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HornResp vs Sigma Studio
HornResp vs Sigma Studio
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Old 13th August 2018, 12:45 PM   #1
Jared is offline Jared
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Default HornResp vs Sigma Studio

I used the same numbers in horn response and in sigma studio to optimize the low end for a super low budget speaker system I am working on for the 'silk purse' contest in the multi-way forum. Unfortunately I see very wildly different graphs of what is going on. I have attached screenshots of both.

Did I screw something obvious up? Which one seems more correct? Unsure how to model this as the whole point of this was to keep it at xmax and if the sim is wildly off then maybe I should just say screw it and go by REW measurements entirely, ignore xmax entirely, and just keep an eye on distortion?
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File Type: png Screen Shot 2018-08-13 at 8.41.14 AM.png (150.7 KB, 321 views)
File Type: png Screen Shot 2018-08-13 at 8.40.48 AM.png (206.3 KB, 324 views)
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Old 14th August 2018, 08:29 AM   #2
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by Jared View Post
Unfortunately I see very wildly different graphs of what is going on.
Hi Jared,

It is interesting that there should be such a difference. Have you tried comparing each of the equaliser gains separately? I suspect that the low shelf responses may not be the same. The sanity check Hornresp low shelf response shown in the third attachment seems about right, although I must confess that I am no expert when it comes to electronic filters :-)

Kind regards,

David

EDIT - Looking more closely at your Sigma Studio chart, I can see now that the low shelf gain is indeed different to that of Hornresp.
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File Type: png Attach_1.png (52.8 KB, 285 views)
File Type: png Attach_2.png (53.8 KB, 268 views)
File Type: png Attach_3.png (55.2 KB, 270 views)
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Last edited by David McBean; 14th August 2018 at 08:39 AM.
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Old 14th August 2018, 06:04 PM   #3
Jared is offline Jared
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Thanks for responding David. What does this mean then? I did not put -20 into hornresp, I put -9 in ? Maybe I have an out dated version?
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Old 15th August 2018, 07:01 AM   #4
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by Jared View Post
I did not put -20 into hornresp, I put -9 in ?
Hi Jared,

The -20 dB test example I included was simply to show more clearly that the Hornresp result for a low shelving filter was as one would expect. It seems that the Sigma Studio Q Factor values for shelf filters are calibrated differently to those in Hornresp, and to match the results you need to either halve the Hornresp value or double the Sigma Studio value. For example, if you change your Sigma Studio Q value from 2.91 to 5. 82, or your Hornresp value from 2.91 to 1.45, you will see that the results become the same.

I have no idea why the Sigma Studio shelf filter Q calibrations should be different to those used in Hornresp :-).

Would it be possible for you to post a screenprint of a Sigma Studio low shelf filter chart with Frequency = 100 Hz, Q Factor = 1 and Boost = -20 dB? Thanks.

Kind regards,

David
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File Type: png Attach_2.png (206.3 KB, 26 views)
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Old 16th August 2018, 07:47 AM   #5
David McBean is offline David McBean  Australia
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Hi Jared,

I did some more investigating. It turns out that the Sigma Studio "Q Factor" is actually S, a "shelf slope" parameter.

The relationship between Q and S is given by the expression:

S = 1/((((1/Q)^2-2)/((10^(G/40))+1/(10^(G/40))))+1)

Where:

S = shelf slope parameter
Q = Q factor
G = gain

A setting of 2.91 for "Q factor" in Sigma Studio is actually a setting of 2.91 for S. From the above equation, when the gain is -9 dB, the equivalent value of Q works out to be 1.403, which is the value that needs to be entered into Hornresp (rounded to 2 decimal places) for the results to match.

The Sigma Studio labeling is very confusing indeed. Rest assured, the Hornresp filter response results are correct :-).

Kind regards,

David
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Old 19th August 2018, 12:27 AM   #6
Dave Zan is offline Dave Zan  Australia
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Originally Posted by David McBean View Post
...The relationship between Q and S is...
Hi David, do you have a link or reference for this?
I see a shelf filter as a cluster of one or more poles, associated with a cluster of the same number of zeros, the pole or zero cluster lower in frequency dependent on which way it shelves.
So I don't see what "the" Q of a shelf filter means, presumably there are conventions, maybe there's a canonical audio shelf filter.
Some kind of shelf slope parameter does makes sense to me but I have no idea if there is a standard way to express it.
Just started to think seriously about EQ for my horn system so thanks for the post, made me realize I had never really considered this question.

Best wishes
David Zan

Last edited by Dave Zan; 19th August 2018 at 12:51 AM.
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Old 19th August 2018, 05:55 AM   #7
3ll3d00d is offline 3ll3d00d  United Kingdom
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It is described in http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
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Old 19th August 2018, 07:08 AM   #8
Dave Zan is offline Dave Zan  Australia
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Thank you, so it's assumed only 2 poles & 2 zeros - a biquad.
I'll have a closer look.

Best wishes
David

Compliments on the latest polar analysis interface, by the way.
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Old 21st August 2018, 09:03 AM   #9
Dave Zan is offline Dave Zan  Australia
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I'll have a closer look.
It still is not clear to me.
Even if we limit the shelf filter just to a biquad there are still two Q's, one for the zeros and one for the poles.
Does Hornresp further limit the biquad and assume the same Q for both?

Best wishes
David
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Old 21st August 2018, 11:30 AM   #10
3ll3d00d is offline 3ll3d00d  United Kingdom
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Quote:
Originally Posted by Dave Zan View Post
Compliments on the latest polar analysis interface, by the way.
thanks

Quote:
Originally Posted by Dave Zan View Post
Does Hornresp further limit the biquad and assume the same Q for both?
FWIW I don't think I've ever seen a definition of a shelf filter that has 2 Qs, have you come across one?
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