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

[loveandbass]

Can I achieve HPF sufficiently with my amps parametric EQ (Eden wt300 in this case)?

 

[agedhorse]

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.
View attachment 3018210

Where did you get this information? Do you know "for sure" that it is correct or by chance did you maybe pick this up on the internet without understanding what the mistake is?

[hint: a filter's slope or a filter's order is independent of ringing or pass-band ripple]

 

[agedhorse]

As a follow-up, here's a set of 4 filters, each 12dB/octave (second order) with different Q's (shown as the inverse of Q), You will notice that they all have the same slope, but the Q represents the resonance at the knee. Resonance is either natural (for LRC filters) or artificial (for feedback type filters), but the ultimate slope is defined by the order which is independent of Q.

 

[agedhorse]

Here's an example of different slopes with the same Q:

 

[Boundary Effect]

Where did you get this information? Do you know "for sure" that it is correct or by chance did you maybe pick this up on the internet without understanding what the mistake is?

[hint: a filter's slope or a filter's order is independent of ringing or pass-band ripple]

The greater the order, the more difficult it is to design a great network. One can design a 4th order network that sounds better, performs better, rings less, than some other 2nd order network. Sure. Orders are independent of pass-band ripple, etc. Use your ears, if you have them.

 

[-Asdfgh-]

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.

Maybe the Behringer isn't so far off at 10, then, although my mk.1 eyeball suggests no compound value. I'd imagined something closer to 24 was more ideal. It's a high roll off start at 100Hz, perhaps. I'll do my own tests with the gear I have, though.

 

[-Asdfgh-]

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.
View attachment 3018210

the Behringer looks like the green line, but starting at 100Hz, but orange, at 80Hz or below its what I assumed would be required.

 

[lowplaces]

Here's an example of different slopes with the same Q:

Could be my OS but I am getting this message....
TalkBass.com - Error
The requested attachment could not be found.

 

[agedhorse]

The greater the order, the more difficult it is to design a great network. One can design a 4th order network that sounds better, performs better, rings less, than some other 2nd order network. Sure. Orders are independent of pass-band ripple, etc. Use your ears, if you have them.

Ringing and ripple are purely described by the math. Higher Q's are accompanied by greater ringing because of the feedback required to increase the resonance (reduce the damping). [another hint: I do this for a living, I understand the math, have an EE degree and have a history of over 35 years designing commercial products that use a variety of filter types and slopes.

When you say "use your ears, if you have them", your comment appears to be intended as insulting which is definitely not appreciated. You are awfully new here, this is not a good way to become part of this family.

There's enough BS on forums in the form of bad information, and the information that you provided is simply wrong. If you understood how filters worked and how their various elements are described, you would then recognize how foolish the statements you made are. The forum members that are here learning more about how their gear works deserve correct, accurate information rather than postings by somebody who (clearly by your posts) doesn't understand the topic. It's looking like you are a new member who is getting into some deep water and can't swim.

 

[Stumbo]

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?

[Invalid or Expired Link Removed]

DC wall power only. No batteries.
There's an always-on (no by-pass switch) unit available. I have that one on the way.
I haven't read about any direct comparisons of fdeck and Broughton.
I also haven't read about any complaints about Broughton.

 

[Al Kraft]

Use your ears, if you have them.

I'm not experienced enough in this area to have an informed opinion, however, I'm absolutely smart enough to know that when people like agedhorse are sharing insights and knowledge, I should listen carefully. One thing I learned very early in my 40 year career as an engineer (in areas unrelated to this topic) is how to recognize when there's a person in the room who is smarter than me on the topic at hand...respectfully, I think you'll find that this is a great life skill that will serve you well too.

I haven't come across many engineers or scientists who are more accomplished in their field than agedhorse, and he deserves more respect than you've shown him IMHO. You should do yourself a favor and take the time to find out who you are talking to before continuing this dialogue.

 

[Stumbo]

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?

 

[Stumbo]

Can I achieve HPF sufficiently with my amps parametric EQ (Eden wt300 in this case)?

Maybe @agedhorse can educate us on the difference between a parametric EQ and an HPF.

 

[NKBassman]

Maybe @agedhorse can educate us on the difference between a parametric EQ and an HPF.

A parametric EQ is simply an EQ that allows you to play with more parameters than you’d otherwise have access to. Ie not just Boost/cut at a fixed frequency. Most parametric eqs will allow you to change the center frequency of the band, and sometimes the Q as well.

 

[NKBassman]

Can I achieve HPF sufficiently with my amps parametric EQ (Eden wt300 in this case)?

Define "sufficiently". What are you trying to achieve?

I see it has a semi-parametric Low band which goes down to 30 Hz. Assuming it's likely a peak/dip filter (not true High Pass), but there's no reason why you couldn't use it to remove low frequencies if that's what you're after.

 

[agedhorse]

A parametric EQ is simply an EQ that allows you to play with more parameters than you’d otherwise have access to. Ie not just Boost/cut at a fixed frequency. Most parametric eqs will allow you to change the center frequency of the band, and sometimes the Q as well.

A parametric eq, as found on bass amps, are bandpass filters typically used in mid bands which is not the same as the bass and treble eq bands (which are shelving filters).

Shelving filters are rarely parametric on bass amps (I can't think of any)

Parametric, as applied to the mid bands typically means sweepable mids, but in some rare cases also allows for the adjustment of the filter's Q (or width).

 

[NKBassman]

A parametric eq, as found on bass amps, are bandpass filters typically used in mid bands which is not the same as the bass and treble eq bands (which are shelving filters).

Shelving filters are rarely parametric on bass amps (I can't think of any)

Parametric, as applied to the mid bands typically means sweepable mids, but in some rare cases also allows for the adjustment of the filter's Q (or width).

Isn't that what I said?

 

[beans-on-toast]

While not a dedicated HPF and LPF, tone controls use them.

The James tone circut can be thought of as a combined low pass and high pass shelving control, the center frequency in the mids where they intersect can be variable to some extent.

Analysis of the James Tone Stack


This is an interesting approach.

[Invalid or Expired Link Removed]

 

[Al Kraft]

A parametric eq, as found on bass amps, are bandpass filters typically used in mid bands which is not the same as the bass and treble eq bands (which are shelving filters).

Shelving filters are rarely parametric on bass amps (I can't think of any)

Parametric, as applied to the mid bands typically means sweepable mids, but in some rare cases also allows for the adjustment of the filter's Q (or width).

Is the formally accepted definition within the industry that when you can select frequency and level (but not Q/bandwidth affected) that it's referred to as semi-parametric EQ and when you have control over all three attributes (level, frequency and Q) it's referred to as parametric EQ?

 

[NKBassman]

Is the formally accepted definition within the industry that when you can select frequency and level (but not Q/bandwidth affected) that it's referred to as semi-parametric EQ and when you have control over all three attributes (level, frequency and Q) it's referred to as parametric EQ?

That's how I see it, but I don't represent "the industry".