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Author Topic: Sonic Sculpting Speakers with Shelving Filters  (Read 13440 times)

blgentry

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Sonic Sculpting Speakers with Shelving Filters
« on: July 02, 2017, 04:34:59 pm »

Over the past few years I've tuned a handful of speaker systems using mostly shelving type filters.  In several cases I've done this directly with DSP Studio in JRiver MC.  You might be wondering why would I use shelving filters.  Or you might be wondering what a shelving filter even is.

Shelving filters are very simple.  Think of the frequency response of a system as a straight line from left to right.  The lows are on the left, the highs are on the right.  A shelving filter pushes one end of the line up higher than the other.  So a high shelf filter at 5000 Hz, would push up all the frequencies from 5000 Hz up to 20,000 Hz up higher than the rest.  Or pull them down if you specify a negative value.

A high shelf filter that's -6 dB at 3000Hz pulls all frequencies above 3000 DOWN by 6 dB.  These are called "shelving filters" because the frequency response becomes a step or a "shelf".  It shifts everything up or down all the way to the end of the line.  A picture would probably help.  Here's one I found:

http://www.hometheatershack.com/forums/attachments/electronic-processing-equalization-devices/8927d1219189200-sub-eq-room-calibration-equipment-question-shelving-filters.jpg

So that's what a shelving filter is.  But why would I want to use these instead of parametric EQ bands?  The simple answer is that shelving filters are good for sonic sculpting.  They are good for pushing around the frequency response of your system in medium to large "chunks".  Parametric EQ bands, even when they are made wide with a low Q are still rather narrow sonically.

What I find with many systems is that they have obvious problems that need to be corrected by moving a lot of the frequency spectrum around at once. Sort of like traditional bass and treble controls. But much more precise and much more powerful.  In fact, the last time I did a really successful tuning on a high end car audio system, all I had to work with were parametric EQ bands.  But the car had such extreme frequency response problems, that we ended up overlapping parametric bands so we could affect large smooth chunks of the frequency response all at once.  The result, graphed on the computer interface looked quite a bit like several shelving filters.  I don't think we made any narrow band changes.  The result was *dramatic* in a good way.  If we had access to shelving filters in the device we were using to tune, it would have been faster and easier to get to the same point.

As an illustration of how I use these let's look at my desktop speaker system and how I've tuned it.  My current desktop speakers are an older set of satellite speakers with their own matched passive subwoofer.  The 10" bandpass subwoofer has passive crossovers built in to it and it sends the mids and highs to the satellites, which have 4" mids and 1" cloth dome tweeters.

This setup was designed to be a home theater system, or just a somewhat compact set of full range speakers to be used in a normal sized room at a normal listening distance of 6 to 15 feet.  This last part is the problem:  The distance.  Have you ever gotten very close to a set of speakers and noticed they they sounded much brighter or more detailed?  That's because highs fall off faster with distance than mids or lows.  So, a speaker that sounds really balanced at 8 feet, is going to sound very bright (lots of highs) at 2 feet.  Guess how far my speakers on my desk are from my ears.  You guessed it!  About 2 to 2.5 feet.

So, these really decent speakers are nearly unlistenably bright at desktop distances.  Shelving filters to the rescue!  My first goal was to reduce the high frequency response.  So I made a negative high shelf filter to move down the highs.  I started at around 3500 Hz and listened.  Then I moved the frequency around and kept listening.  What I figured out was that the high boost on these speakers starts rather low.  I settled on 800 Hz as my knee frequency and brought everything from 800 Hz and higher *down* by 3dB.  Which really helped.  The bottom ends of voices started to have a bit more body.  But there were still too many highs.  I moved up a few octaves and settled on 3500 Hz and made another high shelf:  -4 dB . 

Astute readers will have realized that this means that everything from 3500 and higher is actually down by -7 dB because the two shelves add together.  The frequency response graph, which was originally a flat line now has two steps down in it along it's path to the right.

Now the sibilant parts of voices was vastly reduced and starting to sound very natural.  But there was still too much sizzle on the top end of voices making them sound artificial.  Just a little adjustment:  High shelf -1 dB at 5000 Hz.

By this point things were sounding really nice.  But I noticed that cymbals and other very high frequency content had lost a lot of it's "spit and sizzle".  They sounded overly muted and lacking that high end sparkle.  Again I experimented, but settled on another high shelf, but this time a BOOST:  High shelf, +4 at 10,000 Hz.  This brought the sparkle back without making voices sound weird, or tearing my head off with the treble.  Just some pleasant highs.

There was still something wrong in the vocals, but it was subtle.  I played around with a single parametric EQ band and moved it around a bit until I tamed it:  frequency of 1700 Hz, Q of 1, -2 dB .

Note that I played around with both the step frequency and the amount of cut each time I made these changes.  It took experimentation to figure out each one.  I spent around 2 hours making these adjustments initially, and then over the next day made some minor tweaks until I was satisfied.

Reading through this, it might not be obvious why I'm turning everything DOWN and not turning anything UP.  In the digital domain, it's normally best to cut, rather than boost, because if you boost, at some point you can over flow the digital signal's dynamic range and cause clipping.  So I prefer to cut, cut, cut, and then, if necessary, add back just a bit to bring the overall signal level up closer to where it originally was.  In my case I did just this and added +3 dB of Volume.  I probably could have added more, but I wanted to be conservative to account for many different types of music (and corresponding frequency blends).

The effect of these adjustments was again, DRAMATIC.  The bass is much more prominent and punchy.  But not "one note" or "boomy".  Because I didn't boost ANY bass frequencies.  I just cut everything above 800 Hz, which brought up the bass, the mid bass, and the bottom end of the vocal range.  Voices on these speakers originally sounded thin, bright, and "biting".  Vocals now are rather natural and balanced in my opinion.  The highs are just about right, though some would hear these and think they they lack high frequency detail.  I did that on purpose in order to make these speakers non-fatiguing.  I find extended "detailed" highs to wear my ears out very quickly.  With these speakers, tuned this way, I can listen for several hours, at a moderate to low volume, and be very happy doing so.  Which is the whole point right?

I'm guessing that some reading this are thinking that doing what I've done has completely destroyed the sound of these speakers and that my efforts are misguided at best.  You're certainly entitled to that opinion.  I used to share a similar opinion about equalizers in general.  My acid test for equalizer users is very simple:  Do you ever touch the eq between songs?  If your answer is "of course, I change it for almost every song!", then your EQ is misadjusted.  EQ *can* be done right.  When it's done right, you won't want to change it for every song.  That's how this system behaves for me.

Finally, I think that this process is fairly similar to how speaker designers design and tune speakers.  Moving entire sections of the frequency response up and down is done all the time in speaker design.  Either by selecting drivers with different efficiency ratings, or by adding padding to the passive crossovers.  It's fairly typical to have pads in the tweeter circuit to bring it down in level, as the tweeter tends to be the most efficient driver in a multi-way system.  I'm doing somewhat similar adjustments.  I just happen to be doing it in the digital domain with more precise controls.

This is my new tuning method of choice for speakers and headphones.  I think it works quite well.

Thanks for reading.

Brian.
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~OHM~

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #1 on: July 02, 2017, 05:03:50 pm »

Interesting....So where is the how to guide for a novice like me?
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JimH

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #2 on: July 02, 2017, 05:47:37 pm »

Thanks for taking the time to write that up, Brian.
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Blu99Zoomer

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #3 on: July 03, 2017, 11:39:54 am »

I would echo Jim and say nice write up.  Brian thanks for taking the time to.  I took a quick look at the JR DSP Studio options.  There were a couple of references to filters, but not the shelving type.  I also noticed the parametric equalizer options.  I remember playing with those in a car but years ago.  Automobiles are not the most friendly place to play with sound.  But this ability to change the sound coming out of one's speakers is all very interesting.  I will read further on the site you grabbed the graphs from.  I have a project in mind to try once I understand the concept and how to's better.  Here I would echo OM and say that I look forward to your next installment... ;) 

Best Regards,

Gregg
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DocLotus

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #4 on: July 03, 2017, 12:51:01 pm »

GREAT write up Brian, well thought out.

I've always been very interested in equalization, curves, time delay due to distance, db levels, etc.  They can have anywhere from small to a very big impact on sound quality. When properly added together the sound stage can go from flat/muted/dull to really alive where it can sound so good that all you want to do is listen to the music.

One thing that I've noticed is moving from large Home Theater (McIntosh) to a PC speaker system (dual Logitech 5.1 PC speakers set up in a 7.1 array) is the curves needed are very different between the two. Not just because of the completely different speaker brands or size but due mostly to the lower listening levels. With the Home Theater system I was setting far back (about 15 feet) with the volume cranked up. With the PC speakers, like you I'm much closer so the levels are also much lower. At lower levels most frequencies sound different (less bass, less highs) so the curves needed to correct are also different.

But no matter what the levels are corrected speakers can make a noticeable difference.

As others have said... thanks again for the nice write up.

Doc
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flac.rules

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #5 on: July 05, 2017, 05:28:55 am »



The effect of these adjustments was again, DRAMATIC.  The bass is much more prominent and punchy.  But not "one note" or "boomy".  Because I didn't boost ANY bass frequencies.  I just cut everything above 800 Hz, which brought up the bass, the mid bass, and the bottom end of the vocal range.  Voices on these speakers originally sounded thin, bright, and "biting".  Vocals now are rather natural and balanced in my opinion.  The highs are just about right, though some would hear these and think they they lack high frequency detail.  I did that on purpose in order to make these speakers non-fatiguing.  I find extended "detailed" highs to wear my ears out very quickly.  With these speakers, tuned this way, I can listen for several hours, at a moderate to low volume, and be very happy doing so.  Which is the whole point right?


Provided you don't clip, whats the difference? Boosting bass and turning down treble should do exactly the same?
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Spike1000

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #6 on: July 05, 2017, 07:46:30 am »

Similar thing maybe yes, but not the same. Tone controls aren't 'shelf like' and you don't get to choose the frequency they operate from. You may get an improvement in sound with them but you can't tune them in terms of the frequency they operate over. Brian has multiple shelves 'stacked' (or stepped?) over a given frequency range, these shelves have both 'cuts' and 'boosts' between 800Hz and 10kHz+. Something you can't do with a tone control.

Spike

blgentry

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #7 on: July 05, 2017, 07:49:08 am »

I took a quick look at the JR DSP Studio options.  There were a couple of references to filters, but not the shelving type.  I also noticed the parametric equalizer options.

The DSP section called Parametric EQ actually does a whole lot more than just PEQ.  Click on the Add button inside of PEQ and you'll see all of the different filter types it supports, including high shelf and low shelf.

Have fun.

Brian.
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blgentry

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #8 on: July 05, 2017, 07:51:10 am »

Provided you don't clip, whats the difference? Boosting bass and turning down treble should do exactly the same?

Yes, provided that you *don't* clip.  The problem is, you never know how high the signal level of the music you are playing will be.  If you have boosted everything below 800 Hz by say, 7 dB, then any signal below 800 Hz that is close to full scale is going to clip for sure.  This is why I choose to cut instead.

It's actually a well known practice in the analog world also.  There are several models of stand alone analog equalizers that are cut only; no boost is even available.

Brian.
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Blu99Zoomer

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #9 on: July 05, 2017, 11:04:26 am »

I see it!  I see it!  Oh yeah!!!  Again, your patient explanation is much appreciated .

Best Regards,

Gregg
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flac.rules

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #10 on: July 06, 2017, 02:18:11 am »

Similar thing maybe yes, but not the same. Tone controls aren't 'shelf like' and you don't get to choose the frequency they operate from. You may get an improvement in sound with them but you can't tune them in terms of the frequency they operate over. Brian has multiple shelves 'stacked' (or stepped?) over a given frequency range, these shelves have both 'cuts' and 'boosts' between 800Hz and 10kHz+. Something you can't do with a tone control.

Spike

What you are saying is that finer grained controls can do more than coarser controls. That is of course the case, but when discussing boosting bass vs attenuating treble, its more meaningful to assume the same type of controls in both scenarios. (and more realistic i would say).
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flac.rules

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #11 on: July 06, 2017, 02:20:57 am »

Yes, provided that you *don't* clip.  The problem is, you never know how high the signal level of the music you are playing will be.  If you have boosted everything below 800 Hz by say, 7 dB, then any signal below 800 Hz that is close to full scale is going to clip for sure.  This is why I choose to cut instead.

It's actually a well known practice in the analog world also.  There are several models of stand alone analog equalizers that are cut only; no boost is even available.

Brian.

It is easier not to clip, that is true. (although one could just do the opposite of what you did, and turn down the entire signal). But in your post I got the impression that you ment the quality of the bass itself was also different. But after your clarification, it seems we are in agreement.
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blgentry

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #12 on: July 06, 2017, 06:42:15 am »

But in your post I got the impression that you ment the quality of the bass itself was also different. But after your clarification, it seems we are in agreement.

I was making two separate points and perhaps I should have illustrated that better:

1.  Turning down (cut) works better because it prevents clipping.
2.  Using shelving filters to boost the bass works better than parametric EQ in many cases; particularly when you don't have measurement equipment.  It's easy to really screw up the sound of your system using (relatively) narrow band filters.  You can easily make big spikes.  In the bass, this results in "one note" or "boomy" sound since one very narrow band has been boosted in an effort to get more bass.  On the other hand, shelving filters boost (or cut) a whole range at once, so you don't get these narrow band effects.  Generally speaking I think this is much safer in terms of not harming the sound.  This is just a generalization; parametric EQ certainly has it's place.

So, you read me correctly.  I just didn't make my points clear enough.  I hope this helps.

Brian.
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drmimosa

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #13 on: July 09, 2017, 05:46:08 pm »

Brian, facinating post and great idea. Thank you!

This immediately made me think of the Harmon House EQ curve, which I've read about but never implemented.

https://www.innerfidelity.com/content/acoustic-basis-harman-listener-target-curve

Suppose I would like to make a stock decending "house" EQ curve that cut 1db per octave across the audible spectrum, for a total of 8db slope from (say) 65htz to 16khtz. If I understand your post correctely, the following  high shelf filters could accomplish this curve.

130htz -1db
260 -1db
520 -1db
1040 -1db
2080 -1db
4160 -1db
8320 -1db
16640 -1db

Of course, this is not taking into account room acoustics. The goal is an EQ slope as described in the article, with the hope that it sounds good with my room and speakers. I don't currently have measuring equipment, just will  experiment and listen.

I may be missing something in my understanding of the Harmon curve and usage of it as well. 8db seems a bit much for a cut, so -.5 db may be a better value for each shelf for a -4db slope. The paper I linked to specified a -6db slope as preferred by listeners.

Does this look like it accomplishes what I am trying to do? Also, how significant is the Q value in the shelf filters?

Thanks again for your time spent writing this post!
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flac.rules

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #14 on: July 10, 2017, 03:19:13 am »

The curve is what you get in a good room with a flat respons from the speakers. It is (in general) not a good idea to implement the curve at the signal level.
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blgentry

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #15 on: July 10, 2017, 09:47:52 am »

This immediately made me think of the Harmon House EQ curve, which I've read about but never implemented.

https://www.innerfidelity.com/content/acoustic-basis-harman-listener-target-curve

Interesting.  I own a pair of headphones that were modeled after the Harmon Olive curve:  The NAD HP50s.  They are sublime.  Very non-fatiguing, yet somehow rather detailed also.  Not as detailed as many other headphones, but definitely not lacking in sparkle at all.  They're very seductive.  (If an audio device can be described with that word...)

Quote
Suppose I would like to make a stock decending "house" EQ curve that cut 1db per octave across the audible spectrum, for a total of 8db slope from (say) 65htz to 16khtz.

It would be neat if MC had a DSP filter to do arbitrary slopes like this.  What you're essentially asking for is a low pass filter at 65 Hz with a 1 dB/octave slope.  A low pass filter with an arbitrary slope, would be pretty neat to play with; particularly for this type of application.

Quote
If I understand your post correctely, the following  high shelf filters could accomplish this curve.
...

Yes, I think that will work. It won't be exactly a straight line sloped filter.  But it should produce approximately the response you're looking for.

Quote
I may be missing something in my understanding of the Harmon curve and usage of it as well. 8db seems a bit much for a cut, so -.5 db may be a better value for each shelf for a -4db slope. The paper I linked to specified a -6db slope as preferred by listeners.

You can certainly play with it and see what you think.  You might find that making some custom adjustments to the overall downward slope work better with your room or speakers.  There are lots of possibilities for how you could use this general idea.

Quote
Also, how significant is the Q value in the shelf filters?

I believe the Q value affects the curved part of the response.  The part that's near the knee frequency.  The higher the Q, the steeper the slope of the curved part.  I wouldn't mess with the Q to start with.  I'm far from an expert; this is just my understanding and my advice.

Good luck with your experiments!  :)

Brian.
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mattkhan

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #16 on: July 11, 2017, 06:16:35 am »

You can use rephase to look at how arbitrary filters sum, see attached pic for an example

a few things to note;

- the jriver dsp window asks you to enter a Q value for the filter but it is actually S so the Q value entered in most other apps does not directly translate to the jriver value (it would be better IMO if jriver changed this to actually accept Q). You can convert from Q to S though, one easy way to do it is to paste this formula into https://www.mathpapa.com/algebra-calculator.html and enter values for Q and gain (d in the formula below)

1/((((1/Q)^2-2)/((10^(d/40))+1/(10^(d/40))))+1)

- as Elvis133 says, such a target curve is intended to be a target for your room not the source material, use it to adjust your room response to that target not the source material
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jtconte

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #17 on: July 13, 2017, 07:09:33 pm »

Thanks for the excellent write up, Brian!
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adiebear

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #18 on: July 28, 2017, 02:10:59 pm »

You can use rephase to look at how arbitrary filters sum, see attached pic for an example

a few things to note;

- the jriver dsp window asks you to enter a Q value for the filter but it is actually S so the Q value entered in most other apps does not directly translate to the jriver value (it would be better IMO if jriver changed this to actually accept Q). You can convert from Q to S though, one easy way to do it is to paste this formula into https://www.mathpapa.com/algebra-calculator.html and enter values for Q and gain (d in the formula below)

1/((((1/Q)^2-2)/((10^(d/40))+1/(10^(d/40))))+1)

- as Elvis133 says, such a target curve is intended to be a target for your room not the source material, use it to adjust your room response to that target not the source material
Oh dear! Alphabet soup (Q. S etc.)and mathematical formulae do my head in. The concepts I get. How to implement dsp on my own? Not so much. I wish I could borrow Brian and others in this thread o sort  out the finer bass bits (a pair of Vandy 2wq subs and Eminent Technology LFT8b's in a fairly well treated room). I'm just using Alan Parsons' test tones and combination sweeps over and over and dropping or raising certain frequencies according to my ears (eek!). Now and the I use a friend's high end system (Vivid Audio Giya G1 Spirits for example) as a reference.
Sounds pretty good to me, but could sound better I'm sure. Sigh.
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Wilderness

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Re: Sonic Sculpting Speakers with Shelving Filters
« Reply #19 on: September 30, 2020, 11:34:39 am »

Over the past few years I've tuned a handful of speaker systems using mostly shelving type filters.  In several cases I've done this directly with DSP Studio in JRiver MC.  You might be wondering why would I use shelving filters.  Or you might be wondering what a shelving filter even is.

Shelving filters are very simple.  Think of the frequency response of a system as a straight line from left to right.  The lows are on the left, the highs are on the right.  A shelving filter pushes one end of the line up higher than the other.  So a high shelf filter at 5000 Hz, would push up all the frequencies from 5000 Hz up to 20,000 Hz up higher than the rest.  Or pull them down if you specify a negative value.......

This is my new tuning method of choice for speakers and headphones.  I think it works quite well.

Thanks for reading.

Brian.

Brian,

I can't thank you enough.  I had been having a terrible problem with wince-inducing sibilance with "s" sounds and even worse with "t" sounds for more than a year.  I tried adjusting speaker toe in, purchasing new cables, etc., but those changes only helped a little.  With your advice about shelving in JRiver, I finally solved the problem.

Here are the high shelf settings I used for my bright system:

-3 dB 2000 Hz.
-4 dB 5000 Hz.
-5 dB 7700 Hz.

I set a separate parametric equalization at -6 dB. at 9000Hz.

I am very pleased with the sound I am now getting.  The sibilance is gone, and I am getting more beautiful bass undertones with acoustic guitar.  Sweet!

I owe you a premium beer and/or gourmet lunch, which wouldn't even begin to repay you for the money you saved for me.  I was going to spend thousands of dollars for new audio equipment without any guarantee of success.  Maybe I'll see you at an audio show next year.

P.S.: I think JRiver should feature your advice about shelving.  Many audiophiles have the same problem with sibilance that I had.  They would be so grateful if they could solve their problems with sibilance with shelving.

Allan
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