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Interesting audio mixing/render anomaly

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Ty Ford
Interesting audio mixing/render anomaly
on Nov 3, 2010 at 4:00:00 am

I was exporting clips via Quicktime conversion. The audio was simple dual mono. One person speaking> boom mic> 442 Sound Devices mixer two track mono out>camera. Everything sounds fine in FCP, Both tracks panned hard right and left, full stereo, but when I played back the rendered clips in QT, they were louder and clipped a bit.

I brought one of the clips up in STPro and although the tracks were not close to peaking in STP, they were clipped. Lots of time and experiments later, I found pulling the two mixer faders for the two tracks in FCP back to -3dB (half power point) and centering the pans gave me what I wanted. STPro showed no clipping; peaks at about -3 dB, which is what I wanted and I heard no clipping.

I'll know it from now on, but in the analog or digital audio studio world, that sort of clipping doesn't happen unless you mono the sources and you're really close to 0dB. With pro audio gear, panning two identical tracks results in a 3dB rise that can clip, but not necessarily in the mix buss. Somewhere there's a narrow spot in the FCP audio mix buss before the master fader. Maybe there should be an "Audio In FCP" forum.

Or not.

Regards,

Ty Ford

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Jeremy Garchow
Re: Interesting audio mixing/render anomaly
on Nov 3, 2010 at 4:04:43 am

Did you export stereo or did you separate and export dual mono? This has to be done in sequence settings.


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Ty Ford
Re: Interesting audio mixing/render anomaly
on Nov 3, 2010 at 4:06:52 am

L+R Stereo panned hard L+R.

And put it where you want it. I don't care.

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Jeremy Garchow
Re: Interesting audio mixing/render anomaly
on Nov 3, 2010 at 4:09:44 am

Which is different than how you recorded it, which is true dual mono. In your sequence, open up the settings and change output to true dual mono, not panned stereo. Then assign the outputs to whatever track you want, then export.


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Ty Ford
Re: Interesting audio mixing/render anomaly
on Nov 3, 2010 at 4:15:47 am

In the pro audio world, that's not a hoop you have to jump through.

What if not all of my clips are dual mono? Then changing sequence settings may not be the move to make.

Best,

Ty Ford

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Jeremy Garchow
Re: Interesting audio mixing/render anomaly
on Nov 3, 2010 at 4:28:57 am

You don't have a true stereo source, yet you're treating it as such by faking a pan left and right.

Try this same test with a true stereo source.

Also, why QuickTime Conversion? That process is notoriously unreliable.


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Ty Ford
Re: Interesting audio mixing/render anomaly
on Nov 4, 2010 at 5:19:45 pm

Jeremy,

Thanks for your interest and insight. I've been working in pro audio since 1969, went digital in 1990 with my first DAW and have enough experience to know when something's right or not. The anomaly is what it is. Apple (and I've been a proud Apple owner since 1986) has allowed me to make a living for myself and I appreciate the heck out of them for that. However, their SoundTrack Pro, for example, works and feels like an audio program designed by IT people who have little or no experience with pro audio.

Apple may choose to disregard simple audio conventions, like where or how they choose to route audio in an internal bussing system, or (one of my favorites) disregard compression ratios and metering for gain reduction in their compressors (audio not data), but in doing so they alienate the rather large constituency of pro audio folks who are left trying to figure out, "Why the heck did they do that? I guess they don't know how pro audio works."

I do appreciate your heads up on the sequence settings, but that's another case of WTHDTDT? It never would have occurred to me that a gotcha, er, CONTROL would be placed there.

Fortunately, there are enough question marks popping up about the video features to let me know it's not just an audio thing.

Best regards,

Ty Ford

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Jeremy Garchow
Re: Interesting audio mixing/render anomaly
on Nov 4, 2010 at 5:29:49 pm

[Ty Ford] "It never would have occurred to me that a gotcha, er, CONTROL would be placed there. "

If you would ever have to layoff a 5.1 and Stereo mix on one tape, you'd know exactly where they are ;)

I'm not questioning your experience or expertise. I am just pointing out what FCP can and can't do.

Things operate differently on different systems. I agree that Soundtrack Pro is not that Pro, but whatever. It's not going to be and never will be a stand alone DAW.

I do think, though, that you know you aren't really recording a stereo file so it's hard to truly and accurately judge what's going on.

To bring it in to video terms, there's movies that were shot stereoscopic, and then there's movies that were created to be 3D by a "mono" image. You can tell which is really stereo and which one is two halves of the same hole. Just sayin'.

You can also set downmix levels in those same sequence settings we are talking about.

Jeremy


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