A Trip to the Slammer


Despite the exploding digital revolution, the popularity of analog compressors and limiters shows no sign of waning — and for good reason. There is an ineffable, complex quality to the sound of these processors that is difficult — some would argue impossible — to get from digital.

Whether they need a compressor to put a sharp point on pillowy drum tracks, reign in wildly fluctuating vocal dynamics or add some glue to a mix, engineers often reach for an analog box for its nonlinear qualities. Likewise, analog limiters are still in great demand for creating in-your-face electric guitar vamps, making drum room mics hyperventilate like an asthmatic madman or for pumping up the average level of full mixes before hitting the digital domain.

This roundup takes a look at some of the distinguishing features of recently introduced analog compressors and limiters, specifically those units that were first announced at or since AES 2004. To limit (pun intended) the number of products to a manageable list, we've culled channel strips and other units offering a mic preamp, expander/gate or full-blown equalization in the audio path. (The addition of sidechain filters is welcomed.)

The following information was gleaned from manufacturers' literature and should be used only as a starting point in your research. Be sure to check out the sidebar, “Catch and Release,” for a few arcane tips on what to look for when shopping for your new squeeze.

Alta Moda Unicomp FET-based compressor

The Alta Moda Unicomp (dist. by Las Vegas Pro Audio,; $4,250) is an FET-based, dual-mono/stereo compressor with serious multiple personalities. Users can switch the unit's detection circuit to provide either a feed-forward or feedback scheme for different sonic textures. The sidechain's detector can also be switched to either RMS or peak-rectifier mode. And if the high-voltage, minimalist audio path (which is fully discrete, Class-A) is too clean for that guitar track you're whacking, then crank Unicomp's Warmth control to add second-harmonic distortion in proportion to the depth of compression. A Blend control allows you to mix unprocessed and compressed signals at the unit's output.

Buzz Audio DCS-2.2 combines two independent compressors.

The Buzz Audio DCS-2.2 (, $3,000) true Class-A dual-compressor system combines two independent compressors — one FET-based and the other using an opto cell — under one hood. The two compressors can be placed in series in any order or in parallel configuration. Use the Blend control to mix the compressors' output signals in any proportion when in Parallel mode or to adjust the blend of processed and unprocessed signals. Each compressor section also sports a defeatable transformer-saturation circuit and sidechain insert point; internal sidechain filtering is also provided. Two mono units can be linked, and a stereo-matched mastering version will be available for $3,500.

API Lunchbox owners should also check out the Buzz Audio Essence ($1,000), a Class-A optical compressor designed and approved to fit the API 500 VPR Series rack frames. This mono module uses the Buzz Audio differential drive sidechain to process the positive and negative waveforms in two separate audio paths. A 10-segment LED ladder uses VU ballistics to show input or output level or gain reduction. Other goodies include Lundahl I/O transformers, built-in high- and low-shelving sidechain filters, an external sidechain insert point and a sidechain monitor switch. Multiple units can be linked in one rack.

Chandler Limited EMI TGI12413 Zener Limiter

Chandler Limited ( recently celebrated Abbey Road Studios' 75th birthday by issuing the new EMI TG12413 Zener Limiter (price TBA), which is based on vintage EMI gear used to record The Beatles and Pink Floyd. The new, dual-channel limiter borrows from the '60s-era RS168 Zener Limiter and TG12345 console channel, but adds new controls for increased flexibility, including switchable input impedance (which changes the gain to drive the limiter softer or harder), three different dynamics settings, sidechain filtering, and 11-position attack and 21-position release controls. A stereo-link switch and VU meters cap off this beauty.

The D.W. Fearn VT-7 (, $4,800) dual-channel vacuum tube compressor features an all-discrete, Class-A, all-tube audio path and uses a pulse-width modulator for gain control. A total of eight dual triodes — a combination of 6072A and 6N1P tubes — and Jensen I/O transformers shape this dual-channel compressor's sound. Turning a special control knob for each channel simultaneously adjusts ratio and other parameters for harder or softer compression. A large VU meter for each channel can be switched to show either output level or gain-reduction amount. Channels can be stereo-linked.

The Drawmer 1968ME Mercenary Edition (dist. by TransAudio Group,; $1,995) compressor takes an unusual hybrid approach by combining a FET gain-control element with a tube makeup gain stage. This dual-channel unit features switched attack and release times (the latter including three program-dependent settings) and a sidechain listen function. Tom Hanks will love the unit's switchable Big function, which makes the JFET ignore low frequencies to lessen pumping and keep the bottom end rockin'. And forget tiny overload LEDs — the 1968ME's multifunction meters glow entirely red when levels approach clipping.

Drawmer S3 3-band optical compressor

Where wide-band processing won't get the job done, Drawmer's new S3 ($6,995) 3-band optical compressor offers a solution. This stereo split-band compressor's sonic signature is sculpted by I/O transformers, passive components and 10 vacuum tubes per channel in a balanced, Class-A configuration. This baby cooks — an electronic oven keeps the opto cell's LDRs at optimal temperature to maintain their calibration and performance. The VU meters can be switched to show peaks or re-scaled to accommodate smokin' +30dBm maximum output levels. Adjustable band-crossover points, a stereo balance control, and dedicated gain-reduction metering and bypasses for each band complete the picture.

elysia alpha adds M/S processing for mastering.

The elysia alpha compressor (, $11,999) goes beyond mundane feature sets with the addition of M/S processing for mastering applications. Mid- and side channels have independent access to filtering and can also be linked. The dual-channel, all-discrete, Class-A dynamics processor also features soft-clip limiters, feedback and feed-forward sidechain modes, stereo channel-linking, and built-in HPF and LPF sidechain filters. Parallel compression is complemented by a Mix controller that allows combining unprocessed and compressed signals in the desired proportion.

On a tight budget? The FMR Audio (, $249) Really Nice Levelling Amplifier (RNLA7239) is a single-channel, ⅓-rackspace unit that offers unbalanced inputs that accept TRS connections from console inserts, balanced mic preamps and so on. Outputs are balanced but non-differential (i.e., the cold signal is not driven), and hardwire bypasses output signal even in the event of AC power disruption. A Log Rel function speeds up release time in relation to compression depth to restore punch.

The single-channel Groove Tubes Glory Comp (, $3,499) joins a relatively short list of variable transconductance-based compressors currently in production. The all-tube design wires up large pentode tubes as triodes so that they can be matched and recalibrated by way of front panel pots. This, along with multiple linking setups and switched controls, provides the rock-solid imaging and repeatability necessary for applications such as mastering. Dual-release modes (providing linear or logarithmic/exponential response) and sidechains with built-in filters and external connections increase flexibility. Cranking the Glory knob adds second-order harmonics to the processed signal for a richer sound.

Pro audio equipment designer Stayne McLane says the secret gain-control element in his InnerTUBE Audio Dual Atomic Squeeze Box (, $6,750) is a first and was chosen for its uncanny transparency, even when processing stereo, broadband, percussive material. The all-tube, 2-channel (linkable) compressor uses an outboard power supply (included), octal dual triodes and nickel-core I/O transformers. Attack and release times are program-sensitive. The ratio control has a linear taper, and the unit can deliver more than 20 dB of gain reduction.

The Joemeek Mc2 (, $330) stereo optical compressor takes the “stereo” bit seriously. Included in the unit's feature set is a stereo-width processor that can take program material from mono to “wide stereo.” Unlike many opto compressors, the Mc2 offers attack, hold and release controls; ratios up to 10:1 are offered. Two multisegment LED meters show gain reduction and output level, respectively. Both -10dBV and +4dBm nominal operating levels are accommodated.

The Neve 8051 can be used for surround apps.

The 6-channel Neve 8051 (, $9,650) uses the same feedback topology as the company's 33609 compressor for that trademark Neve sound. Each of the six transformer-balanced audio paths can be conditioned at once by either of two sidechains, using any surround or multistereo format. Sidechain trims and filtering increase the 8051's flexibility for surround applications. Also included are electronically balanced key and LFE filter inputs (one each) and control voltage I/O; the latter is useful for linking multiple units or to a 33609.

Brand new from Pendulum Audio ( is the PL-2 ($2,500) analog peak limiter, which offers both JFET and MOSFET peak-limiting modes for hard- and soft-limiting, respectively. This brickwall limiter's two channels are fitted with stepped I/O controls to accommodate session recall, and both channels and several units can be linked for stereo or surround mastering. The peak-limiter circuit — originally used in the company's Quartet II tube recording channel — stays out of the signal path when program level is below threshold. Gain reduction is shown via 13-segment LED array.

The Retro Instruments Sta-Level (dist. by Vintage King Audio,; $2,350) tube compression amplifier is a near-replica of the vintage (circa 1956) Gates Sta-Level. Users can choose between using either a 6386 tube or a pair of more readily available 6BJ6 tubes (in addition to the other five stock tubes) to drive this mono box. Two or more units can be coupled for sidechain, stereo or surround applications. Custom-wound, balanced I/O transformers and a spartan control set grace this blast from the past, which can deliver up to 40 dB of gain reduction.

Rupert Neve Designs Portico 5043 comp/limiter

The two independent channels of the Rupert Neve Designs Portico 5043 (, $1,895) compressor/limiter duo can be linked for stereo operation and ducking duties. A bus input allows connecting the 5043 to other products in the company's modular and expandable Portico system to create an integrated setup for tracking and mixing. The VCA-based 5043 uses I/O transformers and almost entirely discrete component amplifiers. Both feedback and feed-forward modes of compression are offered, with ratios ranging from 1:1 to 40:1.

Why settle for one gain-control element when you can have two? The Shadow Hills Mastering Compressor (, $6,500) places two gain-control elements — a T4B opto cell and Class-A VCA — in series to shape the compression slope. Alternatively, either or both elements can be bypassed. Choose from among three different custom output transformers — dubbed Nickel, Iron and Steel — at the flip of a switch to get distinctive sounds. A stereo-link function and switched rotary controls accommodate mastering duties, but dual-mono operation is also afforded for tracking and mixing. A built-in sidechain filter can be activated to reduce pumping on bass-heavy material.

The SM Pro Audio OC8E (, $609) multichannel compressor packs eight channels of electro-optical compressors — each having its own VU meter and bypass switch and separate controls for ratio, attack, release and output gain — into a 2RU chassis. Rear panel I/Os are all on ¼-inch jacks. The unit's Class-A, high-voltage signal path is transformerless.

The Toft Audio DC-2 (, $800) FET compressor includes a line preamp with front panel ¼-inch instrument input jacks for each of its two linkable channels. Input and output gain can each be boosted or attenuated up to 20 dB. Balanced I/O connections and VU meters grace this unit designed by Malcolm Toft, recording engineer for The Beatles, David Bowie, James Taylor and others.

Poised for release sometime this winter is the Universal Audio 2-LA-2 (, price TBA) twin T4 levelling amplifier. This dual-channel, tube-amplified unit takes the original LA-2A's all-discrete, Class-A circuitry and adds defeatable stereo-linking and switchable slow and fast recovery times. (The latter is courtesy of a second T4 cell included in each channel.) Ten tubes and custom I/O transformers are part of what makes this puppy sing.

Mix contributing editor Michael Cooper ( is the owner of Michael Cooper Recording in beautiful Sisters, Ore.

Compressor Shopping Considerations

When searching for an analog compressor or limiter to buy, you should consider a whole lot more than just the specs for time constants and ratio, and whether or not there's a tube or transistors in the audio path. Here are some pointers that go beyond the obvious.

First off, the type of gain-control element the unit employs to achieve gain reduction really affects its character. FET-based limiters are ultra-fast, and therefore fantastic for putting a firm lid on boiling guitar tracks or a finely sculpted point on a snare drum track. On the other hand, if you need something more natural- and transparent-sounding to “sit” a lead vocal track in the mix, the relatively slow optical (aka, opto or electro-optical) compressor is your friend.

Maybe you need versatility for handling many different tasks. A compressor that uses a VCA will generally give you that. Typically slower than FET-based but faster than optical compressors, units employing a VCA usually offer wide-ranging attack and release times and the ability to deliver extremely deep compression for taming the most unruly tracks. And while a variable-mu or variable transconductance compressor (which employs a vacuum tube for gain control) is unable to provide very deep compression (due to the tube saturation), the sonic “densification” it lends to tracks is a beautiful thing when you want to bring beef to the table.

For use on the mix bus, you'll probably want a compressor that provides an exponential taper to its ratio control; that will let you fine-tune very moderate ratios (below 2:1) with ease. And while limiters usually offer a maximum ratio between 20:1 and infinity:1, the incorporation of peak or look-ahead detection circuitry will also be necessary for effective use as a “peak” or “brickwall” limiter. RMS-detection circuitry is more effective for compression duties and not for limiting — that's something to keep in mind when looking at a unit that promises both compression and limiting capabilities solely on the basis of its wide-ranging ratio control.
Michael Cooper

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