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High Pass Filter (HPF) and Low Pass Filter (LPF) Mega Thread

#781
Using two HPFs just means you'll have a steeper slope because the effects of the filters add together. Assuming all four filters are 12 dB/octave, if you were to set the D800+'s variable filter at 60 Hz (just as an example), you'd have a 12 dB/octave slope from 60 Hz to 40Hz, then 24 db/octave from 40 Hz to 35 Hz (the FDeck's fixed filter), then 36 dB/octave from 35 Hz to 22 Hz (the D800+'s fixed filter), and 48 dB/octave from 22 Hz on down.

That may be overkill; if I had a D800+, I'd probably experiment a bit to determine whether I still needed the FDeck. If the D800+'s filters do what you need, then maybe you can set the FDeck aside.
 
#782
pfschim said:
so, I did actually read the first 20 pages of this thread, but I did not quite see the answer to this question (admittedly, I may have missed it)

I have been using an fdeck series 3 HPF with my Mesa Walkabout to keep meaningless low frequency info from using up the amps available power.
works great and the fdeck has given the WA some new life this way as it's right on the edge of "not enough clean headroom" for my typical needs.

So, now I have just picked up a Mesa D800+ with its built in HPF. The fdeck is always on since I added it to my signal chain 5 months ago.
Will I be causing any conflicts using both the fdeck, with its fixed 30hz filter and its variable filter set to about 40hz, and the D800+ which has a fixed 22hz filter and a variable sweep filter which I have not settled on its sweet spot yet as I just got the amp yesterday.

If using these 2 HPFs together will not cause a problem in general, is there any advice on how to set them so they work together rather than compete somehow ?

My primary cabs are the exceptional Berg CN112 and CN212 which I use separately, but also combine at times. Jim B rates these cabs 40hz-15khz (but I'd guess that the 40hz is down 10dB at least)

thanks
Click to expand...
Interesting question. I can offer you no expert insight, though I am curious what the slopes on the fixed 22 Hz filter (a bit lower than I expected) and the variable filter are on the D800+. Perhaps @agedhorse can clarify. (The product page -- and the front panel of the amp -- indicate that the variable filter can be adjusted from 30 Hz to 150 Hz.)

The only amp I have with a user-adjustable, variable HPF is my GBE 1200 (from 42 down to 28 Hz, I believe). I've never used my fDeck HPF3 with the GBE [edit: not true -- used it as a buffer with a piezo pickup] as I've always found the built-in HPF to be sufficient with my MAS and AK cabs, but I could see using it if feeding another pre into the power amp input or if using that amp with a (probably very frightened) smaller (or otherwise less robust) cab. Maybe it would be useful when sending a pre-EQ signal to FOH in certain venues, as well... I don't believe that the pre-EQ D.I. is high-passed. Don't know if/how this would apply to your D800+, but might be applicable to other amps.

I don't think the filters in the HPF3 and your amp would "compete" per se -- it's not like they're doing conflicting things -- I'd expect they'd just sum. Could you see some effect from the output impedance of the HPF3 vs. that of your bass? Maybe. When I ran my HPF3 with a passive bass in front of a Monique preamp I noticed that the bass and the pre (specifically the Sensitivity control, which does something with impedance, if I recall correctly) didn't interact as much (noted a similar effect running an active bass into Monique). Could there be some other weirdness -- cumulative phase-shift? -- from "stacking" the two filters (or four, in this case -- two on the HPF3, two on the D800+)? Would it be audible? I don't know. (It might not be much different, in that regard, from running the HPF3 with most other amps with built-in HPF.) That's where I would plug it in and play around. :)

It might be interesting to see the effects of setting the adjustable filters at slightly different frequencies (or even widely different frequencies) vs. setting them to the same frequency. Lots of possibilities. You will, in any case, be getting quite a steep rolloff below 22 Hz!

Since the amp is new to you, you might spend some time familiarizing yourself with it sans the HPF3 before adding that into the path. Depending on where the built-in HPF is relative to the effects loop it might also be interesting to try running the HPF3 into the effects return and listening to what it does on its own (though I don't know if the HPF3, which is unity gain, would drive that properly -- would depend on how hot your bass is and the level of the loop). Might be interesting to try the HPF3 in the loop vs. in front of the amp, too. (When I had my Walkabout, I slightly preferred the results when running it in the loop.)

Curious to see what the more knowledgable cats on this topic chime in with and to hear your impressions as you get some time with the new amp and the HPF3.
 
#783
Craig4003 said:
Using two HPFs just means you'll have a steeper slope because the effects of the filters add together. Assuming all four filters are 12 dB/octave, if you were to set the D800+'s variable filter at 60 Hz (just as an example), you'd have a 12 dB/octave slope from 60 Hz to 40Hz, then 24 db/octave from 40 Hz to 35 Hz (the FDeck's fixed filter), then 36 dB/octave from 35 Hz to 22 Hz (the D800+'s fixed filter), and 48 dB/octave from 22 Hz on down.

That may be overkill; if I had a D800+, I'd probably experiment a bit to determine whether I still needed the FDeck. If the D800+'s filters do what you need, then maybe you can set the FDeck aside.
Click to expand...
More succinctly put than my rambling post (and I thought I'd have the first reply)! Still, it would interesting to play with the two and see.

Generally, though, I favor having less stuff in the signal path if I can help it.
 
#784
Iirc, the fixed filter is about 25Hz and the variable filter is also about 25Hz, when they are cascaded the effective frequency shifts upward to 30Hz. This is due to how the filter parameters/math are defined at the -3dB point individually as well as cascaded.
 
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#786
agedhorse said:
Iirc, the fixed filter is about 25Hz and the variable filter is also about 25Hz, when they are cascaded the effective frequency shifts upward to 30Hz. This is due to how the filter parameters/math are defined at the -3dB point individually as well as cascaded.
Click to expand...
Thanks, Andy. When a frequency is given for an HPF/LPF (like if we say we have a HPF set to 30 Hz), is it generally at the -3 dB/half-power point? And is this what's commonly referred to as the corner frequency?

If I understand correctly, then a 30 Hz HPF is still attenuating the signal a bit above 30 Hz.

Apologies if this has been covered already. I did read the whole thread, but in chunks here and there.
 
#787
MarkA said:
Thanks, Andy. When a frequency is given for an HPF/LPF (like if we say we have a HPF set to 30 Hz), is it generally at the -3 dB/half-power point? And is this what's commonly referred to as the corner frequency?

If I understand correctly, then a 30 Hz HPF is still attenuating the signal a bit above 30 Hz.

Apologies if this has been covered already. I did read the whole thread, but in chunks here and there.
Click to expand...
Yes, correct. This is why the filter alignment is so important, the shape of the response around the corner impacts performance
 
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#788
Stumbo said:
They are not similar. Check out: Passinwind's graphs here.
The slope of the curves is way different so the effects are different.

Would using the volume control on your bass do what you need? Or using the active bass input?
Click to expand...

@Passinwind's post is not talking about the same pedal as what @CH Design is asking about. Passinwind's post is comparing the action of a HPF against a graphic EQ.

The MXR Booster Mini that CH is asking about appears to have a tone control which "rolls off high frequencies" according to the MXR website and Product Manual. But maybe also boosts treble according to Sweetwater?

From Sweetwater:
MXR Booster Mini Pedal Features:
  • Combines the Echoplex's front end with the Micro Amp's boost power
  • +26dB boost (variable) is perfect for breaking up amps and spotlighting solos
  • Tone control dials back or enhances your treble side
  • Great for tone stacking — run into your favorite fuzz or overdrive
  • [...]

I won't pretend to have any clue about the action of that tone control, but it could very well be a simple low pass filter according to the MXR website info. Could be a tilt-EQ or boost/cut shelving EQ according to Sweetwater. I don't really know and couldn't be bothered to look into it any further. :p

Don't forget that even the tone control on your bass is a simple passive low pass filter. Wikipedia
 
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#789
NKBassman said:
@Passinwind's post is not talking about the same pedal as what @CH Design is asking about. Passinwind's post is comparing the action of a HPF against a graphic EQ.

The MXR Booster Mini that CH is asking about appears to have a tone control which "rolls off high frequencies" according to the MXR website and Product Manual. But maybe also boosts treble according to Sweetwater?

From Sweetwater:
MXR Booster Mini Pedal Features:
  • Combines the Echoplex's front end with the Micro Amp's boost power
  • +26dB boost (variable) is perfect for breaking up amps and spotlighting solos
  • Tone control dials back or enhances your treble side
  • Great for tone stacking — run into your favorite fuzz or overdrive
  • [...]

I won't pretend to have any clue about the action of that tone control, but it could very well be a simple low pass filter according to the MXR website info. Could be a tilt-EQ or boost/cut shelving EQ according to Sweetwater. I don't really know and couldn't be bothered to look into it any further. :p

Don't forget that even the tone control on your bass is a simple passive low pass filter. Wikipedia
Click to expand...
I sit corrected. Thanks for the info.:thumbsup:
Btw, I sent a note to MXR-Jim Dunlop and asked about the frequency range and slope.
 
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#791
Stumbo said:
I sit corrected. Thanks for the info.:thumbsup:
Btw, I sent a note to MXR-Jim Dunlop and asked about the frequency range and slope.
Click to expand...
Per MXR/JimDunlop.com email, on the the specs of Booster Mini pedal LPF:

"We do not release information regarding the tone filter for this pedal.

Best regards,
Jon
Jon Fryman
Electronics Technician
Dunlop Manufacturing, Inc.
707-745-2722"
 
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#793
Question for the HPF sages and disciples: I have two sealed Ampeg cabinets, an 810E and a 410HE. Given the nature of a sealed cabinet, do you find a variable HPF to be a good addition for a live setup with cabs such as these?

My go-to amp is a GK 1001RB-II that in "4-string mode" already has a gradual HPF starting around 60 Hz, which also is right where the Ampeg cabs start rolling off according to their spec sheets. I also run my DI out as post-EQ so this affected signal also is going to the mixing board and I only have four string P and J Basses (and a Bass VI for fun). Looking at Eminence's suggested cabinet design documents for drivers intended for this type of cabinet, they often recommend a 75 Hz HPF, however, hence my curiosity. I can't say I've ever felt like I've been hurting for headroom with a 700 watt amp feeding an 8x10, but was wondering if a HPF would have a tangible effect with this setup. Thanks!
 
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#794
With a sealed cabinet, the three benefits of a HPF would be for additional driver protection, for tone shaping where you may prefer the reduction in distortion if driving the speaker hard where the cabinet is well into rolling off, and for improving an amp's performance where it (and the speaker) may not be quite enough rig for the gig.

(Could also be a combination of all three reasons)
 
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#795
beans-on-toast said:
A version of a combined high pass and low pass filter is a wah-wah pedal.

It is a notch filter that is moved up or down when the pedal is rocked. There are wahs that allow the width of the notch to be varied as well as adjusting the center frequency with a knob. The latter is useful for those that want to set the wah at a fixed position. This effect is available both for guitar and bass.
Click to expand...

Is it a Notch ( V shape), or Band Pass ( ^ shape) filter?
 
#797
NKBassman said:
Is it a Notch ( V shape), or Band Pass ( ^ shape) filter?
Click to expand...

In editing the post to clarify, it got deleted. Let’s start again.

A wah is usually a sweepable bandpass filter, but it can also be designed as a notch. It can also be a variable low pass filter with a resonant peak.

There is a bass wah that has a pot to set the frequency rather than using the pedal. This is for those that want to fix the tone without worrying that the pedal will move. It’s an interesting effect that can be used to make the bass stand out.
 
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#800
Stumbo said:
Possible alternatives to HPF/LPF Pedals? Modeling Pre-amps or pedals or cab sims?

Anyone using pre-amp or pedals or cab sims that include H/LPFs or that automatically cut lows/highs as part of the cab sim?
Click to expand...
Absolutely not sure, and admittedly too lazy to do the research tonight, but I suspect that the Tech 21 VT Bass series of products may have exactly some of what you're suggesting baked into their circuitry. I'm almost positive just from listening to it that my VT Bass V2 pedal has varying degrees of these two elements as part of the character knob position.
 
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