The free plug-in this month comes from Brainworx, who claim that their bx_subfilter is `just the ticket for adding clarity and definition to tracks that have troublesome low frequencies`. This plug-in is essentially a resonant high-pass filter, and while you will undoubtedly already have tools in your arsenal that can perform the same function, the bx_subfilter does the job quickly and effectively.
The idea here, is that the HP filter tames the extreme low end of the sound source, whilst adding definition and punch at the cut-off point. You could achieve the same thing using a non-resonant HP filter and a peak filter, but bx_subfilter is a useful one-stop-shop, and it performs job very well.
The plug-in has a simple interface, made up of one slider and two knobs. The slider, labelled `Resonance`, controls the shape of the peak filter, `Tight Punch` controls the cut-off frequency, while `Low End` is a fixed band pass filter that can boost the low-end of your sound source. The frequency of the `Tight Punch` control is displayed, so that you are able to make sure you are cutting at the correct frequency for the key of your track.
The plug-in is available as an AAX plug-in in DSP, Native and Audiosuite versions. VST2, VST3 and AU are also provided. Both Mac and PC are supported in 32 and 64 bit versions. You can download the bx_subfilter from the Plugin Alliance website, and although you will need to sign up to the site to get it, the plug-in is free.