Four Wheel Drive
LA Audio 4X4 Compressor
If your vocalist is up and down like a fiddler's elbow, this classy compressor might be just what the engineer ordered...
On the face of it, the 4x4 is just another 'me-too' compressor — but look again and you'll see an appealing combination of high-quality sound and flexible operation, not to mention the attractive sub-£300 price. Paul White puts it to the studio test.
LA Audio are the company behind the Classic Compressor, the 32-channel MIDI Mute and the 16-channel Multigate, the latter two cramming a terrific amount of processing power into their 1U boxes. On the face of it, their new product is rather more conservative — a dual-channel gated compressor aimed as much at the home studio market as the professional market — but on closer inspection the 4x4 proves to be quite intriguing.
The concept behind the 4x4 is simple, but to my knowledge, no other compressor has taken quite this route. Instead of each channel being a simple gated compressor, the gate and compressor have their own inputs and outputs so that they may be used independently or cascaded together. There's also a pair of side-chain filters, not dissimilar in principle to those pioneered by Drawmer on their legendary DS201. However, the filters are assignable so that they may be switched either into the compressor side-chain for de-essing or into the gate side-chain for frequency-conscious gating. When the compressor and gate are linked in tandem, the compressor input is still operative, which makes it possible to mix an external signal with the gate output.
The compressor itself uses a FET gain cell based on the same principle as that used in the more upmarket LA Audio Classic Compressor. This introduces a certain amount of coloration during compression in a way that is designed to emulate the sound of vintage valve compressors but without the attendant cost and reliability penalties. FETs are also used in the gate circuitry, and although the gate has relatively few controls, it turns out to be very versatile.
Built in a fairly standard 1U steel case, the 4x4 has a fairly busy front panel but the controls are small enough to ensure that it isn't cramped. All the rotary controls are arranged along the bottom of the panel and all the switches along the top. Both channels are identical, except that the extreme right hand switch of channel one is the Stereo Link button and on channel two, the same space is occupied by the power switch.
The rear panel houses the IEC mains input, the fuse-holder and all the audio connections, which are on unbalanced jacks. The operating level has sufficient headroom to operate comfortably at either -10dBv or +4dBu, and both gates have Key input sockets. The compressor has a side-chain insert on a stereo jack.
Each control section is segregated from its neighbour by a vertical line, and the use of coloured knob caps makes doubly sure that you're twiddling in the right area of the front panel. The gate section is graced with blue knob caps and there are just three rotary controls: Threshold, Release and Range. Threshold is fully variable from -54dB to +20dB, while Release is variable from just 5mS to 4S. Range sets the amount of attenuation when the gate is closed, so that instead of the signal being turned right off when the gate is closed, it can be attenuated by any amount between 0dB and 80dB. This is very useful when you simply want to increase the contrast between the wanted sound and whatever is in the background rather than removing the background altogether. A green status LED indicates when a signal exceeds the threshold level.
The lack of a variable attack control is mitigated by the Auto button. When Auto is off, the gate has a very fast attack time, suitable for drums and other percussive sounds, whereas if the Auto function is on, the attack time depends on the rise-time of the signal being processed. As with most professional gates, there is a certain amount of deliberate hysteresis between the threshold level at which the gate opens and the threshold level below which it starts to close, and there's also a hold time of a few tens of milliseconds to prevent the gate chattering when fast release times are set. Both these features add up to more predictable operation and tend to make setting up a little less critical.
Both the gate and compressor sections have their own bypass buttons which disconnect the side-chain control, allowing the signal to pass through the unit unchanged. These are not so-called 'hard bypasses' which physically switch the inputs to the outputs — they simply inhibit the gain control circuitry. An external gate Key input is provided in the form of an unbalanced jack, and a front-panel button allows the gate to be switched from normal to external key mode. A Listen button allows the user to monitor the side-chain signal, and if the filters are switched into the gate side-chain, the effect of the filter may be auditioned during setting up. By leaving the Listen button depressed and the filters assigned, the gate section may instead be used as a useful equaliser.
Both filters have a 12dB per octave shelving response, and have variable frequency ranges of 25Hz-4kHz and 250Hz-30kHz respectively. The Gate/Comp button switches the filters into either the gate or compressor side-chain path, so if the filters are needed in neither section, they must be set so that the Lo filter control is fully anti-clockwise and the Hi filter fully clockwise.
Moving onto the compressor section of the 4x4, this is set out like a conventional ratio-type design, though it actually exhibits a soft-knee characteristic which means that the ratio actually increases progressively over a range of several dB when the signal approaches the threshold. This design has a fixed threshold which is used in conjunction with a variable gain control, so that instead of having a fixed signal level and then tweaking the threshold setting, you have a fixed threshold and tweak the input level. The result is exactly the same; indeed, many professional compressors work in this way.
The compressor has a variable Attack time of 20uS to 20mS and a Release time of 20mS to 4S. The Ratio may be varied from 1:1 (in which case no compression takes place) to 20:1, which is so close to hard limiting as to make no difference. Most practical settings lie between 2:1 and 6:1. Because the input gain has to be adjusted to set the level at which compression occurs, an Output gain control is necessary to restore any gain lost through the compression process. A side-chain insert point is provided in the form of a stereo jack so that additional processing — an equaliser, for example — can be added to the side-chain if required, though with on- board filters, this should rarely be necessary. The socket is wired ring-send, tip return, and the return may also be used to feed in an external keying signal for tasks such as ducking.
When compression is taking place, the amount of compression is shown on the 9-segment LED meter and the side-chain insert point can be switched in or out from a front panel button, so there's no need to keep plugging leads in and out. The Gate In button places the gate before the compressor in the signal path but doesn't disable the compressor input, so it is possible to mix the output from the gate with whatever signal is presented at the compressor input, should the need ever arise.
The Stereo Link switch relates to the compressor controls and to the gate threshold but leaves the gate release and range controls operating independently for the two channels. When linked, both compressor side-chains respond to an average between the two sets of control positions, so it is advisable to ensure that both channels have the same settings, to avoid possible confusion.
Though this is obviously a very well conceived product, some sacrifices have had to be made to satisfy space and cost constraints. For example, on most pro compressors, the meters can be switched between gain reduction and output level, but here, the meters are fixed to show only gain reduction. It would also have been helpful to have had one or two more status LEDs to confirm the switch settings, but neither of these shortcomings is in any way serious or detracts from the usefulness of the unit. Another slight anomaly is that the input and output gain controls still function in bypass mode, making it virtually impossible to match the levels of the processed and bypassed sound. This can present a slight problem when you want to switch the compressor in and out of circuit to evaluate the effect of the current compression settings.
"The 4x4 combines clarity and detail with tonal warmth, even when quite high levels of gain reduction are applied."
Testing the unit gave me a chance to try out the new Sound Check CD which has been put together by Alan Parsons and Stephen Court. As well as containing a useful and very comprehensive set of test tones and various sections of time code in different formats, it also boasts a useful set of solo instrument and vocal parts which are ideal for checking out signal processors such as this.
As it transpired, the compressor turns in a purposeful performance and has a soft warmth to it which is reminiscent of the more expensive Classic compressor. The results were particularly gratifying on the voice and sax test pieces, though it works very well in all routine applications. Being a soft-knee design, it isn't quite so effective when required to apply very stringent control to signal peaks, but for most applications, the compromise between firmness of control and transparency of sound seems to be a good one. Certainly the unit performs well on complete mixes (when set to Link mode) as well as on individual sounds, and though it doesn't have the same sparkle as a true valve design, it does combine clarity and detail with tonal warmth, even when quite high levels of gain reduction are applied. Very high levels of compression can provoke the sound to 'pump', but you'd normally only use such a high setting if you wanted to use the pumping effect for artistic reasons.
Switching the filters into the compressor side-chain allows the unit to be used as a de-esser, the usual de-essing range being between 3kHz and 8kHz, depending on the characteristics of the voice being treated. I'm not a great fan of de-essers as a rule, as you tend to be able to hear them working, but this one is no worse than more expensive, dedicated de-essers, and produces quite usable results so long as you don't over-use it.
Moving onto the gate, I found that this is both simple and well-behaved, handling both percussive and general-purpose sound sources with equal ease. Switching the filters into the gate side-chain means that the gate can be 'tuned' in to the target sound while attenuating unwanted background sounds in a different part of the audio spectrum. This doesn't affect the sound of the signal being gated, as the filters only act on the side-chain signal, but it does make it much easier to avoid false triggering when the background sounds are not much lower in level than the wanted sound. The 4x4's Auto mode works very well with sounds that have a slower attack, such as vocals, but it is important to make sure that you set the gate threshold as low as possible, as it is possible to make the gate click if the threshold is set too high. Simple the 4x4's gate may be, but it handles all routine studio cleanup jobs very effectively and with the minimum of fuss.
LA Audio have come up with a well-conceived and versatile product in the 4x4 compressor that shows surprisingly few compromises given its very attractive price. The ability to use the compressor and gate sections independently as well as in tandem is very welcome, while the ability to switch the filters from compressor to gate is incredibly useful. There are few things I actually disliked about the unit, the main niggle being the way the gain controls and bypass switch are linked, which conspires to prevent you making a direct comparison of the dry and treated sounds at the same subjective level. If price were no object, then I'd feel justified in asking for switchable hard/soft-knee operation, separate gain reduction and level meters and more in the way of status LEDs, but coming back into the real world, this is still a very serious, very flexible product capable of turning in a quality performance at a semi-pro price. If you don't yet have a compressor or a gate, then the LA 4x4 could be your best option for obtaining both. Because all compressors have their own sound, I'd recommend you try one out if at all possible, but in the context of what else is available in this price range, I feel sure you won't be disappointed.
LA Audio 4x4 £299 including VAT.
Key Audio Systems Ltd, (Contact Details).
Review by Paul White
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