The bx_subfilter is the filter section from the bx_subsynth plug-in. It's not news that the secret to big bass lies in controlling the bottom end, and the humble high pass filter becomes hugely more interesting when it is a resonant filter.

Resonant Filters Are For Synths Aren't They?

As someone who got his first analogue synth aged 14 I've always found the idea of adding a resonance control to a filter the most natural thing in the world but to many who come to filters from a studio or live perspective having a peak at the corner frequency could be seen as a flaw, spoiling the transparent operation of the filter. Resonant high pass filters are an obvious choice for anyone who has ever used a combination of a high pass filter with a low shelf boost. I for one know I have have done this many, many times. A resonant high pass filter combines the low cut and the boost elements into a more convenient package and as such is perfect for sculpting the bass energy in a kick drum.

bx_subfilter

While I like F202, the bx_subfilter is a slightly different tool. The F202 is a general purpose HPF/LPF. The bx_subfilter is a more specialised tool which you could use on other sources but I definitely see as a kick drum processor. Unlike most EQ type plug-ins if doesn't feature an EQ curve display and definitely no spectrum analyser, this plug-in requires you use your ears. A word of caution here, making decisions like this about deep bass require accurate monitoring at bass frequencies, something not everyone has. The controls are simple but some need explanation:

• Gain In/Out - Self-explanatory but essential as this filter can introduce large boosts which have to be balanced at the output.
• Tight Punch - This is the filter frequency control of the high pass filter, the range is specifically tailored to bass instruments - 20Hz to 90Hz.
• Resonance - This three way switch controls the size of the resonant peak, it has three values: Low, high and extreme.
• Low End - This is the level control for an additional, fixed bandpass filter which operates around 90Hz. Use this to dial in some extra bottom end independently of the resonant high pass filter. 

bx_subfilter In Use

This video from Plugin Alliance shows the bx_subfilter in use on a kick drum.

bx_subfilter Is Free

Not only is bx_subfilter very useful plug-in but it's absolutely free. Head over to the Plugin Alliance Website to get your copy.