Cleaning up a police interview

[toadmark]

Good evening all, I'm a long time lurker & first time poster.

The local Police have brought me a wav file of an interview that took place in a jail cell. The speech is almost unintelligeble due to excessive room reverberation and background noise. We have to get it to a place where a jury can listen to it easily enough.

I've been playing around in soundforge with EQ, gateing & compession and have had some success in reducing background noise. The room reflections are still an issue though.

Any thoughts/ideas are welcome.

[JulienG]

I can't help much with the techniques, but can I suggest some things to keep in mind:
1. Ensure you keep a copy of the origional
2. Document every setting & tool (so that the defence could recreate the output if needed).

As for technique a few ideas:
* Cedar (or similar) denoise should be helpful, DiNR also is ok
* Try watching a spectrum plot of the sound, and try eqing all non-speech out of it (Just had an idea for a denoise plugin based on that, but I'm not writing audio code this year, essentially do a freqency transform of the input and remove all frequencies below a certain level)
* Try passing it through a vocoder, seriously, gate it heavily and you might get something intelligeable through it
* Also try an expander
* SPL Transient Designer claims to be able to reduce an existing reverb

[Martin]

The de-noiser plugin by Waves i've had a lot of success with on some really bodgy recordings that i've been given... not so sure it will eliminate the echos but in some cases works well by learning the noise profile of the recording and then removing alot of it, worth a try

[Chris H]

Cool edit Pro (i forget what it's called now) is the cheapest software i know that is good at sampling the noise you want to get rid of , then applying the setting to the entire file. You have the entire audio file with noise,reverb and speech. Select a segment of the file with a good example of the background noise,etc, you want to remove, without any speech in it, and the plug in samples the noise. When you apply the de noise process the sampled noise is removed leaving the speech untouched, after working with the perameters to get the best result.
Compared to this approach i find the conventional de hisser/de noiser that filters the sound as in Logic's de noiser just about usless.

[mark rachelle]

amek 9098 compressor has a weird function called ambience that can either make a room wet or dry it out

its a different take on ms

[mark rachelle]

i hope you have you folley and sound fx replacements handy too
that will greatly enhance the jury's listening pleasure

you know punching a phonebook to the stomach

the gun that clicks but doesn't fire a bullet

the sound of water trickling down a leg

should be a real hoot!

[Martinez]

Oh Mark,

you absolutely crack Me up!


but I think that those are the sounds they want taken out of the recording.

actually come to think of it,

are police interveiws usauly done in cells?

[Adam Dempsey]

These usually come from cassette and I've worked on many. Ideally, you'll want to get it sounding better before digitizing it:

-Azimuth adjust (if you can't perform that I'd suggest sending it to someone who can)
-Select the best of the 2 channels, if there is one
-Steep (ie 24dB/octave analogue HPF/LPF - don't eat into things too far)
- 24 bit A/D (will help with any denoise)
- notch filtering
- EQ to highlight the best of the voice(s)
- careful denoise (minimal amounts, maybe as much as 2dB, before artefacts creep in. If necessary run further passes, each using a noise estimate/print from the preceeding process)
- comp/levelling, then an expander.

Room reflections I doubt you'll eliminate but keep in mind all the way: the aim here is intelligibility, not to make it sound "good".

[Jason Dirckze]

are police interveiws usauly done in cells?

Nope...usually an interview room, with a portable cassette recorder, placed somewhere on the table.

It's 2005, you'd think they'd keep up with the times and start recording to HD, or at least Minidisc.

[Kris]

Bias make software called Sound Soap. Or maybe just Soap? I've never used it but i'm guessing it's for cleaning up audio eh?

We get lots of police stuff.... video though. Man, those hollywood shows where they can zoom in to see someone's scar on their right hand or whatever while.... it's such a hoax.

[Howard Jones]

The cassette format is inherently much more reliable than the minidisc format. And you can still buy cassette decks...

[Mark Bassett]

If you work out a way to remove reverb from a recording let me know, you'll be one of the first on the planet to do so and you'll be very rich very quickly.

[Howard Jones]

In theory, you could go back to the room where the recording was made. Do another recording, using the same words spoken at the same volume and make an excellent recording of it. Load this new recording into an editor and remove all the dry vocal leaving only the reverb tails.

Reverse the phase on this and add it back to the recording with the problem. It would sorta work but is hardly practical.

[Chris H]

unless you really really want to get into forensics, you are in for a tough battle
as a veteran of many police tape escapadess i recommmed for your own legal and physical safety you leave it to the police forensics department which is very well equipped and where your job should legally be conducted.....

.

Yep. They have some very sofisticated gear for this. Sort of begs the question why they don't get their own audio forensic dept to do the job????

[Martinez]

good question Chris.

I was kind of wondering that myself,
along with why was the interrigation done in a cell insted of in an
interveiw room.

I can't help but feel that it might be a bit sus.

[rick]

unless you really really want to get into forensics, you are in for a tough battle
as a veteran of many police tape escapades i recommend for your own legal and physical safety you leave it to the police forensics department which is very well equipped and where your job should legally be conducted.....

i bailed out on them many years ago when i actually heard the information they wanted restored.
restoring drug and death deals might look fun on television but , it's a bit too close to home when you are restoring people's voices that you can match to faces ( 5 years in kings cross makes you a "known man")

if it's important stuff you will have to go into court and claim you are a professional in the field.
i had a defense guy question my integrity and experience and we were well prepared with an answer , but really dollar for dollar , risk for risk, i suggest you head back into pop music.

the worst that can happen there is you record over the master vocal.

[wez]

we have been/are looking VERY seriously into forensic work, mainly because we know some people who know some people who can get the contracts... and being able to get the work is the hardest and most important bit BECAUSE -

1) law enforcement agents generally will not deal with you unless you are using CEDAR, or similar (something like the FBI's own software, for example). at a pinch, you might get away with the Algorhythmix plugs, which we are going to trial soon, i hear they are very good. so it will be very expensive.

2) you'll need to be able to have someone get up on the stand and prove their credentials as an 'expert'. pretty damn hard to do in this business.

3) as rick points out, it sounds pretty glam until you have to sit through surveillance tapes of things happening to kids that you don't want to think about. i know people who've done this and they didn't go back for more.

i had more or less decided against it for my business because of all of these reasons. i'm not inclined to do things by halves, and i couldn't justify a CEDAR system. with the new situation i'm in, things are a bit different and it is back on the table. but i have let the people who are spending the money know that i won't have anything to do with it unless it's done properly. conventional music/audio tools generally will not cut it. conventional music/audio people probably wouldn't cut it either.

which does make the original post sound a bit odd. this work is occasionally outsourced, but not to just anyone... and of course the police have their own forensic audio people.

so if you don't mind me asking, how did you get this gig?

[Adam Dempsey]

We supply a simple guarantee of confidentiality and verification slip that the content has not been edited/tampered with, with a check box list of processes applied. That always suffices for the client.

Following a repeated request from a client claiming a blank tape surveillance recording was later erased/edited by police (and there are ways of ascertaining if a tape is blank/unused or erased, pad wear in the cassette shell for one; bias signal another) we have a stringent policy not to get involved whatsover in court and this is discussed with the client before hand. But I agree, these jobs don't tend to come from the police themselves and coming from within a jail cell seems.. dodgy.

Out of interest, I did work on a scoop for The Age newspaper - the first released tape of a well-known former dictator. Full of distortion and with a deadline from hell, I tried everything on that and, no, the most expensive tools were not the solution for that one. In the end, I'd say it was a 40-50% improvement.



- colleague of a certain someone who was arrested by the Feds, detained 5 days without charge then sent back home, only to face Hurricaine Katrina and all costs..

[toadmark]

Thanks guys for all your advice.

To help you all understand whats going on here, we're no where near a major city where top notch facilities are available to do this. The CIB detective who came and saw me said he had been to the local video production place and they had suggested he come to see me. (I consider that good & bad, although possibly mostly bad). I know his police partner quite well.

These recordings sound more like a couple of crims talking with one of them wearing a "wire". I haven't listened to them completely yet, just the first 5 mins of each one. The first one is in a cell and the other two are in a yard and aren't too bad. A bit of EQ and tweaking should get them a bit better to hear. It's the indoors one that is challenging.

I've worked in broadcasting/media/computers since 1986 and have probably the best equipped studio in town (but thats not saying much due the size of the town, but no, I'm not the only one here and I'm only a project studio).

Keep the comments/advice coming ... its all good!