How would you start? ]]>

How would you start? ]]>

http://www.sengpielaudio.com/calculator-dba-spl.htm

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There is no formula for calculating "equal loudness"
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equal loudness is a measured curve, tested idealized with sine tones, with no reverberation:

http://www.sengpielaudio.com/Acoustics226-2003.pdf

What is best to adapt such a curve without degrading the sound? With a FIR filter?

]]>You can hand draw your curve into a Hann window to use with a regular Fir filter, but you should be able to program (expr) the curve for the Hann window from the A weight formula.

It has to be easier than building an Eq to match an A weight curve.

http://www.katjaas.nl/minimumphase/minimumphase.html ........ the [pd spectfilter~] part.

But if you are using this with external components like a microphone and speakers then you need to compensate for their foibles and you could use 07.adaptive_equalisation from the adaptive library to make an overlay for the Hann A-weight curve.

I.e. multiply by the A weight Hann window and multiply again by the inverted curve from adaptive.

I don't think phase will be a concern, but that depends what you want to do with it.

You might be stuck with a download of Pd-extended to use adaptive without too much fuss..

David.