ITU-R arm filter implementation

[penguin08]

I have an array coming from a digitizer. I do an fft on it and then I calculate the frequency bins and apply a 20kHz low pass filter. The next step would be to apply an ITU-R ARM 2 kHz filter on this array and the filter behaves like the green line curve in the picture. All I know is that the 0 dB point is at 2 kHz and the maximum of 6 dB is located at 7 kHz. The implementation has to done in C++.

 

[penguin08]

I know I have to have an array of the same length size as the one of my data, but how do I calculate the weighting factors?

The ITU-R ARM is actually 6 dB shifted compared to the ITU-R 468

 

[FvM]

You'll calculate weighting factors for each frequency bin and multiply it. Calculate the power sum, if required.

A numeric representation of the ITU-R 468 filter is given here https://en.wikipedia.org/wiki/ITU-R_468_noise_weighting

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+6 dB is an additional factor of 2 for all table entries. What's the problem with it?

 

[penguin08]

That I know, I was just stating, I don't have a problem with it

my only issue is what formula to use to calculate the weighting factors?

 

[FvM]

As I said, a formula for the ITU scaling factor is given in the Wikepedia article. You can also convert the dB values read fom the curve into linear factors.