A Rethink of THD/THD+N (or why both tell us almost nothing)

Discussion in 'Audio Science' started by ChaChaRealSmooth, Jul 6, 2020.

  1. Armaegis

    Armaegis Friend

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    Sep 27, 2015
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    New dumb idea: generate tone(s) based on a piece of gear's distortion profile. Use that for evaluation and purchasing decisions rather than listening to the equipment itself.
    crenca likes this.
  2. atomicbob

    atomicbob dScope Yoda

    Friend BWC MZR
    Sep 27, 2015
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    On planet
    You do not need expensive equipment to test a new weighting algorithm. It can be done with the graphs containing FFT presented in the measurements posted, a scale or calipers, a pencil, piece of paper and a spreadsheet, calculator or even a slide rule.

    1. print out distortion graph for amplifier of interest (FFT does not have any weighting applied)
    2. determine dB below 0 for each harmonic desired
    3. remember to convert dB back to linear before performing weighting calculations
    4. apply new weighting algorithm and calculate new metric
    5. convert back into dB or % as desired
    6. Read impressions on amplifier of interest. Best information is usually in the first page or two of impressions post.
    7. Correlate new metric to impressions
    8. Repeat for all amplifiers of interest.

    This only requires time and effort on your part, if you are interested.

    example graph for harmonics 2 through 6 (green circles on right channel)
    20201012 Bachelor GE5654W A04 THD+N  THD  nth-HD FFT 300R - 4+HD+N with 60Hz 0dBu annotated.png

    Now if you were intending that I do the following:
    1. spend 20 to 40 hours coding in a new algorithm into the analyzer, including testing new algorithm measurement accuracy
    2. remeasure a number of amplifiers, requiring 2 to 4 hours for each amplifier for a single measurement (remember amps should be thermal equilibrated before measurement)
    3. gather impressions information
    4. spend time making correlations
    5. post results for instant consumption

    Well, that would be annoying. I've already put in significant time on the 4+HD+N, which I believe is a useful metric, one that may be frequency swept for creating amplifier profile graphs with this metric. I am already on record as abhorring simplification of complex behavior to simple figure of merit numbers. There is another site on the internet that believes in that bullshit idea.
  3. mkozlows

    mkozlows Friend

    Oct 6, 2015
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    Crutchfield does that for speakers.

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