Mpress Yourself

by Stephan Kirschner
Recording Magazin (Germany) – March 2008

Compression is a decisive factor in music production. Sounds can be processed very smoothly, or a drum buss can be driven into excessive pumping… The mpressor addresses everybody in search for a piece of gear that covers all – and really all – aspects of a creative approach to compression.

The enormous sound spectrum the mpressor has to offer is the result of a couple of features not to be found on other units which need some explanation. First of all there is the so called Anti Log function. This feature changes the behavior of the release parameter. The time constant has a great influence on how noticeable the compression process is to the ear (obvious or subtle). If rather inaudible results are desired, linear or logarithmic release characteristics will usually be employed; the latter shortening the release time on increasing gain reduction values.

The Anti Log function turns this control process upside down. This means: If the threshold is crossed and the compression process starts, the release will behave exactly the other way round than the logarithmic curve would – it is long at the beginning and then becomes shorter when the amount of gain reduction starts to decrease. The result is the exact inversion of the classic aim of compressing trying to be as unobtrusive as possible. This renders extremely obvious and wild effects like “reverse” compression possible. More on that later... Let's first have a look at the other exceptional features of the mpressor!

The Auto Fast function optimizes the temporal progress of the attack parameter. The choice of the correct attack setting can often be a very critical issue. If you want to catch those peaks therefore choose a very short attack time, nasty audible artifacts will often be the result. If the attack time is set too long, on the other hand, the compressor will work too slowly and looses its ability to catch the fast peaks. This is where the Auto Fast function comes into play. If a slower attack time between 70 and 100 ms is chosen and the Auto Fast knob is engaged in addition, the mpressor will react to fast and loud signal peaks with an automatic shortening of the attack time. Directly after this process, the original value which has been set with the specific controller will apply again. This really is a great tool for buss and sum compression.

The Niveau Filter can change the tonal character of a complete mix. This filter is extremely easy to handle. The EQ Freq controller determines the center frequency of the filter. Around this center, the EQ Gain controller boosts the bass and cuts the treble, or just the other way round. The third control element of the Niveau Filter is the x10 button which shifts the frequency set by a factor of 10. This results in a frequency range from 26 Hz to 22 kHz and covers the complete acoustic range of the human ear. These three parameters can be used influence the relationship between high and low frequencies comparable to a pair of scales. The mix becomes darker/brighter or more punchy/smoothly respectively. One important thing to know is that the Niveau Filter changes its characteristics in the extreme positions of the EQ Freq controller. Then it becomes a low pass (fully clockwise) or a high pass (fully counter-clockwise) filter respectively. This results in pretty strong changes in level that can be easily compensated with the make-up gain.

Besides all these great novelties, the mpressor can of course be used for “normal” compression and even works as a smooth sum compressor, too. For these applications the two channel unit offers the usual parameters like threshold, attack, release, ratio and output gain. Standard compression tasks are no problem at all. Here the basis is a moderate ratio between 1:2 and 1:5. Then the total amount of gain reduction is set with the threshold at a medium attack and a release around 300 ms. The mpressor has a link function, so that you don't have to transfer every setting of the left channel to the right side for stereo compression. This function couples both channels of the mpressor: the left side becomes the master and the right becomes the slave. Only the control voltage signals will be linked, though. This means that all audio parameters (Niveau Filter, output gain and bypass switch) still have to be set individually for both channels. This circumstance is a side effect of the electronics for both channels being exactly identical, which results in a reduced channel crosstalk and better overall audio quality.

The fact that you can also set negative ratios with the mpressor makes very extreme effect sounds possible. The complete compression process can be turned upside down, and the processed signals sound as if they were played backwards. Let us take a keyboard sound as an example to understand this reverse effect. The dynamic process of a chord consists of a loud attack, the decay and the release phase. Because of a negative ratio setting, especially loud parts will be reduced in a very strong way. A medium attack time and the already mentioned Auto Fast function are a good help for achieving this effect without clicks and distortion. In this application, the release controller determines the speed or the character of the specific sound while it is getting louder. This inverted character of the keyboard sound - starting quietly and then getting louder in its progress - leaves the impression as if it was played backwards. Experimenting with the already mentioned Anti Log function in order to further emphasize the reverse effect is another truly rewarding option. In order to make this really cool sounding effect happen, though, one has find the correct relationship between threshold, release and ratio.

As an mpressor newcomer one tends to be a little bit too careful – so if you want to try it yourself, do not worry to go for gain reduction values of 20 dB and even more. And don't forget to set the bypass button as well as Niveau Filter and output gain equally for both channels if you are processing stereo material in order to achieve this effect. Another possibility of using the mpressor with great benefit in a mix is to process the transients. In order to sound a bit different than the “I compress every signal in my production at least 5 times” mixes, especially drums and other percussive signals can be enhanced with the mpressor excellently, even if the amount of compression is not so high.

The concept behind this way of improving the transients is pretty easy to explain. Here, one does not increase the overall loudness of a signal in order to give it space in the mix. Instead, one makes the signal sound more tight and aggressive so that it will cut through the mix. To do so, we start to compress the signal with a high or maybe even slightly negative ratio setting and a fast release time. The result of this would be complete over-compressed with gain reduction values of 10 to 15 dB. But the mpressor has another very interesting and unique feature to compensate for this: The Gain Reduction Limiter. This function can be activated with a dedicated switch and its amount can be set with the GR Limit controller. In our transient processing example, we can use this feature to set the total amount of gain reduction to a maximum of 6 dB. In this mode, the mpressor does not allow any higher gain reduction than these 6 dB.

The result is that we can hear the effects of a compressor working hardly, but without the strong amount of gain reduction that would usually go with it. This way, our signal receives just the right amount of kick in the important attack phase. The mpressor gives studio work a creative push and invites to experiment. Admittedly, the unit takes a little bit of practice in order to understand all of its new possibilities, but all the more light bulb moments you will encounter. Just boldly sail in and use this tool not only as a compressor, but as an effects processor, too. It is save to say that the sound dimensions the mpressor opens will inspire anybody from the experimental electronic musician to the classic rock engineer.

A trick that is used by many studios for many productions is a parallel stereo compression of the drum tracks. To do so, create a stereo submix of your drums in your DAW. Compress this stereo buss quite heavily, for example with a ratio of 1:10 and short attack/release times. This strong amount of processing will sound as if the track was recorded with ambience microphones: not a lot of punch, but long decay of toms and cymbals. Now add this heavily compressed stereo mix to your normal drum track, and there it is: the sound you always wanted to produce.