# EQ and dynamic range



## rewjack (Aug 24, 2011)

Hi
I've been doing DSP correction for a long time now. I never was opened to use automatic EQing because it was doing corrections at places that I would not touch.

It seems that there is a great evolution in this DRC buisness. I see that many users went for different softwares. I am now using only the Jriver's DSP parametric EQ for crossovers creation and frequency corrections.
In doing it, I took a lot of experience with REW's measurements Tools. I need to use mainly IR, ETC and phase graphs to set up the right delays and frequency positions to achieve good transducers transition.

It's a DIY speaker project based on multipoweramp (4 ) a RME AES 32 sound card and 4 Dacs to manage 8ch. Did a lot of acoustics too in the room.

So I'm at the point where EQing is the last step to bring the icing on the cake. I actually do little correction in HF over 100hz because I was never happy with results, the impression of killing freedom in some aspects. I understand that EQing is the last thing to be performed in tuning a hifi system but it just corrects the audio signal at the microphone location, or close to. I understand the direct, first reflections and the summation/cancellation processes implied and work with them.

I am aware of the REW's EQ tool for convolution and I gave a try. I saw other softs like Accourate that uses FIR based corrections. 

My concerns and my questioning are mainly focused on the target line position and repercussions on corrections. To be more precise, I could not figure out how it could be done without creating distortion when applied on dips, especially narrow and deep ones. It is argued that placing the target line at the bottom of the dips won’t result in creating distortion, all right. Leveling every frequencies at this amplitude and further boosting the whole thing? I was worried that this could induced a reduction in the DYNAMIC RANGE, explaining my disappointment with results. Thus I don't have anything to clearly answer this questioning. Before spending money and time on new software, I need more explanations and advices.

At my actual state of knowledge, I'm a bit confused about EQ softwares and there is too many threads on the subject going in to many directions.

I'll be more than happy to read you about this interesting topic.
Thank you

jacques


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

The short answer is that equalization will definitely affect dynamic range. Boosted filters – at least from outboard hardware equalizers – will increase the noise floor in the frequency range where the boost occurs. Equalization also taxes amplifier power. However, the latter can easily be alleviated with higher efficiency speakers or more powerful amplifiers, the former with better-quality hardware.

Regarding full-range equalization in general, I’ve always felt that the people who claimed it was a bad thing fell into one of two categories: Either they had never actually done it themselves, or had tried it using cheap equalizers and/or didn’t know what they were doing (which actually amounts to the same thing). So based on their bad experiences, they go out and spread the news all over the web about the futility of equalization. 

Certainly, full range equalization can be tricky, and it is easy to make a mess of things if you don’t know what you’re doing. The first thing is to start with good equipment and measurement technique. For the former, you want a calibrated mic. You won’t get an accurate frequency response reading with a non-calibrated mic, and you certainly don’t want to be applying equalization to the main channels based on an inaccurate graph. For the latter, the mic should be pointed at the speaker being measured.

Beyond that proper equalization is simply a matter of understanding and following a few basic principles and practices.

For starters, the idea that equalization “only corrects the audio system at the microphone location” is a half-truth. It’s a fairly accurate statement for frequency content below the transition frequency, i.e. the point where the room drastically influences response. However, above the transition frequency, the direct signal dominates over reflected signals, so you’re mainly hearing the sonic characteristics of the speaker themselves. And any deficiencies in frequency response they may have can be addressed with equalization, at least to some extent.

Equalizing narrow depressions or peaks should be avoided. In the upper frequencies, these are typically the result of comb filtering and aren’t actually audible. The best thing to do is apply 1/3-octave smoothing to your frequency response graph. This gets you a graph that eliminates the comb filtering and is a better representation of what you’re actually hearing (note, low-frequency subwoofer graphs should use no smoothing). With 1/3-octave smoothing in place, you’re mostly looking for broad anomalies in response. These are easy to equalize and give most audible improvement. Here’s a good case study you can read through. 

Also keep in mind that above about 300 Hz you need to use matching filters for the left and right channels. Using mismatched filters above that point, even if measurements of the individual speakers seem to call for it, will do strange things to the imaging. At least that’s the case with outboard equalizers. I don’t know if it applies to software-base solutions like you’re using, but it’s something to be aware of and listen for. I typically play a pink noise signal through both speakers and apply matching filters in real time, using REWs’ RTA feature. Below 300 Hz it’s no problem using independent filters for each channel.

Regarding your question about the Target line, it definitely is not a good idea to put it at the bottom of the depressions in response. As you noted, that only means you’ll be equalizing the whole curve down to that point, which will take a whole slew of filters. That violates one of the iron rules of equalization, which is to use only as much as is needed to accomplish the desired result, which is smooth response. Not to mention, it means you’re essentially using the equalizer as a level control, which is really bad form. 

So it’s best to locate the Target somewhere between the worst peaks and depressions. Cutting response across the board and then boosting up the overall level will “cost” just as much headroom as locating the Target somewhere in the middle and using some boosted filters. There’s no free lunch – any equalization taxes headroom. You have to have enough going in, or deal with it the way I described in the first paragraph. 

Bottom line, if you equalize correctly, there should be no issues with distortion.

I’m sure I’ve left something out, but that’s all I have for now. Hope this helps.

Regards, 
Wayne


----------



## dougc (Dec 19, 2009)

Great stuff Wayne, as always


----------



## rewjack (Aug 24, 2011)

Hi Wayne
This is a great reply. 
Everything is instructive, and for my today's concerns I've kept some details of it.


Wayne A. Pflughaupt said:


> The short answer is that equalization will definitely affect dynamic range.



EQ software developpers that have reply to me didn't want to answer yes or no. I experienced it and I'm glad to ear it from someone like you.




> Regarding your question about the Target line, it definitely is not a good idea to put it at the bottom of the depressions in response. As you noted, that only means you’ll be equalizing the whole curve down to that point, which will take a whole slew of filters. That means you’re essentially using the equalizer as a level control, which is really bad form. Not to mention, it violates one of the iron rules of equalization, which is to use only as much as is needed to accomplish the desired result, which is smooth response.


I don't want you to get involved in a particular software developer discussion, I'm sure you have all you need. I had this reply about a question about this target line and corrections applied.

"anything above the target curve (not necessarily a line) gets reduced and anything below the target curve does NOT get corrected. The resulting filter is normalized to max. 0 dB for the filter frequency range."
So I guess it goes in the same direction of your comments?



> So it’s best to locate the Target somewhere between the worst peaks and depressions. Cutting response across the board and then boosting up the overall level will “cost” just as much headroom as locating the Target somewhere in the middle and using some boosted filters. There’s no free lunch – any equalization taxes headroom. You have to have enough going in, or deal with it the way I described in the first paragraph.


So I understand that statement that I had from someone, to have no effects at all by using a 64 bits process may not be all true?



> Bottom line, if you equalize correctly, there should be no issues with distortion.


 Outside deep and narrow dips even in lower frequencies? I say that for my 65hz 18db dip (60-70hz) It's a 1/4th wavelength cancellation room mode located at 1,3 meter from the back wall.

Thank you again for the reply
jacques


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

dougc said:


> Great stuff Wayne, as always


Thanks for the kind words, Doug. :T



rewjack said:


> I don't want you to get involved in a particular software developer discussion, I'm sure you have all you need. I had this reply about a question about this target line and corrections applied.
> 
> "anything above the target curve (not necessarily a line) gets reduced and anything below the target curve does NOT get corrected. The resulting filter is normalized to max. 0 dB for the filter frequency range."
> So I guess it goes in the same direction of your comments?


There’s no problem boosting depressions in response, despite what is commonly said, as long as they are not caused by room nulls (which are primarily only present in the lower frequencies). It’s based on the false idea that boosted filters will enact a headroom penalty, while filters that cut will not. The truth is, any equalizing gets a headroom penalty – see more on that here and here.




> So I understand that statement that I had from someone, to have no effects at all by using a 64 bits process may not be all true?


Sorry, I don’t understand what you mean.




> Outside deep and narrow dips even in lower frequencies? I say that for my 65hz 18db dip (60-70hz) It's a 1/4th wavelength cancellation room mode located at 1,3 meter from the back wall.


I’m not sure what a 1/4 wavelength translates to in bandwidth, but any dip that severe is most likely a null and will not respond to equalization.

Regards, 
Wayne


----------



## rewjack (Aug 24, 2011)

Wayne A. Pflughaupt said:


> There’s no problem boosting depressions in response, despite what is commonly said, as long as they are not caused by room nulls (which are primarily only present in the lower frequencies). It’s based on the false idea that boosted filters will enact a headroom penalty, while filters that cut will not. The truth is, any equalizing gets a headroom penalty – see more on that here and here.



These examples are very helpfull. In all my questions in forums about EQing a deep dip at 65hz (listening position) I mentioned that it was certainly a null zone (cancellation) caused by the proximity of the back wall in relation with the wavelenght. So I had several replies saying that Acourate or Audiolense will be able to correct it. I replied that I beleived them for other freq where the dips were not caused by a cancellation phenomena. No one seems to agree on that, in fact they ignored it and never came back on this aspect, digital EQ was supposed to get rit off this one as well as any others. This is where I was confused and not persuated at all of their understanding. You gave me several examples where EQing would do the job with some restrictions to be considered, like headroom penalty. The replies I had from these equing softwares users were all positive and no side effects are mentioned, i's doubtful to me.



> Sorry, I don’t understand what you mean.


OK, the 64 bit thing is an answer for my dynamic range questionning when EQing. It is argued that math processing at 64 bit will be so effective that even boosting dips will have no noticeable effect on dynamic range. A kind of, do not worry about it, the software is taking care of it by computation???



> I’m not sure what a 1/4 wavelength translates to in bandwidth, but any dip that severe is most likely a null and will not respond to equalization.


This is interesting. I knew that cancellation will occuered in a room somewhere but it was vague in my mind where it will happen. All nice animations showing waves crossing themselves are very nice but I wanted to locate them in my room. I knew that behind my chair there was that big hole centered around 65hz. I've decide to map the room at this frequency to visualize it and see the distribution pattern. It endded with a nice SPL map (see attached file). I've looked around to found an easy model explaning this phenomena. I found this example in 



> CATCH A WAVE
> FROM http://realtraps.com/art_waves.htm
> Let's continue with the example of a 40 Hz. wave. In a medium-size control room, 19 feet deep, a sound wave's compression peak will hit the back wall, reverse direction, and combine with the next rarefaction valley at one quarter of its wavelength, or seven feet from the wall in the case of 40 Hz. The rarefaction valley is one half of a wavelength, or 14 feet, behind the compression peak. Thus, after hitting the wall, the compression peak and the rarefaction valley, moving toward each other at equal speed, will meet at a quarter of the wavelength from the wall, or approximately seven feet. Figure 1 at left shows the 40 Hz. wave hitting the wall at five different phases of the wave form. Note that no matter what phase of the wave is hitting the boundary, there is always a cancellation at the 1/4 wavelength point.


This was matching the excat position of my 65hz dip at 1,3m from the back wall (1/4th of a 5,29m wavelenght). It worked fine for me. I found that for 80hz it is at around 1 meter (4m/4), 50 hz around 1,7m). It fits all my low frequency dips locations (see blue régions in PDF figures). I've worked a lot more on this later and made many changes (including demolition of the back wall) with new maps.... 

Though, is there a debate on these software real effectiveness, I'm still confused about many contradictions? All users seems to loved them. I, myself, like to do corrections manually using all DSP available processing in Jriver's parametric EQ options, each dip and bump individually. 


Thanks again for giving me a more objective overview of EQing. 
Regards, 
jacques


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

rewjack said:


> These examples are very helpfull. In all my questions in forums about EQing a deep dip at 65hz (listening position) I mentioned that it was certainly a null zone (cancellation) caused by the proximity of the back wall in relation with the wavelenght. So I had several replies saying that Acourate or Audiolense will be able to correct it. I replied that I beleived them for other freq where the dips were not caused by a cancellation phenomena. No one seems to agree on that, in fact they ignored it and never came back on this aspect, digital EQ was supposed to get rit off this one as well as any others.


It’s hard to tell for sure in your case, since you haven’t shown us the frequency response graph you’re dealing with. But if the null in your room is deep and narrow, as shown in the graphs previously linked in this post, it cannot be equalized, no matter what the people at the other forum tell you. You can try it and see for yourself! 




> OK, the 64 bit thing is an answer for my dynamic range questionning when EQing. It is argued that math processing at 64 bit will be so effective that even boosting dips will have no noticeable effect on dynamic range. A kind of, do not worry about it, the software is taking care of it by computation???


Okay, I get it now. No, I’d be surprised if the software equalization would endure a significant headroom penalty by boosting, even if boosted severely. However, eventually you enter the analog world, and that’s where the headroom penalty will show up, in the form of clipping in the amplifier at the boosted frequency. Or of not there, in the speaker itself.




> Though, is there a debate on these software real effectiveness, I'm still confused about many contradictions?


I don’t see why software-based equalization would not be as effective as something hardware-based. In fact, I would expect the software EQing to be better, if anything.

Regards, 
Wayne


----------



## Dual-500 (Aug 1, 2010)

"Wayne" nailed it and did so very eloquently.

How do I eq? I use DBX Driverack PA+'s in my system, setup the mic and us the "Autotune" feature to get a baseline starting point, then smoothe out eq settings, paying particular attention high boost areas of more than +6db.

System tuning and room adjustments, speaker placement whathave you is as much an art as it is a science.


----------



## marty1 (Jun 29, 2010)

Just out of curiousity Wayne, why would you not use smoothing for subwoofer response?

Marty


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

With subwoofer graphs you don’t get the comb filtering you see with upper-range graphs, so smoothing isn’t all that necessary. With unsmoothed graphs, it’s easier to pinpoint the exact frequencies of peaks and troughs, which allows for more accurate EQ filters.

Still, some smoothing, perhaps 1/12 or 1/6-octave, certainly can be useful – IMO it gives you a better representation of what bass response actually sounds like. But it’s best to use unsmoothed for equalizing, especially manual equalizing.

Regards, 
Wayne


----------



## marty1 (Jun 29, 2010)

So 10-200hz would be no smoothing anything above 1/3 correct.

Also would you say auto eq is better to leave off and manual eq'ing better as the auto eq may apply too many filters?

Marty


----------



## Wayne A. Pflughaupt (Apr 13, 2006)

I’ve never used an auto EQ system, so I can’t say definitively. However, if you see it’s using more than say, 6 filters for the sub, then I’d be concerned that it was going overboard. Either that or the sub needs to be re-located.

Regards, 
Wayne


----------



## marty1 (Jun 29, 2010)

It only eqs diwn to 60hz so not really affecting sub too much

Marty


----------

