Hi pass filter - essential or snake oil?

[SecretSam]

Thanks Dave. I'll look that up (or more likely, get someone competent to look it up).

I have been reminded yet again of the breadth and depth of the expertise given freely on the forum. I'm really grateful to you all.

[SecretSam]

I suspect that the 12dB filter slope might have been chosen with phase shifts in mind.

+1 to this - many of the hi(-ish) end analogue boxes (such as Dangerous Music BAX EQ and Silver Bullet), tend to offer 12dB/octave low cut filters for this reason.

Butterworth filters are best for lowcut filters, as they roll off less near the passband (typically 12db/octave works well, especially with a tiny boost an octave above).

The SSL Fusion does offer 18dB/octave though.

Martin

The Broughton Audio pedals from Canada are all 12dB/octave as well. It seemed like a rather shallow slope, but clearly there is a scientific explanation.

[Wonks]

Probably because 12dB is enough to reduce subsonic frequencies to a level where they won’t cause any damage, but the filter is ‘gentle’ enough on the lower bass frequencies not to be noticeable or cause resonance when brought in.

And as an extra filter on a bass amp setup, it is adding to a situation where a lot of manufacturers don’t think it necessary to build one in.

[BigRedX]

As a bass guitarist who uses a Hi-Pass filter live, the advantages are definitely noticeable. For a conventional bass rig, my preferred device was SFX Micro Thumpinator, however since I since I switched to a Line6 Helix and RCF 745 powered cab, I simply use the global EQ on the Helix to do the same thing.

The HiPass filter does wonders to "tighten up" the bass sound as it is removing all those frequencies that are essentially inaudible to the average human but are taking up amp power and speaker excursion to produce.

When I was using the Thumpinator it went as close to the end of the signal chain as possible (last device in the amp's effects loop) so that it would remove all unwanted low frequencies, especially anything being unknowingly boosted by other devices further "upstream".

Bear in mind that most Class D bass amps now include some sort of Hi-Pass filtering as standard, so having a dedicated unit is becoming more and more redundant.

For the guitar unless you are favouring a very bass heavy sound and significantly down-tuning it's not as important.