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

#1,901
dabis said:
And this one plot it's very important to me: I set the HPF at 85 Hz and then the signal goes to my amp head, where I bumped a little the eq., 2dB at 40Hz and 2KHz. Note that the rolloff it's not at 85Hz but at 55Hz due to the impact of the eq. These are my typical live settings.
View attachment 3794409
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In that vein, here's a model from a new DIY amp build I'm doing right now. It's actually a preamp retrofit to one from 2015 that I kept putting off while I was building new ones. Listed control settings are on a scale from .01 to .99, which is an LTspice convention. So basically we're looking at bass and low mid controls at 2 o'clock, treble slightly higher, then the variable HPF swept across it's full range, which in this build is something like 20-145Hz. This would be my basic "scoop" setting in real life, and as you can see the bass peak can vary from ~35 to 240Hz. As I've mentioned a number of times, this interactivity is something I find very cool and valuable, expecially in difficult rooms.

PW8B_FRC.jpg
 
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#1,902
Passinwind said:
In that vein, here's a model from a new DIY amp build I'm doing right now. It's actually a preamp retrofit to one from 2015 that I kept putting off while I was building new ones. Listed control settings are on a scale from .01 to .99, which is an LTspice convention. So basically we're looking at bass and low mid controls at 2 o'clock, treble slightly higher, then the variable HPF swept across it's full range, which in this build is something like 20-145Hz. This would be my basic "scoop" setting in real life, and as you can see the bass peak can vary from ~35 to 240Hz. As I've mentioned a number of times, this interactivity is something I find very cool and valuable, expecially in difficult rooms.

View attachment 3815732
Click to expand...
Awesome. Actually I realized this interactivity reading your posts through this entire thread :thumbsup::thumbsup::thumbsup:. It's like having a parametric low-mid-low control. Seeing that on my homie measurements was illuminating.
 
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#1,903
Passinwind said:
In that vein, here's a model from a new DIY amp build I'm doing right now. It's actually a preamp retrofit to one from 2015 that I kept putting off while I was building new ones. Listed control settings are on a scale from .01 to .99, which is an LTspice convention. So basically we're looking at bass and low mid controls at 2 o'clock, treble slightly higher, then the variable HPF swept across it's full range, which in this build is something like 20-145Hz. This would be my basic "scoop" setting in real life, and as you can see the bass peak can vary from ~35 to 240Hz. As I've mentioned a number of times, this interactivity is something I find very cool and valuable, expecially in difficult rooms.

View attachment 3815732
Click to expand...
Very nice voicing concept Charlie...I'll bet this allows for very musical adjustments plus great utility in almost any setting.
 
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#1,904
Al Kraft said:
Very nice voicing concept Charlie...I'll bet this allows for very musical adjustments plus great utility in almost any setting.
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Yes. @Passinwind would you please let us know something else of this preamp? diagram and/or eq specs?
Also, do you think there's some benefits of having an HPF installed on the preamp (post input gain I mean) rather than as an outside pedal?
 
#1,905
dabis said:
Yes. @Passinwind would you please let us know something else of this preamp? diagram and/or eq specs?
Also, do you think there's some benefits of having an HPF installed on the preamp (post input gain I mean) rather than as an outside pedal?
Click to expand...
Not sure wht Charlie's answer will be, but as a systems engineer (albeit not in this particualr field) my feeling is that any time you can put all the variables within one designer's trade space to work, you will get the optimal synergy in the elements to meet your key design criteria. When that designer also has user experience, you're additional miles ahead as the trades will be made with a full appreciation for what matters most and how things can be optimized for the use case(s).
 
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#1,906
dabis said:
Yes. @Passinwind would you please let us know something else of this preamp? diagram and/or eq specs?
Also, do you think there's some benefits of having an HPF installed on the preamp (post input gain I mean) rather than as an outside pedal?
Click to expand...

I did a build thread on the original version of that amp here: A DIY 500 Watt Bass Head

For the retrofit of my new preamp and HPF/PEQ board I have changed the EQ up a bit, the main difference is that I moved the midrange control center from around 500Hz down to 240Hz. The idea is to just let the parametric EQ section cover all the mid and high midrange now. I found that I rarely used the 500Hz knob (my basses mostly have 700Hz midrange controls already), and almost never bypassed the PEQ, so why not try a whole different voicing this time? So the parametric can sweep from ~270-2.7KHz now, which covers everything between the midrange and treble controls, and can interact with either one or stay out of their way, as desired. Full parametric EQ tends to put a lot of people off and I'm always looking to make things easier and more intuitive, but still very powerful when we need that. I'll know in a few days if I've succeeded in that or not, I guess.
Yel_wink.gif


As for the HPF location, in my case I made that section modular so I could try it in different spots in the signal chain. Where I have it now (post all EQ) allows me to patch in other preamps through the Aux In and then have the HPF avaiable.There is a good case for having it just post- input gain or even completely in front of the preamp input. But in working with one of my tube preamps I worked up the possibilty of intentionally generating subtle distortion in the lows and then filtering out the unwanted subharmonics later, which kind of speaks to how music mixed for AM radio in the fifties and sixties let us hear some bass through a 3 inch speaker. Or later, getting a fat bass response out of an LP without the stylus jumping the groove. In a nutshell, psychoacoustics. Cleaner is not always better IMO and IME, so as usual, it just depends on what you want. Investigating stuff like this is why I bother with DIY building, especially these days when there are so many great commercial products already available.
 
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#1,907
Passinwind said:
I did a build thread on the original version of that amp here: A DIY 500 Watt Bass Head...
Click to expand...
I think I'd been there... all I read earlier there have sense now, :bookworm::bookworm::bookworm:. I will reread during the week. Found interesting the Jensen transformer before the power module...

Passinwind said:
... For the retrofit of my new preamp and HPF/PEQ board I have changed the EQ up a bit, the main difference is that I moved the midrange control center from around 500Hz down to 240Hz. The idea is to just let the parametric EQ section cover all the mid and high midrange now. I found that I rarely used the 500Hz knob (my basses mostly have 700Hz midrange controls already), and almost never bypassed the PEQ, so why not try a whole different voicing this time? So the parametric can sweep from ~270-2.7KHz now, which covers everything between the midrange and treble controls, and can interact with either one or stay out of their way, as desired. Full parametric EQ tends to put a lot of people off and I'm always looking to make things easier and more intuitive, but still very powerful when we need that. I'll know in a few days if I've succeeded in that or not, I guess. View attachment 3816029...
Click to expand...
Sometimes I dream on an EQ that only has 1 parametric control, no bass no treble. Something like 100Hz-2000Hz. I know it's a nonsense but dreaming is free... HPF + 2 peq would be ideal, no bass no treble again :whistle::whistle::whistle:
Passinwind said:
...As for the HPF location, in my case I made that section modular so I could try it in different spots in the signal chain. Where I have it now (post all EQ) allows me to patch in other preamps through the Aux In and then have the HPF avaiable.There is a good case for having it just post- input gain or even completely in front of the preamp input. But in working with one of my tube preamps I worked up the possibilty of intentionally generating subtle distortion in the lows and then filtering out the unwanted subharmonics later, which kind of speaks to how music mixed for AM radio in the fifties and sixties let us hear some bass through a 3 inch speaker. Or later, getting a fat bass response out of an LP without the stylus jumping the groove. In a nutshell, psychoacoustics. Cleaner is not always better IMO and IME, so as usual, it just depends on what you want. Investigating stuff like this is why I bother with DIY building, especially these days when there are so many great commercial products already available.
Click to expand...
Smart and clever.
 
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#1,908
dabis said:
Sometimes I dream on an EQ that only has 1 parametric control, no bass no treble. Something like 100Hz-2000Hz. I know it's a nonsense but dreaming is free... HPF + 2 peq would be ideal, no bass no treble again :whistle::whistle::whistle:
Click to expand...

How about a PEQ plus swept frequency resonant HPF and swept frequency resonant LPF? I know a guy who may be working on that right now...
CoolGP.gif


Although I think Josh Broughton has already made a pedal a lot like that: https://www.broughtonaudio.com/product-page/resonant-filter-equalizer
 
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#1,909
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#1,910
shwashwa said:
yes but it needs a narrow mid band pass, and a blend knob.
good luck getting one though...
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Better than the chance of getting one of mine, unless you want to build it yourself! Why a blend knob though? Looking for an SF-2 type of functionality, or ??
 
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#1,911
Passinwind said:
How about a PEQ plus swept frequency resonant HPF and swept frequency resonant LPF? I know a guy who may be working on that right now...View attachment 3816094

Although I think Josh Broughton has already made a pedal a lot like that: https://www.broughtonaudio.com/product-page/resonant-filter-equalizer
Click to expand...
I was thinking on something like the Alembic most common instrument internal preamp (LPF with a +8dB on the freq. cut, PAN, VOL) but head friendly: Input Gain, HPF with +3dB on the freq. cut, peq. 100-2000Hz, Master. 4 knobs, Class-D module to taste :rolleyes:
 
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#1,912
dabis said:
I was thinking on something like the Alembic most common instrument internal preamp (LPF with a +8dB on the freq. cut, PAN, VOL) but head friendly: Input Gain, HPF with +3dB on the freq. cut, peq. 100-2000Hz, Master. 4 knobs, Class-D module to taste :rolleyes:
Click to expand...

Nice, I like all of that. You might want to keep on eye on my open source preamp thread in the Pickups and Electronics forum, we will be working up DIY standalone resonant HPF and LPF boards quite soon. I won't do clones of anything commercial, but I have been asking for wish lists anyway.
 
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#1,915
shwashwa said:
Yes! Sf-2
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Figured as much. :cool:

I was actually just messing with modeling some similar concepts last night. I never bothered to take a pic of the schematic for the only one I worked on since clones are not my thing, but in retrospect it would have been nice to have to spur some new ideas. I think plenty of the talented pedal designers here on TB could probably get pretty close if they felt like it.
 
#1,916
#1,917
Balog said:
I'm not really sure I understand what "resonant" means in this context.
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There's an explanation and some graphs in the first post of this thread: The Passinwind Open Source Preamp

CliffsNotes: a way of emulating the frequency and transient responses of various pickcups, or possibly also speakers, mikes, etc.
 
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#1,919
Hey ! Finally bought a Carl Martin Contour'n'Boost !

At first, i put the HPF/LPF at the end of the chain and had some issues with my Catalinbread Dirty Little Secret cause the lowest setup for the HPF is at 65Hz and it was cutting out some of the character of the DLS that i liked. The DLS was initially at the end of the chain so i tried to switch both pedals and it worked pretty well.

Also when i first tried the HPF it felt strange cause when the HPF was on, the sound was drastically changing, like i couldn't recognize my tone. So maybe it's because of the cut @65Hz which is too high or it 's because i just heard the real sound of my B string for the first time, i don't know.

But i've been playing for a few days now and i can clearly see some improvements. Especially with my fuzz tone. The bottom end is much clearer and now have a nice, beefy sound. Besides that, the lower mids, which i really like, are now more defined. Also tried to play at full volume and the speaker moves way less when i pluck hard as expected.

So at the end, it got rid of what was wrong and highlighted what was already nice in my tone. A must have for sure.
 
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