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Thread: DBX 260 Output Phase Adjustability Question

  1. #1
    Senior Member 1audiohack's Avatar
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    DBX 260 Output Phase Adjustability Question

    Hi All;

    I know a few of us use the 260 and I wish to experiment with the phase compensation portion of it however I can not get it to make any difference. Here's what it says on page 38 of the user manual for the 260 in section 4.12

    "The output section 480, 481 and 482 DriveRack units provides the user with the ability to control output levels of the unit and adjust phase compensation of loudspeakers within the signal path. The output level control is located in the signal path before the compressor/limiters; this means that the compressor/limiter directly affects the output level. The parameters for the Phase Compensation effects are as follows and are adjustable.

    Shift On/Off
    This parameter is used to turn the selected output phase parameters on or off. When level is off, phase is zero degrees and polarity is positive.

    Polarity On/Off
    This parameter is used to reverse the polarity of the output signal.

    Phase 0 to -175 degrees
    This parameter sets the amount of phase within the selected output path. The phase is referenced to the upper frequencyof the selected output crossover band. "

    OK, one thing jumps out, the fact that it says "The output section 480, 481 and 482 DriveRack". Well this is in the 260 manual AND when you are connected to it via GUI with the crossover page open, you double click on the channel of interest (1-6) and the menu group opens just like the manual say it will.

    So far so good, you can toggle on the shift swith and flip the polarity and it works (measurable and audible), I can also slide the phase button however it has zero effect. I finally routed it (the 260) straight through my TEF for a electrical only transfer function measurement and can read zero shift at any frequency.

    No one on the DBX Forum could answer this and referred me to ProSoundWeb. I have not poised the question there as yet nor have I called DBX Tech.

    Anybody know if this is a functional parameter within the 260? It would be VERY cool to be able to insert a sloped correction for group delay into my subs!

    "
    If we knew what the hell we were doing, we wouldn't call it research would we.

  2. #2
    Senior Seņor boputnam's Avatar
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    Quote Originally Posted by 1audiohack View Post
    ... I can also slide the phase button however it has zero effect. I finally routed it (the 260) straight through my TEF for a electrical only transfer function measurement and can read zero shift at any frequency. ... I have not poised the question there as yet nor have I called DBX Tech.
    I think your smarts have answered your question - this is not a function available on the 260. You either should upgrade units or accept the limitation(s) of the 260.

    But, I'm curious about the desire for a "sloped correction for group delay into my subs". First, the Subs band pass is the latest acoustical arrival in the system - the Mains/Highs (and Fills) all need to be delayed to the Subs arrival time. This relates to the HPF on the Sub band pass which imparts a big delay to that signal. This is what you need align to, and not the other way around. Filters affect time inverse to frequency - a similar filter type imparts greater delay to lower frequencies. It's simple physics.

    Also, IME, sloped correction is not commonly available, and most of us just use a 180° inversion on the Subs when needed (assuming your Mains are flown and Subs ground-stacked). A sloped time-correction will have time smear all through the frequency region affected, vs a perterbation at the point of inversion. I just point this out - not knowing which would be less audible.

    Conversely, if you are merely working on group delay for a system physically coherent (i.e. stacked together), again, common approach is picking a delay for the Mains that aligns them with the Subs near the region of crossover. Use the Impulse Response in Smaart to measure the Sub band pass arrival time, and then that of the Mains - you will need to add delay to the Mains to align the two band passes in the acoustic domain. Once done, re-measure the Subs and Mains separately to verify
    Last edited by boputnam; 06-05-2010 at 01:21 PM.
    bo

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  3. #3
    Senior Member 1audiohack's Avatar
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    Quote Originally Posted by boputnam View Post
    I think your smarts have answered your question - this is not a function available on the 260. You either should upgrade units or accept the limitation(s) of the 260.

    But, I'm curious about the desire for a "sloped correction for group delay into my subs". First, the Subs band pass is the latest acoustical arrival in the system - the Mains/Highs (and Fills) all need to be delayed to the Subs arrival time. This relates to the HPF on the Sub band pass which imparts a big delay to that signal. This is what you need align to, and not the other way around. It's simple physics.
    You're right of course on all of the above.


    A sloped time-correction will have time smear all through the frequency region affected, vs a perterbation at the point of inversion.
    Absolutely right, however if the correction is the inverse of the group delay of the sub system, theoretically you could get rid of the time smear that exists in output of the subs. The way I read it you get to cause a phase change that goes increasingly negative with decreasing frequency i.e.; adding delay with increasing frequency. This would increase the delay required for everything else in the system but if you could get the sub(s) to be time coherent within their own passband you would have accomplished something.

    Conversely, if you are merely working on group delay for a system physically coherent (i.e. stacked together), again, common approach is picking a delay for the Mains that aligns them with the Subs in/near the region of crossover. Use the Impulse Response in Smaart to measure the Sub band pass arrival time, and then that of the Mains - you will need to add delay to the Mains to align the two band passes in the acoustic domain. Once done, re-measure the Subs and Mains separately to verify.
    Again agreed.

    If this works the way I hope it might I will buy a DBX4800. I want one anyway, but I need to find out if and how this feature works.

    Thanks Bo.
    Last edited by boputnam; 06-05-2010 at 01:21 PM.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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