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tgourlie

FFT / TDS / Spectrum Analyzer in conjunction with a Parametric EQ

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Anyone use these items on their two ch systems? I am considering putting in a Parametric EQ in my system. Generate pink noise, take readings at source and at listening position (or speaker terminal if youjust want system eq'd). Take the difference of the two readings and set up your parametric accordingly. Thoughts?

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This was something done very often with PA's in the 80's, but has since

been abandoned because the approach makes some bad assumptions.

Basically, you will probably find that you can get the frequency

response to measure flat, but it will probably sound off. The reason

has to do with the fact that there are things going on in the

time-domain that are influencing the measured frequency response. So

one side of the argument claims that you can never use EQ to fix these

problems, while the other side claims that EQ can be used to an extent.

Figuring out to what extent the EQ will be beneficial in your situation

will at the very least require you to do some more advanced analysis

than simply measuring pink noise.

Do you already own the gear, or are you looking to make a purchase? If

I were to try using EQ anywhere, I'd probably concentrate on knocking

out peaks in the bass response.

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I do not have any eq equipment yet. So basically the TDS could measure the time-domain issues, but you couldn't correct the issues without causing damage or losing some of the original signal?

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TDS can measure all of the time domain issues as well as the frequency domain issues. Additionally it can resolve the complex signals that comprise and contribute to the frequency domain 'result'. Thus, while these (and other domains) provide valuable information, the time domain is the domain of primacy for treating acoustical issues as all others are derivative.

The vast majority of frequency domain issues are created as a direct result of time domain issues and must be corrected in the time domain. Once these issues are addressed, EQ can be used. But EQ can only be used to address the direct signal. It will not correct the issues resulting from multiple summed signals arriving at different times.

{Therefore, while EQ was viewed as a primary tool prior to the advent of time domain analysis fathered by Dick Heyser (as it was then the only 'tool' available, and when you only have a hammer, well, you hammer! - regardless if the task requires cutting wood and driving screws... You do it with the hammer!), EQ is now of only very limited use in the acoustics of 'spaces'. Think of it as a tool to shape the signal that is presented to the speaker. It ceases to be of substantial use thereafter in the signal chain.}

Don Davis, the 'inventor' of the 1/3 octave equalizer while at Altec has written on this limitation of EQ rather extensively. May I suggest his Sound System Engineering, 3rd Ed authored along with Dr. Eugene Patronis.

(Also, a spectrum analyzer is of no real use in acoustics, unless you are concerned with analyzing the RF spectrum in order to ascertain where you can assign wireless frequencies in a heavily congested metropolitan area! ...in which case it is indispensable!)

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Anyone use these items on their two ch systems? I am considering putting in a Parametric EQ in my system. Generate pink noise, take readings at source and at listening position (or speaker terminal if youjust want system eq'd). Take the difference of the two readings and set up your parametric accordingly. Thoughts?

Reviewing your initial question, just a comment. You could of course use it, but you do not insert TDS or FFT into the signal chain. You could purchase a TEF or EASERA or SMAART or a slightly more affordable format such as Praxis or the much more affordable ETF system (~$300 plus mic & pre-amp), but that may be overkill and inappropriate if you are desirous of a piece of equipment that will function like an EQ as they are analytical tools and not pieces of gear designed for actively adjusting your system - as in, they do not have knobs to 'fix' or adjust parameters...

{Again, you may be very familiar with the gear and its use, but I am erring on the side of assuming less intimacy rather than more. I add this as if I do not clarify, many become offended as they are surprised to find that I am unable to read their minds and that I do not know all that they may or may not know... In other words, I'm just not sure how familiar you are with the actual equipment and how it operates as opposed to the usefulness of the concepts... And in that regards, if you will PM me, I will be glad to try to answer any questions you may have about the various configurations and uses of the various analytical gear.}

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Thanks for the info on the issue being in the time domain. That does make sense. If you would eq it, you would basically be running yourself in a circle. Have you had any experience with deqx products? http://www.deqx.com It seems like this is what we would be talking about.

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FWIW I use a Behringer DEQ 2496. Usign the mic and pink noise generator it made a very noticable improvement with my B&W N801's. The speakers sound extremely good without the eq, but when the eq is switched on, the midrange does clean up quite a bit (which is one of the strongest abilities of these speakers). Excellent results for about $350. I could have never dialed in the eq that well. I also used it to balance my subwoofer, which integrates extremely well using the eq.

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