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The difference between analogue
and digital technologies
In analogue video and audio equipment, the signal is generated,
processed or recorded with an almost infinite number of discreet
levels between zero and maximum - and the maximum level is
normally set to allow "headroom" - signals which often
for very short time intervals, can overshoot the working
maximum, without detriment to the result. In the days of
analogue audio and video, the amount of signal headroom was an
important indicator of the quality of the technology. Because of
the limitations imposed by broadcasters and particularly
analogue transmitting equipment, video signals with overshoots
were usually clipped within each piece of processing equipment,
whilst for audio signals, compressors and limiters would be
inserted at critical stages in the production chain. Besides the
clipping, limiting and compression circuits themselves, the
magnetic tape medium also performed a certain degree of
limiting, in that magnetic tape has a somewhat soft saturation
curve, by which slightly over-modulated signals are damped in a
way that is more discreet and warmer than absolute limiting
algorithms. This was not only a limitation of magnetic tape, it
was also one of its creative attributes.
With digital audio and video equipment, the signal is generated,
processed and recorded in samples - for example 44,100 times a
second, and each sample may have an amplitude value of one
discreet number between - for example - 0 and 255. The digital
circuitry rounds each sample either up to or down to the closest
appropriate level - not only as an entire signal, but also its
components when these are sampled, processed and recorded
separately.
The advantage of digital over
analogue technology is its lack of inherent noise and its
ability to be processed and replicated many times without any
loss or distortion of the signal. The disadvantage of digital
over analogue is that digital processing often requires
compression or the disposal of signal components that supposedly
are indistinguishable to the human ear or eye, to save space
(bandwidth) and processing power through the signal chain.
Another vital disadvantage is that if the signal input exceeds
the nominal maximum input level (for example 255) the digital
equipment and its software has no additional data space with
which to record and reproduce such signals, instead the signal
must be clipped - digitally - often with very discernable
results. For this reason, the reference level of digital
recordings is set typically between -9db or -20db relative to a
maximum signal level of 0db, because above 0db, there is no
headroom.
Another challenge with digital
signals, particularly video signals, is that the often employ
compression algorithms, which implies that the signal, once it
has been passed through different parts of the production chain
and subjected to several forms of compression, is no longer
digitally identical to the original digital recording. (For this
reason, we archive our recordings so that in the future, we can
always go back to the original before applying whatever
compression standard may be most popular in the future).
Therefore it would be an
oversimplification to say that digital is always better than
analogue per se. Digital technology has evolved rapidly, and
continues to to so, not least because it is easier for
manufacturers to offer better quality at a lower price - though
often at the cost of less functionality.
So, whilst we have embraced digital
production technology, we have not completely abandoned the
analogue world. Besides access to archive material, for which
legacy VTR formats are still essential, there are many
situations in which analogue technology still meet the
requirements of our production work - and in some cases, may
even be superior to digital technology. Though more demanding in
terms of calibration, maintenance and operation, analogue
technology - particularly in the audio domain - remains a vital
aspect of our workflow. The art in the modern world is to be
able to combine analogue and digital technology and working
methods to achieve the optimal result.
For example, many voiceovers and
instrumental recordings benefit from an initial analogue
recording process - employing for example a Nagra audio recorder
- where the analogue electronics and the magnetic tape medium
offer a softer, warmer sound with better handling of sudden
transients than can be achieved using digital technology. Such
analogue recordings are then ingested and edited digitally.
Similarly, if we need an analogue
copy of an analogue master or original recording - especially to
deliver it to other professionals who will process it digitally,
there can be situations where the best solution is to make a
direct dub copy between the appropriate formats, thus avoiding
introducing intermediate digital compression into the signal.
For this reason, we maintain access to most analogue and early
digital video and audio tape formats in our facilities. |
