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

Discussion in 'Amps and Cabs [BG]' started by Stumbo, Mar 12, 2018.

  1. Stumbo

    Stumbo Guest

    Feb 11, 2008
    With all the interest in HPFs and LPFs these days, it's time to put together all the info TBrs need to make an informed decision about purchasing one or both.

    HPFs and LPFs are tailored equalizers that significantly attenuate (make much quieter) muddy/sub-sonic lows(HPFs) or clanky/janky highs(LPFs) in amps that are turned up, help tame boomy stage and venue acoustics, help protect speakers from over excursion (speaker cone movement beyond its limits) and will get you to love your B string or down tuning even more.

    If you ONLY play quietly at home through an amp, you may not need an HPF and/or LPF. It WILL help headphones and recordings.

    A little known fact is that PAs, guitar players, keyboard players and kick drums(FOH or run through their own amp) can improve their tone and reliability (and the mix) by using an HPF. Guitar players would benefit from an adjustable HPF set much higher than a bass player, around 100hz-120hz.

    If you would be so kind to post your success stories (or not), warnings, pics, settings, rigs, amps, cabs, applications, basses, builders, prices, links, etc. it will be very helpful and educational.
    All questions, comments, pics, fans, owners, potential owners, passersby, builders, designers and sound engineers are welcome!
    I thank you as do all TBrs learning about these great tools in our quest for the best tone for metal! I keed, I keed. :)

    Maybe not. :whistle:

    HPFs are also known as Rumble, Sub-Sonic or Low-Cut Filters. Filter as in "filter out". Sub-sonic means below an acceptable audible level.

    The terms High Pass Filter and Low Pass Filter are somewhat unintuitive.

    HPFs do not just deal with highs or treble.

    An HPF lets frequencies above a set level pass. For bass, it's usually frequencies around 35hz for fixed level HPFs and between 25hz-160hz for adjustable HPFs. These frequencies are chosen by the designer/builder.

    LPFs do not just deal with lows or bass.

    An LPF lets frequencies below a chosen level pass, usually between about 5khz to 15khz. They let higher lower frequencies than those pass. LPFs are usually adjustable. These frequencies are chosen by the designer/builder. For the user, depending on your sonic goals, your ears pretty much decide on which frequency to use.

    For adjustable filters, the frequency level you choose depends on a few variables: bass, amp, cab, band instrumentation, venue, effects and your ears.
    Limiter : Different than an HPF/LPF, is a circuit that limits the maximum level of a signal. It's a circuit that allows signals below a specified input power or level to pass unaffected while attenuating the peaks of stronger signals that exceed this threshold. Limiting is a type of dynamic range compression. Clipping (audio) is an extreme version of limiting. Many amps have Limiters built in.

    HPF/LPS run on very small amounts of current in pedal format (switchable or always on) and are usually hooked up between the instrument and the input jack, in the amp effects loop or between a preamp and power amp. They are usually powered by batteries or low-voltage power supplies(wall warts).

    Many amps have fixed frequency, always-on HPFs built in, though some being adjustable with a knob on the front of the amp. Some effects have an HPF or LPF built in.

    If you have other effects, placement in the signal chain depends on your sonic goals and your ears. Check out the TB Effects Forum for more info on this topic.

    Why you need an HPF
    Part 1
    @Mike Arnopol, MAS Cabs
    From: Is this good? Boom Bass Cabinet

    Most cabs that say 30hz---are down more like 20db at 30hz. But--your perception about 30hz extension is valid . The reason is that almost all cabs claiming this are reflex cabs. Here's the problem with that extension with a reflex cab:*

    1. most of the information at that frequency is coming out of the port. That quality of bass is very poor and uncontrolled. The great home hifi speaker designer John Dunlavy told me " I don't want to hear any bass coming out of a port." Ported enclosures are a cool compromise--you can get loud, have a small enclosure, and have good efficiency. A compromise is in the bottom octave or so. A sealed box that actually goes that low will have a much better quality of bass---but they will be huge, won't go as loud, and would be low efficiency.

    2.All of the drivers that I know that aren't designed exclusively for subs--all of the woofers used in bass cabs---have a free air resonance of 40 to 50 hz. They don't work well under that.
    3.Most reflex cabs are tuned (typically) in the 42 to 50 hz range. What this means is that any frequency under that tuning frequency--the speaker behaves as in free air. Which means that it's flopping around aimlessly.

    What this means is that when you play a note under that tuning frequency--typically under 42hz (or higher in many cases) The speaker is just flopping around trying to reproduce that note.
    What happens is that since the cone movement is uncontrolled, the second harmonic (octave) is being reproduced poorly as the cone is uncontrolled.

    The second harmonic is what we key off of for pitch. That second harmonic then is boomy and uncontrolled. This is the reason that many guys (correctly) say that having that extension causes too many problems on stage---not the fact of reproducing 30hz.

    People should use a HPF set to around 40hz. All of a sudden the B string tightens up and you lose the boom. Running a reflex cab without a HPF will result in a crappy B string sound .

    There are however, some cabs that are of a different design that don't unload and can reproduce the B. When you hear a cab that goes that low and play on the B string---all of a sudden it sounds and feels like the other strings. The fundamentals in that range---while not really needed for an effective B string--do add a pretty neat cushion that does not get in the way.

    *Note: A bass reflex system is a type of loudspeaker enclosure that uses a port or vent cut into the cabinet and a section of tubing or pipe affixed to the port. This port enables the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies as compared to a typical closed box loudspeaker or an infinite baffle mounting.

    Part 2
    @agedhorse, designer, MESA, Genz Benz
    from: 8 ohm cab question

    There are different metrics used by different manufacturers (and even different models within a brand) that might be used to describe exactly the same power.

    For example, on an amplifier that is rated at 500 watts "RMS", it is also going to be capable of delivering 1000 watts peak, because the mathematical definition of the peak voltage of a sine wave (used for ratings) is 1.414x the RMS voltage, and when this 1.414 factor is squared in the power equation, it results in 2x.
    The same thing applies to speakers, but with an added twist based on some old colloquial information that you may not be aware of.
    Speakers tend to be rated in two ways, the first being the same "RMS" (or continuous average) and peak that we discussed above for amplifiers.

    The second way, which is more common in the pro audio industry, is 'RMS", "program" and "peak... the meanings being different here.

    "RMS" is the same, program is defined as 2x the RMS value and comes from when speaker manufacturers were very conservative in their ratings and clipped/compressed program is excluded, and peak which is defined as 2x the program power or 4x the peak power.

    So, a speaker rated at 500 watts "RMS" might also be rated at 1000 watts "program" or "2000 watts peak.

    Which units that are being used is often left to the imagination (or the marketing departments). Also, most speaker power ratings are based on a "must survive, damage allowed) time period of 2 hours. When you extend this test to say 200 hours it's common to see a 1/3 reduction in power rating.

    Another factor is that the (speaker) mechanical part of power handling starts falling rapidly at low frequencies (often below 60Hz), right where the biggest demands are placed on them. At say 30Hz, the power handling might be only 50% of rated speaker power.

    The challenge is that you have an amp like the Subway, which is rated at 400 watts RMS into 8 ohms, and somebody buys a "500 watt" cabinet thinking that it will be fine BUT it's 500 watts "program" or only 250 watts "RMS" and maybe not so fine. It's even worse if these numbers are peak units.

    Therefore, it's not anywhere near as easy as it seems, and this is one big reason IMO why many cabinets fail through no direct fault of the user.

    @fdeck, builder, hpf V3
    You can go as low as you want with any speaker diameter. What you give up when you try to do that, is volume.
    There's a rule of thumb in speaker design: Small, loud, low. Pick any two. As a result, speakers made with smaller drivers tend to sacrifice low end so they can still reach acceptable volume. Or, they use a larger number of small drivers to approximate the behavior of a single large driver.

    Part 3
    Why do I do this to myself...
    I've changed my rig so often that I end up dumping gear that I need later on. Discovered at two gigs recently that I once again need a HPF. I'm pushing my amp into limiting on the low end at some stupid loud gigs. After proudly proclaiming that a HPF isn't necessary, I'm now regretting the two that I've sold. Should have just left in mu rig the whole time, dummy.

    Why you need an HPF/LPF
    Broughton HPF LPF question

    I'm interested in getting one of these for a couple reasons. I have and like using an HPF to tame the boom in a lot of rooms/rigs, and I have recently discovered that I like using a LPF to help me dial out some of the crispy treble, while keeping the upper midrange fullness that I like for fingerstyle playing and soloing.
    Question is: is the HPF as effective as my Fdeck V3? AND, does the LPF work in the way I mentioned?
    Can I use it to shelve out some of the string noise-y, hissy, clanky sound that is not readily tame-able with most traditional treble controls?

    How steep is the curve on the shelf?
    thanks for any input.

    @Asure Skies, Builder, Broughton Audio says:
    The HPF and LPF are both 12 dB per octave butterworth response filters. I use the LPF in the way that you describe: to filter out ultra high frequencies (string noise, fret buzz) but still keep the lower treble/upper mid frequencies.

    @JimmyM says:
    So how come nobody ever complains about guitarists wanting to control what goes out to the PA? Or keyboard players?
    But dang, a bass player wants to do it, and bass players line up to tell them they're egomaniacs and jerks and they need to leave everything up to the sound tech? Wow, what a beaten-down bunch of shlubs!

    How dare anyone tell me what to do! It's my show, not theirs! I refuse to be beaten down into the status quo! I'm always happy to listen to competent people if they think I'm doing something that's making their gig impossible, but I've had too many try to take me down a road that I don't want to go.

    ---I hate tweeters on electric bass and have told the sound tech of my disdain for them. But the sound tech loves the sound of guys like Marcus Miller and Victor Wooten (I do too but not for my thing), therefore I end up with tweeter frequencies in the PA.

    Low pass filter is for them.

    ---In our band, if you have too strong frequency response below 60 hz or so, it creates mud. But the sound tech is younger and grew up with hip hop and EDM and loves those frequencies and pushes them hard despite me being quite vocal about not liking them.

    High pass filter is for them.

    ---I have had sound techs tell me I need to plug my bass straight into a DI, despite my use of effects.
    When I tell them that I use effects and want them in the PA, I have been told things such as "You will not have effects in my PA" or "We'll set up a mic for your cab and blend them," then they never turn on the mic.

    Well sorry...but when you're on my gig, that is MY PA until the gig is over. So you're getting effects in the DI and you will like it. Don't worry...between my professional use of effects and my H and LPF, your speakers are safe, Mr. Sound Tech.

    But when you demand that the guitarist doesn't use effects, then and only then will I take your demand that I plug my bass straight into the PA seriously.

    On the other hand, our sound tech yesterday showed me his iPad with my channel pulled up...he says, "Man, I have to add a lot of bass to your channel to make it sound right out here" and shows me the graph with a hump at 100 hz. I explained to him that I usually try to send him a fairly flat signal that he can easily tweak as he needs, other than my H and LPFing. Then I told him that I loved how it sounded in the house (and you're darn tootin' that I go out there and check it out, so I know exactly what it sounds like), and he gave me the thumbs up.

    So you can see I'm very cooperative and leave a lot to the sound tech's discretion. But H and LPFing and effects are non-negotiable. Those who know what I want don't care, and those who do care don't get a choice in the matter. Isn't it enough that I gave up my awesome Heil mic and went to a DI? What do you want? Blood?

    Why you need an LPF
    NPD: Broughton Audio Low Pass Filter

    @JimmyM says:
    So every now and then, I lament the sorry state of what's available in the way of speaker simulation (high dollar rack stuff, sims married to larger pedals that do other things, etc.), and one day I was commenting how Markbass was missing the boat by not putting their VLE (Vintage Loudspeaker Emulator) control in a 1590a box and selling it, and I said, "First indie pedal builder who does it gets my money." Welp, Josh Broughton (Azure Skies) was the first one.

    It's a low pass filter (obviously) that gives you a gradual sloping rolloff of highs without affecting the other frequencies, allowing you to emulate the freq response of tweeterless cabs, which is a must for as much overdrive as I use. All the way left is full highs up to 16khz, all the way right cuts highs above 160 hz.
    I found my favorite 5k rolloff somewhere between 9:00 and 10:00 (have to experiment a little more to find it exactly), which is very similar to how the VLE behaves.

    Close enough for rock and roll...I strap it to the board and take it right to the gig.

    Other than the 5k rolloff I had dialed in, it was dead transparent, so I was quite happy...
    Last edited by a moderator: May 29, 2018
  2. I like being able to plug into any little backline "rig'' and drop a low B bomb without farting it out.
  3. bholder

    bholder Affable Sociopath Gold Supporting Member Supporting Member

    Sep 2, 2001
    Vestal, NY
    Received a gift from Sire* (see sig)
    Seems to me to be a good argument that we need better drivers. ;)
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Or better overall designs, but that increases cost.
  5. Better drivers, more cost. And maybe not the bang for the buck you'd expect.
    I suppose there comes a point of diminishing returns.
  6. Wasnex


    Dec 25, 2011
    Nice to see the HPF considered in the context of cabinet design and tuning.

    About 30 years ago I used to EQ my SVT and Ampeg 810 using a couple of bands of parametric EQ to peak my open E string. I believe in total I was using about 14-18db of boost depending upon the sound I wanted. The system was crossed over at 200hz to a pair of JBL E120s. This setup felt really quick and responsive, and the sound was very tight and controlled. I received lot's of positive comments about my sound.

    Using the same SVT, E120s, and EQ technique with a pair of EVM 18Bs in small cabs ported at 50Hz produced a loose sound that a respected educator described to me as "woomy." I have a pair of 18Bs in some huge TL405s that are ported in the high 20s. They only need a few db of boost to be flat to 40hz. It's amazing how much better the 18Bs sound in the bigger cab. However, the sub frequencies can be a bit obnoxious with an amp like a Mesa M9 especially if you bypass the amp's HPF by engaging the deep switch. Adding an HPF in the low to mid 30s would probably help eliminate nasty artifacts that I suspect are below the fundamental of the low B.

    Currently I have the 18Bs in the little cabs set up to cover 50-100hz with a steep HPF (48db/octave) at about 48 hz. With a couple of mid/high packs they sound great with bass, but don't really confer the same heft and weight as the larger cabinets.
    DrMole, Scootbass1, RandM and 2 others like this.
  7. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    I use a HPF religiously with my DB to avoid feedback. While the HPF effect is audible, it's interesting that I can set the rolloff quite high (like 100hZ or more) before the open E note starts sounding weak.

    I have no use for a LPF, I just use the speaker's natural rolloff. I turn off the tweeters in any cabs that have one.
  8. Wasnex


    Dec 25, 2011

    IMHO, some would find a 3K LPF useful on a DI to somewhat simulate the roll off of a speaker. When I am running sound I usually don't engage an LPF on bass unless the signal is really bright and obnoxious or perhaps extremely hissy.
    javi_bassist, mesaplayer83 and Stumbo like this.
  9. MrLenny1


    Jan 17, 2009
    New England
    ??? Do I need a HPF or LPF ???
    Educate me, Please.
    I use Active 5 string basses and
    Eden 2x10 XST cab rated for low B IIRC.
  10. You need a HPF to tame the lows.
    You need an LPF to tame the highs.
    Chances are you need to tame the lows more than the highs.
  11. GrapeBass


    Jun 10, 2004
    Graphic Designer: Yorkville Sound
    Initially I bought mine to help while recording direct but the uses for it live are great. While most cabinets don't go so low, adding something that tempers it will prevent LF content that could muddy up your sound but also interfere with other instruments (such as keys and drums). It also helps your power amp The Low Pass filter tames the HF much better than your tone can as it is not centered at a specific frequency, you dial in where is appropriate. I find this helps open up space for the drums (cymbols etc.) and other instruments that need more crispy highs.
    butterfingers1, RandM and Stumbo like this.
  12. mesaplayer83


    Jun 27, 2017
    I have found a variable HPF to be way more useful than I ever thought it would be - with ZERO drawbacks... For those looking for an external HPF, I would strongly recommend fdeck's HPF-3...
  13. dukeorock

    dukeorock Owner BNA Audio Commercial User

    Mar 8, 2011
    Nashville, TN
    Authorized greenboy designs builder/Owner of BNA Audio
    I have a couple fDecks and a Broughton Audio HPF/LPF pedal. I used to strap an fDeck to my upright tailpiece to get impedance sorted as close to the source as possible. Works great, but these days I just use the HPF in my Grace Designs Felix pre.
    I use the Broughton HPF/LPF with my tube amp...cleans up some low end slip and gives me extra headroom on the amp. Just use the LPF as needed
    butterfingers1, GregC, PWV and 4 others like this.
  14. mesaplayer83


    Jun 27, 2017
    I can get highs under control quite easily without added outboard gear - after using it for a little while, I will definitely be keeping my HPF... IMO, HPFs shine their most when used with smaller rigs - mine really allows me to get the most out of my Rumble 200 Combo, for an example...
  15. I keep a Rane PE17 in a small rack of misc gear, which, in addition to the five bands of parametric EQ, also has a high pass filter and a low pass filter. Great for keeping excessive lows and irritating hiss out of unknown equipment. When needed, it usually it gets patched in at FOH. But I've also used it to clean bass amps and other problems on stage. I have another that lives permanently in my wireless acoustic rack for the low pass and to tame howlers. When you need it, there's nothing better. It's older and I'm sure discontinued, but can be found relatively cheaply. Digital mixing has meant that I'm using it less than previously at FOH.

    Last edited: Mar 14, 2018
  16. hintz


    Jun 5, 2014
    wahiawa, HI(Oahu)
    Subbed, I wanna learn more about this
  17. Roxbororob

    Roxbororob Supporting Member

    Jun 8, 2015
    My fdeck HPF was one my biggest bang for the buck gas buys. Like another TBr it tamed my SM400. It is my always on pedal with any amp even DI to FOH.
  18. I keep my FDeck HPF v3 on my pedalboard. I set the frequency knob to about 1:00, which (in the absence of any helpful markings) I suppose is somewhere around 70 Hz. This setting tightens up the low end while still giving a good, powerful sound.

    I don't use an LPF, but I don't seem to need one. Maybe if I had an amp that exaggerated the treble I would want an LPF. My typical amp setup at the moment is an Ampeg SCR-DI into the effects return of either an Eden Traveler 400 with an Eden 4x10" cab or a Fender Rumble 500. The Eden setup sounds better, but the Fender is much more portable.
    dukeorock and Stumbo like this.
  19. mesaplayer83


    Jun 27, 2017
    Yup - same here... I've also gotten excellent results using my same pedal board for my AEB gigs and on my electric bass gigs:

    wmmj, lowplaces and Stumbo like this.
  20. wraub


    Apr 9, 2004
    ennui, az
    The high pass filter in my pre is only 30 Hz, but it's always on. I'd (almost) never play without one.
    lowplaces, Stumbo and mesaplayer83 like this.