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TOPIC: Noise from FIR processing in DA-8

Noise from FIR processing in DA-8 5 months 3 weeks ago #45946

  • k98luka
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Hello!
This is my first post on this forum: My question/concern is about the noisefloor in OpenDRC DA-8.

I am running the 96kHz plugin and are using the device to apply PEQ and FIR filters for x-over purposes in an active stereo three way speaker system.

The linear-phase FIR filters is really making a great difference in the instrument seperation and soundstage, and enhances transients. Overall, the linear phase crossovers is making the whole difference, and I cannot revert back to only IIR filters now.

The product is really great, except for that the FIR filters seem to cause the OpenDRCDA-8 to generate an excessive amount of noise. If I disable the FIR filters, the electronic noise disappears.

I tried to make more simple FIR filters only adjusting the phase (and not the magnitude) - the noise is a little bit less but still audible from the listening position.

oIs there anything one can do to solve this problem? Would perhaps the 48kHz plugin improve this noise issue?

Would appreciate any comments, ideas or input on this topic.

thanks a lot in advance and for a great forum

Karl

PS adding the XML file for the "noisy" filter

File Attachment:

File Name: 20200111Co...ion4.xml
File Size:236 KB


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Noise from FIR processing in DA-8 5 months 3 weeks ago #45947

  • Reimanis
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I have the same problem. I use 48khz plugin and noise decreased.
There is grounding problems, when i use with balanced outputs noise disapears.
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45948

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Thanks for the rapid response!
Seems this can be solved then, this is excellent news!
But I wonder how did you use balanced outputs from the DA-8?
Can I connect all three pins on an XLR connector if I open the device (meing is the design balanced?)
I suppose a simple RCA/XLR converter where I leave pin wont do the trick?
thanks,
Karl
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45949

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No, only way is rebuild an existing one. You need unbalanced to balanced converter kit.
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45950

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OK. Sorry for not following completely here, but if I buy a RCA to XLR converter kit, do I also need to rebuild the DA8?
/Karl
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45951

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No, thats all.
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45952

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thats fantastic news! Just to confirm, if I convert all RCA outputs to balanced XLR via somthing like this:

www.aliexpress.com/i/32857451808.html

is then my noise issues solved?

Karl
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45953

  • Reimanis
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You need to try. I made dac and output stage newly. All the noise is gone.
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45954

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Hello again,
I will try wiht the RCA/XLR converter kit, for sure. Thanks a lot for sharing this info.

I do not have the knowledge how to rebuild the circuitry around the DAC and output stage, so I will wait with that. But if that further improves snr or other audible qualities I would like to try to do rebuild the device as you have done also. Is it difficult? Did you buy a new dac or only improved the circuit layout for improved grounding or other reason?
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45955

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My friend is electric engineer. He made everything from scratch. Better dac chip and balanced output stage. New power supply.
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45965

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Hello again,
It would great if someone from the minidsp support team could comment on the above issue with noise and the associated proposed solution to rebuild the output stage to a balanced one. Seems logical to me to do this, should there be an intrinsic grounding oroblem in the da-8. I wonder however if there may be other tips and tricks available to solve the problem? And I wonder, how common is the problem with noise from this device? It seems to be present (for my device ) only when computing intense fir filtering is loaded to the sharc.
Best,
Karl
Last Edit: 5 months 3 weeks ago by k98luka.
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45966

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Karl,

You don't have linear-phase crossovers active in your configuration file. You have the normal IIR crossovers active.

Your loaded FIR coefficients in the mid/tweet section show minimal amplitude corrections. But you have some phase unwrapping incorporated in those we can't see?
Also, you don't have any FIR coefficients loaded in your low-pass filter, so that's definitely not linear-phase, and it also creates a large latency difference to the mid/tweet sections.
Noise issues notwithstanding, your whole approach here is confusing. I'm not sure what you're hearing that's impressing you, but it's not associated with any linear-phase characteristics.

Here's what I would suggest: Make your approach just the opposite of what you're doing now. Turn off the IIR crossovers, and implement your crossovers via the FIR capability. Then, make your wiggly amplitude adjustments using the normal (IIR) PEQ portion of the plugin.

Dave.
Last Edit: 5 months 3 weeks ago by dreite. Reason: correction
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45972

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Hi Dave,

Many thanks for looking into this an sorry to be causing confusion!

First, you are right, the FIR filters have been de-activiated in the XML file that I have uploaded. The reason is due to the reason mentioned above in this thread, that by enabling the FIR filteringing, there is an excessive electric noise from the mid and tweeters.

Furhter, in the XML file that is uploaded there is no SPL magnitude correction. Only phase is corrected by the FIR filter. (1200 taps for the mid and 300 taps for the tweeter). This improved the humming noise just a little a bit vs the situation where both SPL+phase processing was done viathe FIR capability. As you also have observed, the bass unit do not have any filter applied yet (would love to have linear phase here also but the taps are not enough to go down in frequency at 96kHz (as you can see, the bass have a LR 48dB filter applied at 150Hz).

I am hoping and trusting that the FIR coefficients is doing some work with the phase. I would appreciate if you could educate me about the reason why you think that the phase has not been adjusted by the FIR coefficients that has been uploaded?

I will try to adjust the filtering according to your suggestion, thanks fo the hint.

Lastly, may I ask if you own a OpenDRC DA-8 and in case you do, have you had any problems with noise, similar to what me and Reimanis have experienced?

best regards,

Karl
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45973

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When looking at the correction for a loaded FIR file the phase is not visible. That's why I asked you if it was incorporated and we couldn't see it. Your FIR correction files DO show an SPL magnitude correction. (Wiggly lines on both of them.)
You've described a problem, yet the files you uploaded are a different setup that doesn't exhibit the problem? :)

Regardless, you have differing (pure) delays in all three branches of your setup, so there's no way the result could ever be linear-phase.

I do have an OpenDRC-DA8 unit. In fact, I think I have the first one. :)
I don't notice more noise with it than any of the other miniDSP units I have. (It's pretty much inaudible in all cases.)
That said, I haven't done many configurations with extensive FIR filtering, so I may not have noticed the effect you're hearing.

There is noise-shaping involved here. I would try the 48khz plugin to see if you notice any difference.

Dave.
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Noise from FIR processing in DA-8 5 months 3 weeks ago #45982

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Hi Dave,
Thanks again for your comments.

To clarify: The FIR filter in the file that I uploaded file is making noise when it is enabled. If it is disabled, (as it is in the uploaded XML file), the noise probelm is non-existing.

I am planning to test the 48kHz plugin to see if it helps.

Since you say you have not made any extensive FIR filters, I would be curious to learn from the devteam or other user that has experience from implementing FIR filters in the Open DRC DA-8 rgarding the correlation between FIR procecessing any potential noise problems?

(PS. the delay is added due to different latency in the MF and HF FIR filters. I cannot measure the phase at the moment due to other hardware issues, but I will try to upload a phase measurment of the system as soon as I can measure again...)
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