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CEDAR Single-Ended Noise Reduction System (part 6)


Bureau service

Up until recently CEDAR has been operated purely as a bureau service, and this
facility is still available from Cambridge Sound Restoration. A potential user
of this service may either send up a DAT cassette which Cambridge Sound Restoration
will descratch using either the 1-pass or 2-pass process. If the DAT is accompanied
by an engineer, the Dehiss and EQ, which need subjective decisions, can be done

The environment in Cambridge Sound Restoration’s headquarters is far removed
from what a studio engineer might expect, appearing more like a cross between
a computer dealer and a hifi demonstration room. For the standard unassisted
bureau service the operator works with headphone monitoring which, although
good for hearing clicks, strikes me as not being entirely adequate •for
evaluation of audio quality. In the more normal au dio domain it is well known
that some things, such as pitch-related phenomena, while clearly audible on
speakers are difficult to hear on headphones. Both the 1-pass and 2-pass scratch
removal processes can have a damaging effect on the music if taken too far,
and correct judgement is essential.

Dehissing and EQ can be done using Cambridge Sound Restoration’s monitoring
system which offers a choice of small Rogers loudspeakers or (original) Quad
electrostatics in an as yet acoustically untreated space. I was disturbed that
the left and right channels of one of my test pieces were treated with casually
set different parameters, even though I was ‘assured’ that this would
only result in a slight imbalance in the distortion in the two channels.

But despite these points, the proof of the pudding is in the eating, and I
was able to take home the CEDAR demo DAT and another DAT of some tracks which
were processed during my visit. One of the most remarkable examples on the demo
is a jazz 78 which had been broken and glued together – glued together amazingly
well but still with some horrendous scratches. On this example, processing has
wholly beneficial effects, as it does on other examples such as one which had
scratches which, so I am told, occurred at a rate of around 2500 per second.
There is no doubt that CEDAR can produce very listenable results from previously
unlistenable discs.

When the scratches on a disc are less major, some possible doubts about CEDARisation
might set in, such as that there might seem to be less top end, and there might
appear to be some slight compression. This is very difficult to judge, one has
to be very aware that the ear is so easily fooled into thinking that artifacts
such as scratches and crackles are part of the music that taking them away inevitably
results in a sense of loss. On balance, I think that for declicking 78 rpm records
the system works well.

When it comes to Dehissing I was less happy. There are two very illuminating
examples on the demo DAT. One is a fairly noisy recording of Schumann’s
Piano Concerto, probably 1950s, which after Dehissing is as silent as a modern
digital recording, apart from a little modulation noise. Perhaps it’s a
matter of aural education but there is such a contradiction between the restricted
frequency range of the recording combined with high distortion levels and the
almost digital silence, that it somehow just doesn’t sound right. Maybe
it has been overprocessed and with a little noise left in it would have been
OK. The other example is a stereo recording of Prokofiev’s Classical Symphony
which in its original form is very present and vivid, but loses sparkle along
with the noise in the processing. An example which actually is very successful
is a live recording that was made unusable by •dimmer noise. CEDAR was
able to eliminate this problem c ompletely.

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The last track on the demo DAT is a recording of Noel Coward which has been
Descratched, Dehissed and EQ’d. This gives a good opportunity to hear the
artifacts of overprocessing. On the CEDAR version there is an effect very similar
to the phasing of a poorly aligned NAB cartridge which is definitely not on
the original. If you get a chance to hear the demo it’s very clear just
after the words ‘What avails the sceptred race’. (No blame is attached
to Cambridge Sound Restoration’s judgement on the degree of processing
applied as the customer’s engineer was present during the restoration).

My tests on tracks I had taken along to Cambridge Sound Restoration confirmed
that the demonstration tracks were typical examples of CEDAR at work and not
tracks which had happened by chance to work particularly well. My personal conclusions
are that Descratching is excellent and has a lot of potential. Dehissing definitely
works, but it is not without side effects and needs to be carried out with extreme

David Mellor

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David Mellor