Problem with THD and THD+N measurement

[adcpc]

Hi,

I'm trying to a SNR measurement from an audio signal in LabVIEW. However, I cannot measure SNR correctly. After investigating I found that sometimes I can have a higher THD than THD+N. As I believe that this is not possible there should be a mistake somewhere in my VI.

Here the analysis part of my VI :

And sometimes, here is the result when distortion is high :

Any idea for resolving this ?

Thanks

Message Edité par Alexandre.DaCosta le 01-16-2009 09:28 AM

[adcpc]

Nothing about this ?

[Marian_O]

Bon soir Alexandre,

are you using simulated input signals and could post your signals? How many harmonics are you calculating?

Best regards

MarianMO

[adcpc]

Hello Marian,

No, I'm not using simulated input signals but audio input signal from a usb sound card.

The Distortion measurement VI is set to calculate 20 harmonics.

Thanks for you help.

Have a nice day.

Alexandre

[adcpc · Accepted solution]

It seems to be resolved now. The problem could appear when audio acquisition was too short (under 50 ms).

If audio acquisition is long enough then THD+N is always higher than THD.

Thanks,

Alexandre