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Installation, Introduction, The lx20 expander/compressor – Drawmer LX20 Dual Expander Compressor User Manual

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LX20 OPERATOR’S MANUAL

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INSTALLATION

The LX20 is designed for standard 19" rack mounting and occupies 1U of rack space.

Avoid mounting the unit directly above power amplifiers or power supplies that radiate

significant amounts of heat. Fibre or plastic washers may be used to prevent the front

panel becoming marked by the mounting bolts.

INTRODUCTION

Many studios start as a small concern, but quickly expand into serious, productive

environments. Often, this means selling some of the budget equipment, in order to

replace it with equipment of the necessary quality to match the upgraded studio.

Now that you have bought a

DRAWMER

unit, you have a piece of equipment

which will serve your needs, regardless of the size and quality of the studio.

The compressor is one of the basic tools of a recording studio. Its function is to

reduce or ‘compress’ the dynamic range of a signal so that quiet passages are

audible whilst loud passages do not overload the recording medium, resulting in

excessive amounts of distortion. It performs this function by sensing the level of the

signal and adjusting the gain continuously, so as to give a more constant output.

Essentially, a compressor contains two basic sections: the signal path, which

contains a voltage controlled amplifier/attenuator (VCA) and the ‘side chain’, which

senses the level of the signal and provides the control for the VCA. There are many

ways in which a compressor may be arranged internally, each method producing a

different ‘personality’, thus lending itself to a particular application. A linear

compressor produces the same amount of compression for each increase in signal

level. Threshold, controls the point at which compression occurs, whereas Ratio

adjusts the amount of compression applied to the signal for each increase in level

above the threshold.

An alternative is the ‘soft knee’ characteristic. With this method, the ratio is

increased automatically as the compression increases, which has the advantage of

being easier to use as only one control is required to adjust compression. In some

applications, a ‘soft knee’ characteristic can be more acceptable than linear, but this

would depend on many factors, not least of which is the individual’s opinion.

Because compression effectively increases low level signals, it also increases the

level of background noise, although this is not created by the compressor itself. For

example, compressing vocals will also increase the level of headphone overspill,

breathing etc. This can be overcome by the use of an expander, which is the

opposite of a compressor. Signals below the threshold level are attenuated, so in

the above example, when no vocals are present, the unit will shut off, thus

eliminating the unwanted noise.

THE LX20 EXPANDER/COMPRESSOR

The LX20 is dual channel, ‘soft knee’ compressor with the addition of an expander

and is designed for simplicity of operation. It is suitable for use at system levels of
!10dBu or +4dBu, by changing internal jumper links. Power supply voltages of 115V

or 230V are accommodated via a rear panel switch. The LX20 has a side chain

access point at the rear. This is used to make the compressor section respond in

different ways to various frequencies, which is useful for ‘de-essing’. Another useful

feature of the LX20 is the mute facility. This enables each channel to be shut off