The Audyssey Pro Installer Kit Thread (FAQ in post #1) - Page 8

Originally Posted by LarryChanin

Hi Guys,

Returning to the thrust of Fitz's remarks the reason for the Audyssey high frequency rolloff is to account for differences in the acoustic environment between the recording studio and the typical small listening room. It really doesn't have anything to do with the "X-Curve".



Larry

Originally Posted by LarryChanin

Returning to the thrust of Fitz's remarks the reason for the Audyssey high frequency rolloff is to account for differences in the acoustic environment between the recording studio and the typical small listening room. It really doesn't have anything to do with the "X-Curve".

Originally Posted by BobL

If we are trying to recreate the acoustical space of recordings we must first determine where the recording took place. Most movies the final mix is not done in a recording studio but in a dubbing stage. This is a medium sized theater with a mixing console in the middle. It is considered large room acoustics and would definitely be far field.

High frequencies are frequently boosted in this environment because high frequencies dimminish quicker than low frequencies. When you transfer a soundtrack to a DVD/B-ray this will make the material sound bright if not compensate for in the transfer. It is the reason for many THX/theater/cinimea modes in processors.

For reference most home theaters will show a natural roll off at ~6-8 khz depending on the distance if the seating. This shouldn't be compensated for with EQ as the tonal changes make it vey noticeable. Theaters being a larger space roll off at ~2khz and is routinely compensated for with EQ. I'll explain further.

If we back up a bit and look at how loudspeakers are measured at typically 1-2 meters from the speaker. This measurement is the reference for that speaker. If we listen 10-20 feet from that speaker we will still be able to tell the timbre of the speaker. Just like if you were across the room from a friend with a stuffy nose you can tell his voice sounds different than normal. Compensating for this small amount of roll off in small rooms can often make the source sound un-natural.

In a large room sitting 50-100 feet or more from the screen with roll off that starts at a lower frequency and is steeper we need to have some compensation so dialogue doesn't sound distant and lose the illusion of dialogue taking place as if we were in the room.

The good thing about dubbing stages is they are acoustically similar as they have standards. Also there aren't that many of them (~20) so it is easier to recreate their acoustical properties.

Music and TV are a whole different animal. Most of these are recorded in recording studios which vary quite a bit acoustically. Some are very near field with speaker (monitors) sitting on the mixing console. Other have baffle mounted speakers (like in wall speakers) which are 10-20 feet from the mixing console. Most have acoustical treatments in the room but there is no standard and the room acoustics differ greatly. As the previous poster mentioned the high frequencies may be boosted because the room has lots of absorption. Unless you know the exact recording studio a piece was mixed in, it is highly unlikely you will recreate the acoustical space for music or TV.

Large room vs small room each has its own set of acoustical issues. Large rooms deal with much more reverberration while small rooms have standing waves problems. Where is the cut off between large and small. Well opinion vary but IMHO once your space is bigger than 50 ft x 50 ft you are dealing with large room acoustics. I don't think anyone would argue that 100 ft x 100ft is a large room.

Defining near field depends on the person but the recording studio with monitors on the console I think everyone can agree is near field. From a technical standpoint nearfield is less than 2 wavelengths, usually referred to in other areas of electronics. Far field is greater than 2 wavelengths. For audio this would be a tough definition because wavelengths change with frequency. A 20hz wave is greater than 50ft and 20khz is less than an inch. I'd say nearfield is less than 2 meters but there is no definition and not all recording studios would be considered near field.

Originally Posted by bodosom

I suppose I was unclear. I was using far-field in the context of theater equalization -- the nominal purview of the 202M et. al. The Allen article calls the space from 0-15 feet near-field and 40 feet far-field.

Originally Posted by bodosom

I don't listen in the far-field. I suspect few people do at home.

Originally Posted by fitzcaraldo215

Au contraire. Most home listening is done in the far field. Unless your speakers are about 1 meter away, it is farfield listening where room reflections start to become significant. That is the meaning of "far field."

But with music, you have a live sound reference in live concerts. With movies, I really do not know exactly what Meryl Streep's voice sounds like.

No, I think there is broad professional consensus that bass should be measurably flat in your room (at reference level).

I have several friends with Anthem D2V's with ARC. It provides very similar results. We once did a listening session of a D2V (ARC calibrated) vs. an Integra DTC 9.8 (Pro calibrated MultEQ XT) side by side in the same room. There were no obvious differences in the sound; they were virtually indistinguishable with Mch SACD - hats off to Integra for matching the sound of a > 4X more expensive unit!

Originally Posted by LarryChanin

Thanks for your response, but I have to admit that I'm confused by your remarks quoted above.

Originally Posted by fitzcaraldo215

Larry - I may have overblown the connection to the X-curve. I think the more complex version of my meaning fits with yours. I believe the X-curve and the HF rolloff in Audyssey are both derived from largely the same underlying property of acoustics. That is the difference in response between direct, close in, so-called "near field" measurements vs. those in the more reverberant "far field". I think the previously cited papers on the X-curve make this underlying cause clear.

Obviously, the X-curve itself was developed and is intended for large auditoriums. But, the same measurement issue occurs to a significantly lesser degree with sound in home listening rooms when room reflections come into play. We see this in the 3 standard rolloff curves built into Pro. It is only #3 that is intended for large spaces and tends to be more like the X-curve with much more rolloff. #'s 1 and 2 are Audyssey's adaptations of the underlying idea, not of the X-curve itself, based on their own research for typical smaller home theaters. Chris's explanations also including acoustic treatments in mixing/mastering studios may also be a factor, although studios do vary. But, the distance from the speakers is itself sufficient to cause the underlying HF measurement phenomenon based on the ratio of direct to reflected sound.

In any case, the key is how much room reverberation is involved with the mike to speaker measurement positions. "Near field" and "far field" are kind of red herrings. Sorry I introduced them, but acousticians talk in those terms all the time. They are merely proxies for the amount of direct vs. reflected sound. And, what Audyssey is all about is correcting for adverse effects of those room reverberations.

Flat HF response would be fine for typical computer/workstation speakers. But, in real rooms under typical listening conditions, an adjustment is needed to the measured HF response for the effect of the room. The Audyssey rolloff of the target curve gives us an approximation of that. But, for geezers like me without much hearing above 15K, I cannot say that the effect is profound. More important may be the very slight rolloff in the target curve below 15K. In any case, I very much like what Audyssey has done to the resulting sound using Pro curve #1.

Originally Posted by BobL

Hi Larry,

Enthusiast or Professional? Both!

I have worked in recording studios to help my friend which owns a couple of them. I currently work as a custom integrator where we mainly design home theaters with an occasional small or home recording studio. I have an engineering background with a focus on acoustics. I have had many trainings on acoustics and HT, including THX, HAA, Dolby Labs, other dubbing stages as well as many other HT education opportunites.

As an enthusiast I like to design and build speakers and play keyboards. Of course without MIDI I'd really stink

Bob

Originally Posted by bodosom

If you have some references for that I'd appreciate seeing them.

Originally Posted by LarryChanin

Audyssey is not concerned with these equipment limitation related aspects justifying low and high frequency roll-offs and as we know is flat in the bass region.

Originally Posted by markus767

Or did I just misunderstand your point?

Originally Posted by bodosom

Indeed. My original question was about simulating the tilt found in Harman systems given the significant preference for it. It seems to me that far too many people complain about "thin" bass post-Audyssey and want to turn up their sub(s). I used to think this was simply an adaptation but perhaps it's a deeper preference.

Originally Posted by fitzcaraldo215

[...] I think there is broad professional consensus that bass should be measurably flat in your room (at reference level). It sounds more like live music to me that way, as well.

Originally Posted by bodosom

If you have some references for that I'd appreciate seeing them.

Originally Posted by markus767

That's like asking for proof if the sun is coming up tomorrow like it did the last 4 billion years.
See papers by Harman, K+H, Geddes, Genelec or University of Essex.
Or did I just misunderstand your point?

Originally Posted by bodosom

It's hard to say. Perhaps I didn't have one. I was thinking that 202M has broad professional acceptance and calls for roll-off starting at 63Hz.

Originally Posted by LarryChanin

Hi,

In the early days Dynamic EQ wasn't available to restore perceptual flatness. So many folks in the past complained about MultEQ having thin bass after EQing flat AND listening below reference level. Personally I believe today with Dynamic EQ enabled most complaints about thin bass is probably due to listeners simply being used to boomy bass.

Its true, due to the way human hearing sensitivity works, that when listening below reference a boost in the bass is usually preferred by listeners.

Larry

Originally Posted by SoundofMind

^Be my guest.

Originally Posted by LarryChanin

Pulling things back into context, Fitz was discussing EQing for flat bass at HOME and at reference level.

Originally Posted by pepar

What training?

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Originally Posted by bodosom

Sure and I still wouldn't mind some references that support (and possibly clarify) the position.

I've heard casual remarks that suggest various things.

Originally Posted by GPBURNS

I mostly prefer midrange compensation off however the occasional soundtrack can get a bit harsh at reference levels- mostly older stuff and non HD codec films
My room is overly damped/treated (my preference) so could see myself preferring it on in non treated room

Originally Posted by LarryChanin

Surely for such a basic issue as spectral balance you must have already read that departures from a flat frequency response introduces timbre changes that colors the accuracy of sound of recordings.

Originally Posted by BobL

Music and TV are a whole different animal. Most of these are recorded in recording studios which vary quite a bit acoustically. Some are very near field with speaker (monitors) sitting on the mixing console.

Originally Posted by bodosom

Perhaps we're talking about different things. E.g. none of the Audyssey REFERENCE curves are flat (at least not with my AVR). I suspect this is representative of RC products.

As part of the first tests, listeners were required to “draw” (using sliders on a computer screen) a frequency response, describing what they thought they heard in terms of spectral balance. This is a task that obviously could not be asked of average listeners, but these listeners had been through a training program (Olive, 1994, 2001) and were able to estimate the frequencies at which audible excesses and deficiencies occurred. When these data were compiled, the results indicated that all of the highly-rated loudspeakers had been judged to have very flat curves.[...]

In these experiments, trained listeners were able to draw curves of spectral trends—crude frequency responses—describing what they heard in the listening room. All of the high-scoring loudspeakers were described as having flattish spectra (above the transition frequency), a trend that matches the flattish on-axis/listening window curves for all of the corresponding anechoic measurements.