What is the effect of output signal with the same sampling frequency but different number of samples?

[Bill Choy]

Hi,

I'm using PXI4461 for audio measurement and there is a question about analog output. I'm using the Basic Multitone vi for generating multitone signal. The sampling rate is 200k and my question is how to determine the number of samples. I used an audio analyzer to measure the distortion of the output signal with 200k and 1k points and there are no different except the update rate. What number of samples is suitable for 200k sampling rate?

Thanks,
Bill

[pawel]

I am not sure if I understood well, but normally the sampling frequency is exactly number of samples per second.

regards
Pawel

[Bill Choy]

Yes, but you can see the sampling info contains sampling rate and number of samples in all waveform generation VIs.

Bill

[LesHammer]

The Sampling Rate determines the maximum frequency that you can see (the rate/2 according to Nyquist).
The number of samples divided by the rate determines how long you will sample. This sample time can only be determined by you. Do you need .1 seconds worth of data, or 1 second? But note that the MINIMUM frequency that you can detect is 1/(Sample Time) or the Sampling Rate/Number of Samples. So if your system has a minimum and maximum frequency specification use that as your guild.

Les.Hammer@CompleteTest.com

[Bill Choy]

Is it necessary to use a large number of samples to generate signal? If the generation is run continuously, there are no different of .1 or 1 second data. The DAQmx write function will generate signal continuously even I input 1 cycle data points. Am I right?

[LesHammer]

Yes, if your generator is in a continuous mode one cycle worth should be fine. If it is a pure tone that should be easy to compute.

Les