AF100 LPCM audio in FCP 7.0.3

S

SamanthaG

New member
Sorry if this has been asked before, I haven't been able to find this mentioned anywhere. I have recorded LPCM audio with my AF100, but in FCP 7.0.3 Log and Transfer the only option I see is AC3 (either Matrix or Plain stereo). After I import a clip set to AC3, in FCP item properties it says the clip is 48K, 16-bit Integer. Does FCP override the AC3 setting to bring in the higher quality LPCM audio? Can someone please explain if I am missing something here?

Much thanks,

Samantha
 
Hi Samantha,
LPCM is a linear-quantized form of PCM audio. It is a lossless format.
You're used to hearing LPCM because it's the format that CD audio uses.
AC3 (on the other hand) is a lossy compression format originally developed
by Dolby for surround sound. It uses compression techniques similar to the
(much hated) Fraunhofer encoder (used for MP3).
When you ever have a choice for audio quality, opt for a lossless format
(like PCM / LPCM).
Now to FCP and how it decodes LPCM audio. There are two ways to represent
stereo information .. one is Left->Right .. and the other is known as Mid-Side (where
the audio information is one MID channel and one SIDE channel. To get to Left -> Right,
you do:

Left = Mid + Side (think summing the mid and the side channel)
Right = Mid - Side ( think summing, but flipping the phase of the Side signal)

Mid-Side is sometimes referred to as Matrix.

They are completely analogous and L/R vs. M/S carry the exact same stereo information
(albeit in a different format).

On the AF100 .. always always choose LPCM .. not AC3.

In FCP, I always opt for the "Plain Stereo" option .. particularly if you place audio suite
plugins in ... or bounce out to external audio mixing tools. The pipeline is slightly more
complex if you use the Matrix setting ... so I try and reserve as much CPU for the video processing
as possible.

The import option on the FCP Log and Transfer settings, the "AC3 Audio" setting is somewhat of
a misnomer .. it applies to both LPCM and AC3. I always set it to "Plain Stereo"

Hope that helps,
jeff
 
Thanks Jeff. That is very helpful. Great to know I'm not missing a preference setting in FCP and there's no issues using LPCM with the AF100.

- Samantha
 
Nope, LPCM works great although I wished it imported a little faster in FCP.... it was horribly slow before 7.0.3 . but it's
still slower than I would like in 7.0.3.

jeff
 
jmarkham said:
Nope, LPCM works great although I wished it imported a little faster in FCP.... it was horribly slow before 7.0.3 . but it's
still slower than I would like in 7.0.3.

jeff
Click to expand...

Time to move from the darkside Jeff.

:Drogar-BigGrin(DBG)
 
I've moved to Premiere for the most part .. I tried MC .. but didn't much like it. Premiere is
a very good tool.
 
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