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Thread: Target Curves

  1. #1
    [WBF Founding Member] RUR's Avatar
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    Target Curves

    The good news for TacT owners is that target FR curves are selectable and highly adjustable. Armed with a laptop, we can insert/move/delete filters to our hearts content in search of “the perfect curve”. Adjustment may be made in increments as small as 0.8Hz and 0.1dB. Furthermore, multiple curves are supported and selectable with the push of a remote button, so we can design and use multiple curves as individual mastering and/or the mood suits. Not enough bass on a particular recording? Pick a curve with more bass emphasis. Want more bloom in the midrange? Pick a curve with a touch of midrange push.

    Unfortunately, finding the ideal curve isn’t necessarily easy. Sure, the TacT comes with a variety of target curves to try and, if one of them is the perfect fit, you’re done. In my case, and probably in many/most others, that won’t be true and one is left to tweak a supplied curve or to develop one from scratch until nirvana is achieved. Depending upon your temperament, you may find this (generally extended) exercise to be fun – or frustrating, so I thought I’d start this thread with what I believe to be basic principles, a couple of enjoyable curves, and an invitation for fellow users to share their own curves and experiences.

    Last year, Harman International conducted a series of preference tests for Room Correction (RC) products. The results were published in an AES paper, but the basics may be found on Sean Olive’s blog here. Of importance to this discussion is that Harman found that “the most preferred room corrections produced the smoothest, most extended amplitude responses measured at the primary listening seat” and that “preferred room corrections have a target response that has a smooth downward slope with increasing frequency”. The former probably requires no explanation while the latter is attributed to the belief that listeners prefer a certain amount of room gain because the recordings were mixed with similar room gain. The most preferred response is the topmost of six shown here on slide 24 of the associated Powerpoint briefing. Note the smooth downward slope and that FR falls roughly 10dB from 20-20KHz.

    In a recent thread describing his own experiences with DSP/RC, Marty posted that his target curve approximates a curve resulting from Bruel and Kjaer’s research into room response preferences, presented in a 1974 AES paper*. B&K’s curve looks like this:



    And shows a slight 2.5-3dB “hump” (relatively flat) from 20-200Hz, falling off evenly from 200Hz-20KHz and ending at ~-3dB. I wanted to try Marty’s curve and created a TacT target curve approximation, which looks like this



    And for which the *.cor file may be found attached as BandK 0dB for WBF 6-9-10.COR.

    In my system/room and for my absolutely subjective tastes, I find both the Harman and B&K curves to be a bit rich in upper bass, masking vocals and important spatial detail. Basically, I use a straight slope from 20-20KHz, though much shallower than Harman’s.



    The associated TacT *.cor file may be found attached as kensexample for WBF.COR

    As with any TacT curve, measured response will vary from the curve actually input and desired, so a bit of filter tweaking must be done in order to achieve the curves shown. Finally, and as mentioned at the outset, I have the various TacT presets set up with variations of "my" desired curve, adding more/less bass, mids or highs so that I can select a curve which sounds satisfying for a particular genre or to “fix” perceived mastering issues. All entirely subjective, of course!


    * That paper cannot be directly linked, but may be found here in B&K's library by searching on "Relevant Loudspeaker Tests".
    Attached Files Attached Files
    Last edited by RUR; 06-10-2010 at 03:59 PM. Reason: Missing filename

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    Site Founder And Administrator Steve Williams's Avatar
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    I am not seeing the attached COR files. I thought that I added them properly for you
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    I see them attached Steve. The graphic icon though is wrong perhaps due to file types being unknown.

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    [WBF Founding Member] audioguy's Avatar
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    RUR: To demonstrate my lack of technological prowess, how were you able to get a JPG or PDF file of your target curve to attach to your post? Once I figure that out, I will be able to post them.

    The article that was done in the Harmon paper did shows some of the curves and preference. I'm not looking at them as I type this, but IIRC, the one most preferred by listeners was fairly close to your straight line drop from 20 to 20K by about 10db over that entire range which is slightly more of a drop than your target.

    The problem with all of this is that as volume changes, so does our perception of bass. The TacT 2.2XP has a feature called dynamic volume but I have yet to try it. Have you?

    And you are correct that much of this is preference. Earlier today I was listening to the Chinese Drums cut on one of the Burmeister Demo CD's and the more bass in the target curve the better it sounded particularly since I was driving 8 15 inch drivers in my subs--and since there were no vocals to screw up, so much the better.

    Clearly the TacT is a tweakers paradise (or an OCD's worst nightmare!!)

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    If the image is on a server some place and you have a URL for it, then you can show it inline by putting [img] and [/img] around it. If you try to host it here, it unfortunately shows up as thumbnails. RUR's posts link to external sites and hence, show up inline. Is this what you were asking?

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    [WBF Founding Member] audioguy's Avatar
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    I use photobucket for that purpose. I was trying to understand how he captured the target curve plot from the TacT software that he could then post, not how to post it.

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    At the risk of answering the wrong question again , you can use Print-screen function to grab any window on your PC, then take it into mspaint, crop and then save. Of course, RUR is going to chime in probably and say that TacT software can actually save those screens and make me look like a fool for second time tonight .

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    [WBF Founding Member] RUR's Avatar
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    Quote Originally Posted by amirm View Post
    At the risk of answering the wrong question again , you can use Print-screen function to grab any window on your PC, then take it into mspaint, crop and then save. Of course, RUR is going to chime in probably and say that TacT software can actually save those screens and make me look like a fool for second time tonight .
    That's exactly how I do it, Amir - printscreen to Paint. Crop the image with Photoshop and voila!

  9. #9
    [WBF Founding Member] RUR's Avatar
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    Quote Originally Posted by audioguy View Post
    The problem with all of this is that as volume changes, so does our perception of bass. The TacT 2.2XP has a feature called dynamic volume but I have yet to try it. Have you?
    I sure have, though it's seldom used as my reference volume doesn't change much. What I haven't done is to customize the actual DRC curves i.e. the stock Fletcher-Munson curves are still being used.

  10. #10
    [WBF Founding Member] audioguy's Avatar
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    Amir/RUR: Thanks. Once I get back home I will give it a whirl.

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