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HOLM Impulse - Timelock, creeping offset??

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  • HOLM Impulse - Timelock, creeping offset??

    Okay so I'm trying to use Holm Impulse timelock feature. I could see after the first couple attempts there was something off. After messing with it for a while I figured out what was happening but I don't know what is causing it.

    The delay seems to be constantly increasing. The longer I wait between measurments the greater the time offset becomes. Can anyone speculate what could be causing this?

    I did these 3 measurements exactly 1 minute apart.


  • #2
    Re: HOLM Impulse - Timelock, creeping offset??

    I've never used this feature when using HOLM, but have read some accounts form others of small shifts. What I recall was a case or two of a shift after the first measurement, but none afterwards. It may be that those tests were done rapidly, however. There wasn't anything related to correlate it with time between measurements.

    dlr
    WinPCD - Windows .NET Passive Crossover Designer

    Dave's Speaker Pages

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    • #3
      Re: HOLM Impulse - Timelock, creeping offset??

      What was the distance between mic and speaker?

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      • #4
        Re: HOLM Impulse - Timelock, creeping offset??

        Originally posted by feyz View Post
        What was the distance between mic and speaker?
        For those measurements it was probably a couple feet. After my initial measurements didn't work as intended I moved things around a little to troubleshoot, and used a lower volume. I'm not sure what difference that would make though because according to the software the speaker was moving away from the mic, which it wasn't.

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        • #5
          Re: HOLM Impulse - Timelock, creeping offset??

          Are you using it correctly? You have to take the first measurement unlocked. Then lock it for the remaining measurements. Nothing else can change between measurements.

          The time lock is supposed to place the T=0 position *** number of samples from the start of the data collection where *** is determined by the code from the first, unlocked measurement.
          John k.... Music and Design NaO dsp Dipole Loudspeakers.

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          • #6
            Re: HOLM Impulse - Timelock, creeping offset??

            Originally posted by johnk... View Post
            Are you using it correctly? You have to take the first measurement unlocked. Then lock it for the remaining measurements. Nothing else can change between measurements.

            The time lock is supposed to place the T=0 position *** number of samples from the start of the data collection where *** is determined by the code from the first, unlocked measurement.
            Yes, I used auto detect on the first measurement, set zero then made the other measurements. Nothing else changed.

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            • #7
              Re: HOLM Impulse - Timelock, creeping offset??

              Just tested on another computer and I have the same problem, but in the other direction. The shift goes toward the negative. Either way I suppose I don't really need this feature but thought phase matching in simulation might be more accurate if I did it this way.

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              • #8
                Re: HOLM Impulse - Timelock, creeping offset??

                That kind of thing can happen if the record (ADC ) clock isn't locked to the play (DAC ) clock of the soundcard. Some audio soundcards (for instance, the ones using TI PCMxxxx chips such as the Behrengers) use entirely separate timing sources for the two functions.
                Free & Free-form simulator/designer for Passive Crossovers
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                • #9
                  Re: HOLM Impulse - Timelock, creeping offset??

                  Digging this back up because I haven't seen a definite answer and would like to use this feature but have the same issue. I am not sure it is the soundcard as I have tried it on 3 different computers with the same results. This leads me to believe it may have something to do with my mic preamp's communication to the computer ( blue icicle that connects with usb ). If people who have or don't have this issue could post their setups it might be useful. I have a emm 6 with blue icicle pre and have tried it on a ibm thinkpadt60, my home brew i3 pc and a older dell pc. All have integrated sound cards and all have the same issue. Laptop and pc both have win7. Old dell has xp.

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                  • #10
                    Re: HOLM Impulse - Timelock, creeping offset??

                    I don't seem to have the problem. I have an HP Pavilion dv7-3060us laptop (64 bit Windows 7 Home Premium, Service Pack 1) and an old first gen M-Audio Mobile-pre USB. I've been careful to disable all the sound card enhancements (bass boost, virtual surround, room enhancement and loudness EQ). Here's the procedure I used:

                    - Setup and take initial tweeter measurement. See the first two attachments for Holm setup. I just noticed I had the "invert signal" on. That was an oversight, but shouldn't cause any differences.

                    - Move microphone back enough to show delay. Enable the Holm timelock feature. See the third attachment. Be sure to select the time lock radio button AND click the "Use" button.

                    - Take a second measurement. The second impulse measurement shows as delayed.

                    - Wait 15 minutes and take a third measurement. In my case the impulse exactly overlaid the second. You have to turn off one of the two to distinguish that there are two impulse responses. See the last attachment.

                    - Wait another 15 minutes and take another measurement. Same result - indistinguishable from the second measurement.

                    Hope this helps,
                    Ed
                    Attached Files
                    "Everything is nothing without a high sound quality." (Sure Electronics)

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                    • #11
                      Re: HOLM Impulse - Timelock, creeping offset??

                      One thing I noticed in my first attachment: I always have the "Keep Stream Active" checked and never click the "Restart Stream".

                      Ed
                      "Everything is nothing without a high sound quality." (Sure Electronics)

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                      • #12
                        Re: HOLM Impulse - Timelock, creeping offset??

                        Well I used a Tascam 8 track as a pre and what do you know, time lock worked perfectly :applause:I did not change anything on the pc side so my conclusion is that it had to to with the blue icicle, possibly just the way it was hooked up.
                        A couple othe thingd might be the usb communication to pc (i'm not too educated on this), or possibly the blue icicle's a/d converter messing things up. Not sure but I think the tascam stays anolog through the signal chain but records digital.

                        Things that stayed the same
                        PC and settings on pc and holm
                        Microphone
                        HDMI out to Emo pre amp then amp to speaker.


                        What changed
                        Mic preamp
                        Mic to preamp, preamp headphone out to pc mic in.

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                        • #13
                          Re: HOLM Impulse - Timelock, creeping offset??

                          I also just realized I still get crazy phase response on the measurements after the first one? The first has one wrap right around the xo frequency. Any taken after that have mutiple wraps ( well over 20 ). Is there something I forgot to do or did wrong?

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                          • #14
                            Re: HOLM Impulse - Timelock, creeping offset??

                            Originally posted by bwaslo View Post
                            That kind of thing can happen if the record (ADC ) clock isn't locked to the play (DAC ) clock of the soundcard. Some audio soundcards (for instance, the ones using TI PCMxxxx chips such as the Behrengers) use entirely separate timing sources for the two functions.
                            Sorry to bump an old thread, but has anybody tried Holm time lock with a USB mic? Based on what Bill said above, it doesn't seem like it would work, since the clocks on record and play sides won't be synchronized in that setup. But I've not read anywhere of anybody trying it, and I don't have a USB mic myself to try it with.

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                            • #15
                              Re: HOLM Impulse - Timelock, creeping offset??

                              Must not have been paying attention when the first 'bump' was made. This doesn't really address your question, but if anyone was curious, I was also using a Blue Icicle paired with an EMM-6 when I noticed this problem. I never resolved it and just did without the timelock feature.

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