In
its 1st March 2006 issue, Securizine reported that, ‘Hit TV cop
series, Life on Mars, set in 1973, demonstrates just how far the police
service has come on a number of levels.’ In a curious twist, it
also demonstrates how the art of noise suppression and audio forensics
has progressed over the past thirty years. Gordon Reid, managing director
of Cedar Audio, explains.
Life on Mars is set in Manchester in the early 1970s, an era in which
many of the sounds that pervade 21st century life did not exist. The
sounds of traffic, sirens, mobile telephones, and the general background...
these were either non-existent or very different in 1973.
The producers of the series therefore needed a tool that would allow
them to eliminate the background noise from location shots, retaining
just the dialogue and foreground sounds so that the appropriate ‘atmos’
could be added in the post-production studio at a later stage. The tools
that they chose to remove the background noises were the CEDAR DNS1000
and DNS2000 dialogue noise suppressors, which are in daily use at many
forces throughout the UK, performing the same tasks in crime prevention
and forensic audio investigation contexts as they do in TV production.
James Feltham at Hackenbacker Audio Post Production explains, ‘We
had to take great care with the location noise for Life On Mars; filmed
in noisy central Manchester we had to remove unwanted jet noise and
modern motorway sounds that would not have been commonplace back in
1973. The DNS2000 was an ideal tool for working quickly to remove this
noise. As well as being quick and simple to use, it offers the flexibility
to achieve instant results removing the unwanted noise without affecting
the dialogue.’
But in an unfortunate twist, the exposure of undercover techniques on
programmes such as Life On Mars means that undercover recording has
now become a much riskier venture than it once was. Rub downs of undercover
officers are more common so, to avoid exposing officers to increased
dangers of detection, the use of probes in a target's home, workplace
or vehicle has become more common.
Nevertheless, the greater use of probes brings with it a new set of
problems. In particular, a well-trained undercover officer wearing a
body recorder may be able to steer the target away from a noise source,
but you normally have just one chance to install a probe and you are
then at the mercy of whatever is happening in its vicinity. When large
amounts of unwanted noise are picked up, it can make listening to the
wanted speech very difficult and tiring, so the ability to carry out
good quality filtering is important. In particular, making speech more
listenable and more intelligible aids transcription and makes recordings
more presentable for the courtroom and juries.
The other major source of recordings is, of course, the public, who
record incidents and, in particular, telephone calls. These recordings
are invariably of poor quality and are usually made on low quality equipment
such as handheld dictation machines and cassette recorders. The resultant
recordings are noisy, muffled and one side of the conversation is often
much clearer than the other.
To counteract many of these problems, CEDAR's dialogue noise suppression
systems offer users a fast and intuitive way to reduce the background
noise content of recordings or live surveillance. For example, the noise
inside vehicles or from loud air-conditioning units and domestic appliances
can render many recordings unusable. Until recently, forces tried to
improve the intelligibility using processes such as low-pass and high-pass
filters, noise gates, dynamics processors, or techniques developed from
analogue encode/decode noise reduction systems.
Unfortunately, these often proved inadequate. Filtering is not selective
about what it removes, and there is no relationship between the input
and the filtering effect. Gates have no effect when the desired signal
is present and their use leads to unnatural gaps in the signal. Other
processes can generate pumping, distortion, and other unnatural effects.
In contrast, the DNS1000 and DNS2000 were designed specifically to clean
speech recorded in noisy environments, helping to improve both listenability
and intelligibility. The DNS1000 in particular is extremely quick and
simple to use, and highly suited to situations where computer-based
restoration and enhancement is inappropriate. Consequently, this device
is used in police forces and security agencies worldwide. The DNS2000
is an implementation of DNS technology designed for use in forensic
laboratories equipped with Pro Tools(tm) systems.
So, whether you're cleaning up location footage of police officers going
undercover in 1973, or cleaning up the audio gathered by undercover
police officers in 2006, the tools are the same.
Life meets Art.
CEDAR
Audio Ltd produces a wide range of noise reduction and speech enhancement
products for audio forensic investigation and real-time surveillance.
These range from simple to use standalone devices such as the DNS1000
to full computer-based systems for the laboratory. The company works
closely with other UK manufacturers of audio acquisition and recording
devices to provide complete forensic solutions, and has presented numerous
papers to train officers on the uses of such equipment.
For further information, please contact Alan French on 01223 881771,
or email forensic@cedaraudio.com.