Understanding THD

Discussion in 'AV Receivers' started by Robert Hoffman, Mar 25, 2004.

  1. Robert Hoffman

    Robert Hoffman Stunt Coordinator

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    Sorry if this has been discussed before, but I didn't find it following a quick search of the archives. Could someone explain to me the concept of T.H.D., and at what point it becomes something that I should look at when examining the specs of amplifiers? I was browsing some ads, and noticed that a Sunfire amp had THD of .5%, while Bryston is around .0025%. Is that an audible difference? Thanks for your help,

    Rob
     
  2. MingL

    MingL Stunt Coordinator

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    I have done some tests on my own about acceptable THD.

    THD of 1% is noticeable in sine tones. 1% THD is rarely noticeable in actual music material.

    THD of 5% is very noticeable in sine tones. I can't determine how to measure 5% THD in music material.

    0.5% is acceptable and you may never notice it over 0.0025%, which some amps claim. Lower THDs are better, but anything lowerer than 0.5% THD is more than enough.

    FYI, Tube amps have very bad THD..... they still sound good. Go figure.
     
  3. Chu Gai

    Chu Gai Lead Actor

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    As a singular figure of merit provided by companies, THD offers very little to hang one's hat on. There's a couple of reasons for my stating this. One is that the way it's measured it is more properly called THD + noise. Secondly, without knowing the order(s) of the noise and their relative magnitudes, hence looking at their particular contributions to the snapshot number, it's difficult to make any sort of informed decision. If you're lucky enough to have had a review of the product in question that delved deeper into this by providing a plot of the distortion, a better idea could be obtained.
    Now it's certainly possible to build an amp where the distortion is so low that no matter what it's order is, it couldn't be heard.
    Consider the following website, http://www.pcabx.com/technical/nonlinear/ and why don't you take the time to download some or all of the samples, burn them to a disk, and play them on your system and get a feel for this.
     
  4. Robert Hoffman

    Robert Hoffman Stunt Coordinator

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    Thanks guys for the responses. I'll check out that web page.

    Rob
     
  5. Chu Gai

    Chu Gai Lead Actor

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    If you do, take some time and post back what you found or heard or didnt' hear [​IMG]
     
  6. ChrisDixon

    ChrisDixon Second Unit

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    I like the lab reports that show distortion as a property of how many watts are driven into how many channels. It takes two ambiguous stats and makes them more comparable across systems. What we really need is an updated version of that big table that was floating around a few years ago of consistent lab ratings across receivers.

    Chris
     

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