When it comes to choosing a compressor, the modern audio engineer is not short of choice. With so many out there, what features, if any, can set a compressor apart from the rest?

Anyone new to audio could be forgiven for wondering where all hyperbole around compressors comes from. Certainly, the choice of design can have an impact on the processed audio but there seems to be far fewer conversions about the contribution of the engineer. The truth is engineers who actually use audio technology day in, day out will have a small number of high quality tools that they rely upon, but not for the reasons others might have us believe.

The number of available parameters on some compressors can be overwhelming when there’s a job to do other than learning the tool itself. For that reason, many pros go for two things: the sound, and the ergonomics, on the understanding that if it’s quick and sounds good then it is good. Compressors that afford the engineer these things cut through the froth and get back to their primary purpose of controlling levels quicker than fader moves can.

The Swiss Army Knife

People often compare really useful gear or audio plugins to the famous multi-function tool of Swiss Army fame. This isn’t to say that the box or audio plugin offering extra functionality needs all of its knobs and buttons to be used; the idea of an advanced tool is to offer many functions, of which the user chooses only the one(s) needed.

Sometimes, certain situations will arise when some specialist control is needed. Certain features not found on all compressors can mean the engineer may not use their ‘regular’ compressor, but instead reach for the thing that has the specific parameter they need.

Can Your Compressor Do This?

PSP have been around since the early days of the DAW, and were one of the first developers to come up with a saturation algorithm that was accepted in the early 2000’s by those with a true basis for comparison who were moving to digital from analogue systems. Since the days of their well-known Vintage Warmer, the company has developed a huge number of software tools with fresh takes on all things analogue. Their Impressor audio plugin manages to offer some genuinely useful features not found on so many compressors.

1 - Variable Link

It could be argued that to make a compressor useful for both channel and buss duties, it needs to have switchable linking in its detector circuit. Why? In stereo or multichannel applications, this determines whether loud events will dip all channels or just the channel in which it occurs. Furthermore, a compressor that offers a mix control between the two allows the users to dial in a best-of-both setting which can be especially useful on music buss duties.

2 - Mixable Sidechain Input.

The majority of compressors offer external sidechain inputs to trigger the detector circuit. This has many uses, with using the kick to pump the entire mix being a good example. In this scenario, the engineer might also want buss compression to respond to peaks in the mix itself; being able to roll some internal triggering back in addresses this.

3 - Variable Auto Release Response

While not ordinarily at the top of every mixer’s shopping list, auto release is good to have. With the success of any design being so programme-dependent, different compressors will work better than others on a given mix. Being able to adjust the behaviour is an unusual feature, despite its usefulness.

4 - Input And Output Metering.

The tried and trusted tradition of metering that is switchable between input, output, or gain reduction is useful, however switching between modes is one more button or click adding to any number of extra moves over the length of a project. Underneath Impressor’s skeuomorphic GUI lies extra dual mode functionality where the L meter shows the input and the R meter the output (post-compression).

PSP continue:

The PSP Impressor is an incredibly accurate, a fully-featured, high-precision compressor designed to process whole mixes, busses or single tracks. PSP Impressor emulates the magical classic characteristics of compressors with valve and opto-electronic circuits as well as classic modern compressors. PSP Impressor also features a highly configurable side-chain. The side-chain filter has a significant effect on PSP Impressor’s sound and operation. Depending on your side-chain filter settings, the filter also lets you use the compressor as a de-esser or to reduce the pumping effects of heavy kick drums and the like.

Watch composer Alberto Rizzo Schettino’s detailed walkthrough and test of PSP Impressor:

Other features include:

• A wide range of soft knee characteristics

• Peak or RMS level detection

• External or internal side chain signal with a smooth bell-type filter

• An output algorithm which can operate as either a brick wall limiter or soft saturation algorithm to preserve peaks above 0dBFS.

• New high resolution, scalable GUI.

• VST3 support.

• FAT quad sampling option.

• Entire compression engine runs at internal quad sampling for proper compressor modelling when FAT is disengaged and 16 x sampling when the FAT is engaged.

• High sample rate support up to 400kHz.

• Feedback and feedback + feedforward compression modes, PSP MixPressor runs only in feedforward mode.

• New side chain filter modes: HPF and Equal Power. PSP MixPressor only had its powerful Bell type side chain filter, however HPF gives PSP Impressor a more classic touch, and the Equal Power results in extremely transparent and well balanced compression of complex tracks, drum groups or even entire mixes.

• Four Auto Attack and four Auto Release modes instead of just two modes for each.

• Refined compression Shapes for added versatility.

• Adjustable VU reference level.

• Adjusted ranges for most of knobs to make them more user-friendly.

• Input - Output knobs link.

• New output Limiter.

• Other algorithm refinements to make the PSP Impressor the natural tool of a choice for vocals, drums, acoustic guitars and other tracks, groups, and even during the mastering process

Simplicity Vs Power

On the understanding that most working engineers use the simplest tool allowed by the task, few would deny that freeing the mind from endless functionality offered by modern gear is a good thing. That said, specialist tasks require specialist solutions, and the minutiae they can sometimes bring is still worth navigating when the need arises. Rather than getting more of the same, the next compressor you use could have those extra functions that are genuinely useful.