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DDRC-24 gain structure and internal headroom 5 months 2 weeks ago #52911

  • asx77
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@mdsimon delays implemented where? My plugin has different delays on left and right because they’re closer to me than the sub. I did these ahead of running Dirac which made a small additional tweak. But when comparing with and without Dirac, it’s the same speaker.. so what delays are you referring to?

Thanks

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DDRC-24 gain structure and internal headroom 5 months 2 weeks ago #52912

  • Ultrasonic
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I thought you just had to make sure measurements were a min of 30cm / 12” apart. One centre position with all others 50cm away seems excessively far. Where have you read that?


I took it from info. from Flavio Fellah of Dirac Live shared here:

www.hifiwigwam.com/forum/topic/138704-mi...ents#comment-2620420

Edit: my low and high points are 30 cm apart vertically but all points are on a 1m diameter sphere.

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DDRC-24 gain structure and internal headroom 5 months 2 weeks ago #52913

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I thought you just had to make sure measurements were a min of 30cm / 12” apart. One centre position with all others 50cm away seems excessively far. Where have you read that?


I took it from info. from Flavio Fellah of Dirac Live shared here:

www.hifiwigwam.com/forum/topic/138704-mi...ents#comment-2620420

Edit: my low and high points are 30 cm apart vertically but all points are on a 1m diameter sphere.


Ah ok. He also mentions a 30cm minimum between. I think I read this as meaning you can have measurements 30cm apart but you should also ensure that you’ve expanded to cover an area with at least 1m diameter.

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DDRC-24 gain structure and internal headroom 5 months 2 weeks ago #52914

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Doing a bit of reading to remind myself, I thought that using a timing loopback isn't an option for me as I'm using a USB microphone? (A UMIK-1)

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DDRC-24 gain structure and internal headroom 5 months 2 weeks ago #52915

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A couple of days ago I got @tw99's method of using my SHD as both source and 'microphone' to work and with no filters applied both the amplitude and phase responses were perfectly flat. Is this related to what you are suggesting or not? Apologies if this is a dumb question :oops: . If there is a way I can improve my measurements I'd like to understand how :) .


Yes, I was referring to using the SHD as USB output and input. In that case you are essentially using the SHD as a sound card and should have access to all 4 outputs. Certainly when making acoustic measurements with the UMIK you cannot do this but I have found that acoustic loopbacks work well in that case.

But the point still stands that the behavior you show is most likely the result of delay in the system. I imagine you can flatten a large portion of the high frequency phase response by adjusting the "Offset t=0" in REW under the SPL & Phase tab.

Michael

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DDRC-24 gain structure and internal headroom 5 months 2 weeks ago #52916

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I should also add that when looking at measurements where you are looking at an entire system response looking at phase is not super important. The only time I really look at it is when I am setting up an active crossover and measuring two drivers separately. In that case it is important that you have a common timing reference for each measurement.

Michael

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DDRC-24 gain structure and internal headroom 5 months 2 weeks ago #52917

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One thing this shows is some imperfect behaviour below 10 Hz, although whether that is the SHD itself or another factor I have no idea.


I meant to reply to this earlier to say I saw similar with the DDRC24. Each config has the same set up so running the sweep with Dirac off you'd expect all curves (straight lines) to look the same. However take a look at the Left channel differences across the same identical Configs



Starts getting a bit fuzzy approaching 20kHz too. Not sure what happens after as cut the sweep off at 20kHz.

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DDRC-24 gain structure and internal headroom 5 months 2 weeks ago #52955

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Yes, I was referring to using the SHD as USB output and input. In that case you are essentially using the SHD as a sound card and should have access to all 4 outputs. Certainly when making acoustic measurements with the UMIK you cannot do this but I have found that acoustic loopbacks work well in that case.


Just to check, by 'acoustic loopbacks' are you referring to REW's 'acoustic timing reference' option, or something else?

But the point still stands that the behavior you show is most likely the result of delay in the system. I imagine you can flatten a large portion of the high frequency phase response by adjusting the "Offset t=0" in REW under the SPL & Phase tab.


I've had a bit of a play with this. I also used the 'Estimate IR Delay' option and using its suggested -0.0213 ms delay makes the difference shown in the graph below. Here the green line is as posted above where the Dirac frequency range was limited to below 150 Hz, and black is with this time delay applied.



So not a pure time delay effect if I'm understanding this correctly but possibly more in line with what you'd expect now?

Edit: thanks for making me look at this by the way. It's obvious now you've pointed it out but I'd missed the effect the small differences in arrival times from my two speakers were having here.
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DDRC-24 gain structure and internal headroom 5 months 2 weeks ago #52956

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I should also add that when looking at measurements where you are looking at an entire system response looking at phase is not super important. The only time I really look at it is when I am setting up an active crossover and measuring two drivers separately. In that case it is important that you have a common timing reference for each measurement.


Yes the only time I've made use of the phase response plots for normal frequency sweep measurements is for optimising the crossover region between my subwoofer and main speakers (using the necessary fixed acoustic timing reference).

This is obviously different to looking at the phase response of the applied filters though, which interested me given Dirac Live's claims of making improvements to the impulse response in part by making some phase corrections.

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DDRC-24 gain structure and internal headroom 1 month 1 week ago #55341

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Guys - after having had success with the method in the past, I've come back all these months later and just can't get REW to send a (loud enough) sweep to the minidsp!



I just get too low a level! My normal PC sound ('ding') make the DDRC meters spring to life but the sweep results in nothing other than frustration!!



I've got the DDRC24 as the default in/out devices.

Where am I going wrong? Heeeelp!
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DDRC-24 gain structure and internal headroom 1 month 1 week ago #55345

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Your mic is plugged into the laptop and that input is selected? If you speak into it, the meter reacts strongly? It's not the laptop's mic that's selected? (I have done this!)

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DDRC-24 gain structure and internal headroom 1 month 1 week ago #55347

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Why is mic input showing as DDRC? Shouldn’t it be Umik?

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DDRC-24 gain structure and internal headroom 1 month 1 week ago #55348

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Hi guys,
I don’t want a mic connected. What we’re doing here is selecting the miniDSP as both output and input device. If you do that and run a measurement sweep both with and without Dirac on then you can see what filters Dirac applies.

It’s a great method discovered way back on page 2 here. If I set up the MiniDSP as default output I can see a signal on REWs out meter. But problem is (and this is so frustrating because I’ve taken measurements like this previously) I can’t pic anything up on the input. REW doesn’t seem to see the miniDSP as an input like it used to and I’m wondering what I’ve done wrong in the settings.

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DDRC-24 gain structure and internal headroom 1 month 1 week ago #55350

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Ahhhh headache over.. I found it. I had to change the default format to 44.1khz. No idea how it changed but feel better now!

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DDRC-24 gain structure and internal headroom 1 month 1 week ago #55351

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Cool!

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