Drawmer DF320 Universal Noise Filter - Used

Drawmer DF320 Universal Noise Filter - Used

The Drawmer DF320 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 DF320 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.

This is a used item. The unit is in very good condition with only minor signs of use. Please see images.

Conventional gates or expanders can only remove noise during low level sections or pauses in the material being processed but the DF320 is active at all times, regardless of the signal level.

The DF320 works on the established psychoacoustic 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.

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 DF320 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.

Auto mode causes the filter to track the frequency content of the input signal rather than its amplitude and so even low level passages may be processed without any significant loss of high frequency content. Which mode to select depends on the character of the material being processed and this may be decided empirically by the user.