Random noise displayed on a wideband oscilloscope, with a vertical sensitivity of 20mV/cm and bandpass of 20MHz. SNR(dB) = 20 log10 (p-p video signal voltage/p-p noise voltage) + 15įigure 3. The SNR is consequently calculated as per the formula: Various organizations use conversion factors between 14dB and 18dB. To measure the SNR, the “quasi” peak-to-peak amplitude of the noise is carefully estimated, and a conversion factor is added to obtain the RMS noise value. Oscilloscope measurements of luminance SNR necessitate a conversion from peak-to-peak noise voltage, as displayed on the oscilloscope screen, to RMS noise voltage. Specialized equipment gives a direct reading as per the formula above. Where the p-p amplitude (reference) of the video signal is 714mV for the 525/60 system and 700mV for the 625/50 system. SNR(dB) = 20 log10 (p-p video signal voltage/RMS noise voltage) The typical test signal for the measurement of noise is a flat field at the black level (i.e a luminance level of 0 IRE). Given the low sensitivity of the eye for fine luminance details, moderate amounts of triangular noise affecting the luminance are quite tolerable. The pattern is relatively coarse in the case of white noise and fine-grained in the case of triangular noise. The effect of random noise on the luminance component of the picture is seen as a fluctuating pattern of black and white specks.
RCA VIDEO NOISE REDUCTION TV
To measure random noise, the timebase of the oscilloscope is set to display one TV line. Certain authorities also use a weighting filter approximating the eye response. The upper limit ensures that irrelevant high frequency noise is removed from the measured signal. The lower frequency limit ensures that hum is not measured as random noise. For this reason, the noise is measured in a frequency band extending from 10kHz to the upper limit of the video band (4.2MHz in NTSC 5MHz, 5.5MHz or 6MHz in PAL). It is evident that a serious error is possible in the measurement of the SNR unless arrangements are made to make the noise and the signal bandwidth equal at the point of measurement.
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