How can I improve this AutoPowerSpectrum result ?

[Lab]

I acquired 990Hz sound signal[sine wave] by LineIn port of a sound card.Attach file reflected AutoPowerSpectrum result.You could notice that Y-value of n=22,24 highly affected the value of THD,SNR(it is very important for me).I used ScaledWindow()[selected hanning window],AutoPowerSpectrum(),PowerFrequencyEstimate(),HarmonicAnalyzer() functions in turn in my program .How can I improve result?Change size of Hanning window?Add sampling number?I have no idea...thank you very much

[Robin D'Souza]

Hi
If you are looking to increase the SNR, you should sample for a longer period of time. If you want to accurately measure the frequency, you will have to sample faster. Also, if you are really looking for good dynamic performance check out NI�s Dynamic Signal Analyzers (DSA) boards at Dynamic Signal Analyzers.
Thank you.
Robin D
National Instruments