by Craig Tollis
January 29, 2007Something that's come up on several recent
edit jobs, and that I've been asked about, has been the use of mono
versus stereo sound sources.
modern non-linear editing systems, including Final Cut Pro and Avid,
now tend to assume that you are dealing with sound in stereo pairs.
That is, your source will have two channels of sound that are designed
to be sent to left and right speakers during playback. For many
consumer and music sources, this is a pretty good assumption. For
professional sound, however, it can get you into trouble.
For example, your modern camcorder is likely to have a pair of
microphones set into the front of it, and makes a stereo recording
of the subject you're shooting. Music from CDs, mp3s or other common
sources is likely to be a stereo mix created in the recording studio.
On the professional side, however, a boom mic or other single capsule
mic is inherently mono. Lavalier (tie clip) mics are usually mono
too. Sound effects and "natural sound" recorded on location
are probably mono, particularly if they were recorded with a boom
So, even when there are two tracks of audio on your capture source,
they may not be a stereo pair, but two completely different sound
sources. How this is set up will depend on the decisions made by
your sound mixer during shooting. In an interview, for example,
there may be one track used for the interviewer and one for the
interviewee. There might be one track from a lav mic worn by the
interviewee and a second safety track from a boom mic or reference
track from a camera mic. For a dramatic piece, there might be multiple
booms, or a combination of booms and lavs.
In these situations, it's important to listen to the sound from
each track separately and pick which one is best for your application.
(Note that depending on the action this may change during the take!)
Most edit systems will let you temporarily mute tracks. There will
generally be one track that will be either louder, clearer, cleaner
or otherwise preferable. You can discard the poorer quality audio
clip that you won't be using. Mixing a poorer quality track with
a better quality track typically degrades the overall quality and
doesn't gain you anything. You'll probably need to pan your single
track to center too.
general rule is to consider your sound source. Most natural sound
sources are inherently mono - a voice, a closing door, a bell, a
hammer striking a nail - the sound comes from one specific place
and is best recorded by a single well positioned microphone. The
editor or sound engineer can then mix it, equalize it, pan it, and
add reverb or echo to give it a spatial position within the final
mix that corresponds to how it appears in the picture.
A recording that is intended to pick up a number of sources, ambient,
atmospheric or environmental sound that has spatial quality, may
be in stereo. For example, the sound of machines in a factory, traffic
in a street, or people working in an office.
In this case, make sure you pan stereo sound left and right, if
your edit system has not already done this by default. It is particularly
valuable for music, where the sound engineer has probably gone to
some effort to create space and depth in a stereo mix, which will
add impact to your production.
If in doubt, stop and take a listen. Primary sound should be clear
and easy to understand. Natural sound or ambient sound should say
something about the location and set a mood. Sound effects should
be reasonable and motivated. As with all production elements, ask
yourself - what do I want from this, what does it add?
Got questions? Ask Craig at firstname.lastname@example.org.