When you want to put the squeeze on your music, or cut out that annoying background hiss and hum, the LA Audio CCX2 may be just what the doctor ordered. Martin Walker dons his stethoscope and examines it further.

LA Audio specialise in building high quality signal processing tools at very competitive prices. The GCX2 is a dual channel, soft-knee, gated compressor, aimed at the lower cost end of the market and comes in a smart 1U rackmounting case. Unusually for such a low cost unit, the inputs and outputs are fully balanced, yet are designed so that no level loss occurs when they are used unbalanced. This is an important point as most small PA desks have unbalanced insert points.

Each compressor has three fully variable controls — Threshold (-30 to +20dB), Ratio (1:0 to 20:1), and Gain (-20 to +20dB), as well as two modes of Auto attack/release setting (slow or fast). Rather than having the user set fixed values, each setting is program dependent and adjusts itself to best suit the current signal. Compressor action is monitored by a ladder of six red LEDs, sensibly calibrated to show 2, 4, 6, 10, 15, and 20dB of gain reduction.

The gates have just two controls — Threshold level (-50 to +16dB) and Release time (30ms to 3 seconds). Attack time is fixed, but at under 1 ms, it should catch everything you throw at it, without removing your transients — providing you set the threshold sensibly. Both compressor and gate have their own bypass switch, so that you can easily compare treated and untreated signals. Each of the two channels can be used separately, but the addition of a central Link switch allows Channel 1 to act as a Master, controlling both channels of a stereo signal from a single set of knobs. A green power LED completes the front panel.

On the back panel, each channel has an input and output at professional +4dBu levels using XLRs, and an additional input and output labelled -10dBV to connect to 'consumer' level devices, using stereo jack sockets. All are balanced, with the jacks using the TRS (Tip, Ring, Sleeve) wiring that allows either mono unbalanced or 'stereo' balanced leads to be used (see 'Cable Wiring Tips' in the November 1996 issue). It is nice to see such versatility, although it might have been even more useful to have employed some of those combined XLR/jack sockets and a +4/-10 switch so that people using jack-to-jack leads at +4dBu levels didn't have to make up special leads — but then I guess it's a matter of cost. However, it is nice to see each pin out clearly labelled, and the option of working balanced (mixer insets permitting) is particularly welcome in any live application, where there can be nasty interference (from high power lighting circuits and dodgy mains feeds) conspiring to add unintended buzzes to your music.

Yet another very welcome feature, particularly at this price, is the compressor side-chain inserts on TRS jacks (Ring - send, Tip - return), and to finish the back panel with a smile, there is an IEC mams socket. The whole unit is rugged and well built, and at only six inches deep, including the knobs, it should fit into even the slimmest of racks.

PUTTING ON THE SQUEEZE

Setting up the compressor is quick and easy. The level detection is of the RMS type, which means that it is the average signal level that dictates the amount of compression, rather than the peaks. This is similar to the way the human ear works and tends to produce a more natural sound well suited to live work, although you may get some short peaks finding their way through the system unchecked. For solo instruments or vocals, the Fast auto setting is normally more suitable (the actual times are program dependent, but in this mode, the attack will be about 5ms and the release about 1 second). These settings ensure that transients of any significant duration are invariably caught, keeping the output level well under control at all times.

For a complete mix, the Slow auto setting may be more suitable (attack about 10ms and release about 2 seconds), as it will let most of the transients through so as not to obscure high frequency detail. If the attack time is too fast when a whole mix is being compressed, low frequency sounds such as bass drums and bass guitars tend to cause high frequencies to be 'sucked out'. However, there are no hard and fast rules, only guidelines, and your ears should always be the final judge.

Once your signal approaches the Threshold level, the soft-knee characteristic gently starts to add compression until the full Ratio setting is achieved. This is generally more suitable for live use than a hard-knee version. Using the soft-knee approach means that the output signal will sound far less 'processed', and this will result in a more natural sound.

One consequence of using any form of compression is that background hisses and hums tend to be emphasised, and this is why the gates are included. With just two controls, these are a doddle to set up and use — just set the threshold slightly above any background mush in the absence of any stronger signal, so that the noise disappears, and then increase the release time until your desired signal dies away smoothly and gradually, rather than being chopped off in its prime.

The Link switch makes it far easier to use the unit on a stereo mix, as only one set of controls needs to be adjusted, and this stereo linking can be clearly seen, since only the left-hand (master) channel gain reduction LEDs are active in this mode. A good point for live use is that the clear pointers on the knobs themselves make it easy to verify settings on a murky stage. On the downside, without a torch, you'll have to memorise which knob is which, as the front panel labelling is a subtle silver on dark grey, and not at all easy to read in low lighting. Having said that, there are only five rotary controls to set up for each channel, and their position and adjustment should become second nature after a few practice runs.

The bypass switches show whether either the compressor or gate is in circuit, but again, it's not easy to see in low light. Either a separate bypass LED indicator or a different coloured end cap on the button itself would have made their position far clearer.

LIVE AND KICKING

For live use, the GCX2 will probably find favour keeping over-enthusiastic vocal performances under control. The only thing to watch out for is that compression will increase the likelihood of feedback in live vocal situations, so you should use as little gain reduction as possible to do the job. In fact, most live engineers tend to use compressors more as limiters (high ratio, high threshold), so that gain reduction is only applied to excessive peaks. For live dance music, bass synths are likely to have more guts with some compression applied, and with the return of the analogue synth, particularly those vintage ones, it is well to bear in mind that manually reprogramming sounds between numbers is far less fraught with the safety net of a bit of compression, since synth output levels can vary widely as settings are changed.

With the Link switch on, a complete stereo PA mix can be controlled — to prevent either power amp overload or the overall mix exceeding a set peak sound level. Overloaded power amps are the most common cause of driver failure, particularly tweeters. On an artistic level, a bit of overall compression can ensure that the band sounds 'loud' without exceeding the limits of the PA or the local sound level regulations.

With the addition of the side-chain insert sockets, you can turn the GCX2 into something more exotic — with a parametric EQ for instance, you can tune it to provide de-essing of vocals (to remove sibilance from 'ess' sounds), or by plugging in a different audio signal to the return path, you can control the overall level of the mix dependent on the volume of the controlling signal. This is known as ducking (commonly used by DJs during announcements), but it can be useful in helping a solo to stand out by dropping backing sounds slightly. To do this successfully, you'll need a mixer with groups so that you can route all the signals to be ducked via the same pair of subgroups.

For the many people producing live dance music, this side-chain insert may also find use for creating radical gating effects, where pad sounds are chopped on and off by a completely separate sound source such as a hi-hat line. Having said that, a keyed gate is easier to use for this application, but at least it's possible with the GCX2. One thing that foxed me at first, however, when I tried this out with the stereo link on, is that both inserts are still active. If you want to gate a stereo sound with an external signal using only one insert point, then the solution is to push a dummy jack plug into the other insert socket, so that only one is active.

CONCLUSION

The GCX2 is a very cost-effective package — it is easy to use both as two separate mono compressor/gates or, with a flick of the Link switch, to control a stereo mix from one set of controls. The use of soft-knee compression always results in a more natural and less obvious sound, which suits the majority of applications, particularly in a live context. The two Auto settings are likely to give quick and effective results with the minimum of knob twiddling, and at this price point, this is probably what most people would prefer. In fact, a number of pros prefer auto compressors, simply because there isn't the time to fiddle with settings in depth.

The addition of the gates removes the main bugbear of compression — the increase of background noise when bringing up low level signals. The beauty of having the side-chain insert is that not only can you set up more elaborate treatments, such as de-essing by using external EQ, but by using just the return path, it opens up the possibility of a lot of creative gating and ducking effects. Given its good balance of performance and price, the GCX2 should do well.

GCX2 £189 inc VAT.

SCV London, (Contact Details)