NPD: Broughton Audio Resonant Filter Equalizer (RFE)

[MartinB]

Direct from Canada 🍁...

 

Quote

The Resonant Filter Equalizer creates unique tone control by combining a high pass filter, low pass filter, and middle equalizer. Both filters have their own resonance control, allowing a bump at the cutoff frequency, accentuating the effect of the filters. The semi-parametric middle eq includes a variable frequency control.

 

The resonance of the filters ranges from -3dB all the way up to +15dB. The -3dB setting is what you would expect from a standard, non-resonant filter. Adding resonance to the filters boosts the level of the cutoff frequency.

 

The filters have a slope of -12 dB/octave. The filters are the same in performance to the other standard Broughton filters, with the added ability of increasing resonance.

-- https://www.broughtonaudio.com/product-page/resonant-filter-equalizer

So the cool thing this does is let you have a boost in your EQ, immediately followed (or preceded) by a steep cutoff. This can be also be achieved using digital effect like the HX Stomp by combining multiple filters, but to the best of my knowledge the RFE is the only analogue, single-box solution on the market.
 

I couldn't get a head-on photo without shadows or reflections, so here's a bit of the stock one so you can read the labels:

Aaaaaaaand here come the graphs...

First the high pass filter:

Yellow: minimum resonance (-3dB) 7:00 on the dial
Green: medium resonance (6dB ish) 12:00
Purple: maximum resonance (15dB) 5:00

Left trace: minimum frequency (25Hz): 11:00 on the dial
Middle trace: medium frequency (80Hz): 6:00

Right trace: maximum frequency (190Hz): 1:00

 

 

The mid filter:

Yellow: minimum resonance (-15dB) 7:00 on the dial
Purple: maximum resonance (15dB) 5:00

Left trace: minimum frequency (200Hz): 11:00 on the dial
Middle trace: medium frequency (750Hz): 6:00

Right trace: maximum frequency (2kHz): 1:00

 

 

And the low pass filter:

Yellow: minimum resonance (-3dB) 7:00 on the dial
Green: medium resonance (6dB ish) 12:00
Purple: maximum resonance (15dB) 5:00

Left trace: minimum frequency (330Hz): 11:00 on the dial
Middle trace: medium frequency (1.5kHz): 6:00

Right trace: maximum frequency (20kHz): 1:00

 

 

But what does it sound like?

 

Bypassed:

 

 

All controls at "default" (12:00 resonance, 6:00 frequency):

 

So what you're hearing is a small bump around 80Hz, with lows beneath that rolled off. And small bump around 1.5kHz, with highs above that rolled off. The mid filter's not doing anything here.

 

And after some twiddling until it sounded nice:

 
High pass at 1:00 resonance (7dB), 7:30 frequency (60Hz) (all values approximate)
Mid at 10:30 (-5dB), 5:00 (800Hz)
Low pass at 1:00 (7dB), 5:00 (2.5kHz)

 

 

Bypassed with a plectrum:

 

I forgot to write down the settings here, but it's an example of the odd, characterful sounds you can create:

 

 

 

Bypassed with flats, a foam mute, and a Poundland Jamerson impression:

 

 

The RFE can be used to mimic the way old-school speaker cabinets often had a frequency peak right before they started rolling off the lows and highs:

 

High pass at 3:00 resonance, 7:30 frequency
Mid at 1:00, 9:30
Low pass at 12:00, 5:30

Which gives an EQ curve like this:

 

It's pretty cool! As I mentioned, this kind of thing is easy enough to achieve in the digital realm, but there's something very direct and satisfying about having all the physical controls there to be fiddled with. It also works great with guitars, and can be powered with higher voltages in order to take line-level signals - there's probably fun to be had combining this with synths.

[Gareth Hughes]

Thanks for the graphics - really helps get my head around what this can do. Appreciate you taking the time to do this.

[Magister Ludi]

ditto-what he ^ said

 

[fretmeister]

That  seems to be a very good bit of kit!