The latest studio tool from Alesis is the CLX-440, a four-channel digital dynamics processor that includes compressor, limiter, expander, and gate functions,

The latest studio tool from Alesis is the CLX-440, a four-channel digital dynamics processor that includes compressor, limiter, expander, and gate functions, all in a two-rackspace box that sells for a remarkably low price. This attractive piece of gear promises to enhance the flexibility and capabilities of any personal or professional studio without costing a small fortune.


At a glance, it's all but impossible to tell that the CLX-440 is a digital processor (see Fig. 1). The unit's interface is reminiscent of classy analog gear, providing individual knobs for each function and eschewing the menu-heavy LCD-screen navigation that's characteristic of many digital processors and recording devices. With only ¼-inch jacks and no digital I/O, even the unit's rear panel is devoid of evidence that the device is digital rather than analog.

The CLX-440's front panel features a sleek, silver-matte finish with 30 matching beveled knobs. All labels are screened in simple black lettering. In addition to an Input and Output knob, each stereo channel has separate sets of controls for the compressor (top) and expander (bottom) sections. All sections contain Threshold, Ratio, Attack, Release, and Knee knobs; the compressor sections also provide a Detect knob, and the expander sections provide a knob labeled Hold. Each stereo signal path through the CLX-440 has a Limiter Threshold knob at the end for setting the threshold of the dedicated output limiter. The output limiter provides extra insurance against overloading a digital mixdown deck. Although that feature might seem redundant (limiting is also available at the compressor stage), it actually comes in handy in certain situations.

A slightly domed, backlit power button glows when the unit is on. Similar red or green backlit buttons provide a bypass option and sidechain and key engage for each channel. A fifth backlit button engages a global look-ahead function that delays the input signal by 2 ms. (That compensates for the 0.02 ms latency characteristic of the digital processor, allowing for the immediate onset of compression.) Each channel also provides a recessed red LED, labeled Limit, which lights up when limiting occurs.

Four 12-segment LED meters for each stereo channel indicate input and output dBFS levels as well as gain reduction for the compressor and expander. However, if you're looking down at the unit at all, the meter window's overhang all but obscures the tiny numbers labeling the meters.


The rear panel of the CLX-440 is simple and uncluttered, providing 14 balanced ¼-inch TRS jacks in two neat rows (see Fig. 2). Channels A and B each have jacks for left and right input, a stereo direct out (which is the sum of the left and right inputs), a compressor sidechain input, an expander key input, and impedance-balanced left and right outputs.

The unit can receive from two stereo sources, essentially providing four channels of compression, or you can use it as a dual mono processor by simply plugging in to only the left input of either channel. A handy switch lets you select +4 dBu or -10 dBV signal levels.

The CLX-440 employs Alesis's proprietary technology (based on the company's patented semiconductor design), including 24-bit, 128× oversampling Sigma-Delta A/D/A converters and 48 kHz internal processing. According to John Hancock, Alesis's director of product development, that translates to less extraneous circuitry and thus lower cost for the end user.


In the studio, I tested the CLX-440 on vocals, bass, acoustic and electric guitars, flute, kick drum, snare drum, drum overheads, and several stereo mixes. I also tried it out on a couple of location recording gigs, which included a live multimic mix to DAT and a simple stereo recording to 2-track. For sonic reference, I put the Alesis unit up against two other VCA compressors in its price range, the dbx 266XL and FMR Audio's RNC1773.

In my home studio, I used the CLX-440 with a Mackie 1202-VLZ and an Allen & Heath 16:2 mixer, processing signals from ADAT, DAT, and CD-R. At Ex'pression Center for New Media, I put the CLX-440 through its paces on a Neve VR Legend console, using CD-R and analog tape as sources. I used the CLX-440 for the standard applications of compression, limiting, and gating, and, working with fellow instructor Dave Bell, I experimented with the unit's sidechain and key functions. In both locations, I used the CLX-440 on several mixes.

Overall, I was pleased with the processor's performance and had fun trying out all the possibilities it has to offer. The unit's full complement of controls, its “extra” features such as the Detect and Look Ahead circuits, and the fact that it lets you to set the balance between input and output levels all make the CLX-440 quite flexible.


The CLX-440 uses a stereo-detection feature that, according to Alesis, prevents shifting of the stereo image. The left and right inputs on each stereo channel are linked so that the hotter side determines the amount of overall gain reduction (based on the selected channel settings).

To test this feature, I ran a stereo mix through a single stereo channel and then, for comparison, ran the left and right channels of the same mix through individual channels in mono, varying the parameters a bit. The linked stereo channel performed as promised, avoiding the occasional imbalance that resulted from running the mix through individual channels.

While working on stereo material, I adjusted the compression controls to achieve different amounts of gain reduction. I was pleased by how clean and transparent the sound was.

A continuously variable detector between peak and average (RMS) levels from the input signal is another nice touch. That feature, called Detect, lets you choose between compression and limiting based on peaks in the material, average input levels, or anything in between. Naturally, the RMS selection allows for a clearer, more dynamic and transparent sound, whereas peak selection clamps down harder on the signal, resulting in a bit less clarity due to the reduction in range. The CLX-440's continuously variable Knee controls (settings range from Hard to Soft) gives users even more options.

CLX-440 Specifications Inputs(4) ¼" balanced TRS (all -10 dBV or +4 dBu switchable)Outputs(4) ¼" impedance-balanced TRS; (2) ¼" direct (all -10 dBV or +4 dBu switchable)Sidechain Inputs(2) ¼" balanced TRSKey Inputs(2) ¼" balanced TRSMaximum Input/Output Level+19 dBu (@ +4 dBu nominal)Internal Sampling48 kHzA/D/A Converters24-bit, 128× oversamplingCompressor Threshold-60 to 0 dBFS (continuously variable)Compressor Ratio1:1-•:1 (continuously variable)Compressor/Expander Attack0.02 ms-1 sec (continuously variable)Compressor/Expander Release100 ms-2 sec (continuously variable)Compressor/Expander Kneehard-soft (continuously variable)Compressor/Expander Detectpeak-RMS (continuously variable)Look-Ahead Delay2 msLimiter Threshold-20 to 0 dBFS (continuously variable)Expander Threshold100-0 dBFS (continuously variable)Expander Ratio1:1-gate (continuously variable)Power Supply90-230V, internally switched; IEC connectorFrequency Response20 Hz-20 kHzDynamic Range103 dBATotal Harmonic Distortion + Noise< 0.003%Signal-to-Noise Ratio-103 dBADimensions2U × 6" (D)Weight5 lb.

On the individual tracks during mixdown, the compressor performed uniformly well, responding smoothly and sounding very clean. The unit doesn't impart any distinctive character to the sound like some compressors do, and it allows for transparent processing that you can adjust for a variety of effects. Because of its transparency and great flexibility, the CLX-440 was consistently reliable on vocals, bass, and drums. At extreme settings — with the attack set to 0.02 ms on a strummed acoustic guitar, for example, and ratio set at 8:1-I was able to coax compression artifacts out of the device, but typical settings sounded natural and transparent.

Using the sidechain and a parametric equalizer on a Neve console channel, I fashioned a de-esser for a vocal track. (By the way, Alesis recently introduced the PEQ-450, a parametric equalizer designed to be used in tandem with the CLX-440.) I also experimented with the key input on the gate, both to create a gated-reverb effect for a snare drum and to add some 40 Hz whomp to a kick drum part. The sidechain and key functions both worked well and resulted in good sounds.

The CLX-440's response and character were similar to those of the 266XL and the RNC, but the CLX-440 had more clarity under heavier compression conditions and offered a higher degree of makeup gain. Even when I used the CLX-440 to apply a squashing 18 dB of compression to a guitar track, the sound maintained a great deal of transparency, and although the reduction in dynamic range was evident, the processing didn't throw a wool blanket over the sound. Other features that set the Alesis compressor apart from the dbx and FMR Audio compressors are its input-gain control and input and output meters that allow you to visually gauge the gain structure when balancing levels during processing.


The CLX-440 is well suited to a variety of applications; I found it especially helpful in facing the challenge of effectively compressing a flute track. That task was tough because breath sounds and bleed from headphones had crept into the flute mic and were emphasized when the compressor released between passages. I used moderate ratio and threshold settings on the CLX-440 to attain 6 dB of gain reduction on just the shrillest notes, and I used the expander/gate to reduce the ambient sounds that faded up between passages as the compressor released. The expander setting was tricky, as were the attack and release settings for compression, but some careful tweaking and balancing effectively tamed the problem without sounding unnatural.

For certain applications, I was concerned about the digital processor's inherent latency, so I checked out the possible effects that characteristic might have on stereo material and on individual sources with significant bleed from adjacent instruments. I also tested the look-ahead function, which delays the input signal by 2 ms to facilitate the immediate onset of compression if desired.

The timing test that produced the most obvious results involved sending a bass signal through a prefader aux and bringing it back into another channel of the Mackie 1202-VLZ so that I could process one signal and combine it with the original. Not surprisingly, some comb filtering was evident when the two signals were blended, giving the bass a hollow, growling sound. Engaging the look-ahead function further emphasized the phasey effect.

Admittedly, the test was a little out of the ordinary and was performed only to hear the timing delay. On individual, isolated sources, the inherent 0.02 ms delay is pretty much imperceptible, and stereo material run through a stereo channel shouldn't suffer from latency problems. The delay may pose some issues, however, if you use the compressor for, say, overheads on a multimiked drum set. The latency that results from A/D/A conversion creates the potential for a noticeable effect on the sound of the overheads and the stereo image when all the sound sources are mixed together. Of course, you won't encounter phase issues in every situation, but as long as you're aware of a digital processor's latency characteristic, you can avoid or otherwise compensate for any odd artifacts.


The Alesis CLX-440 is a flexible, feature-rich, and very clean-sounding dual-stereo digital dynamics processor. Its wealth of features might prove overkill in some instances — in live situations, for example, there isn't much time for tweaking — but its range of control options is certainly welcome in the studio. The accompanying reference manual is informative and well written, covering in detail not only the functions of the processor, but also the basic principles and applications of compression and expansion — a real boon for the uninitiated.

The CLX-440 performed well with a variety of instruments and vocals, compressing without coloration or loss of high-end frequencies under high gain-reduction conditions. Although its inherent latency might introduce phase issues when processing sources with bleed from adjacent instruments, the delay is virtually imperceptible in most cases. Remarkably transparent and effective, the CLX-440 offers lots of quality sound-shaping options without costing an arm and a leg. This processor promises to be a valuable addition to any studio looking to expand its dynamics-processing capabilities.

Karen Stackpoleoperates Stray Dog Recording Services and teaches sound arts at Ex'pression Center for New Media. Special thanks to Dave Bell for his contributions.


dynamics processor


PROS: Affordable. Feature-laden. Flexible. Clean, transparent sound. Informative and well-written manual. Visually obvious gain structure.

CONS: Potentially complex range of options. Numbers on LED meters difficult to read. No digital I/O.


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