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12 bit from ADC to Q15 for a FFT

elgarbe

I have a project on a STM32F103 using the ADC.

I'm trying to make simple VU meter. I made a litle circuit (a resistor divisor and a decoupling capacitor) to put the audio signal into de uC. Becouse of the resistor I get 2048 counts for no audio input.

So, when I put audio to the systems I get my ADC sampling it around 2048. Now I want to convert 16 bits unsigned (but centered at 2048) to Q15 to use CMSIS FFT_Q15

Is there any CMSIS function to do that? Is there a simple way to do that?

Thank!

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  • 0
    FFT has a nice effect : it "splits" your signal in frequencies !
    First bin of FFT output represents DC part of your signal.
    You can consider all your samples to be of the form (2048 + s[k]), directly perform FFT on it. If s(t) is a centered signal (average value of 0), you would end with FFT output:
    0 : 2048
    1 : ...
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  • 0
    FFT has a nice effect : it "splits" your signal in frequencies !
    First bin of FFT output represents DC part of your signal.
    You can consider all your samples to be of the form (2048 + s[k]), directly perform FFT on it. If s(t) is a centered signal (average value of 0), you would end with FFT output:
    0 : 2048
    1 : ...
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