Can you even hear below 30Hz? Highly unlikely. 20Hz is the low threshold of human hearing. Why even worry about it?

hueseph, I don't think it's a matter of whether one can hear below 30 Hz. This is an important discussion. I find it quite necessary to frequently filter out sub sonics. Sub sonics can actually modulate your audio, adversely affect dynamic range limiters & pass a lot of gas, sonically that is. So it's actually prudent with instruments that do not have much low frequency harmonic content to high pass filter those particular instruments. This is certainly keeps things a little cleaner and helps to isolate the most important parts of the audible spectrum that we really need to hear.

Most of this type of filtering is readily available in just about every piece of professional & semi professional software. Whether you are utilizing FFT filters, parametric filters, graphic equalizer filters, etc.. We are talking about fundamental bandpass equalization. I mean how much of that 20 Hz of the bass drum do you think you really need for it to sound like a monster bass drum? Answer: not much. And in many ways, I do similar filtering to the high frequency content in many instances. I don't want a full bandpass of 20 to 20,000 Hz. I want everything to be in its place where applicable. So filter out that grunge I say. You're not going to miss it and neither will we.

Remember to clean up your frequency response after making your bed
Mx. Remy Ann David

hueseph, post: 351439 wrote: Can you even hear below 30Hz? Highly unlikely. 20Hz is the low threshold of human hearing. Why even worry about it?

We may not be able to hear it, but it still ends up taking up energy that could be better spent making the rest of the frequencies that we can hear louder. Sure high compression or limiting can do that, but I like to give the music some dynamics and still be loud. Most mastering engineers have steep effective HP filters, but I am wondering if anyone has found a useful VST plugin that dramatically reduces or removes 0-20Hz energy. Most graphic and parametrics that I have found only go down to 20Hz.

Any high-pass filter automatically blocks d.c. An HP filter set to 20Hz means that its response is 3dB less at 20Hz than at (say) 1KHz, but it keeps on going down below 20Hz and has no response at all (infinite attenuation) at d.c.

If you are getting the very low frequencies in your mix after applying HP filters on all input channels, you have something else wrong. As an example, I have seen this happen in digital mixers where an effects processor fed by an Aux and returning via a stereo input wrongly had some Aux level set in the stereo channel. This created a d.c. coupled feedback loop, and the d.c. level ramped up over a time course of a few minutes and then there was a loud crack as it wrapped around. Easy to diagnose once you you are alert to the possibility, but very puzzling to those who have never seen it before.