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The Silencer

Dbx 563X

The latest addition to the dbx range of half-rack studio processors is the 563X Silencer, a handy device for removing 'hiss' from recordings or even digital samples. Gareth Stuart puts it to the test.

The latest addition to the dbx range of half-rack studio processors is the 563X Silencer, a handy device for removing 'hiss' from recordings or even digital samples. Gareth Stuart puts it to the test.

Do you suffer from hiss? Tape hiss from your good old analogue masters, or 'digitally preserved' hiss on your PCM, RDAT and CD masters? Or even noisy samples perhaps? Well, now that the dbx 563X Silencer is available you might consider tidying up your hissy recordings.

The Silencer is a single-ended, part-band dynamic processor. In normal recording usage it would be connected after the tape machine, last in the audio chain before the amplifier. Its level characteristics are those of a progressive noise gate, but operating only on frequencies above 1.6kHz - hence the 'part-band' (bandwidth) description. It starts to work as the high frequency components of the audio signal you are feeding it fall below the set threshold. Or, in other words, as the input signal level drops so the Silencer gradually reduces the level of high frequencies - from 20kHz down to 1.6kHz. The loudest peaks in the input signal don't need any de-hissing, simply because the hiss is masked by the signal, whereas with quieter signals (of any duration) hiss can be obtrusive to the point of distraction. It's during these moments that the Silencer is most effective - removing hiss by simply filtering out the higher frequencies.


On the front panel there's an LED showing whether the Stereo Slave mode is in operation or not, a bypass button for switching between direct and processed signals, and a horizontal line of LEDs specifying the frequency range to be processed (1.6-20kHz). Below these is a slider labelled 'Quieting', which controls the amount of the effect, and on the far right there's a gain trim control governing the level of the high impedance input.

The rear panel houses four jack sockets - input, high and low outputs and stereo strapping, and a pushbutton regulating the operating mode - Master or Slave. 'Master' would be selected either in single channel use or in stereo mode, where one 563X unit would control the overall effect of two units 'strapped' together. You select 'Slave' only when the unit is to be controlled by another Silencer.

The stereo slave concept allows two units to be strapped together using a stereo jack-to-jack lead; if you try using a mono jack-to-jack lead the system defaults to a setting that results in maximum dehissing - effectively filtering out all frequencies above 1.6kHz.

The 563X is a single channel, mono-only device. When linking two of them together for stereo operation, one unit must be switched to the 'Slave' status (the yellow LED confirms this) in order that the amount of de-hissing on both channels is exactly the same, thus preserving the stereo image. The amount of de-hissing is governed by the 'Quieting' fader. As the fader is moved right (increasing the effect), the LEDs above show the resulting high frequency reduction. Fully left allows for the most subtle effect, depending upon the input level (I'll come back to this), fully right gives the effect of sticking cotton wool in your ears! You will find that some signals are so quiet that amplifying them is necessary to make the Silencer work efficiently. Quiet, unamplified signals cause the Silencer to over de-hiss - resulting in a dull, muddy sound. The answer here is to use the high impedance (Hi-Z) inputs, as they have a gain trim allowing signals to be amplified. This simply raises the de-hissing threshold so that only the very highest frequencies are processed, leaving the sound clear and with less hiss. It's important to remember that when linking two units for stereo, the gain trims should be set the same on both devices.


I first used the Silencer to de-hiss an analogue reel-to-reel master tape. It worked well, but it needs to be used quite subtly. For instance, one introduction to a song featured a regularly tapped woodblock soaked in long decaying reverb. With heavy processing from the Silencer, it wasn't difficult to hear the high frequencies of the woodblock being filtered out as they decayed in reverb - an interesting effect but not what I had in mind at the time, ie. a natural sounding, less hissy tape.

It was pretty good at cleaning up old 'analogue mastered' classical compact discs, though. This was an instance when it was necessary to use the Hi-Z input to boost the CD's output. Before doing this, quiet passages were being de-hissed above 4kHz, giving a tremendously muddy sound.

Apart from cleaning up noisy tapes, the Silencer works particularly well as a quasi-expander/noise gate where, instead of turning down the volume below a threshold, it filters out high frequencies. With this in mind it can be employed for all sorts of things - such as de-hissing sound samples or synth patches bathed in quantisation noise, and for cleaning up noisy tracks on the multitrack during mixdown. However, the main application for this machine - or rather the thing that it does best - is de-hissing noisy recordings.

The Silencer is simplicity to operate, and whether you fully appreciate the technicalities of how it's doing what it does to the sound or not, the audible effects of changing various parameters are immediately obvious. Judge for yourself whether or not the Silencer is an essential tool for your studio. I can tell you that it's an effective processor, easy to use, well built, and undoubtedly good value for money.

Price £113 inc VAT.

Contact Scenic Sounds Equipment Ltd, (Contact Details).

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C-Lab Notator

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Spectrum Synthesis

Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Sep 1988

Gear in this article:

Studio FX > dbx > 563X Silencer

Gear Tags:

Noise Reduction

Review by Gareth Stuart

Previous article in this issue:

> C-Lab Notator

Next article in this issue:

> Spectrum Synthesis

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