sundance 2006 - Zoael

Sounds of Silence Wakes
Up Audio Industry
Alternative Sound Tracks for Silent Films
ROAR. THUNDER. CRASH.
Explode. Theater owners install
the best theatrical sound exhibition
systems available to enhance
movie watching because fundamentally,
sound is a most vital part of the
film experience. It’s hard to fathom
why then, in cinema’s earliest days,
the inventor of the first 35mm film
gauge (late 1890s), gave no thought
to accommodate musical accompaniment
on a printed sound track. Was
the guy deaf?
So, silent films were composed
using the full frame - an aspect ratio of
about 1.17:1 and standardized in 1926
as the Academy Silent Aperture of
1.33:1. With the introduction of optical
soundtracks printed on release
prints, one-tenth of an inch (100 mils-
100/1000 inch = 1/10) of the film was
BY ROBERT HEIBER, PRESIDENT,
CHACE AUDIO AND JAMIE HOWARTH,
PRESIDENT-PLANGENT PROCESSES
MACHINE SPEED INSTABILITY
in the motion picture and
audio recording process is a
well-known phenomenon. Two artifacts
commonly known as “wow” and “flutter”
can conspire to ruin a sound track.
Heretofore, rejectable wow and flutter
anomalies were unsolvable audio problems—absent
finding an alternate
“unflawed” source. These audio roadblocks
have now been removed thanks
to a unique technology called Clarity
Audio Restoration (Clarity) by
Plangent Processes. Clarity is a combination
of proprietary DSP (Digital
Signal Processing) and hardware for
the playback of 35mm magnetic sound
film and audiotape to correct wow and
flutter due to machine speed instability.
It is well known that even “Rolls
Royce” audio recorders and playback
machines like Albrechts and Studers
have a published wow and flutter specification.
“Wow” refers to irregular cyclical
motion, which creates variations in
the pitch of a sound track (usually at a
slow rate), while flutter is attributable to
similar deviations in the transport at a
higher rate of occurrence. Regardless of
the quality of the equipment, all analog
recordings suffer from these flaws.
When gross errors occur, even the
untrained ear can hear the problems
associated with wow and flutter. More
lost for the image. A new picture ratio
standard of 1.37:1 emerged and called
the Academy Reduced Aperture.
Since silent films did not accommodate
a soundtrack, the original silent
film negatives were not suitable to
PRESENTED AT
AMIA CONFERENCE
make sound prints. That became a
problem in the case when new prints
of Harold Lloyd’s silent comedies were
needed for exhibition with an optical
sound track.
A common solution is to optically
reduce the image and make new prints
that would accommodate the soundtrack
area. However, it’s a time-consuming
process and the result can still
affect the image through a build-up in
subtle errors manifest as masking phenomenon,
and listener fatigue. Clarity is
the first technology addressing these
problems utilizing a novel method of
“re-timing” the audio signal.
To re-time the audio signal, the special
Clarity transfer equipment recovers signals
in the ultrasonic region that can be
found on the tape or film along with the
audio of the original recording. Ascribing
to these ultrasonic components, the
properties of a moving clock (think varying
sample rate), and mathematically
retiming these signals such that the clock
is crystal-steady, the dsp now “knows”
the speed fluctuations of the original
machine occurring at the moment it
made the recording. By inverting the
error signal, and conforming the corresponding
audio to it, Clarity’s DSP
retimes the audio to a fixed and stable
time base. The result: perfectly pitched
audio with no wow or flutter.
Conventional wisdom suggests that
analog degradation is the result of two
factors: the quality of the recording
electronics and the recording characteristics
of the magnetic media and heads.
No one would argue that in the early
days of magnetic recording, both the electronics
(tubes) and early tape formulations
contributed to sound quality degradation.
However, once manufacturing
71
contrast. An alternative solution is to
use a digital soundtrack, which does
not infringe upon the picture area.
Two of the three digital sound formats,
Dolby Digital (SR-D) and Sony
Dynamic Digital Sound (SDDS) meet
this criteria. DTS doesn’t because it
records a time code control track in a
tiny area unused in standard analog
optical recording.
Another issue is projection speeds
for the films since 1920s films often
ran at 20fps while all modern projectors
run at 24fps for sound prints.
This speeds up slower films with
24fps projection; often giving action
sequences too much of a “Blair
Witch” jerky look. While some theaters
are able to adjust projection
speeds and run the film slower, a
soundtrack pitch changes to a lower
processes for both audiotape and magnetic
sound film were standardized, they
were very quickly considered high fidelity
media. When solid-state electronics made
their appearance in amplifier design, the
electrical component also became more
reliable. Since it is standard practice to
align the replay electronics of the film or
tape machine to the alignment tones
recorded onto the film or tape, it is possible
to very accurately replay a tape with
very little -if any- degeneration from the
electronics or media.
As noted earlier, no analog recording
mechanism is immune from these
artifacts.. Thirty-five millimeter magnetic
sound film is particularly vulnerable
to another type of periodic fast
flutter known as “sprocket-cogging.
Sprocket-cogging, as the name
implies, is a function of the sprocket
drive of 35mm film. With 4 perforations
per frame and 24 frames per second a
96Hz (4 x 24), audio artifact can be
found in magnetic sound film, not unlike
“perf buzz” in optical sound. Though the
sprocket-cogging is at a fairly low signal
level, it creates an intermodulation distortion
component that also affects the
purity of the sound, and creates listener
fatigue, or “ear glare”.
In addition to these factors, the capstan,
bearings, rollers and reel motors all
create an ever-shifting pattern of beat
frequencies that intermodulate with the
audio. These mechanical instabilities
cause everything from bass cancella-
register whether digital or analog. So
pitch correction would be required
to compensate for this slower nonstandard
projection speed.
Empirical speed tests showed that
a SR-D track could be slowed down to
20.3fps before the failure rates
became excessive. In modern exhibition
the analog track is the backup for
the digital, these silent prints indeed
would be silent if the digital track fails
since no analog track could be printed
on the film. After comparing tests at
22fps and 24fps, it was determined to
release the film at 24fps for consistency
in exhibition. There is another
option. Rather than making new digital
soundtracks for all of the films, several
shorts ran with “synchronous”
CDs. These tracks are cued to start
with the “start mark” in the projector
gate, similar to a Vitaphone presentation.
These tracks worked with surprisingly
accurate results.
Unconventional, inventive ways
that use digital sound technologies are
excellent examples of emerging technologies
for saving film history.
Audiences of today and the future can
now see these original images and
experience theatrical sound as they’ve
come to expect.
Wow…Flutter…Analog Artifacts…Gone
PRESENTED AT
AMIA CONFERENCE
tion, to lower midrange mud, up
through grainy sidetones in the
midrange, and on up into the clouding of
the high frequency with interstitial haze
and transient blurring. The effect of
these artifacts was not well understood
during the heyday of analog recording,
because the problems were difficult to
quantify, and were measured with an
antiquated international standard that
didn’t provide a useful metric regarding
the audibility of these faster wow and
flutter components. Regardless of the
lack of documentation regarding these
flaws it is indisputable that they were
always there. Furthermore it is evident
that removing wow and flutter artifacts
with Clarity not only reduces obvious
pitch fluctuation, it also reduces or eliminates
the characteristic roughness
and/or muddiness caused by high-frequency
flutter. This helps to explain
why a tape or film copy, whose frequency
response “by the tones” measures
identically to the original is found to be
perceptibly “duller” in character and
offers a more sensible explanation for
the true cause of generation loss. analog
signal degradation attributable to
machine speed instability is not theoretical.
Clarity Audio Restoration by
Plangent Processes can analyze and
compensate for these inaccuracies for
the first time ever. The result-legacy
recordings that can now be presented
with wow and flutter specs comparable
with today’s digital recordings.