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

[Wasnex]

A couple of points, if I may:

"Myself and a lot of other people - famous professionals, even - got by just fine without anything more than those three items for decades."

While this is mostly true, it's also true that boomy rooms and blown drivers have been a problem for working bassists since electric bass was first invented - so, "got by just fine" isn't exactly true...

Next - a HPF isn't really an "effect", as much as it is more of a signal management tool much like the EQ section of your amp... And as for "hearing it", you don't really hear it, but definitely experience the positive results of properly using one... Truthfully, I think you're doing your fellow bassists a disservice by trying to dissuade them from trying a bit of technology that has been well proven to work as advertised... I also "got along just fine" for over 3 decades without a HPF, but now that I've used one, you can bet that I'll continue to use it...

It should be noted that many amps have an HPF built in. IMHO, whether one benefits from an add on HPF depends upon the amp and speaker they use, and the tone and volume they are want.

Given speakers that are flat to 30 hz, I can hear and feel the effect of a boost in this frequency region. However, with most amps/speakers I have used, boosting sub bass just wastes power and muddies up the sound because the speakers were not designed to operate in this range. Selecting an HPF just under the tuning frequency of a reflex cab usually provides a fairly noticeable improvement in sound with little or no perceived loss in low end.

It should be noted that boosting EQ at a frequency that is below the cabs cutoff still produces a perceivable change in the sound. I believe much of this is a result of "frequency doubling." Basically if you feed a reflex speaker a boost below it's cut off, you probably won't hear much of an increase at the tones fundamental, but you will hear an increase in output at the 2nd harmonic (octave)...given the fundamental of the B is ~ 36hz, this puts the 2nd harmonic at 72hz. Perhaps this is why (IMHO) a boost centered in the 70 to 100 hz region tends to be much more effective for fattening up the overall sound of the bass than a boost at 35 hz or lower.

 

[Stumbo]

OK, I'll start by pimping one of my favorite applications for the variable HPF that I've included in my last several DIY amp and preamp builds. It's not so much about protection for drivers as for use as a tone control enhancement. For example, here's a model of what happens as I sweep the HPF frequency while leaving the bass control boosted at 6/10:

View attachment 2949215

And then with bass boosted to 8/10:

View attachment 2949216

And finally, some measured ("real world") frequency response curves in a slightly different DIY preamp, with various settings for both the bass control and the HPF:

View attachment 2949217

Note that all of this is old hat to users of classic studio EQs like Pultecs, for instance. There are many, many ways to skin felis catus. View attachment 2949218

Oh: and apologies of the goofy scaling and image size differences, I just grabbed stuff that was already on my computer.

Great stuff!

 

[N. Kentucky Bass]

Perhaps this is why (IMHO) a boost centered in the 70 to 100 hz region tends to be much more effective for fattening up the overall sound of the bass than a boost at 35 hz or lower.

Boosting in this area competes with the kick drum. If you're up-leveling this discussion in terms of EQing a band, wouldn't it be better to HPF the bass even higher, say about 100Hz to eliminate conflict -- especially if the mixer uses a typical kick-heavy approach ...

 

[NKBassman]

Boosting in this area competes with the kick drum. If you're up-leveling this discussion in terms of EQing a band, wouldn't it be better to HPF the bass even higher, say about 100Hz to eliminate conflict -- especially if the mixer uses a typical kick-heavy approach ...

If you have someone else mixing your band for FOH, best to leave those decisions up to them and not HPF too much before it even gets to the PA. Keep it to a minimum for what you need to feel comfortable on stage so that the FOH guy has what he needs to work with.

 

[N. Kentucky Bass]

If you have someone else mixing your band for FOH, best to leave those decisions up to them and not HPF too much before it even gets to the PA.

I agree. I was questioning the wisdom of boosting bass below 100Hz. If the bassist does that at the beginning of the chain, the clashing result will be mud no matter what the sound person does. Esp if the sound person favors the heavy kick approach.

 

[Wasnex]

With all the interest in HPFs and LPFs (basically tailored EQs. that cut off lows and highs that either cut muddy lows or clanky highs-or both, help adapt to boomy venue acoustics and help protect speakers from over excursion), I think it's time to put together all the info TBrs need to make an informed decision about purchasing one or both.

If you would be so kind to post your success stories (or not), pics, settings, rigs, amps, cabs, applications, basses, builders, prices, links, etc. it will be very helpful and educational.

Probably not relevant to bass, but the use of the LPF is an important consideration with sound reinforcement especially with high power systems.

On occasion I have used an LPF in a live sound environment to eliminate feedback. The frequency is highly dependent on the natural overtones of the source. You don't want to set the LPF so low that it significantly darkens to tone of the source.

Usually feedback is audible, but it can also occur at ultrasonic frequencies. We blew a couple of tweeters and I noted some hum and weird sounds coming from the monitors just before the tweeters blew. It felt like a very high pressure full range sound was being produced, but audible sound was barely perceptible to my ears. I can't really describe the sound but I learned to recognize it and engage an LPF any time I heard it...no more fried tweeters.

The meters on the power amp showed the tweeter amp was clipping and the woofer amp was also putting out significant power. I believe what happened is the tweeter was feeding back at a level that caused the tweeter amp to clip so hard that the power supply started injecting hum and other garbage into the woofer side of the amp. I believe the sensation of high SPL I experienced was subharmonics of the ultrasonic feedback. Perhaps @agedhorse horse can explain.

 

[Taustin Powers]

Correct.

Thanks! Do you know at what frequency the D800‘s HPF is set?

 

[Wasnex]

Boosting in this area competes with the kick drum. If you're up-leveling this discussion in terms of EQing a band, wouldn't it be better to HPF the bass even higher, say about 100Hz to eliminate conflict -- especially if the mixer uses a typical kick-heavy approach ...

I don't think most bass players would apply an HPF to their amp at 100hz, but I would be quite comfortable with it on my rig providing I had PA support. It doesn't really sound like bass, but in my experience it makes it a lot easier to hear individual notes. In fact, one of my favorite rigs was a GK 800RB biamped into a Bag End S15 and a Ramsa WSA200 (12 plus horn). The 15 was stacked on a rolling rack with the 12 on top. I am sure this rig produced almost no output below 100 hz, but it allowed me to hear every note and nuance in my playing at very low SPL. The only fat in the sound was coming back from the subs. Every bass player who used our back line hated the sound of that rig.

FYI, with the rig I mentioned in post#6, I boosted at 40 hz and used a relatively narrow band cut at 80hz. Not many amps have an 8 band parametric available for this level of tone shaping. I used this rig without PA support, so a 100hz HPF would not be desirable.

I usually EQ kick with a narrow band peak at the tuning frequency of the drum...usually in the 60-80 hz range. For mixing purposes, it can be helpful to slot the bass at the same frequency with an equally narrow band cut. However, at the SPL that I frequently mix at, applying a 100 hz HPF to the bass channel in the PA may be too low. I rarely mix at a level where I can get the mains above stage wash, so I might pull the bass completely out of the subs and high pass the bass channel at 200 hz or higher if the room has a lot of low frequency build up. It's glorious when you get a room that allows you to run the bass in the subs and set the channel HPF just below the instruments fundamental...sadly this hardly ever seems to happen with indoor gigs, even when the musicians are all wearing IEMs.

 

[Wasnex]

I agree. I was questioning the wisdom of boosting bass below 100Hz.

Keep in mind that EQ can be bell shaped or shelving. I believe bass controls are usually of the low pass shelving variety.

 

[agedhorse]

Thanks! Do you know at what frequency the D800‘s HPF is set?

It's right about 30Hz.

 

[Al Kraft]

It's right about 30Hz.

Was this an easy/intuitive/automatic choice for you based on your experience, or one where you did some soul searching and experimenting? I ask because the I notice that the Berg amps have a default set around 40 HZ (fixed on the Forte).

There seems to be a group of folks who believe the real tone game starts at 60/80HZ for bass (5/4 string) rather than at the fundamental. As we look at speaker specs and consider what most cabs are capable of, there is some logic to focusing more on that first harmonic and minimizing (to some extent) what we try to make happen below it. I guess the trick here, as always, is finding the right balance.

As always, not meant to be a challenge, just curious on how you view that trade space...without giving away your trade secrets of course!

 

[agedhorse]

It was the result of player listening tests along with my experience at FOH. I really wouldn't want it any lower than 30Hz, making it adjustable on the 800+ allows a higher setting. It depends very much on the application, the speakers being used, the acoustics and the sound guy. 30Hz is a "happy minimum" value.

 

[baxter_x]

folks who believe the real tone game starts at 60/80HZ for bass

That's exactly where I set my HPF! I use only 5 strings basses.

 

[Joebone]

Great thread.

Makes me wonder if I should be looking at the Subway D800+ for my next amp for the built in HPF. Was looking at the D800 or the Quilter BB800 initially...

Don't hesitate. I'm still, marginally, an A/B guy, but the 800+ is a great amp, with two exceptional features: the HPF, and dual variable mids. I recently did a thing where I boosted 1600hz (approximately - no periodic markers on the frequency dials) to cut through under the guitars, but then could suppress fret noise with a cut around 2200 hz. Happy, happy, happy!

 

[Joebone]

The variable HPF in the 800+ is a great idea. But, some bass amps already have a " built in ", fixed HPF in their designs, something that I think is never talked about in their manuals, unless you look hard in the spec sheets. For example, the Shuttle line of amp heads have a built in HPF. I for get where exactly it is set, but using an outboard HPF, like the Fdeck, may be counter-intuitive, or not with these heads. Perhaps Agedhorse can comment on this ?

Yes. And I'm convinced that something akin to an HPF cut-off is why the fabled Thunderfunk amps are so darned effective.

 

[PraiseBassing]

Some good conversation in here. As a bass player and sound man, do not let anything keep you from protecting your gear and getting your tone. If you are doing those two things, the sound engineer will have what they need to do their job.

A HPF is not the best way to seperate bass and kick in my experience. Side-chaining a compressor lets the kick get through better than a HPF on the bass.

I don’t have a specific figure to reference, but with most subwoofers, let alone bass guitar cabs operating somewhere around -3dB at 40ish Hz and -10dB around 30-35 Hz, a HPF at 40-50 is nothing but a good and safe thing to do. Only in extreme cases would this not be true.

A HPF like the fDeck(12 dB/octave) set at 70 Hz is only taking away the signal that most systems can’t produce. Even the NV610 is probably right on the edge with that setting considering it is rated with a “response” down to 48 Hz. The sealed enclousure may cut the response so that you can’t hear the lower frequencies, but the reality is that the speakers are still attempting and straining to reproduces those frequencies.

 

[Arjank]

I don't use a HPF in my current setup, but when I would use it I would set it at a frequency 1/4th below that of the tuning frequency if the cab is ported. E.g. if the port is tuned to 50hz I would set the HPF to approx 38hz. It also depends on the steepness of the HPF (12, 24 or 48 dB/oct).

 

[BadExample]

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 mixer have meant that I'm using it less than previously at FOH.

View attachment 2947775

Dig it! I could use one or two. Great manual with sound advice too:

"If a -15 dB cut won’t cure the problem, the
resonance is extreme and must be dealt with in other ways.
For example, move the speakers or the mics; hang some
drapes; move some walls; burn down the building; or simply
unplug the system and go home—something must give!"

 

[Bassbeater]

Anybody familiar with this unit? They seem to really like pass filtering.
VFE Pinball tilt
Link Removed

 

[dukeorock]

Anybody familiar with this unit? They seem to really like pass filtering.
VFE Pinball tilt
Link Removed
View attachment 2949968

Seems more like band passing as an effect, since the HPF only goes down to 100hz. I’m really liking this one