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Broadcast Audio Query

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John Davies
Broadcast Audio Query
on May 2, 2012 at 4:18:53 pm


Having strayed into the 'Audio Professionals' forum for the first time, I feel a little lost and out of place.

I have some audio to deliver for broadcast and have never had to deal with audio on such a level before. I have the direction of... 'The required set up level is zero level (PPM 4) @ 0 dBm with 18dB of digital headroom Programme sound peak levels should not exceed +8dB (PPM 6)' - Having Googled numerous parts of this, I could do with this translating for me.

I don't expect someone to break it all down for me as this has probably been asked hundreds of times before on here, but a link to a guide or rundown of what this means to an audio newbie would be greatly appreciated.

I'm running out various 4 x 22m mixes and have so far been bringing in to Audition, adjusting certain levels, bringing peaks down and applying a hard limiter to even out some parts. Now this has been brought to my attention (PPM / 18db Headroom) I thought I should stop in case I'm going down the completely wrong route.

Any help appreciated, thanks.

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Andrew Rendell
Re: Broadcast Audio Query
on May 2, 2012 at 8:28:34 pm

I'm guessing that you're in the UK as that's a normal UK broadcast spec (it's the 18dB digital headroom that suggests so, most of the world uses 20dB).

OK then:

"zero level" aka line up tone (the 0dBm, although that's really a redundant term in digital audio nowadays) is at -18dBfs, i.e., 1kHz tone set to -18db in your workstation.

A PPM is like a VU meter, but with a very fast "rise" time and a slow decay, so it rides the peak levels rather than giving an average. Hardware PPMs are quite expensive but I use PPMulator+ (generally via Audio Hijack Pro on the Mac) and it does the job nicely.

Line up level is at 4 on the PPM and the units are 4dB apart, so PPM6 is 8dB above line up level. That's your maximum peak level. Usually speech is best with the meters peaking roughly midway between 5 and 6 and music about half a unit or a whole unit lower, because music tends to sound subjectively louder for the same peak level and PPMs aren't good for judging subjective loudness. (That depends somewhat on how you use EQ and compression, so do use your ears to make a judgement. Personally I like only a little compression and only use a limiter as a "legaliser" to catch any odd peaks that I've missed.)

Hope that helps.

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Peter Groom
Re: Broadcast Audio Query
on May 3, 2012 at 8:30:47 am

Good explanation from Andrew. Ill second a vote for PPMulator. Its the cheapest accurate device youll find. Dont know how of if it can be linked into audition tho.
If youre still unclear / struggling, let me know or send me an email and ill talk you through it on the phone as were both in the UK.

Post Production Dubbing Mixer

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