FabFilter Pro‑Q 2 Help
One of FabFilter Pro-Q 2's best features is that it's very easy to equalize both stereo channels in a different way. This is a great way to surgically remove unwanted sound artefacts, or even to add stereo effects.
To make this even more powerful, Pro-Q 2 offers both Left/Right and Mid/Side channel modes. In the default Left/Right mode, each EQ band works either on both stereo channels, or on the left or right channel only. This is controlled by the stereo options at the lefthand side of the band controls:
As soon as one or more of the EQ bands are operating on a single channel, the EQ display switches to per-channel mode, where it shows two overall frequency response curves: a white one for the left channel, and a red one for the right channel, as shown by the picture above.
The Channel Mode parameter in the bottom bar switches between Left/Right and Mid/Side operation. In Mid/Side mode, the incoming stereo signal is converted into Mid (mono) and Side parts, which you can then easily filter independently. This is often an even better way to fix artefacts or modify stereo information because it represents the stereo signal in a more natural way.
In Mid/Side mode, everything works as described above, except that the stereo options above change to M/stereo/S buttons. In addition, the display shows the two overall frequency response curves in white (Mid) and light blue (Side) so you know at a glance in which mode Pro-Q 2 is currently operating.
Independent channel equalization is very useful when dealing with stereo audio containing unbalanced frequency content over the stereo field. Let's say you want to combine a stereo drum recording with a stereo accoustic guitar recording. The drum recording contains more low-mid frequencies in the left channel (for example a low tom-tom), and more high frequencies in the right channel (like cymbals or a hi-hat). The guitar sound, recorded with a mic capturing the sound-board/hole panned left and one capturing the fretboard/neck panned right, might have similar frequencies as the drum recording, making it hard to combine them in a balanced way. By using independent left/right channel EQ-ing, it is possible to balance these elements so that they do not fight each other. Instead of EQ-ing the whole stereo track of the drums and guitars one can simply EQ where it is necessary to get the two elements to complement each other.
Mid/Side EQ is perhaps most commonly used to bring some stereo elements further up within a recording, either by cutting certain frequencies in the mid channel or by boosting the wanted frequency range in the side channel. It is great for adding a bit of depth to typical hard panned rock/heavy guitar recordings where you boost the "bite" frequency range of the guitars (around 2-4kHz) with a quite narrow eq. Combine this with cutting some of the "mud" away from the side channels will give the illusion of huge guitars that still sit well within a mix.
Independet Mid/Side equalization is also often used during mastering. For example, raising high frequencies in the Side channel can freshen up the sound, while a low-cut filter in the Mid channel can work very well to clear up the low end.
Consider using linear-phase processing when filtering both stereo channels (either in Left/Right or Mid/Side mode) differently to avoid introducing unwanted phase changes.
FabFilter Pro-Q 2 can also work as a mono equalizer plug-in, but in this case the stereo options and the Channel Mode parameter are not available, of course.
When loading 'stereo' presets (containing EQ bands that work on e.g. the left or right channel) in the mono version of Pro-Q 2, all EQ bands are treated as if they work on the mono channel. You should be aware that this can sometimes yield unexpected results. For example, if a stereo preset contains two bands working on the left and right channels respectively, at the same frequency, with gain=+10 dB, this will result in a +20 dB peak in the mono version. Therefore it is best not to use any presets that use per-channel processing in the mono version of Pro-Q 2.
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