I would like to please dispel the following audio myth...

Discussion in 'Home Theater Projects' started by Jones_Rush, Nov 10, 2003.

  1. Jones_Rush

    Jones_Rush Stunt Coordinator

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    It goes something like this: (I heard it mainly from TacT RCS users)

    "A truly ruler-Flat, 20hz-20khz frequency response, even with time domain corrections, is not somthing to be desired when listening to music through speakers. It sound too bright, uncomfortable etc...".


    My take on this is that people who say this, do not have a TRUE linear system.

    To check out what the heck I'm mumbling about, and why is it even connected to the DIY forum, please read page 16 of this thread.

    Happy reading... :)
     
  2. Wayne A. Pflughaupt

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    The link bounced, Jones.

     
  3. Allen Ross

    Allen Ross Supporting Actor

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    i live in a dorm, linear isn't in my dictionary
     
  4. Darren_T

    Darren_T Second Unit

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    I think you are outta luck. First you have to find a way to prove something that is totally subjective, then you have to prove your subjective opinions are fact. Doesn't matter which side of this argument you take, I don't think you'll get a consensus.

    Good luck! [​IMG]
     
  5. Pete Mazz

    Pete Mazz Supporting Actor

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    The type of material you listen to also has a role in this.

    Or should I say the way some music is recorded these days....[​IMG]

    Pete
     
  6. Jones_Rush

    Jones_Rush Stunt Coordinator

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    I don't understand, did you read the link I provided, or didn't you ?. Please, read it first!.

    The reason why I am in a very objective position to judge this situation, is becasue I too said the exact same thing as I quoted above. You'll have to take a look at the graphs, and see the changes yourself, between a "semi" linear system (what most people who have TacT RCS and similar devices use, including me up to several days ago), and a "true" linear system.


    Wayne,
    I base my assertion ONLY on my personal experience with my audio system at home (which is used in a VERY untraditional way). I've included enough graphs in that post to try and tell the story as clear as possible.

    Btw,
    The link I provided above is fine, AvsForum.com was down before, but it's up again now.
     
  7. ThomasW

    ThomasW Cinematographer

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    Sometimes it's best to leave things in their own bailiwick!

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
     
  8. Jones_Rush

    Jones_Rush Stunt Coordinator

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    Sure Thomas, but in order to judge correctly, one needs to have all the facts in front of him, and only then to try and make decision.

    Be honest and tell me that your system ever sounded anywhere near as flat (in both frequence AND time domains), as the one in the last waterfall graph.

    I used my room correction device at numerous rooms (big, small, dumped, live etc.) and NEVER got even close to the almost unbelievable results of that last graph.
     
  9. Jones_Rush

    Jones_Rush Stunt Coordinator

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    Ok, in order to overcome the link problem, I'll copy&paste that post into this thread.

    Take notice that this post is #304 in that thread, so some things will look out of context in relation to this thread, but you'll get the general notion.

    btw, "DRC" is a digital room correction code (free to use) for the PC, which turns every pc with a capable sound card, into a competent digital room correction device.

    Here is the entire post:




    "Update!

    Sorry for not being able to participate in the thread frequently. The semester has begun, and I have VERY little time for anything apart from studying... :-(

    Anyway, there was one thing I needed to finish.
    During the semester vacation, I have ordered foam tiles, in order to absorb some reflections in my room. I wanted to enjoy both worlds, ie. both DRC and acoustic treatments.

    To my dismay, the foam factory wasn't fast at all, and I only received the foam tiles after the semester has already begun.

    I have spent the free time I had during the last two weekes, in order to place the foam in my listening room, using a LEDE configuration ("Live end, Dead end").

    The process was VERY tiring, especially since I also needed to frame the tiles and cover them with some fabric (in order for everything to look nice too). I covered the wall behind the speakers, some of the side walls near the speakers, the first reflection points at the ceiling, and one spot exactly behind me (since I got reflections from the closit behind me).

    After I finished (and also during the process), I measured everything, and created new filters.

    Here are the Before/After Waterfall plots:

    First of all, just in order to get your eyes straight, here is how the first 4 milliseconds of a waterfall graph should look like, with a perfect speaker in an acoustically perfect room for audio reproduction (This is actually the first 4ms of a Dirac Delta IR, which of course has no late reverb, which is needed for pleasant stereo reproduction), now this, and only this, is "truly ruler-flat", in terms of frequency/time/amplitude :

    [​IMG]



    And now back to reality :) ...

    This is how my room measured before the LEDE treatments, and without DRC (and remember, I use the nOrh 9.0 speakers and some pretty good Carver amp, this is pretty expensive gear):

    [​IMG]

    You can see that the direct sound is very uneven, plus there is WAY to much reverb in the first milliseconds. I've been told that my room is pretty typical, acoustically wise. This is the way I heard music in my room for years, basically up to this semester vacation :).


    This is also before the LEDE treatments, but WITH DRC applied:

    [​IMG]

    You can see that the direct sound is much more even, and can also discern that the reverb is somewhat mitigated (better spread?) in comparison to the non-DRC IR. This is quite a positive impact nevertheless. The fact that there is still so much reverb in the first few milliseconds, make me use DRC with a target response which is a bit warmer (the bk-2.txt file), otherwise, if I try to go for trully flat response, it sounds overly bright and fatiguing.


    This is WITH the LEDE treatments, but without DRC:

    [​IMG]

    You can clearly see a VERY positive impact on the reverb. The difference is quite staggering, one might say. Sonically, the sound is much more focused. The imaging becomes really superb. The direct sound is almost unaltered, of course.

    And now, to the crucial test, LEDE + DRC :


    [​IMG]

    Holy ****!!!, yes, I know. The resemblance to the Dirac Delta Waterfall is almost disturbing.

    At first I used the bk-2.txt target curve, which compensate for reverb anomalies of a typical room by lowering the amplitude of the higher frequencies. Only problem was, my room no longer exhibit the typical acoustical problems, hence, the sound was way too warm for my likings. At this point, I emailed Denis and told him my findings. After seeing the almost unbelievable IR results, he told me to try and use a flat target curve. I did, and OMG!!!.

    The sound quality I get is simply beyond words.
    If you remember, at the beginning of this thread I was afraid that DRC will do something to the top end frequencies. And up to this day I wasn't sure what exactly it does. Today I found out. It *corrected* the tonality of my speakers, definitely! (although the results before LEDE were somewhat controversial, in this regard). It is unbelievable. My speakers are somewhat bright, and I had no clue. In simple words, without DRC, my speakers sound too bright, and not very detailed (as I found later, the "bright" frequncies masked other frequencies, which caused a detail reduction). The sound is subjectively very good even without DRC, but when I apply DRC, the feeling is like I stop hearing the singer's voice through the speakers, and start to hear it like he is practically in my room.

    The acoustic treatments by themeselves, make the imaging simply superb, but the songs still sound like they are played through some very expensive speakers. With DRC applied, it does not seem like the sound is reproduced by speakers anymore, it sounds like the performance is being played inside my room by real people. This is the closest thing to a Star Treck Holodeck I have ever experienced, sound wise.

    This is simply the most frightening "They are Here" experience I have ever heard in my life. The amount of realism is simply scaring, and I'm NOT exaggerating, you need to hear in order to believe it can be true.

    Because you can't hear it with me, maybe the best thing you can do is take a look again at the images, and take into consideration the pretty substantial differences between the Dirac Waterfall and all other Waterfalls, except the LEDE + DRC one.

    Btw,
    I know there is a consensus that when a sound system is very revealing, then less-than-optimum recordings sound bad. This is NOT the case here. Everything sound WAY better than what it sounds before the treatments and DRC. I believe that the logic behind this fact is that lower-than-optimum recordings are bad enough as they are, there is no point in believing that letting the acoustics in your room + speaker's anomalies, ruin it even further, will make it sound more pleasant. And even if it might be true for some people, I can tell you with confidence that this is not the case in my situation. Bad recordings sound better! (on the other hand, now that I think of it, it could be that the recordings which I thought were "bad", were simply "incompatible" with the bad acoustics of my room before I fixed it...).

    I think that this post proves that DRC is a VERY beneficial tool, whether your room acoustics sux, or excellent.

    This post also puts in perspective the importance of acoustics in relation to other factors in the sound system. It makes me laugh how much time I spent in the past worrying about my sound card's DAC, and the ASIO in order to bypass the "horrific" Kmixer SRC bug, while all the time I was listening through this graph:

    [​IMG]

    What a joke..."
     
  10. Mike SJ

    Mike SJ Supporting Actor

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    Jones, so are you for or against having a "ruler flat" response curve?
     
  11. Jones_Rush

    Jones_Rush Stunt Coordinator

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    Mike,
    Read the post right before yours (you posted yours a few seconds after I posted it).
     
  12. ThomasW

    ThomasW Cinematographer

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    MODERATORS please move this thread to a more appropriate forum.
     
  13. Mike SJ

    Mike SJ Supporting Actor

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    Well, there are too many plots to really get a good read on. I do not know all the DIY nomenclature, so I could be missing the point, but what graph is accurate? or which do you listen to now?
     
  14. Jones_Rush

    Jones_Rush Stunt Coordinator

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    Mike,
    As written in that post, the first one (the Dirac Delta), is the most linear. Only problem is that it is purely computer generated. All the other graphs are real from different states of my system and room. Is there any graph of them which look VERY similar to the Dirac one ?. :)
     
  15. Wayne A. Pflughaupt

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    Jones,

    Sorry for jumping to conclusions in my first post (I guess I can shift blame to AVS if they were down at the time [​IMG] ). I can see now what you were talking about – true linear response vs. what you get from most speakers/rooms (I thought you were stirring up another flat response vs. house curve thing).

    And I must say it’s very impressive. What kind of digital correction are you using?

    Mike,

    The curve at the top of each graph is the “original” reading. The curves in “front” (beneath) it show time domain response – delayed, and including the effect of room reflections. Make sense? The graph labeled “LEDE + DRC” is the “end of the road” – the effects of acoustical treatments and digital room correction. As you can see in that graph, the effects of the room have been virtually eliminated. Pretty amazing.

    Regards,
    Wayne A. Pflughaupt
     
  16. BruceD

    BruceD Screenwriter

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    Anybody else notice that the lowest frequency represented on the 3D waterfall charts is 200Hz?

    I find the bass modal room response (peaks and nulls) more of a problem below 200Hz than above 200Hz.
     
  17. Jones_Rush

    Jones_Rush Stunt Coordinator

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    BruceD,
    The reason why you see no information below 200hz is just because that screen in ETF wasn't ment to show it. As you can see from the images, the high frequency waterfall uses a 0.7ms Gate Time, while in order to get meaningful results in the bass region, you need something like a 100X longer gate.

    Here you go:

    First, for all the BFD users (btw, I am one also :)), try to beat THIS 2D graph:

    Before DRC:
    [​IMG]

    After DRC:
    [​IMG]


    Now, about the Waterfall graph, you need to know that psycho-acoustically (and also physically), bass frequencies are different than the higher frequency spectrum, in the sense that they have longer wavelength, and this is why you won't see a short lasting direct sound, like with the higher frequency waterfall. At least some experiments that I know of, indicate that to the human ear, the reverb of the frequencies in the bass region, need to fade off gradually over a long period of time, in order to sound pleasant. Furthermore, the sensitivity of the human ear to lower bass frequencies (below 200hz), is very low, and this is why a geometrically perfect waterfall is kind of an overkill. IMO, both the 2D and Waterfall graphs shown here are overkill in terms of bass accuracy. Our ears simply can't appreciate the difference after a certain threshhold is met, and I think it is met pretty much before it gets to the levels of these DRC graphs. I base my words on the experienec I had with the BFD. I noticed that small (to even moderate) changes, went mosetly unnoticed. The only positive change with BFD, that I can honestly say I can hear, is the attenuation of the two big peaks. All of the other changes that I made, in order to try and bring the 2D graph to flat, went unnoticed by my ears (in a blind test I did). Of course with the BFD we have no control over time anomalies, so I couldn't check how sensitive we are to small changes done in that domain. I can only guess, that big changes will go noticed, while smaller ones will probably be a waste.

    Here are the waterfall plots:

    Before DRC:

    [​IMG]


    After DRC:

    [​IMG]
     
  18. Jones_Rush

    Jones_Rush Stunt Coordinator

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    Wayne,
    Regarding the DRC code I'm using, it was (and still is) developed by Denis Sbragion, over a period of 3 years, at his spare time. He once said that he did it out of frustration. He really needed it, and couldn't understand why no one else has developed such a code for the PC, considering the the tools to make it are available for about 10 years now.

    The code is just that, a code. Don't look for a fancy GUI. I liked DRC so much that I've written a Step by Step Guide, which I think is easy for anyone to follow.

    As to how does DRC compares to other Room Correction devices on the market today, I can only say that I know of one guy (Patrick) who at the beginning of 2003 compared DRC to his TacT RCS 2.1 device, and said he finds it very hard to hear any difference between them. This was with DRC V1.7, while the current version is V2.3, which added quite a bit of features (some of them are really important).

    I won't lie to you, setting up DRC won't be as short as setting up a TacT unit, but I hope that with my guide, and some (really) basic knowledge of how to use a computer, anyone could accomplish the task with ease.

    One note,
    Whoever tries to use DRC, get a good mike (at least the ECM8000). I first tried to use the Rat Shack. Don't repeat my mistake... :)
     
  19. Chu Gai

    Chu Gai Lead Actor

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    I personally commend your efforts into obtaining a better understanding of your system. Now go out and get some beer and pizza!
     
  20. Jones_Rush

    Jones_Rush Stunt Coordinator

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    LOL!, thanks Chu.
     

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