16mm film is projected
with a mono optical
track. The current type is called variable
area.
A transparent line in a black background.
The relative width of the transparent part (not the area) is varied in
accordance with the sound waveform. (35mm uses SVA - Stereo Variable
Area)
The frequency
response for optical is roughly flat between 100Hz and 6-7Khz
- it falls away rather quickly at both the low & high ends. Typical
home sound systems are flat between 45Hz and 18KHz. Professional gear is
flat between 30Hz and 21KHz. In either case wow & flutter is imperceptible
and signal to noise in home systems or better is a healthy 85dB
(Decibel), with a more noticeably noisy 55 dB in normal audio cassettes,
Minidiscs (depending on material) etc.
Because the film
must be motionless in the gate
but moving constantly in front of the sound
(optical) head, there is a small amount of
wow & flutter inherent in the
projector - compounded by friction in the sprocket holes. This friction
causes the film to pull from the various sprocketed wheels in a jerky fashion.
The most critical
stage in the process seems to be before the optical negative is made: using
16mm magnetic film as the mix medium
exacerbates the wow & flutter. If the original material is kept digital
or high quality analogue then the optical will perform reasonably well,
albeit with poor frequency response and dynamic range.
The projector and
its associated sound system is usually the weakest link in the chain. Very
few cinemas treat 16mm with respect. The optical system is rarely kept
aligned and sound systems are usually not well calibrated.
If (1) the original
material was kept away from 16mm magnetic (dialogue is usually not a problem
here because of the natural pitch fluctuations of the voice) and (2) the
film lab’s optical writer is in good repair, and (3) if the technician
knows his/her stuff then the resulting answer print will have a surprisingly
good sound on a well maintained projector with a proper set of amplifiers
and speakers.
In order to minimize
the wow and flutter it is best to avoid long sustained tones which don’t
have vibrato: long held piano chords are the worst as everyone is familiar
enough with piano to know that it never has vibrato! Also problematic are
bells with long decays, etc. It is wise to filter out the very low end
when auditioning music or effects. If the very bottom is crucial to the
sound it may not work on optical. Fortunately the ear is very good at reconstructing
low frequencies from accurate higher harmonics.
It is best to have
a sound mixer familiar with how optical changes the sound. He or she will
be able to adjust the original material for the best mix.
The dynamic range
of optical is also quite limited due to an extremely high noise floor.
If one sound is much quieter than another it may in fact disappear. It
is therefore best to reduce dramatic dynamic changes. The completed
mix is passed through a compressor
and a severe limiter
as extreme signals will damage the mechanical
wings or shutters which shape the light for the optical negative.
As the 16mm optical
is mono (single channel) it is advisable to do all preparation work in
mono. This is of particular importance for composers, who are accustomed
to working in stereo. Collapsing a stereo mix may result in phase cancellations
and/or reinforcements which will alter the intended result. Better to do
a separate stereo mix for the video.
The master mix
should have calibration tones at -12db
(digital) or 0 dB (analogue) at 100, 400, 1000, 10000 Hz. Some labs also
like pink noise. It
is advisable to ask the lab what tones they require.
The mix should
always have a "2
beep", or one
frame of a 1000 Hz sine tone which begins
2 seconds before
the picture starts. In film this beep synchronizes to the first frame of
the 2 in the Academy leader countdown. In video it occurs at 0:58:00:00
and lasts until 0:58:00:01 (before
1:00:00:00 or
picture start).
When preparing
multiple tracks, each track should have a 2 beep. The synchronization of
all the tracks to the picture is then easily perceived by the mixers. If
it sounds like (1) a very loud 2 beep, or (2) if it is too long or has
multiple attacks then the tracks are out of synch.
The 2 beep is critical
when one is constructing a master for the lab which makes the optical.
They use it, along with time code, as a fail-safe.
Some labs will
not accept anything other than 35mm or 16mm magnetic film, Most will accept
time coded DAT. 35mm film is usually mastered to 35mm multi track with
Dolby SR. DAT back ups are the norm.
Some documentary
and low budget filmmakers are turning to Super 16 which is a film stock
that uses the entire film for the image. It cannot be used as a single
system projection medium: Most Super 16mm films are blown-up to
35mm or seen as videos. It is possible to have a double system but they
are custom set-ups and rare.
Interesting to
note that some of the touring ski film shows stripe
the optical with time code and synchronize a multi track tape
to the projector with Longitudinal Time Code.
Preparing for
the Mix
Put a two beep
on all tracks!
01:00:00:00 always
is first picture of reel 1. Multiple reels are usually designated by the
hour (reel 2 = hour 2, etc.)
Same time code
format for all elements
Allow for generous
pre-roll and post-roll (minimum 30", 2 minutes is best)
If using magnetic
film stock - make sure you are using new SMPTE leader and the leaders all
are precise.
Clean all magnetic
film tracks with velvet before mix
Junk fill must
be emulsion side out! (Emulsion is akin to sandpaper for the heads)
Don't use grease
pencil - use alcohol based markers for marking.
Check all splices,
look for worn sprockets.
In ProTools: (1)
check for hidden tracks, (2) check volume and pan envelopes, (3) clear
unwanted regions from list (4) Backup! Backup!
Dialogue:
Where voice level
is different (almost all) from actor to actor split tracks by
character
Dialogue tracks
recorded on location always have extraneous noise (traffic, room-tone,
camera noise, etc.) Volume will change with camera angle/set-up. If so
then split tracks to allow for matching levels.
When splitting
- allow for fade-in and outs.
Where there are
holes in the ambiance caused by splitting tracks or other reasons try to
provide at least one continuous ambiance to fill things in. This can be
a refrigerator, a traffic hum, wind, a river, etc. Track should run through
the entire scene.
Music
If 16mm then provide
only Mono mix. Collapsed stereo is not the same - there may be phase cancellations,
etc.
If you want cross
fades between music cues - provide two tracks.
Music should be
brought in as three tracks (six for stereo) - percussive material, "pads"
and melody instruments. This way any offending part (re: dialogue) may
be changed without sacrificing the level of the entire cue. If there is
no time for this then the mixer treats the three faders as one.
If music has been
altered to give it a source perspective (like coming out of a radio, etc.)
provide an unaltered version so that the mixer may change it to fit the
overall sound of the film.
Sound Effects
SFX with radically
varying levels or attacks should be put on separate tracks if possible.
No real rule of thumb other than try to imagine being the mixer faced with
making numerous volume changes on multiple tracks.
If sfx backgrounds
are not clean - provide a fade in so that they can sneak into the mix,
and sneak out.
Ambiance
Must run continuously
through scene. Loops are acceptable but make them long!
Even if you are
using the same background for two different scenes - it is still good to
split the background to accommodate the change in perspective - or at least
note level change on cue sheet. (For example the sound of birds from exterior
vs. interior perspective or the sound of a radio from the kitchen vs. the
radio in the living room.)
Cue Sheets
Always in pencil.
Provide at least two copies (1 copy per mixer)
Although there
is no absolute need for a cue sheet
when mixing on ProTools it is still an excellent idea. It is easy to forget
about a particular track or region and if one is sitting a little back
from the mixer's screen one might not "see/hear" that a particular region
is missing.
Mix Protocol (conventional/feature)
Usually begins
with a rehearsal - all tracks up to check sync! Equalization and rough
levels notes are made on the cue sheets. Try not to interrupt the process
- take notes and be ready to answer questions. After rehearsal is a good
time to make comments. Use SMPTE time (or foot count) for notes. Mixer
hasn't seen film before and is really looking at cue sheets and counter.
Actual mix is made
to digital multi track or full coat 35mm multi track (three to six tracks).
Each mixer is in charge of a "track" (dialogue (chief mixer), effects,
music, backgrounds) - watch lights to see if the tracks are being recorded
or "rehearsed".
If you hear something
you don't like and the mixers are not in the process of fixing something
else - speak up.
After the mix there
should be time for a playback. Last chance to watch and make notes and
make changes!
After mix the master
is "laid back" to the print master (straight mix).