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funkydoug

High Pass Filters

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1 minute ago, Al Krow said:

Ah, that's says to me we are trying to achieve different things (which is fair enough).

My goal is simply to eliminate the sub-sonic 'crud' below 20Hz (and nothing more or less) to protect my cabs and tighten up the low end. I'm actually hoping to 'hear' very little in terms of tonal change (the less the better!) but to see / feel quite a lot in terms of speaker excursion being reduced.

With the combination patch I seem to be getting 90% of the way there, so that works for me.

I thought that was what a HPF was for ! My TKS cabs are FRFR so I'm trying to narrow the bandwidth at the bottom end to replicate the response of "normal" cabs. 

If your cabs roll off at 40hz then any HPF you add on top of that will double the rolloff curve. 

Speaker excursion isn't a bad thing - just over excursion. I applaud your belt x2 and braces outlook though :D

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1 hour ago, Al Krow said:

Ah, that's says to me we are trying to achieve different things (which is fair enough).

If I wanted to boost the 30 to 50Hz range, I can easily do that with my amp EQ. In practice, I find myself slightly cutting rather than increasing the bass EQ to prevent a muddy / boomy sound and the boost will, if anything be in the mids, to make sure I am cutting through in a live mix.

For HPF purposes, my goal is simply to eliminate the sub-sonic 'crud' below 20Hz (and nothing more or less) to protect my cabs and tighten up the low end. I'm actually hoping to 'hear' very little in terms of tonal change (the less the better!) but to see / feel quite a lot in terms of speaker excursion being reduced. With the B3n LoEQ combination patch I seem to be getting 90% of the way there, so that works for me.

The HPF is highly valuable as an EQ tool as well though. If you set it to cut at 100 Hz and boost the bass control at 30 or 50Hz the net result may be a boost at something like 60-200Hz depending on amount of bass boost and details of you bass control's response curves, with a steep dropoff below the bass peaking. Voila, you've just changed everything about how you tailor your low end. By way of example, here's what happens in one of my amps when I set the bass control at 6/10 (a mild boost), then sweep the HPF over its entire range, which in my case is something like 25-130Hz.:

 

PW7_1_1_HPFvsBassControlat6_4.jpg

 

So there's your boost in the low mids, if you want it, although a mild gain tweak may be needed too. The beauty of this approach is that you can tailor your bass EQ around specific room nodes that account for much or all of that "boominess" we all fight against so often. In practice this is a lot easier than it looks at first blush, at least IME. It's a very well known old school approach to EQ, as seen in classic Pultec EQs for instance. But if you just want to kill out of band mush, all good to that as well.

 

Edited by Passinwind
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I've not seen any measurements of it but I wouldn't be surprised to see that the Tonehammer is similar. With the AGS switch on (or the Drive control turned up on the amp versions) that engages a LPF and HPF, then you can dial in some serious bass boost yet it sounds tight rather than fill the room with murky sub bass.

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3 hours ago, Passinwind said:

The HPF is highly valuable as an EQ tool as well though. If you set it to cut at 100 Hz and boost the bass control at 30 or 50Hz the net result may be a boost at something like 60-200Hz depending on amount of bass boost and details of you bass control's response curves, with a steep dropoff below the bass peaking. Voila, you've just changed everything about how you tailor your low end. By way of example, here's what happens in one of my amps when I set the bass control at 6/10 (a mild boost), then sweep the HPF over its entire range, which in my case is something like 25-130Hz.:

 

PW7_1_1_HPFvsBassControlat6_4.jpg

 

So there's your boost in the low mids, if you want it, although a mild gain tweak may be needed too. The beauty of this approach is that you can tailor your bass EQ around specific room nodes that account for much or all of that "boominess" we all fight against so often. In practice this is a lot easier than it looks at first blush, at least IME. It's a very well known old school approach to EQ, as seen in classic Pultec EQs for instance. But if you just want to kill out of band mush, all good to that as well.

 

 

Very enlightening, thank you!

And also reassuring me that I wasn't imagining things... I have sometimes used the HPF on my Mesa D800+ adjusting it to what's probably around 80-100Hz and turning up the bass control a bit. It seemed counterintuitive to me, but I liked the way it sounded. I thought people would say I was mad :D !

 

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1 hour ago, mcnach said:

 

Very enlightening, thank you!

And also reassuring me that I wasn't imagining things... I have sometimes used the HPF on my Mesa D800+ adjusting it to what's probably around 80-100Hz and turning up the bass control a bit. It seemed counterintuitive to me, but I liked the way it sounded. I thought people would say I was mad :D !

 

Sound engineers have actually been using that general approach pretty much forever. Yel_wink.gif

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On 01/02/2018 at 13:25, dood said:

The best option before spending any cash would be to find out if you are sending excessive sub-sonic frequencies to your speakers in the first place. You can do this relatively cheaply either with your computer or smartphone - you may need an audio interface too in some cases. I use a few free apps on my phone and either a Line6 Sonic Port or for other situations, a calibrated FRFR microphone.

Something to think about I guess! Also handy for testing the actual frequency response of a whole bunch of devices and components! Tone stacks to pickups, amp to pedals!

Dood - what free apps on your smartphone are you using on your phone to test? Are you just using the phone's built in mics?

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How are you supposed to test if you are sending low frequencies your cab can't reproduce with a smartphone app if A) the cab can't reproduce the signals and B) the phone mic can't pick them up?  If a tiny speaker in a phone can't produce 20Hz, does that mean a tiny mic would also fail to record 20Hz?

Better to test going from the DI output, or a speaker level DI on the speaker output, straight into a recording interface I would've thought.

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Just whilst we are continuing on our HPF discussions, I thought I'd take a bit of time out this morning to go through this excellent / very helpful thread from the start, as there's been stuff that folk were saying from the outset where, for me, the penny has only recently been dropping on! 

Anyway I've taken the liberty of cutting and pasting some of the comments from our more expert brethren into the attached note (and apologies if I didn't get ALL the 'best bits') which I've found particularly helpful, and which I'm sharing in case anyone else would also find a condensed version of 14 pages of the discussions useful.

 

 

HPFs.docx

Edited by Al Krow
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Hi John, just click on the link HPFs.docx and that should download to your computer.

 

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11 hours ago, Passinwind said:

Sound engineers have actually been using that general approach pretty much forever. Yel_wink.gif

Yep, and that's pretty much the principle behind the classic Pultec EQ (which both attenuates and boosts, so you can carve out the desired low end very nicely).

PS: as a general principle, when applying a HPF to bass guitar, you want to at least eradicate everything below the lowest note, because it's just going to be useless rumble. So for a five string that would be applying the HPF at 31Hz and for a four string 41Hz. And I'd recommend a steep reduction of -24db/octave.

Simplest method is to grab the HPF frequency dial (or computer mouse), close your eyes and start upping the cut-off frequency until you hear it have a noticeable effect on the sound, then dial it back a bit. That then gives you a good starting point for fine tuning.

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Broughton - High Pass Filter DI

https://www.broughtonaudio.com/product-page/high-pass-filter-di

Available from May.

  • The variable high pass filter ranges from 25 to 190 Hz with a slope of 12 dB/octave.
  • Has an additional fixed filter is set at 25 Hz at 12 dB/octave to remove subsonic crud => so this effectively becomes a "Thumpinator Plus" pedal in what it delivers
  • Not cheap at $170 in the US = £170 ish over here
Edited by Al Krow
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On 09/04/2018 at 11:16, Al Krow said:

Dood - what free apps on your smartphone are you using on your phone to test? Are you just using the phone's built in mics?

Wow, I somehow missed this post ha ha h!!

Ok, so I have a calibrated reference microphone designed for iPhone and iPad. I'll have to dig out it's model number. Every microphone is lab tested and comes with a profile file that you then drop in to the app of choice. It's been a little while since I've needed it, but I think the app I am using is AudioTools. I also have OctaveRTA, A-T Tools, N-Track Tuner and Pocket Audio amongst other tools for various task... Well, it might be fiddling about, but they are all really useful for learning stuff as well. 

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20 hours ago, Al Krow said:

Broughton - High Pass Filter DI

https://www.broughtonaudio.com/product-page/high-pass-filter-di

Available from May.

  • The variable high pass filter ranges from 25 to 190 Hz with a slope of 12 dB/octave.
  • Has an additional fixed filter is set at 25 Hz at 12 dB/octave to remove subsonic crud => so this effectively becomes a "Thumpinator Plus" pedal in what it delivers
  • Not cheap at $170 in the US = £170 ish over here

Now that's a neat idea. Bit pricey !

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Cannot recommend a Thumpinator enough.  My sound is a bit inbetween hifi and classic ampeg, has remove 'boom' from a few notes, but has also reduced the amount of volume I need to play with - more efficiency somewhere if you will.  I use mine in the effects loop of the amp.

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Guest oZZma

Anyone has schematics for decent high pass and low pass filters (also as separate pedals)?

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Broughton make HPFs and LPFs. I think they even do a combined HPF + LPF pedal in a compact housing!

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