Flat Frequency Response- Not

[DanDan]

Hi, sorry for the glib tabloid title. I would like to stimulate a decent discussion on this. I am well aware that the term Frequency Response is simplistic and only one of many analyses. I would however like to see a discussion staying close to the basic question. Let us assume reasonable sized listening rooms and nothing exceptional to distract.
Should we be listening in a Flat or HF Rolled off environment?

Several of the older reference books I have suggest a tailored frequency response curve in listening rooms. For instance Bruel and Kjaer had a Test Record QR2011. Within the info that came with that, they had a recommended curve which was very approximately
+3 dB at 100Hz and -3dB at 10kHz (from Alton Everest's 2nd Edition)
They claim that this curve will suit most types of music. Furthermore they suggest that a flat response is suitable for listening to far-field recordings, (Broadly speaking, Classical I suppose). Their suggested curve is based on the fact that most 'modern' music is recorded under field conditions.

I have found other recommended curves, e.g. -3dB per octave HF roll off above 8K or even 4K and so on. In general it appears to me that HF was commonly rolled off in the past. Note to self- I must check out what the BBC recommended.

So, where are we at now? Many are speaking of Flat, presumably meaning one would see a flat line on an RTA or Software with Pink Noise stimulus. I believe such a soundfield would be far too bright leading to dull mixes. I am firmly old school on this. I have had a succession of monitors through my room. All seemed bright to me. I settled on ADAM S3A's partly because I could turn down the top to suit me. My room was bass light, which I have improved since. However, here and in every studio I have consulted for, I seem to always end up with the HF section of active monitors turned down.
Apart from the matter of personal taste, mixes done here translate extremely well to the world at large.

I cannot reconcile the old, but presumably wise, practice of HF roll off with the current Flat trend. What has changed? I don't think the sound of popular recordings has changed that much tonally. Great old recordings hold up just fine against any modern attempt, despite the greater bandwidth etc. available these days.


Dan FitzGerald
Sound Sound - Homepage

[andrebrito]

Unfortunately in this forum people give way too much importance to frequency response at the point of becoming paranoid if the room is completely flat.. frequency response is just one of the parameters being studied.

Even in control rooms I don't see any harm on having a slight bass boost and roll off at HF, it just makes the room sound more natural at least to me ears

[DanDan]

Andre, I am very glad you agree. But I would like to hear more.
DD

[andrebrito]

This is a matter of preference really...

Regarding what else can be checked in a room: temporal response, reverberation time if the room is not dry, modal ringing on waterfalls etc etc..

[DanDan]

Hi Andrebrito, of course. Let's assume an average size and acoustically treated control room, so that temporal and other matters are dealt with. When making final adjustments would you aim for a flat or rolled off response?
I am hoping you or someone else might join in with an explanation of the difference between the old books and practice and the current (often implied) recommendations for flat. What has changed?

Best, DD

[andrebrito]

I would prefer a slight LF boost at low frequencies.. the HF roll off happens quite naturally in large control rooms due to air absorption but we are talking about significant large rooms not something like 4 per 3 meters.

[Ethan Winer]

I feel I should have information, or at least an opinion, on this discussion but alas I do not.

[DanDan]

Hi Ethan, I believe there are two schools of thought about this.
One is that a Flat response will let you hear the recording as is. The other, with the Bass tip up and HF roll off, is intended to better represent the 'average' domestic listening situation which will have booms, possible soft furnishings, lots of warming (and confusing) reflections off hard surfaces and so on.
I had a chat with someone at PMC some time ago about this. I had a pair of their monitors on approval. Their plan is to deliver a 'flat' response very evenly throughout the listening space. Part of this plan involved a HF boost on-axis, then keeping the tweeters high and not toed inwards, so that the listener was never on-axis.
Their speaker, the IB1s was the best I have ever heard, with just the one problem, too bright. They suggested using a Sony speaker controller as many of their clients do. They added that it was commonplace to use different Eq's when mixing for different output. For CD one might use our curve, for TV a stronger HF roll would encourage brighter mixing. For film, the X curve. Strangely they didn't tell me I could BIAMP them with only a second amp, no crossover etc. needed. I would have kept them!
I borrowed this little pic from our friends over at studiotips, I am hoping they won't mind. There is a page there called Understanding RTA, which promotes this type of tailored response. Remarkably like the old B and K one, I thought.



Best Regards, DD

[Rod Gervais]

Dan,

Actually - at the levels we're speaking about - it's a flat room either way.

I don't believe that there is any really significant difference between the goals of today and the goals of yester-year. There have been a lot of different methods over time attempting to achieve what is basically the same thing.

That "thing" is a listening room that doesn't really color the sound coming out of our speakers.

If one can acheive that - then one can accurately mix recordings that will translate well in other environments.

When you speak of truly flat versus 3dB boosts here or there - you are (for all intent and purpose) talking the same thing - FLAT. A 3 dB boost or cut in the ranges we're discussing here is almost the same as no boost or cut at all.

As far as the actual roll-off goes - I tend to lean in the direction of the ITU recommendations, which means that you actually have a fairly narrow band through the mid/high lows to low highs - and then it's a wee bit more travel in the high frequencies - both up and down - and the same in the low frequencies (although down is a wee bit tighter than the highs allow in range.

If you picture how most people set up their stereo systems - you'll see why this makes perfect sense.

In almost every home I have ever been in with decent to excellent quality sound systems - the EQ is set up in what I refer to as the "EQ Smile".

Lows and highs are boosted - and slowly smooth out to a fairly flat middle.

The reasons for this are well known - the human ear does not hear sound in a linear manner - we hear low and high mids much easier than we do at either end of the spectrum.

So in order to listen to anything and enjoy it - we have to boost frequencies we are normally fighting to listen to. "Tuning" a room to give us a slight nudge in that direction can only make sense.

When designing a room - if one can acheive +/- 3 dB that really is quite a feat - and is pretty near darned flat (for all intent and purposes).

If you study the Fletcher/Munson loudness curves you'll find that from 500Hz to 2000Hz - the human ear hears sound pretty darned flat - 10 dB tones sound the same loudness to us across that board.

From 2000 Hz to 6000 Hz, 6dB tones sound like that same 10 dB loudness (The scale there actually floats a bit - with the max variance around 5000 Hz - but I am sure you get the picture) So our hearing is he best in that range.

BUT - by the time you get to 10,000 Hz - it takes 20 dB to sound the same loudness as 10 dB in the mid range.

The low end is even worse...... at 100 Hz - it takes 30 dB to sound as loud as the mid range at 10 Hz..... and by the time you reach 20 Hz - 75 dB to sound the same loudness.......

Those little 3 dB bumps you're talking about are nothing more than a window you can fit within to acheive a flat sound rather than an action taken to enhance the amplitude at those frequencies.

When you examine the scale used for listening rooms designed within the ITU recommendations, you'll find that those numbers are roughly the high end of an allowable variance - perfectly flat as well as a slight frown also fits within the guidelines. All of which is considered acceptable variances for design or final treatment purposes.

I have never encountered a set of recommendations from any source that suggested anything other than a range to fit within it's always +/- , never a tight range at all. I would be happy to examine a source that IS rigid if you have one.

Sincerely,

Rod

[nosebleedaudio]

Originally Posted by DanDan

Hi Ethan, I believe there are two schools of thought about this.
One is that a Flat response will let you hear the recording as is. The other, with the Bass tip up and HF roll off, is intended to better represent the 'average' domestic listening situation which will have booms, possible soft furnishings, lots of warming (and confusing) reflections off hard surfaces and so on.
I had a chat with someone at PMC some time ago about this. I had a pair of their monitors on approval. Their plan is to deliver a 'flat' response very evenly throughout the listening space. Part of this plan involved a HF boost on-axis, then keeping the tweeters high and not toed inwards, so that the listener was never on-axis.
Their speaker, the IB1s was the best I have ever heard, with just the one problem, too bright. They suggested using a Sony speaker controller as many of their clients do. They added that it was commonplace to use different Eq's when mixing for different output. For CD one might use our curve, for TV a stronger HF roll would encourage brighter mixing. For film, the X curve. Strangely they didn't tell me I could BIAMP them with only a second amp, no crossover etc. needed. I would have kept them!
I borrowed this little pic from our friends over at studiotips, I am hoping they won't mind. There is a page there called Understanding RTA, which promotes this type of tailored response. Remarkably like the old B and K one, I thought.

Attachment 105180

Best Regards, DD

In a room I built has IB1's, and measured them in the room several times and are pretty flat at the high end, compared to a pair of BM6's which have a slight roll off in the high end, 18 to 20KHz.
One engineer mentioned that the PMC's sounded bright, I told him they were flat, NO peaks..

The over bright could have been corrected simply by adding a high watt resistor in series with the tweeter. IM not a fan of adding an Eq in the monitor chain..

We get used to hearing things a certain way, and if one speaker has more HF we may conclude IT is over bright, this is a general assumption...

[andrebrito]

Rod, I will have to disagree slightly with you on this matter...

Fletcher Munson is applied to sine waves. The decrease/increase of 3 dB is not easily noticeable indeed when using pulse sine waves. In fact you need to be a bit concentrated to actually listen it but the difference can be perceived. I have listen to this examples several times and it is quite difficult to catch it.

But a slight bass boost of 3 dB applied for a large bandwidth at low frequencies is more noticeable, particularly if the music is rich at low frequencies and compressed.

[DanDan]

Hi Y'All, Happy New Year. Thanks for all the contributions so far, and I would welcome more. I believe this is a bit of a problem.
I have been looking through my little library and found no tighter references for you Rod. The best I have is the quotations from the B and K QR2011 test record manual. Most of the older books do recommend various HF roll offs. Alton Everest 2nd Edition quotes two different approaches, both have a HF roll off on the basis of near-field recording and or near-field listening. In John Eargle- Sound Recording I found a some 'recommended' monitor curves. e.g.
Film -3dB Octave above 2K
Studio -3dB Octave above 4K
Another Studio -3dB Octave above 8K
The author continues with 'There is a gradual shift in the recording industry towards flat monitoring, and it is being met among the better hi-fi manufacturers toward loudspeakers with a flat energy output vs frequency'
I will say that this has a ring of truth to me.
The author concludes that a wise approach would be to provide a flat response loudspeaker with switched contours available for different mixing purposes. Exactly as PMC said. I did try that resistor trick, and it worked fine, however it was more of a shelf than a roll off. I believe that such Eq tailoring of speakers is valid in the broad sense, while noting the dangers of 'Room correction' by Eq.
I note that many active speakers have something like this but there does not appear to be a standard except for the X-Curve used by the Film world.
Rod are those ITU specs available? Do you or anyone else have some of the older guidelines, from the EBU or BBC or such? There must be some good research source which gave rise to the older practice.
I note your points Rod, and thanks for joining in. However I must disagree in one area. A curve with +3 at LF gradually sloping to -3 and more at HF would be very audible and will definitely cause very different sounding mixes.
I think we are in a bit of a Limbo at the moment. There was an old practice, perhaps based on some standards. I use this approach, approximately, and it still seems to work very well. Mixes translate.
I do note that the Film people have tied this down with the X-Curve.
Clearly we could adopt Flat as our standard and some appear to be doing so. This would be fine if all domestic playback systems complied. I just cannot see that happening. Furthermore I believe the old practice took account of the room/speaker interaction. (Also Modern rooms may have less soft furnishing, which could push us either way, confusingly.) The more I look at this the more I am convinced of the validity of that old B and K curve. I have found it impossible to work in a flat environment. I end up softening everything. Then when I put up my collection of Reference mixes, my ears bleed from the sudden brightness. I believe this is a problem.
Best Regards, DD
Sound Sound - Homepage

[Rod Gervais]

DD,

although I might not see this quite the way that either you or Andre do - (perhaps it's just my bad hearing after all these years of construction) I do believe that your view has merit.

The reason I say this is because - when it hits the bottom line - what works for you is what works for you.

It doesn't matter whether it would make a difference to me - or to Joe down the road..... it's what works with you - what clicks with your brain - that matters in the end - or at least for you it does.

I would suppose it's that way for everyone else as well.........

Sincerely,

Rod

[Beyersound]

As far as referencing to speakers for music, I have spent decades tuning speaker systems in rooms from 20,000+ seats to studios. The typical listening curve (unweighted) in all situations is a 6-9db boosted shelf at 100hz and below and about a 2db per third octave slope down from 100hz to 250hz for the low end. The high end would be a rolloff at about the same slope down above 8k. For a studio tuning, a 6db shelf up in the low end would be suitable, the high end rolloff would be the same as above. This seems to be the reality of a response curve that will make mixes translate to most playback systems. Concert systems tend to have more low end shelf boost for "excitement". This is a real world, not "Lab Rat" example. Labs are great, but people don't mix in them. I have found in high end mastering rooms, that you must "get used to" their typical lack of real world bass shelf boost. I believe that a truly "flat response reference" is detrimental to mixing in a way that will translate.

[DanDan]

Thanks for the responses. I have just read a survey of Control Room/Monitor responses on the Genelec site. This indicates common practice is Flat at the mix position. As a fairly experienced mix engineer, I can flatly say :-) this just does not work for me. At the risk of trumpet blowing, some of my earlier work has been used extensively for as a reference by the Hi Fi community for reviews and even for the design of a UK loudspeaker of the year. To me this suggests that I do not have an unusual preference, rather the opposite, a most average ear!
I clearly understand the purity of the concept of a flat speaker radiating perfectly into a listening room. However the end user does not listen in such rooms or anything like them. Beyersound have you any research origins for your practice? There must have been some research done in the past which came up with the B and K curve and the others.
Best, Dan FitzGerald

[jrwone0]

Looking at this thread I remembered this documentation on a room correction/eq package which talks about some research on how humans perceive tonal balance...

Link 1
Link 2

It gets pretty technical but what they're claiming is that using new psychoacoustic research they come to results which match pretty well with those old B & K frequency response targets.

The graph I attached is of the frequency response in a room at the listening position for a system that been equalized flat at the listening position using room correction. The typical room is going to cause peaks and valleys in the response which become greater in db magnitude (though not absolute energy) at the higher frequencies as shown in the graph. They are saying that human hearing pays attention more to the peaks than the valleys so the perceived frequency response is really a curve that goes along the top of all those peaks, which they draw on the graph. You can see this curve is upward sloping which means it actually sounds bright not flat. The conclusion is that room correction software needs to target a downward sloping frequency response at the listening position in order to be perceived as flat.

The curve they arrive at is flat until 100hz then slopes down evenly per octave to about -6db at 20khz, which matches the old B & K target curve pretty well.