Ethan Winer

Ethan Winer

Full Audioholic
Folks,

In the (sadly) now-locked thread Acoustic Wierdness, a side issue came up about Floyd Toole's recent article where he says that early reflections can be useful. Since this goes against my personal experience, and that of many others, I posed the following question in a popular forum frequented by audio professionals - the guys and gals who actually mix the music and movies we all enjoy in our home environments:

There seem to be two philosophies of mixing, both for music and DVD movies. One says to avoid all early reflections in the listening room during playback, because all of the ambience and directional cues the mix engineers intended are already in the soundtrack. This makes sense to me, and it doesn't require making the listening room anechoic either, as some suggest. It just requires avoiding all early "first" reflections.

The opposing philosophy says the listening room should be lively and have its own ambience, and the room's character should be part of the total listening "experience" if you will. This does not make sense to me because every recording or movie will then sound very different in each room because the sound of the room will dominate. In my experience, not absorbing (or diffusing) first reflections also has the negative effect of hearing the sound come from the loudspeakers, rather than from a phantom image.

What do the experts who actually mix the music and movies we all love have to say?
One of the participants in that forum is the chief audio engineer for a major TV / movie studio. He hinted at his studio's philosophy in the forum, but due to legal constraints he was not able to speak as freely as he wanted. So later that day he sent me a private email with much more detail. He asked me not to name him or his employer, but said I was welcome to post here the following statement as representative of their approach. I promise you this quote is not taken out of context, and if I named the production company he works for everyone here would know it very well.

It is important that there is not too much individual room sound happening or else the rooms would not translate to each other. I guess that sorta says that we are not letting early reflections get in the way of things.
--Ethan
 
Savant

Savant

Audioholics Resident Acoustics Expert
Why don't you provide a link to the thread?
 
gene

gene

Audioholics Master Chief
Administrator
In the (sadly) now-locked thread Acoustic Wierdness, a side issue came up about Floyd Toole's recent article where he says that early reflections can be useful.
Dr. Toole isn't the first to write about the benefit of early reflections on speech intelligiblity in small rooms. Many others have done similar, though not to his level of thoroughness, in the past.

Here is one example:
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JASMAN000113000006003233000001&idtype=cvips&gifs=yes

I posed the following question in a popular forum frequented by audio professionals - the guys and gals who actually mix the music and movies we all enjoy in our home environments:
Don't make the mistake in assuming the mixing engineers always know what is best for the home environment. Many mixing engineers that we've met in the past had little to no knowledge on proper speaker placement and bass management in the home theater environment.

Surround Panel Discussion

It's a wonder as to why so many of them produce unlistenable CD's these days that are loaded with hypercompression and exceedingly high recording levels > +0dBFs. Though to their defense I can understand the pressures they face from the record labels to ensure they make the LOUDEST CD's possible.

Current Trends in Recording Format Arena

Issues with Exceeding +0dBFS

Case for NOT Exceeding +0dBFS
 
Glenn Kuras

Glenn Kuras

Full Audioholic
Gene wrote:

"Don't make the mistake in assuming the mixing engineers always know what is best for the home environment. Many mixing engineers that we've met in the past had little to no knowledge on proper speaker placement and bass management in the home theater environment."

I will second that!!! It really is crazy how some of these schools teach these kids how to use all that great gear in a studio, but don't even touch on the subject of room acoustics.

Glenn
 
Ethan Winer

Ethan Winer

Full Audioholic
Folks,

First, it is not my intent to create friction. All I care about is having a healthy discussion about the science of audio. Okay?

> Here is one example:
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JASMAN000113000006003233000001&idtype=cvips&gifs=yes <

From that page:

... speech intelligibility tests in simulated sound fields and analyses of impulse response measurements in rooms used for speech communication.
They're talking about making speech more intelligable in airport control towers etc, no? As opposed to faithfully reproducing music and movies in a living room setting.

I also made the point earlier that the direct relation of early reflections to the comb filter changes in frequency response seems the most plausible explanation for why speech could sound clearer in the presence of those reflections:

For example, if the distance / delay creates a null in the tubby range around 200 Hz, I can see how that might make a vocal seem clearer. Especially if it was recorded too tubby to begin with.
> Don't make the mistake in assuming the mixing engineers always know what is best for the home environment. <

I partly agree with that, though as with any field there are good engineers and bad ones. I too lament the lack of scientific foundation by many recording "engineers" in my Audio Myths article

Most engineering fields require a college degree or at least state certification, and for good reason: If you design a drawbridge or high-rise office building, you'd better be able to back up your proposal with irrefutable science proving the design really works and people won't die. But the audio recording field has no such formal requirements. Anyone can claim to be an audio "engineer" and go about his or her business. Indeed, if you can produce recordings that sound good, nobody will argue about math or electronics theory - a great sound is all the credentials you need.
> It's a wonder as to why so many of them produce unlistenable CD's these days that are loaded with hypercompression and exceedingly high recording levels > +0dBFs. <

I assure you this is a very hot subject in the pro audio forums! Most of the "good" engineers hate when their clients demand they make a recording as loud as possible. In this case those decisions are made by the client and/or producer, and not the engineers. Not only do they hate being asked to make everything overly loud, they also hate that they get blamed for it! :D

There are also many excellent recording engineers who really do understand the science of audio and acoustics. This is why I went right to the top and asked the chief engineer of one of the largest TV / movie studios for his take on early reflections.

> Why don't you provide a link to the thread? <

Because I promised the engineer anonymity. His company is large enough to have a legal department that's paranoid about the silliest things, and apparently what he says in public is part of that. That's why I said I promise I'm not lying. :D

> (in this case, rule #7): <

Sorry. I assumed that since this was just a side-issue from what caused to Gene to feel he had to close that thread, it would be okay to discuss it in a new thread.

--Ethan

[Edit: Commercial links removed - Admin.]
 
Savant

Savant

Audioholics Resident Acoustics Expert
Ethan Winer said:
> Here is one example:
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JASMAN000113000006003233000001&idtype=cvips&gifs=yes <

From that page:


They're talking about making speech more intelligable in airport control towers etc, no? As opposed to faithfully reproducing music and movies in a living room setting.
The rooms included in the cited paper range in size from 390 to 7000 m³ (approx. 13,800 to 247,000 ft³). These sizes correspond to, respectively, rooms ranging in usage from a boardroom to a small theater. These rooms are on the large side compared to what is typically dealt with in a home theater.

Something interesting from this paper is that the authors propose a new metric, the "Early Reflection Benefit," or "ERB,"* as a "useful measure of the effectiveness of a room's acoustical design." Since this "ERB" is purely an energy ratio, it would be completely appropriate for use in evaluating smaller spaces. On the other-other hand ( :) ), the authors point out that "(t)he direct sound energy will decrease with distance so that direct speech levels would frequently be unacceptably low at more distant listening positions in many rooms." This is worth noting only because it is arguable that most, if not all, of the seats in a home theater could not be considered "distant listening positions."

Finally, since (arguably) the most important information being communicated in film soundtracks is monaural dialog, i.e., speech, then it is necessary that research like this be reviewed and considered carefully so that home theater acoustics can be more fully understood, and so that better rooms can be designed! :D

Great reference, Gene!!!

* A somewhat unfortunate acronym; in our industry, it could be confused with Equivalent Rectangular Bandwidth.
 
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Rob Babcock

Rob Babcock

Moderator
Ethan must be doing something right- check out the 5 Star rave of his RealTraps here.;)
 
S

sploo

Full Audioholic
Rob Babcock said:
Ethan must be doing something right- check out the 5 Star rave of his RealTraps here.;)
I would of course have to point out that those ratings are BM's subjective interpretation, and that he hasn't performed a proper ABX test ;)

Cheers for the reference though mate (spikyfish), I hadn't seen the review prior to today.
 
Ethan Winer

Ethan Winer

Full Audioholic
Jeff,

> Since this "ERB" is purely an energy ratio, it would be completely appropriate for use in evaluating smaller spaces. <

But focusing entirely on the amount of energy ignores the delay times which is likely very important. I have yet to hear a more compelling explanation than what I proposed - if the presence of early reflections makes dialog sound more clear it's due simply to having comb filter notches at muddy frequencies. And that would be very much dependant on the delay times. This would be very easy to test using a "phaser" effect or plug-in. I'm not saying it's entirely the null frequencies, but that seems most likely, no? If not that, then what?

--Ethan
 
Ethan Winer

Ethan Winer

Full Audioholic
> Ethan must be doing something right <

Thanks Rob, I'm trying!

Sploo:

> those ratings are BM's subjective interpretation, and that he hasn't performed a proper ABX test ;) <

I know you're just kidding, but if you read the article you'll see comparisons of the room with and without traps. That's about as "ABX" as you can get. :D

--Ethan
 
S

sploo

Full Audioholic
Ethan Winer said:
I know you're just kidding, but if you read the article you'll see comparisons of the room with and without traps. That's about as "ABX" as you can get. :D

--Ethan
Yea, it was a pretty cr*p joke on my part (late night, too much beer etc. etc.)... I was reading the review and for some reason thought of Chris' (WmAx) assertions about the problems with people making subjective 'measurements' of their audio gear. I think it's more the fact that it winds people up so much that made me smile :D.

PS Chris, put the Behringer down... I do agree with you!
 
jaxvon

jaxvon

Audioholic Ninja
Ethan Winer said:
> Ethan must be doing something right <

Thanks Rob, I'm trying!

Sploo:

> those ratings are BM's subjective interpretation, and that he hasn't performed a proper ABX test ;) <

I know you're just kidding, but if you read the article you'll see comparisons of the room with and without traps. That's about as "ABX" as you can get. :D

--Ethan

Correction: The comparison of the room before and after traps with a microphone is an A/B test. In addition, we do not know how precise Robbie was with his microphone placement. This alone could lead to large systematic errors in the testing and completely invalidate the "numbers" portion of the review. That said, I still maintain that it was an excellent review in the subjective realm and that I'm sure he, at the very least, perceived improvement in his system after installing the RealTraps.

Note: Paragraph above was edited to convey what I intended.
 
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Savant

Savant

Audioholics Resident Acoustics Expert
Ethan Winer said:
Jeff,

> Since this "ERB" is purely an energy ratio, it would be completely appropriate for use in evaluating smaller spaces. <

But focusing entirely on the amount of energy ignores the delay times which is likely very important.
On the contrary - the ratio as the authors define it compares the energy arriving after 50 ms to the energy arriving after 10 ms. These times are arbitrary in the grand scheme of things. They defined 50 and 10 ms based on Häas, et al, as well as their own conclusions about useful energy. One could easily modify the "ERB" to something more relevant to smaller rooms, if that were deemed necessary.

Evaluating different energy ratios is becoming quite commonplace in large room analyses. Check out this page for some of these large room metrics (D50, C50, CXX, etc.). I think these metrics, or other versions, could wind up becoming more useful in small room analyses. Much like EDT is more useful than RT60...
 
S

sploo

Full Audioholic
jaxvon said:
Correction: The comparison of the room before and after traps with a microphone is an A/B test. In addition, we do not know how precise Robbie was with his microphone placement.
A very good point.

When I took measurements of my room I was very careful to ensure that the mic was on a tripod, and that everything else in the room (objects, furniture, doors & curtains opened/closed etc.) were exactly the same with/without the traps in place.

I know Robbie sent me a PM asking about mic positioning, so I'm hoping I would have told him something sensible (time has dulled my memory)!

EDIT: Thinking out loud - my understanding of the point of true double blind testing is to prevent any bias from both the tester and the subjects. Assuming that nothing changes in the room apart from the addition of treatment, and that a mic/PC are of course not subject to bias, would that therefore be considered as sufficiently 'blind'? I guess that's a question for both acoustic and logic experts...
 

Buckle-meister

Audioholic Field Marshall
jaxvon said:
...we do not know how precise Robbie was with his microphone placement. This alone could lead to large systematic errors in the testing and completely invalidate the "numbers" portion of the review.
Oh please! :) ;)

To be clear, the microphone remained insitu (for exactly your reason) when taking readings for what would end up as before/after plots so that the two sets of results would be compatible.

As for the review, though I was happy with the results at that time, I've since experimented with sub placement and these results, as you will see, are far superior to those in the review.

sploo said:
I know Robbie sent me a PM asking about mic positioning, so I'm hoping I would have told him something sensible (time has dulled my memory)!
You did (I don't forget ;)).
 
S

sploo

Full Audioholic
Buckle-meister said:
Somehow... I mangaged to miss that thread :confused:. Must be losing it in my old age ;)

Very very good set of results there Robbie - nice work.
 
Ethan Winer

Ethan Winer

Full Audioholic
Jax,

> The comparison of the room before and after traps with a microphone is an A/B test. <

Of course.

> I'm sure he heard improvement in his system after installing the RealTraps. <

I'm sure too. And this brings up an important distinction. I see blind testing as useful for separating what's audible from what is inaudible. When someone claims to be able to hear the different between speaker cables, and someone else says there should be no difference between any two competent wires, a blind test is a good way to settle it for once and for all. Likewise all the other barely-audible or inaudible things that always spawn a 12-page heated argument in web forums. But I don't think anyone would dispute the very obvious improvement from adding room treatment.

--Ethan
 
Ethan Winer

Ethan Winer

Full Audioholic
Jeff,

> They defined 50 and 10 ms based on Häas, et al, as well as their own conclusions about useful energy ... I think these metrics, or other versions, could wind up becoming more useful in small room analyses. <

Certainly could be. I also think someone (you? :D) should experiment and compare "real" early reflections with simulated reflections using a phaser type effect. It would be interesting to know how much of the increased clarity is from simple comb filtering as I described above, and how much is from the reflections themselves and/or other factors.

--Ethan
 
J

jlohl

Audiophyte
I also think someone (you? ) should experiment and compare "real" early reflections with simulated reflections using a phaser type effect. It would be interesting to know how much of the increased clarity is from simple comb filtering as I described above, and how much is from the reflections themselves and/or other factors.
I tried to do such a software to simulate early (not only...) reflections. You can download it at http://www.ohl.to/audio-tools-and-thoughts/audio-softwares-and-vst-plugins/room-sound/
It's free. And I'd be happy to hear your comments. Especially because I'm not yet completely satisfied with the audible results !
 
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