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Aphex 240

Dual Logic-gated Compressor
Published January 2007
By Tom Flint

Aphex 240

The latest dynamics processor from Aphex combines a sophisticated gate with an easy-to-use compressor and forces them to work as a team.

The Aphex 240 is a thoroughly modern-looking stereo signal processor, using just 1U of rack space to present controls for both of its gate and compressor sections. The smooth front panel and featureless controls are finished in metallic silver, giving the impression of something slick and simple — which is pretty much what the 240 is all about. Far from suggesting that the insides are full of classic analogue circuits or glowing valves, Aphex have chosen to flag their trademarked Easyrider compression technology, which continuously adjusts the compressor's parameters in sympathy with the source material, leaving the user with just two controls to worry about.

The rather more customisable gate is not without its own innovative control circuitry. Aphex claim that their Logic Assisted gate design 'never hesitates or chatters', having been programmed to complete the full gate envelope even when triggered by the slightest transient, and regardless of whether the signal falls back below the threshold immediately after triggering.

What is particularly special about the 240, however, is that the gate and compressor are linked in such a way that their actions are never in conflict. In practice the compressor is limited by the activities of the gate, so that carefully programmed gating settings are not compromised by the release of the compressor increasing the signal level whilst the gate envelope is in the process of shutting down! The 240's logic algorithm stalls the compressor release until triggering opens the gate once more, at which point compression can begin gain reduction immediately, without abruptly leaping in level.

In short, Aphex have tried to make gate and compressor work together as a single processing unit, instead of being just two separate processors arranged in series.

Missing Link

In Link mode, the actions of the compressors are only partly synchronised. According to Aphex President Marvin Caesar, each compressor is built from two filters which are arranged to form a "convoluted filter system" that places a fast detector within a slow one. For the most part, signals are only affected by the slow filter, on the understanding that slow filters sound more natural than fast ones, but when a sharp transient is encountered the faster and more aggressive filter is triggered, behaving a little like a peak limiter. The Link mode only links the slow filters, referred to by Aphex as the 'baseline', leaving the two channels free to react independently to transients. In practice this means that if only one channel experiences an extreme peak, it won't duck the other channel unnecessarily, so the 240 should be able to retain a more balanced sound. Gating remains unlinked regardless of the mode.

If, for some reason, the gated compression is not wanted, the release can be set to be 'Ungated' if you remove the lid and shift a jumper on the circuit board. This can be done independently for each channel.

I/O & Features

The back panel, divided equally between the two channels, is where all of the 240's I/O is to be found, conventionally enough! Each section has balanced input and output sockets, available in XLR and quarter-inch TRS jack formats. The design of the output circuit makes it possible to use both XLR and jack outputs at the same time, so the signal could potentially feed separate destinations. Also on the rear is one Key Insert TRS socket per channel, enabling external signals to be used to trigger the gate threshold into action. The only adjustments that have to be made around the back are via two switches that change the operating level from the semi-pro standard of -10dBV to the professional +4dBu. Their independence allows each channel to be set up differently if necessary.

Everything else you might want to see or adjust more frequently is on the front panel. The channel sections are identical and are separated by three buttons, all of which light up when activated. The lower two are switches turning each channel on and off independently. The third is the Stereo Link button (see the 'Missing Link' box), for making the two channels work together in unison. Metering comes in the shape of two 10-segment LED meters strategically placed on the far right. These have a dual function, showing the gain reduction of the compressor in red and the gate in green. When the two processors are active together, the gate is represented by a yellow dot within the red bar of the compressor.

The Processors

The gate section of five controls, laid out roughly in the shape of a 'W', commences with a Threshold control, scaled to show a minimum value of -60dBu and a maximum of +20dBu, with nothing other than a set of line marks to indicate the values in between. In fact, all the knobs are similarly blessed with just two values, encouraging engineers to use their ears, rather than specific settings. The knob marked Attack ranges from 4uS to 100ms, Hold from 5ms to 500ms, and Release from 100ms to one second. The last of the Gate pots sets the Depth range from 2dB to a completely closed position of 80dB.

The compressor is described as being 'medium hard' in terms of its knee shape, with a ratio set at 3:1 and a fixed threshold. Its attack and release are variable, but there is no independent control of these parameters. Instead, the Speed knob — simply marked Min and Max — allows the user to define a rough setting. The Easyrider technology takes care of the rest, by analysing the scale and shape of the transients passing through and automatically adjusting the attack and release times accordingly. On the input to the compressor, Aphex have inserted a Drive control, scaled simply 0-10. Turning up the Drive increases the signal level, therefore determining how much of it exceeds the fixed threshold. The output knob, also scaled 0-10, controls the overall level.

Alternatives

Processors containing both gates and compressors are numerous, but of the two-channel types, the dbx 266XL comes closest to being the industry standard. It actually has a very similar specification to the 240, but offers more control over the compressor parameters at the expense of gate section. The compressor itself can be switched from hard to soft knee, has a ratio adjustable from 1.1 to hard limiting, and offers controls for Threshold, Ratio, Attack, Release and output level, as well as a program-dependent mode called Autodynamic, which overrides the attack and release knobs and is conceptually similar to Aphex's Easyrider. The gate, on the other hand, simply has Threshold and Ratio knobs and is not linked to the compressor.

Another alternative is Drawmer's MX30 dual channel gate and compressor-limiter. It too has an intelligent gate, this time programmed to adjust the severity of its ratio according to the characteristics of the input signal. The compressor is partly automated, with program-dependent attack and release times, a fixed soft-knee shape, and variable threshold and ratio parameters. The MX30 also benefits from having a separate peak limiter.

The TC Electronic C300 dual stereo gate/compressor is relatively inexpensive, and actually includes a multi-band compressor for very precise dynamic control, as well as a very useful parallel compression facility. Its main disadvantage, however, is that the user has to choose between Comp/Lim and Gate/Exp modes, so there is no way to apply a gate and compressor together, unless you chain the two channels in series.

However, none of the above interactively link the actions of the gate with that of the compressor.

User Tests

Gates are essential for certain styles of drum recording, so I fed the 240 with a simple stereo kick and snare drum pattern to see how it performed, firstly in stereo, and then by splitting and sending it to either channel. When split and played at a reasonable tempo, it was very easy to tailor each envelope to the individual characters of the kick and snare. Because the triggered gate always completes its envelope, regardless of whether or not the note subsequently falls back below the threshold, it is possible to impose a character on the sounds. For example, a snare is made softer by applying a slow Attack to diminish the initial crack and then using Hold and Release to sustain the body of the sound. Opposite settings generally make for a harder sound, and the Depth amount determines whether it is a stark and dramatic effect or something more soft and subtle. I found that I was able to turn a fairly straightforward alternating kick and snare pattern into something that sounded far more syncopated, by changing the Attack, Hold and Release time of the gates so that the relationship of the sounds changed.

Working in stereo, it was possible to tune the gate's envelope so that it performed as an overall shaping tool, although, at a moderate tempo, the drum tails and attacks were too close together for the gate to be used to the full.

Setting the gate is simply a matter of dialling back the threshold from its shut position until it is being triggered by all the relevant hits, and then working on the envelope shape using the other controls. Obviously the compressor Speed affects the sound character too, as does the amount of drive applied, but the gate setting remains fundamentally intact regardless of the compressor activity.

Aphex 240For sound modules, I found there was plenty of level to set the threshold precisely, so using a separate preamp was not necessary, and the output gain only needed a little boost from the preamp of my mixer.

To test the unit on vocals, I used a TL Audio 5051 voice channel processor as a preamp front-end, bypassing its EQ, gate and compressor sections so that only its input gain stage, phantom power and output level were active. I found the combination worked extremely well, and was particularly impressed with the way the 240 compressor dealt with the material. I usually record vocals through the 5051's onboard compressor using very little compression, as I find that excessive squashing tends to make performances seem claustrophobic and dull. Yet, even with the Drive turned right up, the 240 managed to retain a great deal of character, which I can only conclude is something to do with the convoluted filter design described in the 'Missing Link' box.

Gating vocals tightly can be tricky when a performance is subtle, but the 240 is programmable enough to be used to calm background noise in pauses fairly invisibly, and may even find use as an effect in some circumstances. As Aphex claim, the gate doesn't chatter or hesitate, and the processing is very smooth overall.

The potentially confusing dual-purpose metering actually seems to work very well, and didn't cause me any problems. There certainly aren't any engineering issues to worry about, as the build quality is good, and the clean design and 'W' configuration layout makes the front of the 240 appear fresh and uncluttered.

The only thing that slightly hampers the use of the 240 is the lack of processor bypass buttons, which makes it impossible to switch a section out of circuit to compare how the original unprocessed signal was sounding.

Conclusion

The world is not short of products offering gating and compression, but the 240 does genuinely bring some new ideas to the table, particularly in the way that the two processors work together rather than as separate chained entities.

At £282 it's not the cheapest gate/compressor out there, but it has an expensive sound, or at least it gives the raw material the feel of a good, professional recording. It's also probably not the best studio workhorse available; it has no preamp or digital interfacing options, for example, and the compressor has limitations. Having a fixed ratio prevents the user from performing a commonly used production technique in which the threshold is set down at about -30dB to affect everything in a mix, then a very low ratio of something like 1:1.2 is applied. It also prohibits the use of the processor in the opposite manner, as a limiter.

Gate/compressors are often used for recording drum kits, but having two channels is obviously not enough for that purpose. Still, the price is low enough for professional studios to invest in two or three, in the knowledge that they'll come in handy for a multitude of other jobs, including vocal recording.

The message Aphex want us to glean from their prominently advertised trademarks is that the 240 uses cutting-edge processing to manipulate signals efficiently, minimising the effort required by the user. To sceptics, like me, trademarks are often seen as little more than marketing tools, but it's clear to me from my own tests that in this case the technology behind the trademark is very effective indeed. 

Published January 2007