elysia mpressor Compressor Plug-In
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by Barry Rudolph
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The mpressor is a virtually modeled version of the company's popular hardware hard-knee compressor unit. The same brain trust that designed the Brainworx plug-ins did all the development and translated the all-discrete circuit design of the mpressor compressor to a software emulation that runs as TDM/RTAS, VST and AU plug-in. Like elysia's niveau filter plug-in, mpressor uses oversampling for higher resolution processing. For sessions running under 50kHz sample rates, it uses 4X oversampling; for sessions between 50kHz and 100kHz rates 2X; and for sessions over 100kHz, there is no oversampling.

I installed the TDM/RTAS version into my PPC Quadcore Mac running OS 10.4.11 and Pro Tools HD Accel ver 7.4cs11. mpressor is iLok authorized and is "good to go" in Windows XP, Vista, and 7 PCs and MAC OS 10.4 or above and on Power PCs or MacTel computers..

Like the hardware unit, the mpressor plug-in has significant features that separate it from other compressors and make it attractive to me for its many processing possibilities and creative uses in music production. It would be against design objectives to include a Soft Knee button on mpressor as its designers are proud to focus and concentrate on its hard knee purpose. I'm glad they did!

mpressor GUI

GUI And mpressor's Functions

A look at the GUI and mpressor's functions reveals the many reasons this is a musically creative processor. Being first of all a compressor, mpressor has all the typical controls any compressor but the additional controls, built-in elysia niveau filter, plus the greatly expanded range of compression parameters and values broaden the sonic creative possibilities.

Threshold And Attack Controls

mpressor's Threshold control covers a tremendous range: +16 to -18dB or 34dB. Unless you are trying to compress a very low level recording, this range works well to offer good resolution in dialing in the best threshold setting.

Like all the controls on mpressor, Threshold "mouses" smoothly and the plug-in supports mouse wheel use with quick keys for fine mode and standard position noted in the manual for VST, AU, and TDM/RTAS hosts. VST hosts can also toggle its knob action between circular and linear control.

The SC External button switches the control signal from being derived from the input signal over to an external source coming into the sidechain input. (Your DAW host program permitting). The Ext SC input has a built-in 80Hz/6dB per octave high pass filter to reduce unwanted gain reduction swings due to low frequency peaks in the side-chain.

Things get more interesting with the Attack control. Attack ranges from 0.01MS (10 microseconds) to 150MS--fast! I found mpressor to start gain reductions so fast that I could remove all attack of a sound if I wanted. It is useful for adjusting the "length" of the attacks somewhat in the same way as possible with SPL's Transient Designer.

The Auto Fast mode, when switched in, varies the attack time predicated upon the signal's speed and instantaneous level--short and loud moments trigger faster attack times. Otherwise faster attacks are on an "as needed basis" and for all other audio, attack times are as indicated and set.

Release Controls

Next is the Release time knob with a setting range of 5MS to 1.2Sec. mpressor scores again with a choice between a linear and logarithmic release time curves switched in using a button called Anti-Log.

Most compressors, in an attempt to be "unheard" or appear to do little to the sound employ variations of linear and logarithmic release times--a smooth and natural curve or ramp of the change in gain when a compressor returns from gain reduction back to unity.

After a deep gain reduction from a loud peak such as a snare drum hit, a logarithmic release curve raises the gain back up faster than when using a release time with a straight-line, linear release shape. This action works well for drum compression when using fast release time settings.

Read Barry's Mix Magazine Feature Article On Compression and Compressors

Flipping the log curve upside down, this inverse release time curve or anti-logarithmic releases initially slower after a deep gain reduction. This is wacky and invites all sorts of goofy "characteristics" to the sonic party! (More later on using this feature!)

Ratio And Negative Ratio

Ratios are continuously variable from 1:1 to 10:1 to -4.0:1. That's right a negative 4:1 ratio. Setting ratio is like any other compressor except you can go negative--below 1:1. A negative ratio causes the output level to go lower with increased input signal level. This produces a pronounced pumping and dynamic expansion during the release time period.
(I'll explain this more during my In The Studio testing)


niveau Filter

Post compressor is elysia's niveau filter for tonal shaping the compressed sound. This is a sliding high and low shelving filter with just two controls: EQ Gain and EQ Frequency.

After you set a center frequency position, boosting the gain control raises the level of all frequencies above and reduces all frequencies below this center frequency. Conversely, moving the gain control CCW reduces all frequencies above and boosts all frequencies below. This filter has 6dB/octave slope, In/Out button and a X10 switch to jump the frequency range from 26Hz to 2.2kHz up to 260Hz to 22kHz. I found this filter to "carve" or limit the bandwidth of any sound in a musical way so that it fits better into a dense mix.

GR Limit

Also with an In/Out button, the Gain Reduction Limiter applies a second control signal to the gain controlling engine within mpressor. The GR Limiter section does not pass audio itself but rather offers up to 21dB of protection. Working like a dynamic "lid", GR Limit will not allow level above its setting.


Output make up gain is controlled by the Gain control. Like the hardware unit it is modeled after, mpresssor imparts more harmonic content as this control is cranked. At first use, I thought the output level of mpressor was low since winding up this control produced little increase. It does go up in level but adds more of a broadening effect on the overall sound due to the addition of 2nd and 3rd harmonic distortion.

The mpressor hardware unit (which the plug-in closely follows) is specified at producing a THD+N @ 0dBu at 0.04% and at +10dBu, 0.33%. Very cool but if you need more clean level, make it up with the track fader or by adding another plug-in afterwards.

mpressor GUI
mpressor GUI For Guitar Click Here For All Sound Samples

In The Studio

Here at my Tones 4 $ Studios first up were typical compressor jobs mixers run into everyday: electric guitar and electric bass guitar.

The guitar track sample (all samples are 192Kbps .mp3 files) is a well-recorded rhythm guitar part I needed to hav stand taller in the track. In this example, results are not dramatically different except for the way the guitar now sits in the mix. It is now a more constant element--a almost droning part without much dynamical sparkle to draw a lot of attention to it. I also liked its new intensity caused by mpressor.

mpressor GUI
mpressor GUI For Bass Guitar Click Here For All Sound Samples

For this song my bass guitar track got a similar treatment like the guitar but with a lower ratio and higher threshold settings. I also used a slower attack and especially a longer release time setting. Listening to the sound samples indicates a smoother bass track--mpressor is working in a very 'pro', old-school mixing manner here. I'm going for a cleaner and deeper (Check the niveau setting), fatter bass sound so I did not crank the Output extremely high--just enough to give the bass a little "hair."

mpressor GUI
mpressor GUI For A Snare Drum Track Click Here For All Sound Samples

My snare drum track sample example shows how to mangle a perfectly nice-sounding snare drum recording! Notice the fairly high threshold and equally fast attack and release time settings. I've also set a negative ratio and have the Anti-Log button in. All these settings achieved an extremely clean pumping sound free of nasty compressor artifacts most compressors emit when pushed this far. It has the effect of nearly dynamically reversing the snare drum envelope.

For this song, I actually back it all down--you can go much more extreme than this and elysia's Web site has some more radical examples! This kind of processing works great on a lot of different sound sources. You can carefully set the release time so that the effect is in sync with the session tempo. Locking release time to tempo might make a nice update for this plug. The only plug-in I can think of that has release time lockable to session tempo is called H-Comp--it's part of the WAVES Hybrid Bundle

mpressor GUI
Left Channel mpressor GUI For Converting A Mono Loop Into Stereo
mpressor GUI
Right Channel mpressor GUI For Converting A Mono Loop Into Stereo
Click Here For All Sound Samples

Above are two mpressors I used on a mono drum loop. I duplicated the original loop and panned each track left and right. The differences in the settings on each instance of mpressor are very different. I'm using GR Limit on the right but not the left. I'm also using vastly different niveau filter settings too. Since each side is pumping differently, the next result is a kind of "animation" to the loop without any phase trickery or delay use.

Big Thumbs Up!

I found many uses for mpressor all around my mixes. It is extremely versatile and not just a special effects plug-in. I did get into the Auto Fast feature and found it to work well when first setting up any compression when you are not sure of the "ebb and flow" of a particular vocal or instrumental track.

The negative ratio and Anti-Log release mode are strictly fun! I can do crazy effects like I used to do with the old Eventide Omnipressor unit and now with their plug-in but in a lot more direct, faster and less tweaky way.

The Gain Reduction Limiter is an important tool to control the plug-in's output no matter how extreme you get because it is completely independent from the threshold and ratio settings. My next experiments will be to control the mpressor using the external sidechain input for syncing compression with session tempos.

I'm highly recommending the mpressor for its versatility and unique abilities not obtainable with any other processor. It excels especially in the creative side by radically altering the dynamic envelope of sounds yet it can also behave very civilized when you require.

elysia's mpressor sells for $440 or 290€ for the VST/AU/RTAS version and $590 or 390€ for the TDM/RTAS/AU/VST version. Get more information, try a free 14-day demo or just buy it at: www.elysia.com/software/mpressor/introduction/.

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