Signal-to-Noise Ratio (SNR) (Sound and Vibration Measurement Suite)
December 2007
NI Part Number:
372416A-01
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This topic discusses how to use the SVT SNR without Harmonics VI and the SVT Idle Channel Noise VI.
The following equation defines the signal-to-noise ratio (SNR):
In the previous equation, SNR is equivalent to the measurement of noise in the presence of a signal.
You can approximate the SNR for signals dominated by a fundamental tone. For these signals, the SNR is high and approximately the inverse of the difference between the total harmonic distortion plus noise (THD+N) and the total harmonic distortion (THD).
Use the signal in noise and distortion (SINAD) result that the SVT SINAD VI returns if you require that the fundamental tone harmonics be included in the SNR computation. This measurement is nearly equivalent to the dynamic range measurement. The dynamic range is a property of the channel and usually measured with a fundamental that is –60 dB FS. The SNR is a property of the signal usually measured with a fundamental that is 0 dB FS.
Some specifications call for measuring SNR in a two-step process whereby you measure the full-scale level with the signal applied, and then measure the noise with no signal present. Measure the full-scale level and then use the SVT Idle Channel Noise VI to compute the SNR with no signal present.