In praise of the HPF

[blubass]

I don't know where you get "mandated." HPFs are more than useful for every player, especially those with sub-par cabs. Not mandated, but highly regarded and desired

Where did mandated come from? What I meant by that, was it's not required that manufacturers implement an HPF into their design. So no matter how highly regarded and desirable they are, the engineers don't have to include them. It was an answer to the original question, why aren't they included features in amps; because the manufacturers don't have to include them, so some chose not to.

 

[Jim Carr]

B strings already sound out of tune about 90% of the time. Many tuners, especially clip-ons, don't accurately pick up the low b. As I am sure we all already know, they are very hard to intonate, and many amps/cabs don't seem to reproduce their sound well to begin. Adding a cut anywhere above 29-30hz reduces their apparent intonation even more to my ears. Maybe it's just me?

The sensitivity of human pitch discrimination is actually poor down in the lowest registers of our hearing. Don't forget that any HPF is essentially a broad scoop. You are not able to do much more than cut an octave wide swath that slopes about -6dB per octave, in my understanding. In other words, it is a pretty broad brush.

The perceived out-of-tuneness of low B strings is, IME, related to overloading of the string with physical energy, and the inharmonicity found in the low string as a "vibrating rod"— an issue familiar to the folks in the piano world.

Longer scale length, better strings, good technique, and great amps/drivers help, IME.

 

[Jeff Bonny]

Where did mandated come from? What I meant by that, was it's not required that manufacturers implement an HPF into their design. So no matter how highly regarded and desirable they are, the engineers don't have to include them. It was an answer to the original question, why aren't they included features in amps; because the manufacturers don't have to include them, so some chose not to.

What you talking about? They don't have to wear pants either but they should. How do you think a company that's not wearing pants finds out it should be? CUSTOMER FEEDBACK. Which is what a thread like this is all about. You think what's being said here won't get through to some manufacturers? Directly or indirectly it will and a clear majority here thinks HPF is a useful tool.

In a perfect world I'd always use a B15 or a V4B or an SVT with enough outboard gear to be happy but those don't fit in my gigbag. Part of the appeal of a class D amp is portability. A big part of portability is an uncluttered set of onboard features that solves common problems and reduces the need for outboard solutions. God knows over the years they've tried enough stupid onboard **** like compression and built in tuners. One knob that can make an otherwise horrible situation tolerable doesn't seem so unreasonable to be talking about.

 

[Mark Reccord]

That's one reason why I made the variable HPF in my more recent DIY amps and preamps have max cut at full counterclockwise. That also allows using a much easier pot to source, which is definitely a bonus.

As far as signal chain location, I prefer just after the EFX/Aux return, so my DI send does not reflect my HPF setting and if I use an external tube preamp with huge lows I have the option of tempering that. My preamps are made up of modular building blocks though, so I could readily reconfigure the HPF location if I had a compelling reason to do so.

Dual reverse log taper pots are definitely in the realm of custom order parts.

In 90% of cases a DI feed is going to get a HPF slapped on it at FOH anyway so I don't think having it before the DI feed would be a substantial problem if you decided to do that.

As a sound person, I often use high pass filtering on just about everything save kickdrum (assuming I have access to variable frequency ones), including bass guitar. There are some situations where I won't (dub/reggae in a decent room for example) but most of the time I will, sometimes as high as 100Hz depending on how live the room is. Clearly a 100Hz high pass on bass is fairly extreme but when you're in a great big arena and you actually want the bass guitar to be heard it is sometimes necessary to aggressively cut the low end. It surprisingly doesn't sound as thin as you might think.

All HPFs are essentially roll off the response at a specified rate below the corner frequency, which is usually specified at where the response is -3dB below nominal but they're not all created equal. The order of the filter and the filter topology itself determine how fast it rolls off below the corner frequency and how far above that frequency the roll off begins. I've been fooling around with HPF circuits in my home brew tube DI and I've settled on first order filters (-6dB per octave) at 30, 60 and 100Hz and a fully bypassed setting as well. I went with the first order filters partly because they are much more practical to implement in the gain circuit I'm using but found that they sound very natural and unobtrusive. With a 5-string the 30Hz setting has no real effect on the notes but does filter out thumps and infrasonic stuff and this is noticeably cleaner than with the HPF out. 60Hz thins out the low B a little but IME makes it noticeably more punchy. 100Hz is really noticeable but wouldn't be unusable for bass guitar on a boomy stage. I included it for use with things like acoustic guitar, bouzouki and mandolin. I also put similar LPFs in at 2k, 5k and 10k. The 60Hz/5kHz setting is very reminiscent of the Ampeg 810 response. .

 

[beans-on-toast]

100Hz .... I included it for use with things like acoustic guitar, bouzouki and mandolin.

As you mentioned, filters can be applied at the desk or the DI. There are different reasons for using filters, depending on the application. For instance, LPF's can be engaged at the source on some microphones to help reduce (footfall, wind, etc.) noise. The Neumann U87Ai has a switch for -18 dB +/-1 dB @ 40 Hz. The AKG C414XLS has a switch for 0, 40 Hz and 80 Hz @ 12 dB/octave, 160Hz @ 6 dB/octave. It's interesting to note how AKG varies the sharpness of the filter based on the frequency.

 

[Passinwind]

Dual reverse log taper pots are definitely in the realm of custom order parts.

Aye, and in my design all that's needed is a single section log pot. The curve I end up with is not a classical alignment, but user feedback has been very positive. Especially my user feedback...

In 90% of cases a DI feed is going to get a HPF slapped on it at FOH anyway so I don't think having it before the DI feed would be a substantial problem if you decided to do that.

I only tend to even use a live DI feed a couple of times a year myself anyway, and I would expect an HPF used at the board to be pretty likely in those instances. It might actually work out better all the way around to feed my HP'ed signal to FOH, as I often use my HPF and substantial boost of my bass control in tandem. But it's a bit complicated because of my particular implementation. I factored in all the interstage rolloffs, and they change a bit if I swap module locations.

As a sound person, I often use high pass filtering on just about everything save kickdrum (assuming I have access to variable frequency ones), including bass guitar. There are some situations where I won't (dub/reggae in a decent room for example) but most of the time I will, sometimes as high as 100Hz depending on how live the room is. Clearly a 100Hz high pass on bass is fairly extreme but when you're in a great big arena and you actually want the bass guitar to be heard it is sometimes necessary to aggressively cut the low end. It surprisingly doesn't sound as thin as you might think.

Word. There's also another potentially very useful aspect to having a variable HPF that's thoughtfully integrated into your bass amp: interactivity with the bass tone control. I've touched on that in a few of my DIY threads. Lots of people dislike interactive tone controls, but I sometimes find them very cool, personally. Here's an example of how mine works. This model shows the bass control set at 6/10 and the HPF swept through most of its range. You can see that the bass peak changes from as low as 42Hz all the way up to 240Hz or so. Instead of being handcuffed by a room node, you just might still have some useful bass boosting options. My buddy 4Mal calls this the "punch control." I find this usage every bit as useful as simply cutting sub lows in many cases. There are other things going on with phasing and group delay that I'll just call secret sauce, but you get the basic idea.

 

[Mark Reccord]

Aye, and in my design all that's needed is a single section log pot. The curve I end up with is not a classical alignment, but user feedback has been very positive. Especially my user feedback...

I only tend to even use a live DI feed a couple of times a year myself anyway, and I would expect an HPF used at the board to be pretty likely in those instances. It might actually work out better all the way around to feed my HP'ed signal to FOH, as I often use my HPF and substantial boost of my bass control in tandem. But it's a bit complicated because of my particular implementation. I factored in all the interstage rolloffs, and they change a bit if I swap module locations.

Funny thing about designing stuff, eh? You gotta pick the set of compromises you're willing to live with in order to best match your vision of what the thing should do. Stuff that looks simple from the high level is often much more complex at the implementation level. Even something stupid like 2 switchable filament schemes turns out to me a major headache to lay out on a board. I'd love to get my paws on some of the stuff you've built, though.
[/QUOTE]

Word. There's also another potentially very useful aspect to having a variable HPF that's thoughtfully integrated into your bass amp: interactivity with the bass tone control. I've touched on that in a few of my DIY threads. Lots of people dislike interactive tone controls, but I sometimes find them very cool, personally. Here's an example of how mine works. This model shows the bass control set at 6/10 and the HPF swept through most of its range. You can see that the bass peak changes from as low as 42Hz all the way up to 240Hz or so. Instead of being handcuffed by a room node, you just might still have some useful bass boosting options. My buddy 4Mal calls this the "punch control." I find this usage every bit as useful as simply cutting sub lows in many cases. There are other things going on with phasing and group delay that I'll just call secret sauce, but you get the basic idea.

This is very cool.

 

[domonic]

WE are now changing lanes into the Pultech sound !!!!!

Boost and Attenuate on Pultec EQs

 

[Dave Hill]

My Arkham has a 6dB/octave HPF starting at 100 Hz. The current board sweetheart Noble is 6 dB at 150 Hz! I like the 12bB/octave fdeck set between 40-60 Hz. I believe in going from 6 to 12 dB/octave, you have to use an active circuit(?).

 

[Steve Dallman]

I have an Fdeck series 1 HPF. I tried it on my bass rig (Line 6 5 string variax which has a LOT of sub lows, PF-500 and a couple 12's with humongous low end) and it had a subtle clipping (using it right after the bass, before the amp) and took all the punch out of my bass, even when set at the lowest setting. I was disappointed.

I do use it with my ABG which has an uncontrollable low end and with my piezo saddled guitars with Fishman Power Bridges. It world great to get rid of the thump and low mechanical noise.

But for my bass, not a fan. Perhaps the model 3 would have more headroom, but I'm happy with my bass tone and performance with out the HPF.

 

[Monkey]

IME, fixed high pass filters are built into most consumer grade, and especially budget class amps.
I include in "consumer grade" such great amps like the GB shuttle 6.0, GK mb800, and most higher power micro heads.

Does anyone know where the HPF is set on the Markbass LittleMark II/III?

I usually use an Fdeck Series 3 when playing my 5-string slab through an LMIII into a fEARful 12/6, but I don't know if I really need it. I definitely need the Fdeck with my double basses and find it incredibly useful in dialing in a good sound with a variety of amps, but rarely adjust it at all on electric bass gigs through the LMIII.

 

[Mark Reccord]

WE are now changing lanes into the Pultech sound !!!!!

Boost and Attenuate on Pultec EQs

That was the first thing that occurred to me when I read Passinwind's post. Definitely reminiscent of the way the Pultecs work.

My Arkham has a 6dB/octave HPF starting at 100 Hz. The current board sweetheart Noble is 6 dB at 150 Hz! I like the 12bB/octave fdeck set between 40-60 Hz. I believe in going from 6 to 12 dB/octave, you have to use an active circuit(?).

You don't have to use an active circuit but active circuits are usually better for higher order filters. You can build a 2nd order passive filter but they are lossy and not easy to get to behave the way you want. I tried a few in my DI circuit and didn't like the way they sounded vs. the 1st order ones. I didn't try 2nd order active filters in this project because that would require at least one extra gain stage and I didn't want to fool with the basic gain circuit because it's great the way it is.

 

[Fuzzbass]

Just please don't use a HPF if you are playing on a 5er. Playing a note that essentially doesn't have a fundamental always sounds terrible. I used to hate it when one of the engineers in my studio would put an HPF on basically every track at 40hz. It ruins good bass tone. On a 4 string, go for. If your HPF is adjustable, go for it.

I play 5-string, often tuned a half-step flat, and strongly disagree that fundamental-free low notes "always" sound terrible. F'r instance I think five string sounds killer through an SVT rig, even though the sealed 8x10 cab starts rolling off above 40Hz. Psychoacoustics fills in the missing fundamental well enough.

More on topic: if you're in a nice acoustic environment, I agree that it can be nice to hear those fundamentals through Acme or other high quality bass speakers. However I usually play bar gigs in wonky acoustic environments, and my corporate/festival gigs sometimes happen on elevated/hollow stages that can have resonances with the usual undesirable results: dead notes, wolf tones. An acoustic pad like a Gramma sometimes helps, but often isn't enough. I don't have a dedicated HPF, but I use the DSM OmniCabSim, which has a Cab Size control that's an HPF that goes from 60Hz and up. The reason I got it was to "vintage up" my Bergantino CN210 cabs, but it has worked beautifully to minimize resonances in poor acoustic environments.

TL;DR: The lowest fundamentals can sound nice in the right conditions, but can really muddy things up in poor acoustic environments. An HPF can "tighten up" the low end and help the bass guitar sit better in the mix.

 

[Dave Hill]

You don't have to use an active circuit but active circuits are usually better for higher order filters. You can build a 2nd order passive filter but they are lossy and not easy to get to behave the way you want. I tried a few in my DI circuit and didn't like the way they sounded vs. the 1st order ones. I didn't try 2nd order active filters in this project because that would require at least one extra gain stage and I didn't want to fool with the basic gain circuit because it's great the way it is.

This is how Micah at Arkham felt about the Zephyr too.

I use my fdeck for pretty much everything now, even tuned down 5 string (gasp!). Getting rid of that slight flab tightens up the entire tone envelope, to my ears.

 

[Passinwind]

WE are now changing lanes into the Pultech sound !!!!!

Thanks for the heads up. I actually have zero hands on experience with the Pultec EQ, although I've studied the schematic and the interactivity aspect of the design a bit. I just downloaded one of the free knockoff plugins and look forward to seeing what it has to teach me.

Craig Anderton's ancient Super Tone Control circuit from Electronic Projects For Musicians allows summing blends of the high pass, band pass, and low pass sections, which can have some very fun and interesting results. I became aware of this general approach working on analog synths right around when Craig's book came out, but I know it goes back much further than that.

 

[Brother Goose]

The sensitivity of human pitch discrimination is actually poor down in the lowest registers of our hearing. Don't forget that any HPF is essentially a broad scoop. You are not able to do much more than cut an octave wide swath that slopes about -6dB per octave, in my understanding. In other words, it is a pretty broad brush.

The perceived out-of-tuneness of low B strings is, IME, related to overloading of the string with physical energy, and the inharmonicity found in the low string as a "vibrating rod"— an issue familiar to the folks in the piano world.

Longer scale length, better strings, good technique, and great amps/drivers help, IME.

yessir- that's why I play 35" scale basses and finally got a fEARFUL!

I could def use a HPF to help w some sub-bass frequencies and help protect listeners (speakers) from thunder thumps

 

[Remyd]

Just please don't use a HPF if you are playing on a 5er. Playing a note that essentially doesn't have a fundamental always sounds terrible. I used to hate it when one of the engineers in my studio would put an HPF on basically every track at 40hz. It ruins good bass tone. On a 4 string, go for. If your HPF is adjustable, go for it.

IME and specifically in a live situation, missing the fundamental of a low B is only noticeable to the bassist (and then only slightly) and not at all in the crowd. The low B is at the lower limit of useful hearing anyhow, so even if you could amp it cleanly, people would feel much more than hear. Even an ampeg fridge basically drops everything below 50 Hz, and that's fairly standard equipment. Very few 5 string players complain about playing through a fridge.

Almost all mainstream cabs drop off sharply in response below 40-50 hz, so even if you have the world's most full range amp, the fundamental pitch is restricted. IIRC the first harmonic on the B string is somewhere in the neighborhood of 38 hz and the octave is like 62, which are fairly low, and make up a majority of the impression of pitch to 99.9% of everyone. If you're going through a PA dollars to doughnuts those freq's are already HPF'd and/or compressed to send to a muddy sub to strip all musical timbre and become indistinguishable from the kick.

I'm the wrong person to talk about recording strategy, but I thought that you wanted every freq that comes through a DI and restrict/compress/reverb/whatever in post?

 

[Bass'd on a true story]

I'm the wrong person to talk about recording strategy, but I thought that you wanted every freq that comes through a DI and restrict/compress/reverb/whatever in post?

Still referred to as a high pass when done in the box and generally I use some compression going in, but never anything more than that. I see everyone's point. I think maybe I'm just racist against 5 strings. I look for reasons to bash them. Obviously any difference in intonation is negligible to the point that even most vets don't seem to notice it. I'll get off my soapbox.

 

[Downunderwonder]

I play 5-string, often tuned a half-step flat, and strongly disagree that fundamental-free low notes "always" sound terrible. F'r instance I think five string sounds killer through an SVT rig, even though the sealed 8x10 cab starts rolling off above 40Hz. Psychoacoustics fills in the missing fundamental well enough.

More on topic: if you're in a nice acoustic environment, I agree that it can be nice to hear those fundamentals through Acme or other high quality bass speakers. However I usually play bar gigs in wonky acoustic environments, and my corporate/festival gigs sometimes happen on elevated/hollow stages that can have resonances with the usual undesirable results: dead notes, wolf tones. An acoustic pad like a Gramma sometimes helps, but often isn't enough. I don't have a dedicated HPF, but I use the DSM OmniCabSim, which has a Cab Size control that's an HPF that goes from 60Hz and up. The reason I got it was to "vintage up" my Bergantino CN210 cabs, but it has worked beautifully to minimize resonances in poor acoustic environments.

TL;DR: The lowest fundamentals can sound nice in the right conditions, but can really muddy things up in poor acoustic environments. An HPF can "tighten up" the low end and help the bass guitar sit better in the mix.

SVT doesn't roll off above 40. It's all done at 40. It's rolling off about 70.

 

[Downunderwonder]

IME and specifically in a live situation, missing the fundamental of a low B is only noticeable to the bassist (and then only slightly) and not at all in the crowd. The low B is at the lower limit of useful hearing anyhow, so even if you could amp it cleanly, people would feel much more than hear. Even an ampeg fridge basically drops everything below 50 Hz, and that's fairly standard equipment. Very few 5 string players complain about playing through a fridge.

Almost all mainstream cabs drop off sharply in response below 40-50 hz, so even if you have the world's most full range amp, the fundamental pitch is restricted. IIRC the first harmonic on the B string is somewhere in the neighborhood of 38 hz and the octave is like 62, which are fairly low, and make up a majority of the impression of pitch to 99.9% of everyone. If you're going through a PA dollars to doughnuts those freq's are already HPF'd and/or compressed to send to a muddy sub to strip all musical timbre and become indistinguishable from the kick.

I'm the wrong person to talk about recording strategy, but I thought that you wanted every freq that comes through a DI and restrict/compress/reverb/whatever in post?

the harmonic is always double the fundamental frequency. B is 31/62.