Tuesday, 28 June 2011

Tuesdays Tech Tips: Elysia - Mpressor

If compressors simply did the job for which they're designed, none of us would need more than a single plug-in to cover all of our bases. The way in which gain reduction is applied, however, varies wildly from one plug-in to the next and, consequently, this is an area in which a large number of manufacturers compete for your attention. Some processors are aimed at tackling mastering issues, while others work best on individual instruments and vocal channels. Elysia's Mpressor sits in between, building on the lineage of the German company's high-end Alpha mastering compressor yet providing a tool-set which is perfectly suited to individual instrument processing. It's also iLok protected, runs at 32-bit and is available in a wide range of formats.

From the outset, it's clear that Mpressor goes some way beyond regular compressors. The top row of its eight dials are standard enough, with Threshold, Attack, Release and Ratio dials but the bottom row is more bespoke, with EQ Gain and Frequency controls and a Gain Reduction limit dial to accompany the common output Gain control. Having tone control built in to Mpressor allows for a great range of potential treatments, of which more shortly.

Dealing with the compressor parameters first, Mpressor's Threshold can either assess incoming audio directly, or use a side-chain source, via a click of the red button to the dial's right. The Attack dial allows you to control the speed at which Mpressor will respond to input signals but its corresponding button enables something called Autofast. Attack times are often a compromise—set them fast to catch initial peaks but change the response of sustaining material, or set for the latter, only to miss out on the first moments of a sound's initial transients. Autofast allows you to specify a time as normal but automatically shortens this for sounds which feature fast, loud impulses. This works best when using Mpressor across a mix bus but has useful implications for processing drum loops, vocals and other grouped sounds too.

The Release dial also features a button-based accessory feature, in the form of AntiLog. This inverts the traditional logarithmic behaviour of compression tails and makes the audible compression effect much more obvious. For mastering purposes, I suspect you won't go near it but if heavily compressed program material is your goal on drums, basses, synth stabs and other standout elements, its effect can be powerful. In a similar camp are the negative Ratio values. Whereas Ratio normally determines how limited the volume increase of a signal can become once it has breached the Threshold level, so negative Ratio amounts actually reduce the output volume once a signal is being compressed. In other words, the louder the input signal, the quieter the resulting sound. Imagine this on a drum loop and you'll appreciate the idea—the audio result almost sounds reversed as kicks and snares force level drop while the audio in between pumps up.

The EQ controls are borrowed from Elysia's free-to-download Niveau filter plug-in and its job is to change the relationship between the treble and bass elements of the sound you're compressing. Your two controls are EQ Frequency and EQ Gain. As you increase the frequency dial, more emphasis is placed above this cutoff point and more is cut from frequencies below, though the EQ Gain control can work backwards to reverse this balance in favour of bass frequencies if you prefer. Two modes are available; in the first, the frequency range of this change is from 26Hz to 2.2kHz but with the x10 button engaged, these values switch to offer a range between 260Hz and 22kHz. At their extreme settings the dials can offer standard low or high-pass filtering but their intermediate controls are so flexible that Mpressor could easily become an important EQ tool for its users without recourse to its compression parameters at all.

The final feature of note is the Gain Reduction limiter. This allows you to set a maximum amount of gain reduction and, no matter how loud your signal becomes, the amount of compression will never exceed whichever value you set here. In other words, loud signals can be compressed as hard as you like with the result that they'll never drop below a certain level while quieter signals will allow the virtual output level to climb, to preserve original dynamics. Again, this unique approach works wonderfully; for gentle verse guitar parts which become brick-walled power chords on the chorus, for instance, you can set this parameter carefully and let Mpressor do the rest.

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