Compression is one of the most commonly used methods of processing audio in the modern recording, mixing and mastering. This helps to improve the intelligibility of vocals, tame overly aggressive snare drum, and limit the dynamic range through the mix so that the listener does not have to continue to adjust the volume on the playback system.
Multiband compression divides the frequency spectrum into different sections, or strips, so that each of them has its own unique parameters of compression. This allows a longer attack time for the low band of that bass drum to punch through, while keeping a shorter attack time in a higher band to keep the guitar in check. By using a multiband compressor, it is possible to closely tailor the compression to the different elements in a mix and compress the recording more transparently than with a standard single-band compressor.
The front panel has the compressor section, crossover section, and the big graphic display.
THE GRAPHIC DISPLAY has the ability to control:
- The make-up gain of the compressor (adjustment up and down);
- Crossover (adjustment to the right and to the left).
- RMS detection, a mathematical means of determining average signal levels. The implications of using a compressor with an RMS detection are that the compression will sound natural, but short duration, high amplitude sounds may pass through at a higher level than you expect;
- Peak mode, the gain control responds more accurately to brief signal peaks than in the RMS "averaging" mode. This ensures peaks are more accurately controlled, but at the same time introduces a greater risk that the broadband audio will be squashed unacceptably whenever a loud, short transient sound occurs. For this reason, it may be most effective to use Peak compression when treating individual drum and percussion sounds prior to mixing.
- Threshold determines the input signal level above which the compressor begins to attenuate the signal (adjusting the fader and on corresponding display);
- Ratio determines the intensity of the signal attenuation (adjusting the knob and on corresponding display);
- Knee controls whether the bend in the response curve between below threshold and above threshold is abrupt (hard) or gradual (soft). A soft knee slowly increases the compression ratio as the level increases and eventually reaches the compression ratio set by the user. A soft knee reduces the audible change from uncompressed to compressed, especially for higher ratios where a hard knee changeover would be more noticeable (adjusting the knob and on corresponding display);
- Attack is the time that elapses between the excess of the threshold value and the time to achieve a predetermined ratio (adjusting the knob and on corresponding display);
- Release is the time that elapses between the way the input signal level has fallen below the threshold, and the moment when the compressor stops to weaken the signal (adjusting the knob and on corresponding display);
- Make-up gain. Because the compressor is reducing the gain (or level) of the signal, the ability to add a fixed amount of make-up gain at the output is usually provided so that an optimum level can be used (adjusting the knob and on corresponding display, as well as the graphic display).
- Along the lower edge of the graphic display are 3 crossover displays (Low, Mid, High). These can be dragged to adjust the crossovers;
- Filter mode:
- LR4 - fourth order Linkwitz–Riley crossover is probably today's most commonly used type of audio crossover. They are constructed by cascading two 2nd-order Butterworth filters. Their steepness is 24 dB/octave (80 dB/decade). The phase difference amounts to 360°, i.e. the two drives appear in phase, albeit with a full period time delay for the low-pass section;
- LR8 - eighth order Linkwitz–Riley crossover have a very steep, 48 dB/octave (160 dB/decade) slope.