Very Low Frequency notch filter - suggestions?

[AlanH]

Hi All,

I'm trying to improve (OK, rescue) a live stereo recording of a choir accompanied by a church organ.

One of the organ pedal notes has excited a very specific resonance in the room, such that 16Hz is swamping the programme content.

I'd like to suppress the 16Hz with a high-Q notch filter, but none of the SAW internal FX or VST plugin EQs I have seen so far have notch centre frequencies below 40Hz.

Does anyone know of a high-Q notch filter capable of operating down to (say) 10Hz or below?

I could slap in a regular low-pass filter, of course, but that tends to wipe out all the surrounding organ bass pedal notes, which is very noticeable.

Any ideas would be welcome!

Cheers - Alan

[CurtZHP]

If it was me, I'd just roll off everything under 20Hz. Most playback systems are lucky to get that low anyway.
If there's still weirdness going on, it could be harmonics of 16Hz messing with higher frequency content.

That said, the closest thing I found that might help is the Tokyo Dawn Labs NOVA EQ. It's fully parametric and goes as low as 10Hz.
It's a free download. I've used it on SAW projects, so I'm pretty sure it's stable.

Good luck!

[AlanH]

Hi Curt,

I'll have a play with the Tokyo Labs NOVA - looks good on screenshots and spec - thanks for the suggestion!

As an interim fix, I've run off a version with SAW's built-in low-cut filter set for 40Hz and it's a reasonable compromise. Just seems odd that SAW's HPF won't go lower than 40Hz, when some interfaces go down to DC (!) - there must be some programming / performance reason, I guess.

BTW I found the 16Hz by rendering a version with SAW's internal EQ set to max boost on lowest channel and all other channels set to max cut. Very visible waveform that measures as 16Hz (62ms period), but who knows how it or its harmonics are interacting with the rest of the programme.

Cheers - Alan

[cgrafx]

You could also look at the Dual-Linkwitz-Riley VST Filter. It goes down to 20hz. Try setting it up as a 20hz high-pass with 48db slope.

There is also a "Simple Linear Phase Linkwitz-Riley Filter" on the same page that may also be useful.

http://www.pcjv.de/vst-plugins/effec...ns/eqs-filter/

[MMP]

If you have Izotope Rx’s Dehum, you can set the frequency to the offending note and remove the first few partials.

[Dave Labrecque]

Definitely scout out harmonics of the fundamental (narrowband extreme boost on target frequencies is how I do it) and notch to taste. I once completely removed a feedback wail from a live musical stage performance. It was (of course) in all the mics. I was very surprised how well it worked.

For ground loop hums, too. Look for those overtones and zap 'em!