9234 SNR

[maristu]

Hi,

We have developed a system to measure acoustic noise (LAeq, Fast, Slow... ). The system consist in:

NI 9171+NI 9234+ Labview+ Sound and Vibration toolkit

The data rate is 25.6 kHz

We have been asked about some acoustic parameters and we don't  know how to obtain them from the data sheet.

We need the following parameters:

- SNR (Signal to noise ratio) of the antialiasing filter and how is calculated.

- Is the Dither applied by default in the NI 9234? if yes which is the probability distribution of the added noise and the aplitude of such noise?

-  SNR of the Delta-Sigma

Thank you very much

[Henrik_Volkers]

How about measuring the noise of the actual system?

Apply a defined source impedance (shortcut, 50Ohm, 600Ohm, 10k ??  resistor)  and analyse the signal you measured?

[dsb@NI]

Terminating an input channel is a good way to measure the idle-channel noise. The ratio of the power of a full-scale signal to the idle-channel noise is a best-case SNR. Normally, SNR is measured with a near full-scale signal (-1 dB FS) applied to the input. Connect a DSA device with analog output to your 9234, generate a tone, and use the SVT SNR without Harmonics VI to measure SNR. Even more so than the calculated SNR, the  

measured spectrum may be more interesting/informative to you and your customers than one additional metric.

Unless specifications must be given for each element in the signal path, I agree that system performance is the most relevant performance.