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FIR Designer issue
January 30, 2015 - 4:17 am
Member Since: January 29, 2015
Forum Posts: 10
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i am reading the FX book and came to filters, and i wanted to try out the FIR Designer.
I watched the video and tried to do same things, until i had an issue.
With the optimal method, when m_nIRLength (Order) reaches 350 the m_h_Left[i] produced are all = 0.000000000... ( 0<=i<=1023)

From that value of m_nIRLength, the array is filled only with 0.0000000 always. The only difference i can see, is that the graphic of the frequency response (with filled flag enabled) is empty for values 350<= x = 356.
The audio in real time, totally blocks, and also the impulse response graphic.
Also for some other values of m_nIRLength, i get the audio signal blocked.

I checked with midimapper and avid mbox 3 asio drivers, and got same result. Tried to resize the audio buffer, but nothing.
The CPU load is almost at minimum, i am on a Windows 7, i5 / 8gb ram.

There is something i am missing ?


January 30, 2015 - 7:13 pm
Member Since: January 29, 2017
Forum Posts: 689
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As stated in the book, the Remez Exchange algorithm may not converge for a given set of filter specs with the Optimal method. When it does not converge, the coefficients are zero (or sometimes garbage). So, that is what is happening. For the record, I am using the Parks-McClellan C-code (it's been around for a long long time).

The Frequency Sampling Method filters do not have this issue as there is no search algorithm in that design.

- Will

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