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BSS Opal DPR422

Compressor / De-esser By Paul White
Published February 1998

BSS Opal DPR422

Does the DPR422 have the right combination of price and performance to break BSS into the project studio market?

BSS continue to enjoy their long and healthy reputation in the live sound business, but they've never done quite as well in the studio market, even though their products are equally suited to both applications. This situation is the reverse of that of Drawmer, another respected and well‑established UK company that has compressors and gates in virtually every studio in the land, yet its products are relatively little used in live sound.

In an attempt to capture more of the project studio market, some companies are producing budget versions of their existing pro‑audio products, but that's not the approach BSS are taking with their new Opal range. Instead they've maintained the quality and flexibility of their pro range at a lower price point, by streamlining the manufacturing process. The result is a cost saving to the end user of around 30%, but that still doesn't put the range even close to the budget price bracket.

On the surface, the DPR422 is a fairly conventional 2‑channel, 1U device with mains powering, XLR inputs and outputs, and unbalanced jacks on the side‑chain insert. There's also separate 0dBu or ‑10dBV operating level switching on both channels, but no jack alternatives to the XLRs. In addition to a fairly comprehensive set of controls, there's also an auto mode that optimises the attack and release time constants automatically, according to the input signal dynamics.

Less conventional is the inclusion of two different de‑essing modes: one full‑band, where any detected sibilance pulls down the gain of the whole signal, and a more elaborate mode involving the compressor section, which affects only the gain of high frequencies. If the basic de‑esser is selected, both compression and de‑essing can be used together, but in the frequency‑selective HF mode, the compressor circuitry and controls are used together with the de‑esser Frequency control, to apply gain reduction only to the top end of the audio range where sibilance occurs.


Because this product is aimed at both pro and semi‑pro users, the manual is particularly thorough in the areas of connecting up and basic operation, which is very welcome. Looking at the compressor section first, the control layout is fairly routine, with Threshold, Ratio, Attack and Release as well as the usual Gain control for making up any level lost by compression. Auto mode is selected with a single button press, and overrides the attack and release controls. Auto uses a dual‑stage release function that restores the gain as quickly as possible after a transient has passed, but without making the process obtrusive.

In all cases, the compressor operates in a kind of variable soft‑knee mode, which BSS refer to as progressive compression. Low ratio settings coupled with low levels of compression produce the most progressive transition from linear to compressed, whereas higher settings sharpen up the knee to the point where the unit behaves more like a hard‑knee unit. In most situations this is the way you'd want the compressor to work, so the absence of a soft/hard button isn't a problem. Ratio is variable from Off to Infinite, and separate bargraph metering is provided to monitor the output level and the degree of gain reduction being applied. As with some other BSS products I've seen, the gain reduction meter also shows the level of the input signal compared to the threshold level, where a large yellow LED denotes the threshold. A non‑latching front‑panel button may be pressed to monitor the input signal on the output meter if required. Two illuminated semi‑circular buttons close to the centre of the unit provide independent bypass facilities for each channel, and a stereo link mode links the side‑chains of the two channels for stereo signal processing.

Side‑chain access is via a pair of rear‑panel jacks configured as normalised send and return points, and these may be connected to an equaliser for frequency‑conscious compression, or used to input a control signal for ducking and similar functions. Unusually, the side‑chain access points are balanced, but the manual shows the correct way to wire cables for unbalanced use of both the main and side‑chain ins and outs.

In all cases, the compressor operates in a kind of variable soft‑knee mode, which BSS refer to as progressive compression.

Using The DPR422

The compressor section of the DPR422 is wonderfully predictable in operation, and the BSS metering system, which shows both the signal level relative to the threshold and the gain reduction amount at the same time, makes setting up very simple. At modest settings the compression is transparent enough to use for routine gain‑control jobs, even on complex mixes, while at higher settings the impression of compression increases without ever seeming out of control — a failing on some competing units, even very expensive ones. The compressor does everything a good compressor should do, without trampling the life out of high frequencies or producing excessive pumping, and if you are only able to have one compressor, this one will do a good job in most areas, including mix compression. I even tried it on my wooden American Indian flute and found it added a lot of definition and evenness to the sound, without making the end result seem processed. However, that's not so surprising — after all, Opal flutes are supposed to make your mouth water!

I have to admit that I had less luck with the basic de‑esser (see box) because, although it works, if you try to apply too much ess‑reduction or set the frequency control too low, distortion sometimes becomes audible, especially if you have a low‑pitched voice. Perhaps clearer metering would have avoided this situation. To be fair, though, the manual warns of this potential problem. The frequency‑dependent HF de‑ess mode works far better and all but eliminates that lisping effect simple de‑essers create, but of course you lose the ability to compress separately — in this mode you can only de‑ess. However, when you're dealing with a rogue vocal track, you can always use one channel to compress and the other to de‑ess, so this is still a one‑box solution.

De‑Essing With The DPR422

Only two controls are needed to access the DPR422's basic de‑essing facilities: De‑ess and Frequency. The De‑ess control adjusts the amount of gain reduction applied when a sibilant sound is detected, up to a maximum of around 20dB. Green and yellow LEDs above the de‑esser section provide simple metering, where green indicates that gain reduction is taking place and yellow shows that 15dB or more of gain reduction is being applied. The Frequency control is a user‑adjustable filter that should be set just below the frequency at which sibilance starts, usually around 3kHz or above. Temporarily switching in the HF button and selecting side‑chain listen allows the user to monitor the effect of the Frequency control at the unit's output while setting up.

Basic de‑essing is broadband, so whenever a sibilant sound is detected, the whole audio level drops, which can result in a lisping quality being added to vocals. A more sophisticated approach is to select HF de‑essing, though this requires the use of the compressor section, precluding combined compression and de‑essing.

Switching in HF de‑essing necessitates the use of the Frequency control to determine the area where sibilance is occurring, but now the compressor only acts on frequencies above the setting of the Frequency control. All frequencies below are left unprocessed, so that sibilance causes only the top end to be reduced in level, rather than the whole signal. This reduces the lisping effect significantly. All the compressor controls, including Auto, may be used in this mode, to fine‑tune the de‑essing process, and activating side‑chain listen once again allows the effect of the filter to be monitored. In HF de‑ess mode, the De‑ess control and the green/yellow meter LEDs are disabled — the degree of de‑essing is controlled entirely using the regular compressor controls, while the Frequency control sets the break point above which detection and compression occur.


In most walks of life, calling something predictable is often a thinly veiled way of calling it boring, but when it comes to signal processing you don't need any nasty surprises. The DPR422 compressor is as predictable as you could wish it to be, and the controls do just as they say, especially the Auto mode, which can take care of most programme material without stumbling. The simple de‑esser is less impressive, but the HF de‑ess mode is extremely good, even though it robs you of the compressor.

The DPR422 really is a first‑class performer, combining good sound quality with intuitive operation, clear metering and smooth compression — but it's not a cheap unit. Those professionals who are already BSS fans will no doubt welcome the Opal range with open rack slots, though the project studio owner will probably take a lot more convincing when there are so many other excellent compressors around for the same money or less.


  • Smooth, well‑behaved compressor.
  • Excellent metering.
  • De‑esser impressive in HF mode.
  • Well engineered.
  • Clear manual.


  • Still expensive when you consider how many low‑cost, good‑quality compressors are available at the moment.
  • The basic full‑band de‑esser doesn't always produce great results.
  • HF de‑esser precludes using compression at the same time.


A well engineered compressor from one of the foremost British manufacturers of audio processors, but in the project studio market it faces some very tough competition at much lower prices.


581.63 including VAT.

Published February 1998