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Deeply Compressed

Drawmer LX20 expander/compressor

Drawmer noise gates and compressors have become the undisputed industry standard in the field of sound recording, and their latest unit looks set to make it a hat-trick. The dual channel LX20 offers comprehensive compression/expansion facilities at a budget price. Engineer Gareth Stuart assesses its performance.

Sound engineer Garerth Stuart takes a practical look at Drawmer's latest signal processor - LX20 dual expander/compressor.

The Drawmer LX20 is a dual expander/compressor. It looks good, sounds great, and at £258.75 you shouldn't have too much trouble accommodating it in your wallet - especially if your wallet's designed to accept 19" rack-mount units.

As space is at a premium this month, I must compress what I have to say too. So without further adieu, ladies and gentleman, may I present continuous hard-core examples of literal and musical compressions featuring the Drawmer LX20... (fanfare).


With the LX20 comes a comprehensive operating guide and as you're not necessarily going to use my review to tell you how to use it, I thought I'd have a read and see just how useful/meaningful and helpful it is...

From a user point of view the guide's fine. It covers a few working examples illustrating the LX20's use on vocals and piano, and describes well the function of the various parameters. However, under the 'System Operating Level' paragraph, Drawmer point out that the LX20 may be (quote) "connected internally for the correct system operating level" (-10dBu or +4dBu), and they invite buyers who (quote) "have some technical knowledge" to carry out this change themselves. So, with what purports to be a set of clear instructions/diagrams, the manual 'talks' you through the necessary change-over. Step 1 - remove the underside panel to access the internal electronics...

In the model I was given to review, the 120v/240v mains convertor had a securing screw positioned directly over it which turned out to be just a screw head glued in position. Using a full length screw in place of it would either exert some pressure or, at worst, enter the 120v/240v mains convertor which could damage both the unit and your good selves. Having pointed this out, I'm confident Drawmer will rectify the matter on future units, but I would suggest that you consult your local dealer rather than fiddle with the internal workings.

The next upset came when I found that the helpful diagrams/instructions didn't tally with the circuit board, in that the 'link plugs' which must be re-plugged to change the operating level - (quote) "simply remove the link plugs and replace the alternative in position as shown" - didn't appear in a recognisable form. Certainly, there were little black plugs positioned in the right area of the circuit board, but as they didn't respond to my gentle persuasions with a pair of pliers, and seemed to be stuck solid, I decided to leave them be, pop the panel back in place, and get on with the unit's possible applications.


The LX20 may be operated either as two independent mono signal processors, or as one processor - where the left and right channels of the signal being treated receive the same amount of compression/expansion (stereo link mode). The stereo link mode prevents the image shifting (from left to right) as a result of different levels of signal appearing on each channel.

Just a quickie about the stereo link switch itself: the words 'stereo' and 'link' appear above and below the switch, so don't be mislead into thinking that there's a stereo mode and a link mode. A red LED illuminates when the unit is in stereo link mode, and extinguishes when the two channels are used independently.

Now for an example of when to use the stereo link mode. Imagine a song beginning with a keyboard introduction. The keyboards are panned more left than right, because that's where they sound the best in the stereo image when all the other instruments have joined in. In the mono (dual channel) mode, there is more signal to compress on the left than on the right. As the left channel is compressed more than the right, the image appears to move towards the right speaker, ending up somewhere in the centre. If you use the stereo link mode instead, the same amount of compression applied to the left channel is applied to the right, allowing the keyboards to remain in the desired position.

Stereo link can also be used as a 'ducking' device, where the signal being sent to one side of the LX20 causes the signal on the other side to be compressed. It's a technique in almost constant use on radio stations when the DJ's voice causes a drop in the level of the record being played.

Rather than having to turn the music down and the voice up manually on the mixer, the voice automatically causes the music to become quieter. This technique can be applied during a mix when a short burst of sound (for example the melody line being taken up by a percussive instrument like a xylophone) needs to be heard blended into the overall mix but no louder than everything else. For example, a sustained (chordal) backing track could be momentarily taken down in level to accommodate this brief melodic intrusion.

To explain the concept of 'ducking' then, imagine five people standing in a line (representing the levels of five continuous sounds eg. drums, bass, guitars, vocals, keyboards) with the sixth person (representing the intermittent melody) hovering a pace behind the others, waiting to happen. The moment the sixth person joins the line, one of the others is forced back a pace and, as a result, the overall appearance (balance) remains constant.

The reason for using a machine rather than manually controlling this operation, is so that the track being pushed down in level (ducked) by the melody, may return exactly to its previous level in the gaps between the melody notes - maintaining a precise overall level and balance.


Another widely used current effect is gated reverb - where the sound source, often snare drum, is saturated in reverb momentarily and the reverb's natural decay time is prematurely terminated. Phil Collins' recorded drum sound is an archetypal example of this technique in action.

It's one of those simple but effective ideas, simple to achieve but so rewarding as it gives tremendous body to an otherwise "it's alright I suppose" snare drum sound. Here's one of the ways to set it up using the Drawmer LX20.

First, mike up a snare drum and send the signal into one side of the LX20. Gate the snare (before sending it to the reverb) by switching in the expander. The single knob labelled 'Expander' controls both the threshold (the point below which the signal is turned down in volume), and the expansion rate (the speed at which the volume is turned down below the threshold). As you rotate the knob anti-clockwise so you raise the threshold level and expansion rate, allowing only those signals above the threshold level to be heard.

So why does the effect increase as you turn the knob anti-clockwise? Well, I suppose it's Drawmer's way of reminding you that expansion is the opposite of compression. A compressor will turn down the volume of a signal (by a desired amount) once that signal has risen above the threshold. An expander will turn down the volume of a signal once it has sunk below that threshold.

Anyway, back to business... The 'Compress' and 'Attack' controls can be left fully anti-clockwise, since this effect is concerned primarily with gating the sound, and 'Attack' only governs the speed at which the LX20 may react to an input when compressing it. The 'Release' control may be used to 'soften' (slightly delay) the extreme gating action if the sound is being cut off mid-flow, but for most percussive sounds which don't sustain, it may also be set fully anti-clockwise.

Next, take the output from this channel of the LX20 and feed it into a reverb unit such as the Yamaha R1000 set for maximum reverb time, or into the Great British Spring, with its fixed (and rather long) reverb time. Then plug the reverb's output into the other channel of the LX20 and set it up following the steps taken in achieving the gated snare sound. Either use the 'Release' control on the LX20 to govern the reverb's decay time, or set the decay time on the reverb unit itself (if possible)... season to taste.

Compressing the reverb can really fatten up the sound and gating the GBS reverb, using a Yamaha RX11 drum machine as the sound source gives the most impressive, big, powerful sound.

The LX20's Mute function allows each channel to be independently turned off using a footswitch connected to its rear panel socket. This could be a handy tool in creating a 'dub' mix: the direct signal is 'frozen' and sustained by a digital delay, then turned off (muted) to allow the repeating delay signal to slowly fade away, before bringing the direct signal back into the mix. Grand stuff!


I tackled the Drawmer's side-chain facility last, probably just just as well since it's one of those functions which induces much fiddling about. Creative fiddling, au naturel.

To set it up, the most important ingredient is a lead with a stereo jack one end split to two mono jacks; the 'tip' and 'ring' signals of the stereo jack being sent separately to the mono jacks. The signal to be compressed/expanded goes into the main LX20 Input; the side-chain output (ie. Send) is sent out from the stereo jack's ring and is plugged into the Input of an equaliser; the equaliser Output then returns to the side-chain input (ie. Return) by way of the stereo jack's tip; and then the LX20's main audio Output goes to another channel's input - completing the set-up.

What happens, is that the offending frequencies are boosted by the side-chain equaliser unit, and therefore appear as peaks deserving special consideration by the compressor. As the compressor is more sensitive to those boosted frequencies, they are compressed more than the rest of the signal, leaving a bright, yet less harsh signal.

When this process is applied to voice, it fulfils the task of a de-esser removing unwanted sibilance. But there's no need to limit this effect just to the voice, because whereas a de-esser unit is effective on voice but only has a mild effect on other inputs like drums, guitars, keyboards, this side-chain equalisation produces a very strong effect on all instruments. If carefully set up with the untreated signal panned hard right, and the processed signal panned hard left, one sound comprising low and high frequencies can be made to automatically shoot from left to right channels at any given moment, depending on its frequency content.


Mechanical and instructional niggles aside (not to be ignored, just put aside), I found the Drawmer LX20 straightforward to operate, a delight to use, and a pleasure to listen to. As a budget signal processor costing £258.75 inc VAT, it offers very good value for money in my opinion, and I wouldn't mind hanging on to it, thank you very much!

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The Shape Of Things To Come

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Japanese New Age Music

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 - Nov 1986

Gear in this article:

Studio FX > Drawmer > LX20

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Review by Gareth Stuart

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