick-walled the ass out of it."

Can you give a step-by-step proceedure of how one goes about "brick-walling the ass out of something?" Or is this just some new technical term I'm unfamiliar with?

Subject:RE: audio forensics

Reply by: Weka

Date:7/18/2002 10:06:47 PM

Absolutely. But first pardon my involuntary implementation of an apparent demotic antipodean vernacular terminological inexactitude.

A bountiful application of digital limiter/compression was then called into service in order that a jury of twelve good men (and women) and true might more clearly enjoy a rendering of a gentleman doing unto his fellow man that which the lord did unto the sodomites.
Any clearer

Subject:RE: audio forensics

Reply by: Rednroll

Date:7/19/2002 1:54:58 PM

Crystal!!!

Subject:RE: audio forensics

Reply by: RiRo

Date:7/20/2002 11:33:25 PM

Thanks for the link to the NR manual. It is helpful.

Many of our news interviews are done on the phone, so we pretty well have a system for tweaking them.

We use a stark EQ setting. Kill everything above 4k and everything below 150-200. The bottom is set by ear. When you can hear the difference in the voice, don't cut that. Really, we do this on the high also, but anything much past 4k is just gone.

I will then use rcgaudio enhancer to rebuild some highs. I will go overboard with this. NR is going to suck some down and I can EQ it out later if it is too much (usually there isn't much there to work with), but at this point I want to preserve and enhance what is there.

Then I will do the NR thing.

Then I will re-EQ for optimum sound and finally the brickwall thing (I liked that!).

If you are fixing the entire call, re: both parties of the call, I will do them seperately, especially if the recording device was setup at one party's location. The reason is that party will be much louder and cleaner, and the same settings through this process will sound funky on one or the other.

with any luck, decent lines and a phone that sold for more than $8.49, that should make it pretty good.

Other tips:

Use good equipment to record the call. Phone levels are supposed to be line level (it's where the term came from... a phone line=line level) but the levels are usually very loud for the person at the recording end and way way too low for the other party. Our workaround for this is to use a stereo cassette (reel-to-reel or digital, whatever would work) setting the level for one side right for the near party and the other side right for the far party. This lets you work them seperately, fixing the file for the party you are working, then mute the other party and save as a mono file. This keeps you from having the pumping sound of the compressor if you put it all into one file to start with. The noise is harder to remove that way, and you can lose lots of words while it catches up.

RiRo