Frequency Response/Contour EQ in full range systems.

Ivan Beaver

Graduate Student
Jan 11, 2011
2,300
8
0
Atlanta GA area
Re: Frequency Response/Contour EQ in full range systems.

P.S. Even though I am generally supporting Ivan's position, please don't think I am blindly shilling for him. One of my most recent projects was a complete re-tune of a system that Ivan's company designed and installed, and Ivan tuned. My tuning approach, dsp configuration, and the end result, are noticeably different. The client is happier than with Ivan's tuning, and have retained me to re-work another one of their spaces installed by yet another AV integrator. We certainly approach things differently.
But the question is was the tuning actually mine (There are a couple of us that do alignments) and was it the origional settings?

I know of quite a few cases in which the customer has gotten access to the DSP (even though it was locked) and changed/adjusted at will. Not always for the better. And other cases in which the customer (or the "new guy") wanted to change the postion or aiming of the loudspeakers. That has happened a good number of times-then the "new guy" leaves-and the church realizes what damage the guy did and call us to put it back or change it in another way. We are doing one of those right now.

I will agree that there are different approaches that yield different results.

I also know that the placebo effect is in full effect in "alignments". I go on quite a few service calls in which they want the sytem "retuned"-because they think it needs a tune up-like a car.

I may do a few little things, but nothing that should really change anything. And now the customer is happier-because they think it should be better.

But hey-I could be completely wrong on this in the particular case in question.

Glad it is working our for you.
 

Art Welter

Senior
Jan 11, 2011
815
13
18
Florida
Re: Frequency Response/Contour EQ in full range systems.

Phil,
I used the word "popular" very liberally to avoid examples of penny whistle solos etc..... The David Gunness presentation is what I was thinking of when I began posting on this thread, although I am not echoing the point of his presentation or implying he is of the same opinions as I am...... Also do you know of a copy of IEC268-5 on the web ?
This site has the curves:
http://www.doctorproaudio.com/doctor/temas/powerhandling.htm

I would agree with Phil that "typical" recorded music viewed on an RTA may look similar to the IEC268-5 curve, but tuning a system to mimic the curves would result in a deficiency of HF and LF.
 

Phil Graham

Honorary PhD
Mar 10, 2011
651
1
18
Atlanta, GA
Re: Frequency Response/Contour EQ in full range systems.

But the question is was the tuning actually mine (There are a couple of us that do alignments) and was it the origional settings?
The client asserts the settings were original, has the power to insure that is the case, and could easily pick you out of a lineup. I wouldn't make such a specific assertion flippantly.

At any rate I was trying to agree with you in the thread, while pointing out I do things differently. I feel it was Art who was trying to pull this into an me vs. you situation, and I'm not having that.

I will agree that there are different approaches that yield different results.
That was my point, not to disparage your work. There was absolutely nothing "wrong" with the original tuning. I was brought in to address specific complaints from, unspecified to me, members of the congregation (and probably staff) and that is what we resolved. These were complaints that grew over time and familiarity with the space, not immediate "day one" issues.

I was, evidently, the first person they talked to who didn't think that the system need pulled out and replaced by (flavor x). The reality was the system was integrated well, and that allowed me to play some fancier tricks than what were already in place.

It should be noted that I am neither in the "ruler flat" nor "gentle downward slope" system tuning camps. I've got my own ideas, and those lie somewhere in-between the two broad schools of thought.
 

Ivan Beaver

Graduate Student
Jan 11, 2011
2,300
8
0
Atlanta GA area
Re: Frequency Response/Contour EQ in full range systems.

The client asserts the settings were original, has the power to insure that is the case, and could easily pick you out of a lineup. I wouldn't make such a specific assertion flippantly.

At any rate I was trying to agree with you in the thread, while pointing out I do things differently. I feel it was Art who was trying to pull this into an me vs. you situation, and I'm not having that.



That was my point, not to disparage your work. There was absolutely nothing "wrong" with the original tuning. I was brought in to address specific complaints from, unspecified to me, members of the congregation (and probably staff) and that is what we resolved. These were complaints that grew over time and familiarity with the space, not immediate "day one" issues.

I was, evidently, the first person they talked to who didn't think that the system need pulled out and replaced by (flavor x). The reality was the system was integrated well, and that allowed me to play some fancier tricks than what were already in place.

It should be noted that I am neither in the "ruler flat" nor "gentle downward slope" system tuning camps. I've got my own ideas, and those lie somewhere in-between the two broad schools of thought.
I wasn't trying to be "defensive"-although it may have seemed that way-sorry.

It is just that I have seen quite a bit with the many many installs I have done. There is often a "different story" behind what seems "apparant".

I have seens cases in which a change (most any change) is conceived as being better-just because it is different. Again the placebo effect.

I have no doubt in your alignment capability. Glad you got the work. And better for you to do it than a whole list of other people who would just screw it up and make it worse.

There are also quite a number of cases in which the initial tuning was not done "as good as it could be". These can range from the room not being finished when the alignment was done. But the alignment had to be done at that time because of any number of reasons. To not having enough time to do it properly, for all sorts of "other" pressures imposed by the client. And many others.

Curt Taipale wrote an excellent artical years ago called "whos fault is it?" Which pointed out instances that on the outside would make the installer look like they did not know what they were doing-yet when you know the real story, it all makes sense. I have a long list of those also. In many cases "doing it by the books" will simply mean that you don't get the job.

For example in one large local church we have speaker runs of well over 300' each. Yes the amp room was in the wrong place-we fought to have it moved (and it would be even closer to the main AC panel (a double savings) but we were told NO-and if we would not put it where the sound guy wanted it, they would find somebody who would.

So why not use larger wire than the 12 ga we used? Because by the time it came to the audio system to be installed, the church was already well beyond budget (nothing new there) and they wanted to cut everywhere they could. So I was willing to stick with 12 ga cable and have more money for the things that mattered more.

Sometimes you just give in-do the best with the particular situation you have and go on to the next job.

Sorry to rant, but it can be quite amazing all the "issues" that have to be dealt with in this business.

PS I don't need to know the client-as that is not important for this discussion

Keep up the good work.
 

Tim Padrick

Senior
Jan 11, 2011
551
2
18
Indianapolis
www.padrick.net
Re: Frequency Response/Contour EQ in full range systems.

A not so system tech savvy colleague of mine describes the result like this: "If you tune a system, and I turn my lead singer on, I hear a normal, natural voice, without any channel EQ"

Charlie
Unless his idea of "normal, natural voice" is much different than mine, the system would need to have a wide 10dB to 12dB cut at about 180Hz, a medium width 4dB cut at about 4K, and a similar cut at 10k, because the response of the vocal mic looks like this:
 

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Re: Frequency Response/Contour EQ in full range systems.

The client...could easily pick you out of a lineup...
"It was him, Officer - HE's the one who didn't use a 57 on snare top, I recognized him right away!". I'm picturing a sound police based Gary Larson comic that only a few people would get.

Sorry, I couldn't help it - always time for a little humor, I hope :)~:)~:smile:
 

Brad Weber

Junior
Jan 12, 2011
417
1
0
Marietta, GA
www.museav.com
Re: Frequency Response/Contour EQ in full range systems.

I think one factor in this discussion may be a difference in perspective between systems viewed on a performance basis versus a venue basis. When dealing with installed systems that have to support a wide variety of potential applications you don't necessarily want any particular sound but want to be able to support a range of 'sounds', so it may be better to start with a relatively flat, or perhaps 'neutral' is a better description, system that permits tweaking for individual uses. Conversely, a touring system may be looking to always have a particular sound so it is perhaps better voiced specifically for that performance and tweaked for each venue.

As far as windowing, I like to vary the opening and see how it affects the results. Setting delays, etc. needs to focus on the direct components but the ear does integrate over a period so it is also useful to consider that in the final result. I feel that looking at just one or the other is somewhat looking at half the picture.
 
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Phil Graham

Honorary PhD
Mar 10, 2011
651
1
18
Atlanta, GA
Re: Frequency Response/Contour EQ in full range systems.

I think one factor in this discussion may be a difference in perspective between systems viewed on a performance basis versus a venue basis. When dealing with installed systems that have to support a wide variety of potential applications you don't necessarily want any particular sound but want to be able to support a range of 'sounds', so it may be better to start with a relatively flat, or perhaps 'neutral' is a better description, system that permits tweaking for individual uses. Conversely, a touring system may be looking to always have a particular sound so it is perhaps better voiced specifically for that performance and tweaked for each venue.
Ruler flat generally makes the PA sound either thin or bright at typical (low) church and peforming arts-level volumes, and I think places a little too much onus on unskilled technical volunteers to make a mix sound full. Strategic variations from flat by only 2dB can greatly improve the subjective fullness and smoothness, in my experience.

I fully understand the decision that people make to pursue flat curves. Often times measurements are made quickly in adverse environments, and it is a straightforward goal when you are under the gun.

I think the "pinking" of Rock and Roll PAs, like the traces Brandon posted, results from the nonlinearities of human hearing perception which are highlighted by the much higher levels in the full concert environment.
 

karel.will

Freshman
Jan 13, 2011
35
0
0
Bruges, Belgium
Re: Frequency Response/Contour EQ in full range systems.

Unless his idea of "normal, natural voice" is much different than mine, the system would need to have a wide 10dB to 12dB cut at about 180Hz, a medium width 4dB cut at about 4K, and a similar cut at 10k, because the response of the vocal mic looks like this:
True.
But only if you think that what we hear while talking to somebody sounds exactly like the sound of their voice only centimeters away from their mouth.
Usually, I stand a bit further away... :) Especially if that person is shouting!

I probably take more low mids out than most of my belgian peers. Sometimes the BE asks me to put it back, and I don't have a problem with that.

As I said, just my 0,02€...

Charlie
 
Re: Frequency Response/Contour EQ in full range systems.

Lately I've been experimenting with tonal shape/frequency response/contour equalisation of sound systems. I got this idea last year while attending a L-Acoustics seminar, they talked a lot about tonal shape/contour of their sound systems. Example can be found here:
http://drbentsen.no/wp-content/uploads/2010/12/Full-range-modular-systems-contour-bandwith.pdf

To my big suprise, I found that if I eq a sound system so it sounds pleasing to my ear for full range playback, I end up with a contour nearly identical to what L-Acoustics calls Reinforced Contour, +1dB/oct from 1K and downwards, and a "flat" level from 1K and upwards. It's also suprisingy easy to mix on, although I have to use a bit more lo-mid eq on my input channels, but not as much lo-cut as I used to do.

What's your experience with this kind of equalisation/contour response?
Do you have a preferred way of doing this? Genre/venue/audience spesific maybe?

"enquiring minds want to know" :)
Helge.

I came accross this on the Norwegian sound forums - interesting article on the subject - from Clair Global.

http://clairglobal.com/2011_news/2011/LowEnd.pdf
 
Jan 11, 2011
246
0
0
Buffalo NY
Re: Frequency Response/Contour EQ in full range systems.

Hockey Arena's are a real pain for low end. He makes several strong points but most PA's will throw a ton of SPL into the reverberant field below 300Hz, which is really what he seems to be focused on. That and the reality that many engineers use subwoofers to harm concert goers . :) These pictures show a big difference between 250Hz and 500Hz in terms of directivity which means a big difference in reverberation.
 

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Phil Graham

Honorary PhD
Mar 10, 2011
651
1
18
Atlanta, GA
Re: Frequency Response/Contour EQ in full range systems.

I'm certainly interested in any enlightenment!

Cheers,
Nick
Nick,

I caught Jamie heading out for PLASA. As I suspected, the results you show would be similar for SMAART 7. For those in the peanut gallery, I apologize in advance for the specificity of this, and the lack of exposition. I've got to go pound the pavement, so this is going to be succinct. Here we go:

For SMAART 7:
  1. Sample continuously - multiple frames with frame overlap
  2. Decimate
  3. Anti alias filtering
  4. Multiple DFTs with Hann window
  5. A fraction of each DFT corresponds to the sample points in a portion of the spectrum
  6. Combine them all together to form the final response with equivalent per octave resolution
There is no "secondary" windowing for the early energy. Your 4k boost shows up in a later frame, so the energy is there, but the correlation will be awful, and you can know to exclude the data. Of course you would hear delayed energy at 4kHz standing in the space, so SMAART is doing a useful representation

As I also use Systune, there you can apply a time window (or multiple windows) to the real time IR. I haven't tried it (BECAUSE IT HAS FORGOTTEN MY LICENSE AGAIN!) but Systune should exclude your delayed copy of the energy as you expect.
 
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Phil Graham

Honorary PhD
Mar 10, 2011
651
1
18
Atlanta, GA
Re: Frequency Response/Contour EQ in full range systems.

I wasn't trying to be "defensive"-although it may have seemed that way-sorry.
No worries. You've probably tuned more rooms in these parts than anyone! This is my first room from your affiliated firm that I reinterpreted. I've done substantially more re-work for some of your competitors, trust me... :)

I think we will have to agree to disagree on a "flat above 100Hz" tuning. I personally don't like it, and I've not found tuning clients to prefer it. In a hurried pinch, where you can't listen to the PA, its certainly a worthy benchmark to head towards.

I'm not tremendously far removed from flat, typically no more than 4dB in strategic places, but I find that small bit can make a big difference. I don't know that there's anything magic about my mental curve. I do extensively try to listen to the result, and make minor tweaks by ear. I also try to solicit input from the client(s), and A/B against the previous settings, if any. Placebo effects are hard to overcome, as you say.

Really, though, these are just flavors with plenty of room for art.

One thing that you and I do really differently is mid, low-mid, and low end management in the DSP. I know you guys are always slammed, but we should chat about it at your convenience.

P.S. Hopefully IP-addressable, remotely accessible processors will clean up some of the issues with clients' "improvements" to the starting processor settings and reduce those margin-killing service calls.
 

Nick Hickman

Freshman
Apr 21, 2011
31
0
0
100dB.com
Re: Frequency Response/Contour EQ in full range systems.

Hi Phil,

There is no "secondary" windowing for the early energy. Your 4k boost shows up in a later frame, so the energy is there, but the correlation will be awful, and you can know to exclude the data.
Thanks for passing on Jamie's comments.

For anyone interested, my summary of the topic is that the time window inherent in the DFTs in Smaart will not exclude late-arriving energy (reflections and reverb) from the transfer function magnitude display. People often castigate the humble real-time analyser for being "time blind", but Smaart's transfer function magnitude is equally time blind unless you specifically enable a time window (and then it will perform an IDFT to get the system's impulse response, truncate it at the specified time, and perform a DFT back to give the windowed magnitude response).

You (anyone) can prove this to yourself simply by changing the delay applied to the reference signal: the phase trace will change accordingly, the coherence may degrade (depending on the DFT size), but the magnitude response will just get noisier without actually changing.

To exclude late energy from a measurement in Smaart, use a DFT that's longer than the arrivals in question (not FPPO mode or whatever) and enable an explicit time window.

Of course you would hear delayed energy at 4kHz standing in the space, so SMAART is doing a useful representation
The question of whether it's useful really depends on what you want. As you know, human perception of late arrivals is a bit complicated with such phenomena as the Haas fusion zone. Sometimes you do want to see the direct sound from a loudspeaker and ignore the room.

Nick
 

Peter Morris

Senior
May 8, 2011
950
71
28
Australia
Re: Frequency Response/Contour EQ in full range systems.

Lately I've been experimenting with tonal shape/frequency response/contour equalisation of sound systems. I got this idea last year while attending a L-Acoustics seminar, they talked a lot about tonal shape/contour of their sound systems. Example can be found here:
http://drbentsen.no/wp-content/uploads/2010/12/Full-range-modular-systems-contour-bandwith.pdf

To my big suprise, I found that if I eq a sound system so it sounds pleasing to my ear for full range playback, I end up with a contour nearly identical to what L-Acoustics calls Reinforced Contour, +1dB/oct from 1K and downwards, and a "flat" level from 1K and upwards. It's also suprisingy easy to mix on, although I have to use a bit more lo-mid eq on my input channels, but not as much lo-cut as I used to do.

What's your experience with this kind of equalisation/contour response?
Do you have a preferred way of doing this? Genre/venue/audience spesific maybe?

"enquiring minds want to know" :)
FWIW my experience exactly matches what L-Acoustics is suggesting. Quite some time ago I argued this on the LAB and was slammed for suggesting anything other than flat.

I think there are quite a few reasons why this sounds best, some of them psychoacoustic.

Peter
 

Jay Barracato

Graduate Student
Jan 11, 2011
1,528
2
38
Solomons MD
Re: Frequency Response/Contour EQ in full range systems.

I keep seeing a discrepancy between what the sytems measures and what the ear hears in this discussion. They are two different things.

It doesn't make sense to me to claim that because the ear does not hear flat, you shouldn't tune the system flat. I look at it as stimulus/ response. I think the SE needs to figure out what the appropriate profile for the system is (the stimulus), in order to make the ear hear what they want (the response). I also think it is helpful if the SE can build in flexibility to the stimulus curve so that it can be adjusted in reasonable amounts in either direction. A system that is tuned to the extremes of its capabilities lacks that flexibility.

Personally, I like a system that is about +6 in the sub region, basically flat from 100 to 10-12 k and then gently rolling off. I am not claiming that is what my ear hears, but that is a system that will produce what my ear prefers.
 

Phil Graham

Honorary PhD
Mar 10, 2011
651
1
18
Atlanta, GA
Re: DFT, energy arrivals, and when to use SMAART vs. Systune

For anyone interested, my summary of the topic is that the time window inherent in the DFTs in Smaart will not exclude late-arriving energy (reflections and reverb) from the transfer function magnitude display.
This is not entirely true. The energy is "excluded" by the nature of the averaging of uncorrelated signals across multiple frames. The shortest TC for Smaart 7 is approximately 7ms, according to Jamie. The more averages one does on the uncorrelated energy, the greater the SNR between the first frame arrival and the later frames. Within the TC of each frame, the uncorrelated late energy will increasingly be averaged to the background. FWIW, SMAART 7's direct arrival "window" in the 1kHz octave is functionally 35ish ms, or similar to the Hass fusion zone you mention.

People often castigate the humble real-time analyser for being "time blind", but Smaart's transfer function magnitude is equally time blind unless you specifically enable a time window (and then it will perform an IDFT to get the system's impulse response, truncate it at the specified time, and perform a DFT back to give the windowed magnitude response).
This is utterly untrue, at least by the conventional definition of time-blind in the context of system measurement. An RTA integrates the energy of arrival over a given amount of time, but completely discards the phase information within each arrival bandwidth. You cannot capture the phase, and use it for your advantages, on an RTA. Because SMAART calculates a true H(f,t) by dividing against the reference signal.

If you have a late reflection in SMAART, its energy will manifest itself it both the phase and coherence traces, and those skilled in the art can quickly categorize the reflection as such. Similarly, if you have spectral contamination in the space from spurious noise, this can be readily ascertained. SMAART is not always the best tool for maximum noise immunity, but to say that is time blind is fallacious.

To exclude late energy from a measurement in Smaart, use a DFT that's longer than the arrivals in question (not FPPO mode or whatever) and enable an explicit time window.
Or use Systune, if you care a lot about this. PS, Jamie assures me this "secondary" time windowing of the impulse response is most certainly in the works for SMAART 7, with no inherent limitations to implement it.

This is why I use both tools. SMAART is excellent at putting on the screen a great representation of how I perceive audio, but with much better phase and frequency sensitivity than I could ever claim that my ears have. As such, it is the right tool in my mind for tuning loudspeaker systems to spaces where people are going to listen reproduced audio.

Conversely, if am thinking like an acoustician, and need to know the magnitude spectrum of a 150ms late reflection so I can suggest the proper acoustic treatment location and type, then I'll window the impulse response where around the reflection in Systune, look at the reflection's magnitude response, and work from there. These are different tools for different situations.

Even further, I'll use Systune or an MLS-type stimulus (in Soundeasy) for characterizing loudspeaker behavior when I am designing loudspeaker processing parameters.

Different tools for different circumstances, and I remain firmly in the camp that SMAART TF mode is the clearest and easiest way to characterize with high resolution how people hear real sound systems in real spaces. This is what the Rational folks have designed to, and this is what they achieve very well. Their product also doesn't randomly forget its license, like Systune has done repeatedly for me.

For those that grok DFT, windowing, IR, energy arrivals, acoustics, etc. you can (currently) get more horsepower in this realm from Systune (or ARTA) than from SMAART. Systune is not for the uninitiated, but it is really powerful. Serious designer/integrator/installer-types should buy and dig into Systune, but the world's system techs should stay with SMAART.

More than 0.02,