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4x10 problems in low frequency ranges 6 years 8 months ago #17843

  • Jim the Oldbie
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Wasn't the SUB_EQ filter developed as a workaround to this stuff? Or are you guys already using this filter, and still having problems? (I'm sorry I can't get to my 4x10 right now to run any plots.)

-- Jim

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4x10 problems in low frequency ranges 6 years 8 months ago #17845

  • dreite
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There's four different combinations to try. Both 48khz and 96khz plugins, and selecting either the normal EQ mode or the SUB_EQ filter. This particular 15Hz peak filter that nyt has identified represents sort of a worst-case testing scenario (as it should.) I tried all four configurations and in none of them does the output result look like the depiction in the GUI graphic.

I can post the plots if anybody's interested.

Dave.

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4x10 problems in low frequency ranges 6 years 8 months ago #17851

  • PdxRealtor
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Setting up miniDSP is not easy to a n00b. My main interest at this early stage is to make sure I don't break anything. For example, I have learned that there is a trap that could destroy components, if power on and power off are not done correctly. I live in an area that is prone to power outages, too. I worry about other traps for n00bs.

I am never going to be using microphones etc, I will hire a man to do that, when the room renovations are finshed. In the meantime, I simply want to use my miniDSP to get the bass drivers running.

I strongly recommend that the vendors describe the limitations of their product, as well as the benefits. I feel gulled.


If you want something that is not accurate to be documented, clarified, fixed, or otherwise acknowledged you better get busy and either solve the problem and document your proof or get someone to do it for you. Then, prepare to spend a while getting the DevTeams attention. After all that if you're lucky you'll get some cooperation.

Neat toy....... as has been said over and over and over again..... piss poor documentation and some lack of knowledge by the makers of the product. '

On a positive note the DevTeam is willing to admit when they're wrong. Have fun!

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4x10 problems in low frequency ranges 6 years 8 months ago #17852

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Setting up miniDSP is not easy to a n00b. My main interest at this early stage is to make sure I don't break anything. For example, I have learned that there is a trap that could destroy components, if power on and power off are not done correctly. I live in an area that is prone to power outages, too. I worry about other traps for n00bs.

I am never going to be using microphones etc, I will hire a man to do that, when the room renovations are finshed. In the meantime, I simply want to use my miniDSP to get the bass drivers running.

I strongly recommend that the vendors describe the limitations of their product, as well as the benefits. I feel gulled.


If you want something that is not accurate to be documented, clarified, fixed, or otherwise acknowledged you better get busy and either solve the problem and document your proof or get someone to do it for you. Then, prepare to spend a while getting the DevTeams attention. After all that if you're lucky you'll get some cooperation.

Neat toy....... as has been said over and over and over again..... piss poor documentation and some lack of knowledge by the makers of the product. '

On a positive note the DevTeam is willing to admit when they're wrong. Have fun!


They've admitted it, but haven't fixed it. You want to implement a shelf filter under 30hz reliably? Too bad, find something else, or spend time plugging different values in and measuring until you get something that's close enough to acceptable :/ Hell, even the highpass filters are broken. Bottom line, it's not worth their time, as they've plainly stated. The "SUB EQ" fix is a joke. Peak filter only with limited parameters.

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Last edit: by nyt.

4x10 problems in low frequency ranges 6 years 8 months ago #18023

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woah, those REW measurements do not look good. But on the other hand it's good to know that the the unit can't be trusted in the sub region.
Has anyone tried if the problem also exists when using ustom biquads?

@devteam: can we ever expect a fix for this?
I can understand if you don't have the recources to recode the software since all your new products but it would only be fair to make a final statement, so we can write it off and look elsewhere.

Or at least limit the parameters to a range that works correctly, so nobody can accidentally create wrong and probably dangerous filters (and btw. add a BIG warning that there's no stability check in the biquad section - also a great way for noobs to ruin stuff)
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4x10 problems in low frequency ranges 6 years 7 months ago #18074

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Has anyone tried if the problem also exists when using ustom biquads?

I've just tried it myself and the answer is no.
The SubEQ produces a more or less correct curve, but it looks like it just uses an additional shelfing filter to correct the error.

and remember, no statement is also a statement, in fact a pretty big one. ;)

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4x10 problems in low frequency ranges 6 years 7 months ago #18075

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I see the issues with custom biquads as well. Someone recently tested with 48khz plugin on avsforum and it looked a lot better than the 96khz plugin, though still not perfect.

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4x10 problems in low frequency ranges 6 years 7 months ago #18076

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Has anyone tried if the problem also exists when using ustom biquads?

I've just tried it myself and the answer is no.


Exactly the same coefficients? You can confirm by programming a basic PEQ and then switching to advanced mode and viewing the coefficients. If they're the same as the custom ones you generated then I believe you'll see the same measured result.

Dave.

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4x10 problems in low frequency ranges 6 years 7 months ago #18087

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Has anyone tried if the problem also exists when using ustom biquads?

I've just tried it myself and the answer is no.


Exactly the same coefficients? You can confirm by programming a basic PEQ and then switching to advanced mode and viewing the coefficients. If they're the same as the custom ones you generated then I believe you'll see the same measured result.

Dave.


What I did was comparing a +15dB PEQ boost @15Hz Q=5 with a biquad using the same settings. I've generated the biquad with the excel sheet that's linked on the minidsp website. Both curves look exactly the same and both are not correct, they look like a peak eq + lowshelf, something you cannot create with only one biquad.
So the problem seems to be in the IIR part, maybe rounding errors in the feedback path or what do i know :)

EDIT: Ahh, now I see the misunderstanding. I should have written:
"Has anyone tried if the problem also exists when using ustom biquads?
I've just tried it myself and the answer is YES!!!! It does NOT work either."

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4x10 problems in low frequency ranges 6 years 7 months ago #18089

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Yes, I understood what you were talking about. :)
My experience agrees with yours. Regardless of how you generate the biquad coefficients, the measured result is different than depicted in the GUI pictorial and what it should be.

However, as I mentioned above, you can work around the issue and create nearly exactly what you want, but it's not an intuitive process....unfortunately.

Cheers,

Dave.

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Last edit: by dreite.

4x10 problems in low frequency ranges 6 years 7 months ago #18104

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Thanks Dreite, nyt, and Corrie303 for helping this n00b understand the value of miniDSP for bass driver or subwoofer use.

To recap, this is what i take to be the truth of the matter, for me to have my miniDSP to handle everything below 60Hz, the options are:

48khz and 96khz plugins, and selecting either the normal EQ mode or the SUB_EQ filter.

All four options are not fit for purpose. All fall short.

Further, there is some false advertising by miniDSP as in none of them does the output result look like the depiction in the GUI graphic. miniDSP acknowledge this but the material on the web site and is still fooling n00bs.

There is no reliable miniDSP shelf filter under 30hz, and the "SUB EQ" fix fails.

Therefore I need to go through the process of plugging in values and running iterations.

I accept all this. Now for the next steps: please, which is the better plugin as my starting point, the 48kHz or the 96kHz?

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4x10 problems in low frequency ranges 6 years 7 months ago #18105

  • nyt
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Thanks Dreite, nyt, and Corrie303 for helping this n00b understand the value of miniDSP for bass driver or subwoofer use.

To recap, this is what i take to be the truth of the matter, for me to have my miniDSP to handle everything below 60Hz, the options are:

48khz and 96khz plugins, and selecting either the normal EQ mode or the SUB_EQ filter.

All four options are not fit for purpose. All fall short.

Further, there is some false advertising by miniDSP as in none of them does the output result look like the depiction in the GUI graphic. miniDSP acknowledge this but the material on the web site and is still fooling n00bs.

There is no reliable miniDSP shelf filter under 30hz, and the "SUB EQ" fix fails.

Therefore I need to go through the process of plugging in values and running iterations.

I accept all this. Now for the next steps: please, which is the better plugin as my starting point, the 48kHz or the 96kHz?


48khz is much better. You'll only see issues really under 20hz.
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4x10 problems in low frequency ranges 6 years 7 months ago #18106

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I have a nice, like new condition, rarely used 4x10 in a box for sale. email me if interested and for price details. funnylikehaha at gmail dot com- Matt

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4x10 problems in low frequency ranges 6 years 7 months ago #18109

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>48khz is much better. You'll only see issues really under 20hz.

Oh well, and there I was, following the advice of the miniDSP folks and having bought the 96kHz one.

Now to throw good money after bad.

This stinks.

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4x10 problems in low frequency ranges 6 years 7 months ago #18143

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Dear All,

Just back from Chinese New Year holidays so we appreciate your patience! Sounds like there are quite few questions, we'd be happy to clarify what we thought we clarified earlier on but here is a good summary. Let's see how we can make it concise as possible so everybody from newbie to advanced can understand.
- The limitation here is "fixed point processing". There isn't any bug but more an inherent signal processing limitations. Some here believe we're on a great scheme to con the whole world and completely ignoring the issue it's not as bad.. :-) We could list list some good AES (Audio Engineering Society) white paper that are a great read for some of you who want to read more but unfortunately, we have limitations with our AES library on papers we can share.. Using the keywords shown below and googling might be a good way to find external information that you'd believe maybe a bit better than us.. :-)

- Basically, to make it simple to understand: Low frequency IIR filter + High sample rate + high Q don't work well with each others. It's not a miniDSP thing, it's a math thing. It comes down to the precision of the filters and so called "quantization errors". There is a great read here: www.earlevel.com/main/2003/02/28/biquads/
Hoping it does summarize in simple terms for those of you looking for a technical explanation.
Maybe little you'd know that many products actually will downsample the sub channels so it doesn't run into this issue, run it through PEQ at very low sample rate (e.g. 32k) and upsample again.. On this product we can't unfortunately (one single sample rate), but would have done it to help since nobody would have realized that downsampling + upsampling.. (done everywhere else.. :-)
- Unlike a Sharc DSP where we have all the control we need (and have type 1), on a platform like the miniDSP 2x8/8x8, it's running on a fixed point processor with "pre-built filters". They do happen to work with Type2 which unfortunately isn't that great at the low frequency even if we're running them @ 56bit.
- miniDSP did realize the issue back then (pointed out a while ago by NYT) and did issue a work around on the PEQ for the 96k version which "does" help as we're using a separate biquad to help with the precision issue. @ 48k there is indeed a much better performance overall but if you have high Q + High gain, you'd still be running in similar issue.
- While we did mention the issue to Analog devices, one option would be for us to build a custom filter to make this work. We don't have access to the tools, but could make this happen I guess. Something to consider but to be honest, not 100% sure if we'd have access to these tools. Can get back when we get feedback from ADI.

In the mean time, if there is a general consensus that below 20Hz is an issue, we'd be happy to remove it from the GUi in a new rev. That's something we could certainly do. It's good to know that sometimes, there is a very large user community and not everybody uses the product the same way. Many people here been using it fine, others have issues.. It's always hard to please everybody. :-)

Finally, in an effort to keep this community friendly and working toward the same objective, I'm sure that we're all into finding a better experience if we just work together. :-) Thanks for your understanding.
miniDSP, building a DSP community one board at a time.
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