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Dynamic Duo

Drawmer DL241 Auto-Compressor & DS404 Quad Noise Gate

The latest from Drawmer in dynamic control, reviewed by Dave Lockwood.

Drawmer's DS404 and DL241 offer quality as well as quantity in their dynamic control facilities, finds Dave Lockwood.

The latest in Drawmer's highly respected range of dynamic control devices are the DS404 Quad Gate, with four identical gates (each with the integral side-chain filtering pioneered in the renowned DS201), and DL241 Auto-Compressor, a 2-channel device with an integral expander/gate and a peak limiter in addition to its compressor stage.

Both models have black 1U rack housings, with clear legending and Drawmer's distinctive and very practical bright yellow pointers on all controls. The units have the solid construction and quality feel that we have come to expect from this company; controls are smooth and consistent, switches are positive and connectors are solidly supported. The review models incorporated balanced XLR connectors for everything except the gate side-chains, but jack versions are also available. The compressor features rear panel switches to convert the nominal interface level from +4dBu to -10dBu, whilst the wide threshold range of the gates effectively renders the function unnecessary for the DS404. The only obvious omission is perhaps the lack of provision for external access to the DL241 sidechain. Bypass, on the compressor, is a true hard-wired passive link from input to output, which will enable the unit to continue to pass signal during a fault condition — an important failsafe consideration in installations and live sound work.


The DL 241 is a very comprehensively specified stereo unit which appears to cover practically all normal operating modes in one device. The basic action is that of a soft-knee ratio compressor (the soft-knee characteristic progresses from unity gain to the set amount of gain reduction, over a range of about 10dB). Although attack and release controls are provided, you have the option of switching to automatic, program dependent envelope control. Soft-knee action and program-dependent attack and release is probably the optimum combination in applications where unobtrusive dynamic control is required, unless frequency splitting is employed. There will always be applications however, where the auto characteristic does not produce the desired result; a retarded attack accentuating transients, or an over-fast release causing obvious pumping can be useful effects in their own right, and it is good to have the option of overriding automatic control.

I particularly welcome the inclusion of an additional peak limiting stage on the DL241. Setting up a compressor on unpredictable signals is often a balancing act, compromising between maximizing level, avoiding overprocessing, and protecting against system overload. The comforting presence of the limiter allows you a little more creative freedom in setting threshold and ratio. The limiter has a single control, calibrated 0dB to +16dB, and is taken out of circuit merely by selecting the maximum (+16) setting. To some extent, the system is auto-ranging, for continuous limiting for a period in excess of 20ms (ie. not just 'peak' limiting) will produce an automatic adjustment of system gain. Used correctly, the 'zero response time, zero overshoot' peak limiter is efficient, unobtrusive and very fast — ideal for overload prevention in digital systems, or speaker protection in live sound rigs. Despite the preset envelope, it can also be most effectively creatively abused!

On many sophisticated dynamics control devices the expander/gate section is actually rather basic, almost an afterthought. This has always struck me as rather odd; surely the only time you are likely to use the on-board expander to combat the raised noise floor caused by compression is during recording — if you intend to do it off-tape then you might as well use a more specialised unit. Yet seldom have I felt happy to use the relatively unsophisticated facilities of a compressor's built-in expander in critical applications. The DL241, however, features what Drawmer call Program Adaptive Expansion, and despite being controlled by just one pot (Threshold) and one switch (Fast/Slow release), it proved to be an excellent expander. Adaptive Expansion can perhaps be best understood as an equivalent of a soft-knee characteristic in reverse. The expansion ratio is applied progressively, so that signals around and just below the threshold receive considerably less processing than the lower level residual noise. The net result is an expander stage that is not only very kind to signals, but which is also extremely forgiving and very easy to set up. You could certainly gate a vocal onto tape with it, confident that you will not lose any particularly quiet line endings. If you do get it wrong, the worst it will do is slightly attenuate a piece of wanted material — an easily-remedied problem.

Unusually for a multi-stage dynamic processor, all three elements are strong in the DL241, making it an extremely powerful and versatile unit. Yet none of its control sophistication would count for much if it didn't have a signal quality to match it. Although no band-splitting is employed, and there is no high frequency expansion circuit (as on the Aphex Expressor), high frequency dulling under heavy compression in Auto mode is minimal. At moderate levels of gain reduction the sound remains subjectively as smooth and transparent as the input. However, even when you are using it to squash and pump to an over-the-top extent, it still sounds really good. "Classy" is probably the word for it; nobody minds hearing some of the side-effects of compression, so long as they are the right ones.


Units which cram four gates into a single rack-unit inevitably have to compromise on facilities. Consequently, DS404 gates offer just four controls: Threshold and Release, plus HF and LF stages for the powerful sidechain filter system. However a choice of Soft or Hard gating action makes a fundamental difference to the way the DS404 gates operate. In Hard mode, attack time is fixed at under 10µs, and a Hold phase is automatically applied according to the user-set release time, in order to prevent bounce or chatter around the threshold. This is a traditional gating action, optimised for signals with simple dynamics, such as percussion.

Soft mode utilizes the Programme Adaptive Expansion characteristic developed for the DL241 expander stage. Attack time is adapted to the program content, and expansion is applied progressively with the ratio increasing in inverse proportion to signal level. Combining such fundamentally good expander behaviour with the high selectivity provided by a frequency selective sidechain produces a very desirable gate characteristic indeed.

A Range switch sets depth of attenuation in either mode, but is limited to just two settings, 20dB or 90dB. You can link adjacent channels without external patching, with all four gates triggering on the same key signal if necessary. External keying is possible, and the Key Listen facility for tuning the filters is, of course, included. The option of using these excellent filters in the main signal path, as many people do with their DS201s, is thus retained.


Both the DS404 and DL241 perform their intended functions to the highest standards. The build quality inspires confidence, and they are instinctive and uncomplicated to use. The term 'industry standard' is much-abused, but Drawmer's DS201 is surely as deserving of it as any unit ever made; it good to see the same company, indeed a British company, setting itself new, even higher, standards.


DL241 Auto-Compressor £405.38 inc VAT (£464.13 for XLR version).
DS404 Quad Gate £616.88 inc VAT.

Drawmer Distribution, (Contact Details).

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Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Nov 1991

Review by Dave Lockwood

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> Steal The Feel

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