High shelf and low shelf filter slopes. Does anyone use them?

[Shadrach]

I read a lot about parametric equalizers but most seem to use the standard bell curve with High Shelf and Low Shelf filters. Do people use the filter slope options and what did they find?
What about Notch Filters for a particular narrow frequency band?
What about various plugins to add perhaps a tiny amount of distortion over a limited frequency span to calm a strident frequency?

 

[Jimbob54]

I read a lot about parametric equalizers but most seem to use the standard bell curve with High Shelf and Low Shelf filters. Do people use the filter slope options and what did they find?
What about Notch Filters for a particular narrow frequency band?
What about various plugins to add perhaps a tiny amount of distortion over a limited frequency span to calm a strident frequency?

Your title doesnt really match your post.

As to slopes, all I can say is use a free eq package and try. Try high q and low q shelf filters, pass filters and peak filters.

But yes, slopes matter. Try a 5 dB peak at 1000 Hz with a q of 1 vs a q of 5. Reduce volume first.

 

[terryforsythe]

I have tried modelling some biquads in VituixCad. They provide more flexibility, but take a little more work to get the correct parameters.

I have not used them enough to consider myself proficient at using them. I am working on a project where I am removing my speakers' passive crossovers and going all active. Initially I have modeled the system in VituixCAD using biquads for the crossovers, but IIR filters for the equalization. I may delve deeper into biquads when my equipment arrives and I start tuning the system.

 

[DVDdoug]

With a parametric equalizer you can vary the "Q" which relates to the width and slope of the filter.

There are all kinds of filters you can build with hardware, and more you implement in software. It depends on what you're trying to do or what kind of problem you're trying to solve.

What about various plugins to add perhaps a tiny amount of distortion over a limited frequency span to calm a strident frequency?

Of course, you generally you don't want distortion and a filter shouldn't introduce distortion. There is an effect called an "Exciter", or other similar names from the old Aphex Arual Exciter, which added high frequency harmonics.

It's probably not too hard to create a high or mid-frequency resonance that sounds "strident".

 

[Shadrach]

Your title doesnt really match your post.

As to slopes, all I can say is use a free eq package and try. Try high q and low q shelf filters, pass filters and peak filters.

But yes, slopes matter. Try a 5 dB peak at 1000 Hz with a q of 1 vs a q of 5. Reduce volume first.

Fixed that. Thanks.
Have you tried shelf filter slopes? They can be adjusted on some software. I have 4 slope options in my equalizer.
I read people complaining about a prominent to strident frequency but I've not read anyone suggest a notch filter to deal with it.
It seems most people just use frequency and Q with the standard bell curve.

 

[witwald]

I read people complaining about a prominent to strident frequency but I've not read anyone suggest a notch filter to deal with it.
It seems most people just use frequency and Q with the standard bell curve.

But when set to reduce the amplitude, isn't a parametric filter with adjustable frequency and Q producing a notch filter? I suppose notch filters sometimes are associated with a very narrow bandwidth and a very deep attenuation, but those are all simply user-defined operational settings of a parametric EQ filter adjusted to suit the equalization task.

 

[Shadrach]

With a parametric equalizer you can vary the "Q" which relates to the width and slope of the filter.

Yes, but the Q value extends or contracts a bell curve. The curve should be identical on both sides. With shelf filters which can extend over a wide frequency range the plot is horizontal as standard but one can adjust the slope and it isn't a bell curve. One end is sharp cut off.

 

[Shadrach]

But when set to reduce the amplitude, isn't a parametric filter with adjustable frequency and Q producing a notch filter? I suppose notch filters sometimes are associated with a very narrow bandwidth and a very deep attenuation, but those are all simply user-defined operational settings of a parametric filter adjusted to suit the equalization task.

One might think so but I think a notch filter doesn't have the bell curve tails. Some notch filters span a small frequency selection but drop vertically or close to it, so no bell curve tails.

 

[Shadrach]

Sorry about the sketchy drawing.
This is what I'm on about. Filters can have different shapes and their shape not only effects the specified frequency but also the frequencies either side.
I believe some notch filters have vertical sides.

 

[dualazmak]

I read a lot about parametric equalizers but most seem to use the standard bell curve with High Shelf and Low Shelf filters. Do people use the filter slope options and what did they find?
What about Notch Filters for a particular narrow frequency band?
What about various plugins to add perhaps a tiny amount of distortion over a limited frequency span to calm a strident frequency?

If you use Windows 11 PC for your DSP processing, I would like to suggest you to test and evaluate "EKIO" which has very flexible nicely designed GUI for XO/EQ/Group-Delay/Relative-Gain configurations including GUI control for EQ settings. The paid-up (USD 149, lifetime) EKIO can have unlimited numbers of input/output channels for your multichannel configuration, all in up to 192 kHz processing.

EKIO uses IIR filters. The processing is done using a cascade of second order transposed direct form II biquad sections. Every calculation is done using 64 bit floating point numbers. EKIO also has ABX comparator functionality using two sets of different configurations saved as configuration files.

By using VB-AUDIO Matrix as system-wide ASIO/VAIO/VASIO routing center, EKIO can work as system-wide one stop DSP Center on your Windows PC (ref. here and here on my multichannel project thread).

Of course, if you like, you can use EKIO as simple stereo EQ center feeding EQ-ed stereo signal into single stereo DAC. You can first try this with free trial version of EKIO (which can have only two output channels, i.e. stereo L and R), but you may easily do try-and-error and play with the very much flexible GUI EQ configurations for stereo 2-CH output into stereo DAC.

 

[Shadrach]

I don't have a windows PC. I use Linux on all my computers.
I'm using Pulse, the pipe wire version Easy Effects and the older Pulse Effects. I have Ubuntustudio on one machine.
I'm interested in this for playback, not production, so something simple should do.

 

[dualazmak]

I don't have a windows PC. I use Linux on all my computers.
I'm using Pulse, the pipe wire version Easy Effects and the older Pulse Effects. I have Ubuntustudio on one machine.
I'm interested in this for playback, not production, so something simple should do.

OK, understood well.
I still would like to suggest you, to just try EKIO by making one of your (spare?) PC as Windows 11 machine, if possible.
My two completely silent (standalone) Windows PC (ref. here) are rather outdated ones, but they are just fine as dedicated audio(-visual) playback center with JRiver MC, EKIO, VB-AUDIO Matrix.

 

[terryforsythe]

Sorry about the sketchy drawing.
This is what I'm on about. Filters can have different shapes and their shape not only effects the specified frequency but also the frequencies either side.
I believe some notch filters have vertical sides.

VituixCAD runs on Linux using Wine (I have it running on Linux Mint). You might check it out. It's free.

https://kimmosaunisto.net/Software/VituixCAD/VituixCAD_in_Linux_v0.2.pdf

It provides a shelf filter in the form of a Linkwitz Transform.

With whatever IIR filters you come up with, you can copy the Biquad parameters and import them in an EQ that works with Biquads. Also, you can directly work with Biquads in VituixCAD. It is pretty powerful.

 

[Shadrach]

I may not have made myself clear.
I'm not after suggestions for a parametric equalizer; I've got a few already.
As mentioned above, I have Linux Studio

Linux Studio Plugins Project

lsp-plug.in

Lots of options in the plugins, some better than others.
I also have Pulse Effects and Easy Effects, both look basic but they are quite versatile.

Install PulseEffects on Linux | Flathub

Audio Effects for PulseAudio Applications

flathub.org

I'm interested in how people use their parametric equalizers and what audible differences they found, if any, by not using the standard bell curve Q, instead using say a notch filter to reduce those lower frequency that set up room nodes for example. One could, and I have with some success removed an entire single frequency using a notch filter.
With a shelf filter, with the right slope one can tailor a group of frequencies say from 50Hz to 20Hz.
It seems from what I've read many people just load a preset and perhaps consider this as good as it gets. With a better understanding of how these filters work and some experimentation it's possible to deal with room effects without altering the freqencies that are okay either side of the problem frequency.

Anyway, I was just curious.

I have no intention of using windows anything.

 

[Jimbob54]

Yes, but the Q value extends or contracts a bell curve. The curve should be identical on both sides. With shelf filters which can extend over a wide frequency range the plot is horizontal as standard but one can adjust the slope and it isn't a bell curve. One end is sharp cut off.

Doesn't have to be sharp. Can taper off quite gently.

Shelf filters are very common in headphone land where most need a few dB boost below (say) 150 Hz. Usually a q of 0.7 is used but less than that can work quite nicely.

 

[sigbergaudio]

@Shadrach I think you've misunderstood a thing or two.

1) The brick wall filter all the way to the right in your drawing that you call notch filter isn't really a thing. I don't understand why you want to do it either, no room modes look like that.You can have sharp falloff on each side, but then the peak will typically also be very narrow (not a flat area like you had in your drawing).

2) Beyond that, "notch" filter is just a name for a narrow filter that attentuates. A PEQ point either boost (peak) or cut (notch). How sharp/narrow it is depends on the Q. A lower Q gives something more like a bell curve.


To summarize, a notch filter looks like this:

 

[Shadrach]

@Shadrach I think you've misunderstood a thing or two.

1) The brick wall filter all the way to the right in your drawing that you call notch filter isn't really a thing. I don't understand why you want to do it either, no room modes look like that.You can have sharp falloff on each side, but then the peak will typically also be very narrow (not a flat area like you had in your drawing).

2) Beyond that, "notch" filter is just a name for a narrow filter that attentuates. A PEQ point either boost (peak) or cut (notch). How sharp/narrow it is depends on the Q. A lower Q gives something more like a bell curve.


To summarize, a notch filter looks like this:

View attachment 341931

I had hoped the note "may have sloping sides" covered this. My bad.
So what does one call a filter that completely removes a particular frequency?
I've seen this done in a recording studio.

 

[sigbergaudio]

I had hoped the note "may have sloping sides" covered this. My bad.
So what does one call a filter that completely removes a particular frequency?
I've seen this done in a recording studio.

It's not possible to just remove one single frequency (like removing for instance 1259hz) surgically, but you can use a very high Q filter to reduce a very narrow range. Why are you looking to do this again?

 

[Philbo King]

I read a lot about parametric equalizers but most seem to use the standard bell curve with High Shelf and Low Shelf filters. Do people use the filter slope options and what did they find?
What about Notch Filters for a particular narrow frequency band?
What about various plugins to add perhaps a tiny amount of distortion over a limited frequency span to calm a strident frequency?

I find the phase shift on shelf filters is much less objectionable (less likely to cause unwanted cancellations) than low/high pass filters.

But that is during song editing and mixing. My speakers, JBL 308P, have their crossovers done in fixed DSP which I have never needed or wanted to alter. My room correction uses only peak/cut PEQ filters.

 

[voodooless]

It's not possible to just remove one single frequency (like removing for instance 1259hz) surgically, but you can use a very high Q filter to reduce a very narrow range. Why are you looking to do this again?

Well, you can, but not with these conventional IIr filters. A FIR filter with enough filter taps can remove a single frequency with enough precision and depth. Alternatively a route via FFT and iFFT would do it, but similar caveats apply.