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Author: Topic: Audio line-up - RTFM, but...?

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Posted: Sat, 09 Oct 2004 07:32PM
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Sorry for the long post - as a major Greek guy (or was he Roman) said: I lack the time to make it shorter.

I've been Reading the Friendly Manual again, specifically about Audio. It's not my strong point. Most of my FCP work is cutting event footage to music, so I've lived a blessed 'hassle free audio' life so far, but I've just had a Road to Damascus situation.

Book says (roughly) three types of Audio Level meter in FCP, all look the same but are scaled differently. Others go up to +12 dB - 'There Be Dragons'. The main one tops out at '0 dB'.

Many moons ago, I had been told to keep audio peaks in the -12 region of the main meter by a reputable (Avid) editor. After all, that's where the Tone sits (from 'Bars & Tone' - the highest rated TV programme of video engineers). "Ensure that your Tone output hits 0db at the BetaSP Deck, and you're done."

And of course it's not. In my student notes, Tone was at -4 dB VU, i've been assuming -12db at FCP should mean 0dB at the Deck, yet pulling audio down so no peaks go past -6 dB ... and I realise - all too late in this dust storm of misinformation - that we're in an 'Analog meets Digital and a fight ensues' situation.

After all, Analogue audio with VUs should hover in the 0dB area, and sudden peaks into +6 and (for student films) +12 dB were okay so long as you didn't make a habit of it.

The problem is that for analogue, it all 'hovered' in the 0dB range and for digital, 0dB is the absolute limit, which will decapitate your sound if you go higher. If you're bouncing on a trampoline, in an analogue world, there's a ceiling above you. In the digital world, there's a helicopter.

So: for all our edification, can any FCP Gurus elucidate upon the following...

- Instead of letting audio peak at -12, should we allow those peaks on the Master Meter to approach 0dB without ever lighting the lights? (Answer probably YES)

- When striping a tape and laying Bars & Tone to an analogue deck, should we be setting the standard FCP Bars & Tone level ON THE DECK to 0dB, -4dB or what? It leaves FCP at -12dB. If I set the deck to recieve it at -12, everything's too quiet. See next point.

- Is 0dB Digital the same thing as +12dB Analogue (as I originally suspected)? If so then -12dB Digital would equate to 0dB Analogue, and therefore should be the average, not the limit, of audio. Hence the FCP B&T hitting -12dB.

[is anyone following this? ed.]

- Has anyone heard of a digital version of a Peak Programme Monitor meter? I didn't invest £500 to get a stereo pair, and feel that I should have done, but cannot believe it can't be done in software. Yes, FCP can do VU on a frame by frame basis, but I'd love a PPM version all the same. Not popular in US, I guess.

- FCP has mud slung at it for its audio handling. Is that justified?

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Author: Topic: Re: Audio line-up - RTFM, but...?

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Posted: Mon, 11 Oct 2004 09:08PM
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I would only ask, what your final programme is for?

Broadcast, commercial DVD, Corporate.

If it's a DVD you could push it all the way up to max 0db - but not peaking.
Commercial DVDs probably run a little cooler, select RF modulation protection etc in A-Pack if you want to protect yourself from peaks.

If it's corporate who cares. There's no tech review to trip you up. No fussy broadcaster. Just make the levels sensible and listen properly so the volume in consistent.

If it's for Broadcast, you will need an external PPM meter of some description (I use a Hamlet WFM/PPM unit - around £3500) VU is not an acceptable way to work as it isn't a true flat measurement of loudness and analogue meters read differntly across a range of frequencies. PPMs are expensive but very clever hence the price.

You'll be aware if the audio goes over 6PPM -10db the programme will fail a tech review.

Also it depends on the kit you are laying back to. Digibeta and some other digital formats would have tone at -18db, equal to 4 PPM. An SP deck would be at -4 (I was always taught -3 by BBC bods). So how you kit is wired and if it's pro or semi-pro it may work at -18 not -12. AFAIK There aren't many software based PPMs which don't have some associated hardware to get the best results.

So while FCP doesn't have great metering, is just the same as Avid, I run FCP with the Hamlet unit monitoring SDI embedded audio from an AJA IO, and it's really great. The realtime mixing and keyframing, the ability to select multiple clips and adjust relative or absolute levels, the ability to add multiple audio plugins at once to multiple clips in the timeline. All very useful and alot better then Avid (which I've used regularly since V7)
PS The built-in multiband compressor in FCP is great in it's preset mode for maximising audio volume.

look here for nice little PPMs
about £450 I think.


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