Recording - March 2015 - 47

The Clipping Conundrum
Our writers discuss the big bad problem of clipping in modern audio
Our cast (in order of appearance): Paul J. Stamler, Giles Reaves, Mike Rivers, and Paul Vnuk Jr.

In rare cases, you may need to group all audio/instrument tracks
directly assigned to the mix and lower them as a whole-don't
lower any tracks that are a part of the submix, or the master fader
or any FX returns, as this will end up lowering them twice. You can
of course also lower the master fader and get the same results. But
if you find yourself routinely lowering tracks or the master fader by
more than 3 dB, you're either adding gain where you shouldn't be,
or you need to choose a lower reference level than -12 dBFS peak!
Most plug-ins have input and output level controls. If you boost
the signal within a plug-in by boosting with EQ or increasing makeup gain, you still want the output to be around -12 dBFS for your
peaks when you're done tweaking. Make adjustments to the output level... or the input level if your plug-in doesn't provide an output level control... so that when you bypass the plug-in, the audio
track is at the same level as when the plug-in is turned on.

Also consider parallel processing, to add RMS/average level
energy into a mix while still retaining the original transients.
When done properly, you will be able to raise the average level
(and thus the apparent loudness) without adding much, if any,
peak level.
There are many different ways to apply parallel compression; a
full list is beyond the scope of this reply. I'll just say that I like to use
more extreme limiting with the fastest possible attack time on the
parallel track, so that I don't end up adding much transient/peak
energy to the mix. The compressed track won't sound that great by
itself, but when mixed in with the original (dry) audio, you can usually get things louder than with an insert compressor on the same
submix. Unlike using a compressor as an insert, this won't destroy
all of the track's original dynamics; I use it for drum submixes with
great success, as do many other engineers.

"Ah, clipping, one of my favorite subjects. There are so many places
to clip, and so many ways of going about it."-Mike Rivers

Remember that combining tracks increases the overall level.
The answer, as always, is to leave headroom! Do this by using
your reference level of -12 dBFS peaks for all tracks and by not
adding gain with plug-ins. If you see clipping on a submixed
track and you're not using any plug-ins on the Aux submix master, consider pulling down the faders of all the submixed tracks,
one by one.
Now as for losing power in the vocals, if the vocals are then
too soft once you've followed these strategies, consider that your
mix is too loud-it's all relative!
Final loudness is often best achieved in mastering after you have
mixed your track. Most mastering engineers request that your premastered mix should typically have 3-6 dB of headroom above the
highest peak level (a good idea even if you're mastering it yourself).
Bypass the Master Fader plug-ins and use the Peak Hold feature on
your meters in Pro Tools to check the highest peak as you play the
entire song. If you are tracking all your audio at -12 dB and not
gradually boosting levels with plug-ins and auxes, this won't be a
problem in most cases.
You should compress a track because you want it compressed. In
a few cases you can compress for a little added loudness if you
don't mind the sound of compression... or if you like the sound of
compression! Again, it's simple-if the vocals are too soft, it also
means the track is too loud (it's all relative). When mixing, try to turn
things down that are too loud, as much as (or more than) you turn
things up that are too soft. This will help prevent clipping by not
adding to the overall level of the mix as the project progresses.

Finally, try mastering as a separate process instead of doing
it when you mix. If you must master when mixing, see my previous comments about not clipping the Master Fader when there
are no plug-ins on the track. Then add a mastering plug-in that
can function as a true brickwall limiter-they won't let you clip
when set up correctly! But remember that there's no free lunch;
the more limiting you use, the louder the track will be, but it will
also sound different than what you intended and can be quite
fatiguing and distorted when taken to extremes. Good luck!-
GR

Mike Rivers
Ah, clipping, one of my favorite subjects. There are so many places
to clip, and so many ways of going about it. Yes, Steve, you should
avoid clipping at all costs, and yes, you can avoid it completely.
Having your inputs adjusted to avoid clipping is a good start,
but how effective this is depends on the signal path. If you're
using a mic into an interface box, the chances are you'll be safe
if you watch the meters on the digital side-that is, the Pro Tools
meters-when adjusting the gain.
But you can't be absolutely sure of that. I recently reviewed an
interface that would lie to me if the input level got too high. Even if
I set the input gain quite low in order to keep the digital meters from
clipping and the CLIP light on the interface off, it was still possible
to clip the analog input stage of the interface-because the gain
control was in the signal path after the preamp. So it's possible to
record a signal that didn't indicate clipping, yet was clipped.
RECORDING March 2015

Recording - March 2015

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