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Prep mix for broadcast?

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Joe Bender
Prep mix for broadcast?
on Aug 18, 2010 at 8:24:52 pm

Hi All,

I'm in a tricky situation and could really use some help on this. My documentary Capital recently got picked up by a distributor, who needed a new cut of the film. My collaborator and I made a TV-hour cut and re-mixed the audio for the new cut with our sound editor in ProTools. Unfortunately we mixed it to 0db, rather than the -6db that the distributor needs for broadcast. The editor at the distributor suggested reducing the levels in dubs for broadcast clients - unacceptable, as I see it, since there are some very quiet passages in the film that would be rendered inaudible - or running it through a limiter to bring the levels down. Apparently that can produce some distortion though, which I'd rather avoid if possible. So my question is this: what is the best way, short of re-mixing the whole film (the sound editor is out of the country for the next month) to get the levels to -6db for broadcast? The possibilities, as I see them, are these:

Limiter: what are the risks? What's the best/a good one to use? Is this something I can do myself as a solid video editor but no audio expertise, or should I eat the cost and go to a studio? The distributor's post house has also offered to do this for us; should I again swallow the cost and have them do it? As I see it that would be a less desirable solution, as I wouldn't be in the room and would have little/no control over the process.

ProTools: is there any way to bounce the audio from ProTools with the max level set to -6db? Would this be any different from reducing the levels/using a limiter?

Something else? I'm sure there are tools out there that I'm not aware of, since I'm a dabbler at best in audio.

So what do you think? I'm pretty lost here, so any help will be enormously appreciated!

Many thanks in advance,

Joe


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Michael Martin
Re: Prep mix for broadcast?
on Aug 18, 2010 at 9:45:54 pm

If you don't want to drop the levels in over dub I would not suggest a limiter, that's going to flatten everything out badly. I would try lightly compressing and peak normalizing to -6.

-Michael Martin
Martin Media Designs
Location Sound/Audio Post Production/Sound Design


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Peter Groom
Re: Prep mix for broadcast?
on Aug 19, 2010 at 10:27:02 am

HI
Id suggest that if reducing by 6db is really going to send some of your programmes quieter passages into inaudible, then I doubt the mix is suitable for TV use anyway. It sounds like a theatrical mix with big dynamic range. TV has much less dynamic between the loudest and quietest parts. This is for many reasons but mainly (IMHO) due to the listening environment and home equipment, which is by definition much less than that of a theatre with its high spls and very lo freq handling abilities.

Id suggest a remix is on the cards.
Peter



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Joe Bender
Re: Prep mix for broadcast?
on Aug 19, 2010 at 1:32:23 pm

Many thanks Michael and Peter for your advice. @Peter, I may have overstated the problem re. the dynamic range in my original post. Some passages are quiet, but it's not as extreme as a serious theatrical mix, as we mixed the film overall with both projection and DVDs in mind. With that said, it sounds like I may need to reduce the dynamic range a bit.

By the way, I also misstated our original level above - the original mix peaks at -2dB.

So another question: in working through my limited toolbox looking for possible solutions one thing I came across is a "Match Volume" tool in Soundbooth CS5. It analyzed the file - it tells me Volume -20.11dB, Perceived volume -17.88dB, Peak -2dB - and has an option "Match to Peak Volume," which apparently "Makes peaks equally loud, retaining dynamic range, but also extreme differences in overall volume." I believe this is normalizing the peaks to the target volume. When I use the tool to match peak vol to -6dB the resulting clip has volume -24.11dB, perceived volume -21.88dB, peak -6dB. From those figures it seems like SB just cut the levels by 4db. Does this sound like an acceptable procedure? Is this different at all from the distributor making dubs of the master at a lower level?



Thanks again!

Joe


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brandon smits
Re: Prep mix for broadcast?
on Aug 19, 2010 at 3:42:17 pm

Joe,

I don't think your problem is insurmountable. Paying for a mastering engineer to simply remaster your audio for broadcast should be pretty cheap, but if you have ProTools you have some rudimentary plug ins that can get the same job done. Michael's suggestion is accurate, but maybe not specific enough considering your video background. Decreasing by 4db seems to be about what you need if that peak level is accurate, I'd be inclined to take it down 1db more ton ensure you don't clip the broadcast equipment. I'll outline a process for you to try which will include this step so read on before trying.
Michael mentioned compression, which is the appropriate tool, but compressing properly is truly an art. If you squash the audio too much your noise floor is going to be audible, which you don't want. My advice is to tinker with compression using the results you got from soundbooth. The main 4 parameters of a compressor are Threshold, Ratio, Attack, and Release. Listen to a low volume passage of your project(lowest volume portion if possible). Watch your sound meters to see the level of the volume. You will want to plug this number(in db) in as the threshold setting on the compressor. Experiment with the ratio, <1 to 5 is the range I'd suggest messing with(start at 3:1 and finagle). Keep the attack and release at defaults in soundbooth. Make sure your output gain is at -1 db as i described earlier.

After you try this compression, play it through tv speakers to gauge your results. You should notice that you can hear more of the quieter sounds even at a lower volume on your tv. Let me know if this helps!

8core Mac Pro Early '08 Xeon 2.8 14gb RAM
Apogee Ensemble
JBL LSR 4328 Surround Set up
Euphonix Artist Series Mc Control, Mc Mix, Mc Transport
All wired with Mogami Cable


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Richard Crowley
Re: Prep mix for broadcast?
on Aug 19, 2010 at 2:59:22 pm

So then the problem isn't the max level, because that is trivial to "adjust". The problem seems to be that you used an unusually wide dynamic range, apparently something inappropriate for standard broadcast use. Maybe something to avoid in the future.

I would have to agree with those who say that there isn't a simple solution to this one. Just knock the level down and deliver the first one, and take your lumps. And learn for the future.


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John Fishback
Re: Prep mix for broadcast?
on Aug 19, 2010 at 3:35:07 pm

How about lowering your overall gain to accommodate the -6 peak level, but then raising the gain at those points you feel it's too low. Assuming you received a stereo or 5.1 mix from Pro Tools, this wouldn't be hard to do as you're working with a limited number of tracks.

John

MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.8 QT7.6.4 Kona 3 Dual Cinema 23 ATI Radeon HD 3870, 24" TV-Logic Monitor, ATTO ExpressSAS R380 RAID Adapter, PDE enclosure with 8-drive 6TB RAID 5
FCS 3 (FCP 7.0.2, Motion 4.0.2, Comp 3.5.2, DVDSP 4.2.2, Color 1.5.2)

Pro Tools HD w SYNC IO & 192 Digital I/O, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN


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brandon smits
Re: Prep mix for broadcast?
on Aug 19, 2010 at 3:46:37 pm

this is good advice as well, very video editor friendly. nice set up John!

8core Mac Pro Early '08 Xeon 2.8 14gb RAM
Apogee Ensemble
JBL LSR 4328 Surround Set up
Euphonix Artist Series Mc Control, Mc Mix, Mc Transport
All wired with Mogami Cable


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Joe Bender
Re: Prep mix for broadcast?
on Aug 19, 2010 at 11:08:10 pm

This is all great advice - I will try both the compressor technique and timing the volume for quiet scenes and see which sounds best. Many, many thanks to all of you for responding and for such detailed (and editor friendly) help!


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