plot frequency response feature

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eenrique_dsp
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Last seen: 3 weeks 10 hours ago
Joined: 12/29/2016 - 4:33pm
plot frequency response feature

Hi,

I wanted to ask the following questions

1) I am using the plot frequency response on a target and it is very helpful. For the Biquad Cascade HP

module, I can plot the response even while the target is running. The issue I run into is that when I have

20 biquads cascaded it plots properly but when I increase to 30 all of the sudden the plot freq response

goes flat. 

1b. On a different installation, I also notice that the plotting is different in the sense that this it can only 

handle 6 biquads instead of the original 20 that I mentioned above.  The only difference I can tell 

is that for the PC (6biquad_limit) have an older installation (5.16) and the other pc has both the 5.16 and 

a newer AWE installation (6.x) .  The only speculation that I can make is that maybe the newer installation 

uses a newer and maybe better matlab runtime installation and it affects the plot freq feature. 

1.c Please confirm that when I invoke the plot freq response that it is only computed at the PC side and not

into the target and reported back to the PC. 

2) On the module that I mentioned above, is there any limitation to the number of biquad filter stages?

I understand that part of the limit ultimately is the capacity of the target hardware.

 

Thank you. 

EE

Axel Nilsson
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Last seen: 1 week 42 min ago
Joined: 12/19/2016 - 2:02pm

Hi Emilson,

 

There is no hard limit to the number of stages you can apply to the Biquad Cascade HP module, and as you assumed, the plotting all happens via MATLAB commands on the local PC. 

You also correctly assumed that versions 5.x use an older version of the MATLAB Runtime (R2015.b) than the 6.x versions of Designer (R2017.b). This could explain why you are able to plot a greater number of stages in the later versions of Designer. I see you have a Pro license - if you try these plots while running Pro Designer launched with a newish version of MATLAB, does your performance improve?

I tried reproducing your problem, but even with 100 stages in the Biquad Cascade HP module and using an older 5.x Standard Designer that relies on MATLAB MCR for R2015.b , I get a clean frequency response plot every time. If you launch the Standard Designer edition via a Windows Command Prompt instead of double clicking on the shortcut, you may see that MATLAB is issuing errors while trying to plot the multi-stage frequency response. Let us know if any errors show up in this command prompt.

 

-Axel