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MiniDSP 2x4HD seems to have non-linear response 5 days 21 hours ago #56134

  • EEE
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Hi,

I have been playing around with the MiniDSP and tried to verify its work via REW using a loopback.
The soundcard is calibrated and when I connect in/out directly, I indeed get a perfectly flat response.

Unfortunately, I do have a strange effect for the MiniDSP 2x4HD; the response is not entirely flat, it seems as if there is a 1.5 dB low shelf activated at around 1K Hz.
I can even equalize it to flat by adding a high shelf of 1.5 dB at around 1000 Hz.

I tried several factory resets, different in and outputs, adding a XO high/lowpass at the end or beginning but this strange dip remains.
Did someone encounter this problem before or would have any idea where it might be coming from?

Thank you in advance!

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Last edit: by EEE. Reason: missing word

MiniDSP 2x4HD seems to have non-linear response 5 days 17 hours ago #56140

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Can you post your .xml config file?

I've done many 2X4HD loopbacks and have not seen a shelf. Makes me think that your soundcard playback or capture is not perfectly flat.

Michael

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MiniDSP 2x4HD seems to have non-linear response 5 days 15 hours ago #56142

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Thank you for offering your help.
I am not sure how I can upload an XML file but I did make a screenshot.
imgur.com/a/FumvR7L

The blue line at the top is a simple loopback from audio in to audio out. The soundcard is calibrated and the measurement is perfectly flat.
The red line is the result of the MiniDSP put between in and out with all filters set to bypass (on input, output, XOver etc.).
The purple line was to see that the MiniDSP is really active - I added a lowpass filter and cut off a part at the high frequencies, which worked perfectly.
As you can see, there is a weird dip with two plateaus, which I really cannot explain.

Thanks in advance!



 

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Last edit: by EEE. Reason: Typos

MiniDSP 2x4HD seems to have non-linear response 5 days 12 hours ago #56145

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Do you know what the input resistance/capacitance of your soundcard is???

The miniDSP units all have 600 ohm output resistance (which isn't that low.)  Some soundcards are not high impedance inputs.....depending upon the interface configuration.

Dave.
 

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MiniDSP 2x4HD seems to have non-linear response 5 days 3 hours ago #56153

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Thanks, that was a good idea but I am using a Soundblaster Recon3di. According to the manual, it detects whether to use high or low gain for the output, I am not sure about the input but I do set it to "line in" instead of "microphone". While I could not find the spec sheet for my card, there are several reviews that mention support of 600 ohm equipment. Should/ can I use "microphone" instead?
For my measurement mic with phantom source, "line in" was suggested  in the manual and always worked perfectly. 
 

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MiniDSP 2x4HD seems to have non-linear response 4 days 19 hours ago #56156

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If you see this effect on all four outputs, I would assume this is a measurement anomaly.  Or a non-flat response of your input test excitation interface.
I can see a limitation in your test setup already, because you should see response to 48khz via the 2x4HD.

I've checked the miniDSP 2x4Hd pretty extensively and, with no programming, it exhibits a flat response.

Dave.

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Last edit: by dreite. Reason: update

MiniDSP 2x4HD seems to have non-linear response 4 days 16 hours ago #56158

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I only observe this dip when the MiniDSP is in the loop, all other measurements are perfectly flat.
The loopback just connecting the soundcard is the top line, which shows less than 0.02 dB deviation.
I added a zoomed in version to show this: imgur.com/a/FumvR7L

I would be surprised if you measured the 2x4HD up to 48kHz. It usually stops around 22KHz - which is largely enough in practice though.
Here is an independent review that also comes to this conclusion:
www.audiosciencereview.com/forum/index.p...hd-dsp-and-dac.2674/
 

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MiniDSP 2x4HD seems to have non-linear response 4 days 15 hours ago #56159

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I think you missed my point regarding the possible interface issue created between loopback and DUT insertion.

Anyways, ASR has made numerous errors in some of their equipment reports, so I take everything there with a grain of salt.

I actually have my 2x4HD unit on the test bench and just made a quick test with wideband noise on the analog input.
You can clearly see the response to 48khz.  (This is as expected due to the 96khz sampling rate.)
oplug-support.org/gallery/image.php?album_id=48&image_id=980

But, you're free to believe whatever you want.  :)

Dave.
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MiniDSP 2x4HD seems to have non-linear response 4 days 15 hours ago #56160

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My results are exactly the same as Dave's. I think it is pretty clear from reading the ASR review that Amir had limiting understanding of the 2X4HD and struggled a bit with operating it.

Here are my results, periodic white noise in to TOSLINK input, measurements from a MOTU M4 running at 192 kHz

drive.google.com/file/d/1CuIQ_p37QSKVJi8...xhr/view?usp=sharing

And frequency sweep.

drive.google.com/file/d/1C63DJ7kYNEfK49T...rft/view?usp=sharing

Michael

 
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Last edit: by mdsimon2.

MiniDSP 2x4HD seems to have non-linear response 4 days 14 hours ago #56161

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This is really cool!

"I think you missed my point regarding the possible interface issue created between loopback and DUT insertion"
I think I got it now, I thought you meant the 4 curves - I think you meant the 4 connectors on the back of the DSP.
It is still a mystery to me why the measurements would fail though.
I will try next week to put it into my chain and then measure the speaker response and compare.
If the dip is gone, maybe it is indeed the impedence, as someone suggested?!

In any case, I think we (or rather you) should correct Amir - he comes across as someone who pays a lot of attention to his measurements and is usually very careful with his tests.
I am happy that the minidsp performs much better than he said. :)
 
Would you know of a cheap device that would be good enough to have reliable measures?
Maybe any USB soundcard that is affordable and that works well?

Thanks again to both of you for sharing the curves!

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Last edit: by EEE. Reason: clarification

MiniDSP 2x4HD seems to have non-linear response 3 days 21 hours ago #56176

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In terms of measurement devices not sure what "cheap" means to you, looks like Dave is using a QuantAsylum analyzer which is an excellent value at ~$500, my measurements were done with a MOTU M4 which is $240. Slightly less expensive options are the Focusrite Scarlett 2i2 at $170 and the MOTU M2 at $180.

One thing I would try is running a frequency sweep using the 2X4HD as the output device and input device. This will essentially measure what is happening inside the 2X4HD prior to the DAC. If that measures flat I think Dave's suggestion that your response is a measurement anomaly are correct, if it shows a shelf it likely means you have something buried in your configuration that you are missing.

Michael
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MiniDSP 2x4HD seems to have non-linear response 3 days 16 hours ago #56181

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I think the misunderstanding here is that if a loopback measurement looks perfect and you introduce a DUT and it doesn't look perfect, there's a problem/issue with the DUT.  That's not necessarily the case.
When you add a DUT, you're creating two different interfaces that weren't there previously.  In most cases this wouldn't be an issue, but when you run into something that doesn't make sense you have to consider there might be an issue there.

It's still not clear to me what the issue is here.
I assume this is not some programming buried in the DSP configuration.  You should factory default the 2x4HD and then turn all the crossovers off before doing tests like this.
I suspect some sort of interfacing issue.  That's why I asked about the input characteristics of the soundcard.  Some of these soundcards have very different loading depending upon whether the interface is inst/line/mic/etc.

In any case, you're not going to figure out this issue by introducing a microphone/speaker and making acoustic measurements.  That will mask all this introduce myriad other variables.  :)

Dave.
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MiniDSP 2x4HD seems to have non-linear response 3 days 11 hours ago #56186

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Thanks for all the input. 
I did factory reset several times and removed the default cross overs every time. If I don't remove them, the effect is still the same: a dip but now also the crossover falloff. 
I tried both inputs and all four outputs.
I also used several cables.
Always the same result. 

I was opting for the audio measure because I do think that is working well with my mic because I  also have an antimode and I can verify the before and after and see that it is correctly flattening the subwoofer response. 
1.5 dB would definitely show up in the measurement. When I play with the eq of the Yamaha, each 0.5dB change (even local) is visible when comparing before and after.

250 is definitely too much for me, just to test if the minidsp is working or has a defect... is there anything else I could check? Thanks!

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MiniDSP 2x4HD seems to have non-linear response 3 days 11 hours ago #56187

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I think I got your advice Michael, you mean input output via USB. 
I have not tested that! I will try that tomorrow after work. In my setup so far, I used one laptop to configure via USB, another to do the measurement via the analog connection.

If the result via USB is flat, could it also be that the analog connectors (or something related to those) have an issue?

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