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The SVT Idle Channel Noise VI measures the total power, the median noise density level, the maximum spur, and the signal-to-noise ratio (SNR) within the specified frequency range. The SVT Idle Channel Noise VI can operate on waveform data or the complex spectrum returned by the other audio measurements.

For practical purposes, the returned idle-channel noise is a power-in-band measurement that returns the aggregate noise energy in the specified frequency range. The SVT Idle Channel Noise VI computes the SNR as the full-scale level divided by the idle-channel noise.

The median noise level is normalized by the bin width, df, and is one measure of the noise floor, or noise density level. You might find noise floor knowledge useful in advanced measurements. For example, you can specify the threshold input to the SVFA Spectrum Peak Search VI in order to identify all the spectral components that exceed the noise floor plus 12 dB, or four times the noise floor.

Unlike gain, phase, and crosstalk measurements, idle-channel noise is a broadband measurement in which the amplitude of the fundamental frequency is expected to be zero. Use the frequency range control to limit the bandwidth of the measurement. To exclude DC power, set the start frequency to 8(df), where df is the frequency resolution of the spectrum. Increase the start frequency in the frequency range control to exclude additional low-frequency components from the measurement. You can enter the default values of -1 for the start frequency and –1 for the stop frequency to perform the measurement over the entire acquisition bandwidth.

Note  You can measure the idle-channel noise with the input channel to the device under test floating, terminated, or excited with a zero amplitude signal.