HPF/LPF - how and where do they fit in?

Discussion in 'Effects [BG]' started by oomo, Aug 7, 2022.

  1. oomo


    Jun 21, 2021
    Reading another post asking about whether people use effects or not, saw a surprisingly large number of people using high/low pass filters.

    I've never even considered these, can anyone explain how and where they might be useful?

    Probably also a dumb question, but how do these differ from just turning bass or treble down in eq or amp? I'm guessing maybe they're a hard cutoff at some frequency?
  2. gtirard


    Feb 22, 2020
    Paris, France
    I'm not a specialist, but the HPF (High Pass Filter = Low Cut Filter) cuts everything bellow the selected frequency, it's different from a regular EQ because it's a hard cutoff as you have guessed.

    Bellow a certain frequency, human don't really the lows, it only adds mud, and it puts a lot of strain on the speaker. HPF helps cleaning the sound, and keep the speaker efficient for useful frequencies. Usually, you set the cutoff frequency depending on the room accoustics (as always, "use your ears"). It is recommended to place it last in the signal chain, just before the amp.

    Low Pass Filters are the opposite, it helps removing high frequencies when they're harsh, for example after a distortion or fuzz pedal, in order to soften the tone.
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  3. furym

    furym Supporting Member

    Aug 31, 2014
    Carthage, NC
    LPF can also be helpful to roll of those upper frequencies and mimic a bass cab roll off. Especially helpful for IEM gigs.
  4. It sounds counter-intuitive, but too much low end just robs power from your amp and goes to amplifying stuff we can barely hear. That can also a lot harder on your speakers. If you can remove that junk, it helps makes your tone better. The HPF has a steeper bass rolloff curve than the normal amp controls.This makes it easier to take out the problems without cutting into what you want to keep.

    OTOH... If you just want to replicate mating calls for whales then ditch the HPF. :smug:
  5. oomo


    Jun 21, 2021
    Thanks all, that makes more sense now. So sounds like they're more for dealing with unwanted frequencies at either end of the spectrum, and something you'd have last in your chain, possibly always on.
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  6. Roland GR 88

    Roland GR 88 Commercial User

    Sep 16, 2013
    Ontario Canada
    Retail store manager
    Exactly. I run a few effects in front of the amp and a HPF in the effects loop.
    I use a Broughton that cost $75.00 and wish I’d done it years ago. Probably the most useful pedal I’ll ever own.
  7. dave64o

    dave64o Talkbass Top 10 all time lowest talent/gear ratio! Gold Supporting Member

    Jun 15, 2000
    Southern NJ
    Sometimes a picture is worth a thousand words. This is a comparison of a shelving EQ, which is what the typical bass control is vs. an HPF (credit to ProSoundWeb.com for the picture):


    Notice how an HPF drastically and continiously reduces the level of the low frequencies as the frequency decreases. Compare that to a shelving EQ, which reduces all low frequencies by the same amount, giving you a graphical representation of the level reduction that kind of looks like a ... well, a shelf.

    The article the picture came from can be found here.

    Hope that helps!

    EDIT: I'll add that I have a Broughton Always-On HPF mounted under my pedal board as the last unit in my signal chain. There are some times when I adjust the frequency to its lowest level so that there's minimal effect from it. For example, I do that when I send a DI signal to the house PA (the house sound guy can then adjust the low end as needed for the room) or when our sound guy brings his full PA (which includeds a subwoofer). I also do that when I use my Mesa D-800+ amp, which has an adjustable HPF built in. But I sometimes use other amps that don't have the adjustable HPF and our practice space PA doesn't have a sub, so it's a useful "pedal" in those cases. I can set the HPF frequency as needed, sometimes up to about 50 or 60 Hz, and and also turn up the bass and low mids on my amp. That creates a surprisingly deep tone without boominess and works really well.
    Last edited: Aug 7, 2022
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  8. mrjim123

    mrjim123 Suspended Supporting Member

    May 17, 2008
    I use an adjustable Broughton HPF. It is most useful in taming overly boomy bass frequencies, such as might occur in a boomy room, sitting on top of a hollow stage, or when you sound man has no idea what bass guitar sounds like and wants to impress everyone with his subs. The HPF sits on my pedal board between my Snark tuner and EHX Pitchfork.
  9. J Wilson

    J Wilson

    Apr 22, 2022
    An Undisclosed Location
    I was introduced and learned filters in the Alembic community, as that's the 'tone control' on Alembic instruments, and their remarkable SuperFilter stereo rackmount.

    My Elan Five had their Signature electronic control circuit. In a TB where guys are buying filter pedals like mad, imagine . . . . if they were on the bass. Here's a quick explanation of that control layout with Dave, and Mica Wickersham, daughter (and GM of Alembic) of Susan and Ron Wickersham, the founders. RW always favored filters over conventional EQ methods, since Alembic's inception in the 70's.

    Signature Controls (alembic.com)

    There's not really a parallel with any sort of conventional EQ you may be used to, but if you're of a certain age and experience you may have encountered some of the older 'cut-only' graphic EQ's that used to be more common in recording and some FOH applications which seem to be the closest approximation of filters. It's a completely different world than rolloff's or active cut/boost, but once you wrap your head around it, as clean as a surgical suite and without the excesses the other methods can cause.
    Last edited: Aug 7, 2022
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  10. Isaac_James


    May 20, 2021
    Eugene, OR
    I'm a big fan of the Broughton HPF/LPF pedal. I use mine last in my effects chain; I know some folks prefer to use separate pedals and place the HPF first and the LPF last but I wanted to keep my setup as simple as possible. I keep mine on all the time unless I'm experimenting.

    When I'm running a clean signal, it's a pretty subtle effect. I can hear a difference if I know what to listen for, but it doesn't jump out and grab you. It's when I turn on the fuzz that the difference really shows up - with my LPF dialed in at somewhere in the 3-4kHz mark, a lot of the harsh overtones from my Big Muff just... go away. And with the HPF set to 40Hz, the subsonic mud goes away too, leaving only the creamy center. I have been meaning to make a video demonstrating this and just this morning it's come up twice, so I'll try to do that tonight and share it.
  11. mrcbass


    Jan 14, 2016
    Sacramento, CA
    I use it to tame unwanted frequencies. Before I started using it, my bass felt very boomy or puffy in almost every room. Sounded like I was plucking with marshmallows and I had a very hard time cleaning it up. With the HPF, I can dial out the boom in any room in a second. The LPF function an help tame issues on the higher spectrum. I uses it some, but not nearly as much as the HPF.

    If I was forced to reduce my pedal board down to one pedal, this is it.
  12. Thumpin6string

    Thumpin6string Supporting Member

    Apr 25, 2013
    Shoals Indiana
    I run my Broughton HPF/LPF always on. The HPF gets rid of the mud which destroys speakers and it makes the amp more efficient (seems louder when on). It also helps to cut through the mix. I use the LPF to cut just enough highs to get rid of annoying string squeak and clank. Besides my compressor, it is one of the best purchases I've made.
  13. mdogs

    mdogs Supporting Member

    I have a Broughton always on HPF which does not tell you to which frequency it is set. I worried about this when I bought it, but once I started to use it, I realized the genius behind it, you have to use your ears to decide where to set it.

    I played a show a couple of weeks ago, very large outdoor stage, my power supply on my pedalboard crapped out. I could live with my sound on stage, but when I heard the soundboard recording I was not happy. Apparently the sound guy did not roll off the low end garbage and I sounded bad. If you don’t want something in your sound, don’t send it to the board.
  14. lomo

    lomo passionate hack Supporting Member

    Apr 15, 2006
    It will work if placed last, but IMHO it makes more sense to have it early (right after a tuner), because for most commonly used effects, there's no added benefit to "affecting" a frequency that's too low to be desirable. I prefer to delete those frequencies from the get go. YMMV. My Octaver and envelope filter sound better to me if placed after my HPF.
    Last edited: Aug 7, 2022
  15. Skip Chucker

    Skip Chucker

    Dec 9, 2018
    Definitely want that HPF to go first. That way you don't get an octaver, or a compressor, or an envelope filter triggering off of extreme low end. It's the first thing that I plug into on my board. The LPF comes much later in the chain- I use the LPF either as an outboard tone knob, or to keep fuzz out of the house PA horns and tweeters (because I think fuzz sounds awful when not through anything but a speaker).

    I also have one in the effects loop of my SWR SM-400s, and it stays with that amp.
  16. For bass I put a low cut at 30ish, just below the fundamental for a low B string. Most sound systems can’t reproduce frequencies that low with good efficiency; I set it a little higher for a four string bass.

    For regular bass I put a high cut at 6.5k, because there really isn’t anything up that high for us. If I play my bass VI I may go as high as 8k, which is also where I put it for my electric guitars. (My electric guitars get the low cut higher). There isn’t really anything above 8k except hissing.

    I combine these with an EQ to adjust my sound as needed. I try as much as possible not to boost frequencies unless I have to; instead I prefer cutting other frequencies. On bass I usually don’t have to do much but my electric guitars need much different eq settings from each other, to sound good.
    Last edited: Aug 7, 2022
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  17. Cave Puppy

    Cave Puppy "Humph Bo, he's wond!" - John Lennon

    Jan 13, 2015
    Came here to say this.
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  18. Cave Puppy

    Cave Puppy "Humph Bo, he's wond!" - John Lennon

    Jan 13, 2015
    This is why I have my DI last on my board.
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  19. Phaidrus


    Oct 25, 2009
    Any other HPF/LPF pedal except for the Broughton? Looks like it is not available in Europe.
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  20. I bought an old Aria "Parametric EQ" and haven't really used it. You can set it for HPF, mid boost, or LPF. Playing in a loud rock trio where everything sounds good as is, I kinda don't want to mess with it. Still...