# What's going on here - "flat" sounds terrible!



## Nonlinear (Jun 9, 2012)

I have taken measurements of my studio monitor system using Room EQ Wizard and WM61 microphone. I generated the room measurements by taking 8 readings from slightly different locations to average out localized peaks/nulls. I then used the room correction function to generate a very flat, 20Hz to 10KHz response.

When I played music through this "corrected audio" it sounded TERRIBLE. Way too bright - like tiny clock radios cranked up.

So, I went back and looked at the room measurements and noticed that the speakers themselves have a gentle roll off from bass to treble - about -3dB per octave. They are not "flat". Ah hah! Pink noise. I have an idea! 

I created a new "room correction" curve using a -3dB/octave target curve INSTEAD of a flat target curve and applied it all the way from 20Hz to 20KHz.

THIS "room correction" sounds absolutely fantastic! Smooth and balanced across the entire spectrum.

So, what's going on here? I thought monitoring systems were supposed to be "flat". Why does a linear -3dB/octave roll off curve sound right but a "flat" response does not?


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## jtalden (Mar 12, 2009)

Even below 10 kHz many of us find that a downward sloping curve sounds much better than a flat curve. Harmon identified a downward slope as their preferred EQ target for music material. Many others are just fine with a flat curve.

I believe this is impacted by:
> Room RT values
> Speaker directivity 
> Speaker response smoothness
> Program material, particularly movie vs music sources, but also different music selections as there are no viable standards for the creation processes.
> Measurement calibrations and process used.
> Personal preferences

My personal experience would lead me to recommend that one start with X-curve for movies or a downward sloping curve for music (-1.5 to -2 dB per octave) and then adjust to taste from there. Above 6k I find a little higher roll-off rate is needed. My own compromise curve includes a little more roll-off than this. I initially started with the X curve for small rooms but, the highs were overwhelming even with movie material.

I don't see how anyone is ever going to agree on a target curve given all the variability in the individual situations.


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

Nonlinear said:


> When I played music through this "corrected audio" it sounded TERRIBLE. Way too bright - like tiny clock radios cranked up.


Check out the series of articles on “house curve” that you can find in my signature.

Regards, 
Wayne


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## Nonlinear (Jun 9, 2012)

Wayne A. Pflughaupt said:


> Check out the series of articles on “house curve” that you can find in my signature.
> 
> Regards,
> Wayne


Thank you, I will.

In the mean time I think I have stumbled upon a misunderstanding (at least by me) with how software such as REW works. 

Room EQ Wizard uses a constant amplitude, swept sine wave as the excitation signal for the room response/correction filter measurements. It sends that signal out to the speakers then measures the room response with a microphone and displays that data on a frequency response graph. If the signal coming back has the same AMPLITUDE as the excitation signal it shows up as a flat line on the spectrum graph.

Makes sense, right? But I'm not so sure.

The problem is that we don't HEAR constant _amplitude_ with frequency, we hear constant _POWER_. White noise (constant amplitude) does not sound "flat" - PINK noise sounds flat.

So, if you adjust your room, equalize your speakers, etc., so as to create a "flat" plot on the REW spectrum display, what you have actually done is create a constant AMPLITUDE system. Constant amplitude over frequency sounds very bright (+3dB/octave), not flat, and that is exactly what I was hearing.

So, in order for the room correction EQ to sound correct (using the constant amplitude swept sine approach) it seems it should have a -3dB/octave target slope, NOT a flat target slope. This is not intuitive because the software defaults to a flat target slope (which, outwardly, seems correct).


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## jtalden (Mar 12, 2009)

All the calibrations/standards for frequency response are established using SPL, not sound power. If we want our systems to be comparable to established practices we need to also adjust using SPL. It's true that if we play all frequencies at equal SPL at once then the SPL would increase at 3 dB/octave. Hence, when we use the RTA for SPL response we need to use Pink PN noise rather than White PN noise.

In Post 2 I listed some things that might impact the house curve we prefer and while some of those are relatively minor effects, I see that I forgot one that is relatively major - Volume. Our perception of equal loudness vs. freq changes with the relative volume level. If we listen at a level that deviates significantly from the level that was used in the music production process then the freq balance may seem wrong to us.


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## Nonlinear (Jun 9, 2012)

This subject has me on the brink of insanity! :dumbcrazy:

With all the varibles here, how does one set up a mastering studio and know it's going to translate? Are there no industry standards or documented tests (like Fletcher Munson curves) for what the humans hear as "right" when setting up studio monitor EQ?

It all seems completely subjective - but yet most commercial recordings end up with the same basic frequency balance that sounds "right". How is that possible? Does everyone reference everyone else or what?


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## jtalden (Mar 12, 2009)

Sorry I can't really be helpful regarding studio setup. I was also really only addressing home listening rooms and was mostly just complaining because of the same frustration you have. 

Near as I can tell there is a lot of variation in the production process and I have only been able to find very generic information regarding "best practices" for studio setups. I didn't keep any links as it is not my focus and I never found any info that was very helpful in the translation to a home setup.


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

Nonlinear said:


> It all seems completely subjective - but yet most commercial recordings end up with the same basic frequency balance that sounds "right". How is that possible?


Trust me, it isn’t. For instance, Donald Fagen’s _The Nightfly_ album is overly bright, indicating it was mastered on monitors lacking in high-end response. I’ve also recently heard recordings that I thought sounded a bit dull (lacking high-end), although I can’t remember what they were at the moment.

So yes – there is a certain amount of subjectivity, and there is no industry standard for music production that I’m aware of. By comparison, the film industry does have a room-curve standard, called the X-curve, that’s used in every stage, from production right down the line to the playback systems in theaters.

Regards, 
Wayne


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## JohnM (Apr 11, 2006)

The difference is between capturing the direct sound from the loudspeaker only, as one would measure in an anechoic chamber, and the total sound at the listening position in a room. It is best (in an accurate reproduction sense) for the frequency response of the direct sound from the speaker to be flat. To measure that you need either anechoic conditions or to create a quasi-anechoic environment by gating the impulse response to exclude the contributions of the room. The in-room measurement includes that direct sound plus the contributions of the reflections from the various surfaces of the room. Those have lower levels at higher frequencies due to higher absorption as frequency increases, producing an overall downward tilt in the listening position measurement. Even air has much higher absorption at high frequencies, a 1 kHz tone loses about 0.5 dB after travelling 100m, a 10 kHz tone loses about 16 dB over the same distance.


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## Nonlinear (Jun 9, 2012)

Wayne A. Pflughaupt said:


> ...the film industry does have a room-curve standard, called the X-curve, that’s used in every stage, from production right down the line to the playback systems in theaters.
> 
> Regards,
> Wayne


Ah hah, now I'm getting somewhere! At least that is a good place to start vs. a total "guess" on my part.

Great. Thank you!


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## Nonlinear (Jun 9, 2012)

JohnM said:


> The difference is between capturing the direct sound from the loudspeaker only, as one would measure in an anechoic chamber, and the total sound at the listening position in a room. It is best (in an accurate reproduction sense) for the frequency response of the direct sound from the speaker to be flat. To measure that you need either anechoic conditions or to create a quasi-anechoic environment by gating the impulse response to exclude the contributions of the room. The in-room measurement includes that direct sound plus the contributions of the reflections from the various surfaces of the room. Those have lower levels at higher frequencies due to higher absorption as frequency increases, producing an overall downward tilt in the listening position measurement. Even air has much higher absorption at high frequencies, a 1 kHz tone loses about 0.5 dB after travelling 100m, a 10 kHz tone loses about 16 dB over the same distance.


Thank you, John, for the info.

Now, how do we approach this in reverse - what should the target curve be so that the corrected system _SOUNDS_ flat? My experimenting seems to indicate -3dB/octave (pink noise) is about right. The amount of correction it takes to get there, I understand, would depend on the room.

If a professional audio installer comes into my studio and tweaks the monitor Hf/Lf gain switches, installs bass traps, diffusers, etc., does he just "earball it" or is he measuring to some reference standard (pink noise, etc.)? (I understand room modes, first reflections, etc., are also being addressed but my question is specifically about spectral balance).

I always assumed the goal was a flat response. Now, it seems, it can be anything - whatever sounds good!

So, how would a mastering studio, for example, create translatable recordings in a room EQ'd _THAT_ way?


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## JohnM (Apr 11, 2006)

That's a topic that has troubled people for a long time  

Here is a paper from *1975 *with B&K's view of what the target curve at the listening position should look like in figure 5:








The target curves for various room correction systems have similar tilts downwards at HF.


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## Nonlinear (Jun 9, 2012)

Thank you, John, for that curve. A couple of folks over at the Gearslutz forum also suggested this "B&K" curve so I will definitely give it a listen.

Wayne P. also suggested the "X-curve" in a reply above. Will give that a listen as well.

Thank you all very much!


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

Nonlinear said:


> Wayne P. also suggested the "X-curve" in a reply above. Will give that a listen as well.


No, the X-curve is unsuitable for anything outside the movie business, including home audio and anything related to music recording/production. You can find an article with more details in my signature.

Regards,
Wayne


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## Phillips (Aug 12, 2011)

Wayne A. Pflughaupt said:


> Trust me, it isn’t. For instance, Donald Fagen’s _The Nightfly_ album is overly bright, indicating it was mastered on monitors lacking in high-end response. I’ve also recently heard recordings that I thought sounded a bit dull (lacking high-end), although I can’t remember what they were at the moment.
> 
> So yes – there is a certain amount of subjectivity, and there is no industry standard for music production that I’m aware of. By comparison, the film industry does have a room-curve standard, called the X-curve, that’s used in every stage, from production right down the line to the playback systems in theaters.
> 
> ...


You are so right (talking about home music system) i was chasing a boom in the wrong place, get it sounding ok then play this artist and boom was back again, though not as bad (think it was a harmonic of the mode) Not long after this i was told that the artist sound engineer puts a boost in the 60hz region. 

My music CD, SACD, DVD Audio collection has a large difference from dull, bright, bass light etc. Actually the brightness happens very really in my room. 

Interesting that the movie has a standard and not the music industry, suppose it depends on the music content (Rock, Jazz, Heavy metal etc)?


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## Phillips (Aug 12, 2011)

JohnM said:


> The difference is between capturing the direct sound from the loudspeaker only, as one would measure in an anechoic chamber, and the total sound at the listening position in a room. It is best (in an accurate reproduction sense) for the frequency response of the direct sound from the speaker to be flat. To measure that you need either anechoic conditions or to create a quasi-anechoic environment by gating the impulse response to exclude the contributions of the room. The in-room measurement includes that direct sound plus the contributions of the reflections from the various surfaces of the room. Those have lower levels at higher frequencies due to higher absorption as frequency increases, producing an overall downward tilt in the listening position measurement. Even air has much higher absorption at high frequencies, a 1 kHz tone loses about 0.5 dB after travelling 100m, a 10 kHz tone loses about 16 dB over the same distance.


This has been my approach for my HiFi system lately

I could never understand why flat sounded so well "flat' no life whatsoever, boring so took another approach.

I was told to use Blackman Harris 7 and 12ms window left and right and 6th octave smoothing as general. These settings gave useful data, think from 500hz up.


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