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Spectrum assistant for FFT - How is the signal freq decided?

jdp721

Hi,

How does the Spectrum assistant tool for FFT in ViVA decide on the signal freq for computing the SNR, etc. values?

Like, the input transient wave might have multiple frequency peaks, and I might be interested to get SNR considering the power of only a particular signal freq.

Thanks.

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  • Andrew Beckett

    Actually it does say in the app note how it determines it:

    For calculation of P_Signal (total signal power), P_Noise, and P_distortion, we consider bins (from FFT, range is from startBin to endBin) from Max(signalBin, startBin) to endBin.

    For the range mentioned in “Signals bin” (say this array is arr), get the array index where magnitude is maximum (frequency that has maximum y value). Around this frequency (say freq) we have signal from freq - signalBin to freq + signalBin.

    P_Signal (Total Signal Power) = arr[i] * arr[i] ; i is from (freq - signalBin) to (freq + signalBin).

Reply
  • Andrew Beckett

    Actually it does say in the app note how it determines it:

    For calculation of P_Signal (total signal power), P_Noise, and P_distortion, we consider bins (from FFT, range is from startBin to endBin) from Max(signalBin, startBin) to endBin.

    For the range mentioned in “Signals bin” (say this array is arr), get the array index where magnitude is maximum (frequency that has maximum y value). Around this frequency (say freq) we have signal from freq - signalBin to freq + signalBin.

    P_Signal (Total Signal Power) = arr[i] * arr[i] ; i is from (freq - signalBin) to (freq + signalBin).

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