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VQMA User Manual
Running VQMA in Windows GUI mode
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7.4.7 Noise Measurement page
The most important noise parameter is RMS noise level of Y channel displayed in the upper left
corner of the page using three types of units:
- % of Nominal White
- D1 8 bit levels (in brackets)
- Equivalent mV of analog Y signal (also in brackets)
Other important noise parameter present on this display are:
- Y channel SNR, calculated in three variants: unfiltered, band-limited and weighted.
a) Y channel low-pass filter bandwidth is set to 80% of the maximal frequency (Flimit = sampling limit),
e.g. in 1080i format with 74.25 MHz sampling rate, LPF bandwidth is 0.8*74.25/2 = 30 MHz.
Weighting filter response is also auto-scaled inversely proportional to the frame resolution.
-b) The Y RMS value is derived directly from video data, so it correlates with unfiltered Y SNR.
- UV SNR, derived from band-limited unweighted sum of scaled U noise and V noise
- R, G, B and "Dark B" SNR values, derived from Y and UV SNRs
Note that all SNR values are calculated wrt nominal signal range, i.e. assuming video gain = 0 dB.
Y Noise Spectral Density plots in dB/dF for unlimited and weighted noise spectra allows to see
the effect of device under test frequency response and also to distinguish random noise from the
contributions by regular textures, e.g. from those caused by RF interference or digital clock
pick-up. In the example below Y Noise Spectrum clearly shows "boost" on medium frequencies
caused by strong aperture correction in camera video processor.
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