Drawmer DF330, Руководство оператора

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DF330 OPERATOR’S MANUAL 2
INTRODUCTION
The Drawmer DF330 is a single-ended, high quality noise reduction processor which
may be used to significantly reduce the subjective effect of unwanted noise that might
be present in an audio signal. Unlike tape noise reductions systems, the DF330 does not
rely on the encoding of the original signal and it is effective not only against tape noise,
but also against noise generated by signal processors or electronic instruments. High
quality components are used throughout to ensure the cleanest possible signal path
from input to output.
Conventional gates or expanders can only remove noise during low level sections or
pauses in the material being processed but the DF330 is active at all times, regardless
of the signal level.
The DF330 works on the established psycho acoustic principle that noise is masked or
shadowed by high signal levels or by signals containing a significant amount of high
frequency information. When such signals are present, no processing is necessary. In
the situation where the signal level is low or there is little high frequency content to mask
the noise, then the noise becomes audible.
Two different principles are applied simultaneously by the DF330 resulting in a
significant lowering of the perceived noise level yet without introducing any undesirable
side effects such as noise pumping or noticeable loss of high frequency content.
Firstly, a low level expander, with a choice of three expansion ratios, may be used to
unobtrusively close down the signal path when the signal falls below a preset threshold,
as set by the operator. This expander has fully automatic attack, variable release time
and the user may select from three degrees of attenuation so that, if preferred, the signal
may be attenuated rather than muted by the expander action. This latter feature,
combined with a low expansion ratio, may be used to increase the dynamic range of low
level programme material with a subsequent improvement in signal to noise ratio.
Automatic attack is an essential feature of a high quality expander. Any vocal signal will
be almost impossible to capture correctly using manual attack. This is because almost
every word in every language has a different attack characteristic. A slow attack would
cause
't' sounds to become 'e' due to the loss of the initial transient. A fast attack will
tend to 'click' or sound 'scratchy' when a slow rising signal is present. The DF330
eliminates this problem by sensing the speed of the rising envelope, independently of
the frequency and constantly adjusts the attack time accordingly.
Secondly, a voltage controlled low-pass filter tracks the dynamics of the input signal and
so reduces the audio bandwidth of the signal path at such times as the full bandwidth is
not required, with a consequent reduction in high frequency noise. This filter has two
modes of operation, Manual and Auto.
In Manual mode, the user sets a threshold below which the filter will start to close as the
input signal level falls. This mode is very flexible and is useful on a variety of sound
sources from complete mixes to individual instruments. It also allows the user to decide
on the degree of processing necessary: High quality programme material needs little
processing whereas an excessively noisy source such as an audio cassette without
noise reduction may warrant more severe treatment. In this case, the user can
compromise between the degree of noise that is acceptable and any loss of brightness
that heavy processing may cause.