Behringer SNR2000 - Manual (Page 10)

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DENOISER SNR2000
Fig. 2.1: Operation of the dynamic filter
With a low-frequency input signal present, the dynamic filter will reduce any mid or high-band noise as well as
any disturbing noise tails. If the input signal is dominated by high-frequency components, however, the
dynamic filter will open to its full extent to let the signal pass, maintaining high-frequency information.
2.2 The TAC filter of the DENOISER
Our main goal was to create a filter which cuts off high frequencies during pauses but lets the signal pass
without modification as soon as a usable signal is present. However, its realization poses many problems.
Apart from “intelligent program recognition”, the filter has to meet the following criteria:
1. The control times of the dynamic filter must be fast enough so that high frequencies will not be cut off. Thus,
the sound of signals with a high slope, such as percussive instruments, will not be modified.
2. However, if the control times are too fast, “flutter” may occur, i.e. intermodulation distortion could be produced.
The new BEHRINGER TAC (Transient Attack Control) filter circuit gurantees extremely fast control times
without producing audible intermodulation distortion. In contrast to conventional units based on so-called RMS
rectifiers, the TAC circuitry uses a peak detector. While the RMS rectifier calculates the average or mean
value of the signal, i.e., requires a so-called “integration time”, the peak detector exactly traces the input
signal response. Thus, the TAC circuit is capable of reacting much faster to abrupt level changes produced by
percussive signals. The delay which the integration time causes in RMS rectifiers is eliminated in a peak
detector, i.e, the “kick” of the instrument remains almost unaltered.
2. OPERATION