How to change the duration of the beginning-end of the measurement in REW?

Discussion in 'Official REW (Room EQ Wizard) Support Forum' started by Vladimir_1953, Sep 11, 2018.

  1. Vladimir_1953

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    Hi!
    I'm here for the first time, so please do not get angry.
    How and where to change the duration of the beginning-end of the measurement in REW 2 times?
    By default, 500ms is reported.
    My pulses after the time-correctors appear at around 750ms and therefore there is no minimum phase
    I want to make measurements with a linear loopback to make measurements, because they are more accurate than an acoustic loopback.

    I set up a three-way system in my car.

    [​IMG]

    Line R_Out - R_In Loopback

    [​IMG]

    Acoustic Loopback

    [​IMG]
     
  2. Vladimir_1953

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    Behavior of the minimum phase with an acoustic loopback
    [​IMG]
     
  3. Vladimir_1953

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  4. John Mulcahy

    John Mulcahy REW Author

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    I'm not entirely sure what you want to do, but you can change the t=0 position of the impulse response using the t=0 offset controls in the Impulse graph. If you need to export impulse responses with a specific timing the export impulse response help explains how to use the IR window to do that.
     
  5. Vladimir_1953

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    The measured pulse has such parameters:

    [​IMG]

    Due to the large distance from the reference signal, I can not see the unfolded phase:
    [​IMG]
     
  6. Vladimir_1953

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  7. John Mulcahy

    John Mulcahy REW Author

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    For that you can use the t=0 offset controls in the Impulse graph to shift the reference time back to 0. Make sure you apply the same offset to all the measurements to preserve their relative timing.
     
  8. Vladimir_1953

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    Thank you for the lesson!
    Are your recommendations already applicable to ready-made measurement schedules or will they only work for new measurements?
     
  9. John Mulcahy

    John Mulcahy REW Author

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    The t=0 offset can be changed for measurements you have made. When you make a measurement with a loopback the loopback acts as the reference for t=0. Your system appears to have approx 727 ms latency hence the hefty time delay in the measurements, you will need to manually remove that using the t=0 offset controls for each measurement you make or have already made.
     
  10. Vladimir_1953

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    At what stage and in what section should I change the parameter T = 0?
    In the basic settings before the measurement or already in the results?
    If there are screenshots of these changes, please attach for correct understanding.
    Thank you in advance!
     
  11. John Mulcahy

    John Mulcahy REW Author

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    In the results.
    offset.png
     
  12. Vladimir_1953

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    Did I understand you correctly?
    [​IMG]

    [​IMG]

    I have 6 speakers and they are installed at a different distance from the microphone
    Value T = 0 set one for all, so that the relative phase is displayed correctly? For example: 725ms for everyone?

    How to save the file with the minimum phase received?
    How to see the received minimum phase from all the speakers in the window Overlays?

    Sorry for my English...
    I'm helped by Google / translate
     
    #12 Vladimir_1953, Sep 13, 2018
    Last edited: Sep 13, 2018
  13. John Mulcahy

    John Mulcahy REW Author

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    Yes, that is the adjustment I meant.

    If you want to preserve the relative phase of the speakers you will need to make the same adjustment to each.

    Minimum phase responses are generated as required, because they can be regenerated whenever needed they are not saved with the measurement. There isn't an option to overlay the minimum phase responses, I can't think of a situation in which that would be useful. The minimum phase response has the same magnitude response as the measurement but a different phase response and different impulse response, it isn't a proxy for the measurement. If you want to see the phase response of the measurement with REW's best estimate of the time delays removed use the Estimate IR delay button.
     
  14. Vladimir_1953

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    If you change the measurement default window from 150ms-0-500ms (51,45 meter-0-171,5 meter - all right ????) to a smaller 3ms-0-10ms (1,03 meter - 0 to 3,43 meter) calculation algorithm Your program will not suffer? In my car audio setup, the distance to the furthest speaker is 1.5 meters, so I want to exclude the reflection of sound waves in the measured signal by reducing the measurement window.
     
  15. John Mulcahy

    John Mulcahy REW Author

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    Sure, that's fine. You can see the windowed region on the Impulse graph. Low frequency information will not be valid below about 100 Hz though, the shorter the window the higher the low frequency cutoff.
     
  16. Vladimir_1953

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    Thanks for answering! I will try.
     
  17. Vladimir_1953

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    Today's measurements have shown that a decrease in the measurement window affects exactly the range below 100Hz.On the phase graphs, the MB-MR-TW range did not see any changes ..
    This was said by the respected John!
     
  18. Vladimir_1953

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    What settings need to be changed in the Analysis window (and other windows) when changing from the "Use loopback as timing reference" measurement mode to the "Use acoustic timing reference" measurement mode to get real Impulse response and phase results?
     
  19. John Mulcahy

    John Mulcahy REW Author

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    Just select "Use acoustic timing reference" on the Measure dialog (under the SPL/Impedance buttons). To see phase without the influence of transport delay you will need to remove any delay of the measured channel relative to the reference using the t=0 offset controls.
     
  20. Vladimir_1953

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    John, thanks for the answer!
     
  21. Vladimir_1953

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    One more question.
    If the delay time of each of the 6 speakers is different, I have by hand to remove one common delay for all, bringing their time as close as possible to the mark t = 0?
    Or use the button for everyone "Estimate IR delay".
    But will the real phase of each speaker be correctly displayed relative to the reference one?
     
  22. John Mulcahy

    John Mulcahy REW Author

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    If you want to see phase of each relative to a reference speaker the measurements will need to be shifted by the same amount. You could use Estimate IR Delay on the reference speaker to see how much to shift that then shift the others by the same amount.
     

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