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

[PraiseBassing]

If you do the math, that's exactly what I said. What your picture shows is what happens when you combine 2 filters at full boost with 1 band of separation between them, which was a supposed selling point. In practice, this application is rarely beneficial because that's not how a graphic eq is used. Myself, I do not care for constant Q eq's in PA applications.

I’m just trying to get as much information out on as many different levels so that anyone who reads this can understand.
I’m far from an expert myself, but weekly I work with many musicians who have less than a basic understanding of how different things affect sound. Even basic things such as off-axis monitor placement and how it hinders their ability to hear the monitor mix.

I’ve learned that diagrams and simplifications can help them understand best and leave the in depth discussion as a topic for them to pursue further if they wish. (This is where the conversation would go next on this subject if people want)

 

[agedhorse]

Out of interest, I tracked down a test someone did of a Behringer GI100, which is what I have. It seems to have a roll off of about 10dB/octave from 100 Hz. That 's a higher and gentler roll off than an ideal HPF, I'd guess. I 'll check against an Ampeg 8x10, though

I think there's guitar simulation on that DI, perhaps the test didn't understand the application of the product itself?

 

[-Asdfgh-]

I think there's guitar simulation on that DI, perhaps the test didn't understand the application of the product itself?

It was a test of a number of guitar speaker simulators, so the purpose was understood. But I was curious about the response. HPFs in the UK are only found buried at the end of rainbows.

 

[NKBassman]

The GI100 sound surprisingly good on guitar. Never tried it on bass.

 

[NKBassman]

I think there's guitar simulation on that DI, perhaps the test didn't understand the application of the product itself?

Yes, the GI100 is a guitar cab sim DI,

 

[StuartV]

Okay, I read the 1st page and the last 3 pages of this thread. No time/patience to read the whole thing. Can somebody save me the time and catch me up a bit?

I have been using an FDeck HPF v3 for a few years now. But, it has always bugged me that it's really setup for use with an upright and not an electric bass.

For electric bass, it should have the input and output jacks swapped sides (and also maybe be on the sides), it doesn't need a knob for volume attenuation, and it should have a Bypass switch that turns it off (so you can leave the input and output cables plugged in all the time without killing the battery).

Is the Broughton L+HPF the way to go these days as an upgrade from my FDeck? As far as I can tell, FDeck has not come out with a model newer than what I have that would address my issues.

One thing I note is that the FDeck has a 24 dB/octave slope for everything below 35Hz. The Broughton appears to only have 12 dB/octave, period. That slope on the FDeck seems better, but maybe really not needed?

 

[NKBassman]

(and also maybe be on the sides)

Blasphemy!

One thing I note is that the FDeck has a 24 dB/octave slope for everything below 35Hz. The Broughton appears to only have 12 dB/octave, period. That slope on the FDeck seems better, but maybe really not needed?

This is something that's always intrigued me about the FDeck VS the Broughton. It's really two 12 db/octave filters working together, with one fixed at 35 Hz and one variable. If you set the variable one to 35, then you effectively get a 24 db/octave filter. Whether that's "better" or not depends on your goals.

 

[agedhorse]

It was a test of a number of guitar speaker simulators, so the purpose was understood. But I was curious about the response. HPFs in the UK are only found buried at the end of rainbows.

The reason I stated this is that HPF's for guitar applications are generally better sounding if they are not as steep as commonly encountered in bass applications. For bass, generally the steeper filters work better. This is an important distinction.

 

[-Asdfgh-]

The reason I stated this is that HPF's for guitar applications are generally better sounding if they are not as steep as commonly encountered in bass applications. For bass, generally the steeper filters work better. This is an important distinction.

The reason I stated this is that HPF's for guitar applications are generally better sounding if they are not as steep as commonly encountered in bass applications. For bass, generally the steeper filters work better. This is an important distinction.

Indeed. It was about as steep as I expected, which is to say not as steep enough.

 

[-Asdfgh-]

The GI100 sound surprisingly good on guitar. Never tried it on bass.

It beats fizzy distortion without one, but definitely had a vintage character due to the high roll off point

 

[Stumbo]

The reason I stated this is that HPF's for guitar applications are generally better sounding if they are not as steep as commonly encountered in bass applications. For bass, generally the steeper filters work better. This is an important distinction.

What do you recommend for a guitar LPF slope?

 

[agedhorse]

What do you recommend for a guitar LPF slope?

Somewhere between 6 and 12dB/octave, but it depends on what tones you are going after.

 

[Stumbo]

Somewhere between 6 and 12dB/octave, but it depends on what tones you are going after.

So, ideally, bass should be steeper? 24 db/octave?

Most of the HPF pedals that I've seen specs on use 12db/octave.

 

[agedhorse]

Again, depending on the tonal approach, I find that 12dB/oct in conjunction with a second 12dB/oct compound slope 24dB/oct filter generally provides the best of both worlds... 24dB where speaker protection is needed and 12dB where tonal sculpting is needed.

 

[Craig4003]

Again, depending on the tonal approach, I find that 12dB/oct in conjunction with a second 12dB/oct compound slope 24dB/oct filter generally provides the best of both worlds... 24dB where speaker protection is needed and 12dB where tonal sculpting is needed.

Which basically sounds like an F-Deck HPF 3, unless you disagree with the lower filter being fixed at 35 Hz. For an LPF, I would think a shallower slope would be preferable (6 or 12 dB at most), but of course it depends on the tone you want.

 

[Hundred proof]

Stumbo will probably know this ... I've been told that the red "bass" switch on the Sunn 200s actually rolls off bass to match the natural 200s cab roll off and increase the effective efficiency of the rig?

 

[agedhorse]

Which basically sounds like an F-Deck HPF 3, unless you disagree with the lower filter being fixed at 35 Hz. For an LPF, I would think a shallower slope would be preferable (6 or 12 dB at most), but of course it depends on the tone you want.

Similar concept, though I typically choose the lowest frequency point closer to 30Hz for (adjustable) electric bass applications unless the amp's intended to be used with speakers limited in low end performance.

The problem with the shallower slope is that you will end up affecting things that you may not want to alter, 12dB/octave seems to be about the happy medium for most players. I wouldn't want to go steeper than 12dB/oct not less that 6dB/oct certainly.

 

[StuartV]

Similar concept, though I typically choose the lowest frequency point closer to 30Hz for (adjustable) electric bass applications

Since the low B on a 5-string is 32 Hz, I would definitely prefer the lowest point to be 30 - 32. But, in practice, for live sound, the FDeck's 35 seems to be just fine.

I finally ordered a pedal board, so I can mount my small collection that I use, and stop having to re-cable and uncable everything together every time I play. I was thinking I would get a new HPF at the same time and do everything at once. But, with the FDeck having the extra roll-off - and the fact I already have it - now I'm thinking maybe I'll just stick with it. It IS narrower than the Broughton (I believe) and my board is going to be pretty packed, as it is.

I think, anyway.

Can you use the LPF on the Broughton to dial an electric bass down to sound more like an upright? Or do I just need to get some foam and hack some kind of bridge mute setup onto my bass?

 

[agedhorse]

The HPF's specified frequency is 3dB down (1/2-power), which is why I selected the bottom frequency of 30Hz (on the 800+) BUT this also assumes that the speakers can handle this extension. It can always be rolled up from there to taste.

 

[Boundary Effect]

Filters ring. The greater the order, the more ring. If the XO frequency is in a critical band, the more the "ring" is an issue. So for LF driver protection/amplifier power conservation, being down at 30Hz, higher order is acceptable. Above that and in the frequency content of our instrument, low order filters will have less effect on the "character" while shaping the contour of our sound.

A 100Hz high-pass filter at -6dB/oct, -12dB/oct and -18dB/octave, what does that look like? To begin, the frequency point for the filter is -3dB from nominal. So a 100Hz filter is attenuating above 100Hz. How much? None of this is linear.
Please look carefully at the XY values on my image:

White = the filter frequency.
Blue = test signal, a sweep from 16Hz to 500Hz @ -17dBfs. Not perfectly linear.
Green = HPF at 100Hz, 6dB per octave.
Red = HPF at 100Hz, 12dB per octave.
Orange = HPF at 100HZ, 18dB per octave.