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2.2.4 AUTO switch
The AUTO switch allows to automatically control release time and cut off frequency of the TAC filter. Thus, by
depressing the AUTO switch, the RELEASE and CUT OFF controls are deactivated. Release time and cut off
frequency of the filter are now automatically derived from the input signal.
Generally, good results will be achieved with the AUTO function. However, with complex sound sources
e.g. classical music featuring a great amount of disturbing noise fine tuning should be done with the
RELEASE and CUT OFF controls.
2.2.5 FREQUENCY meter
A precise 8-digit LED meter indicates the current operating point of the filter. The LEDs keep you informed
regarding lower cut off frequency, release time and frequency range of the audio signal. If no LED lights up, the
cut off frequency is set to 800 Hz. If, on the other hand, all LEDs light up, the bandwidth is above 20 kHz
and the filter has no influence on the usable signal.
It proves quite useful to set the SENSITIVITY control in that way that the noise floor causes the first LEDs
to light up.
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Please note that this meter is merely supposed to help you adjust the controls. It is re-
commended to perform A/B comparisons with the FILTER IN/OUT switch to find out which
setting suits your demands!
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Please also note that after power-up the unit needs a few minutes to warm up. While the unit
calibrates automatically, the LEDs might indicate values that deviate from the values stated
by the controls and scales on the front panel!
2.3 Operation of the expander section
The noise reduction system of the DENOISER is based on two signal processing techniques, which can be
used separately but may also be combined with each other: in addition to the dynamically controlled low-pass
filter mentioned above, the DENOISER features a so-called downward expander which uses a second noise
reduction process to eliminate remaining interference noise.
A downward expander automatically reduces the overall level for all signals below an adjustable threshold and
therefore extends the dynamic range of the program material.
Changing the variable release time and the expansion ratio enables the expander to operate as a noise gate.
Expanders generally function with a flat ratio curve, so that the signal continually fades. Noise gates however,
can be seen as a special type of expander. They normally work with a more exaggerated ratio and radically
attenuate the signal if it falls below the threshold.
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The following explanations also apply to the gate function, because the gate is a special form of
the expander.
12
DENOISER SNR2000
2. OPERATION
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