User Manual - TRS-RenTelco

Option SD/HD Detailed Measurement Information
this example). If the extra spectral content is removed by filtering, the resulting
sinusoid will have the amplitude shown in the results.
Generally, if the signal has undergone processing without a required anti-alias
filter (as in re-sampling for format conversion, or signal reconstruction), each
burst may contain one or several frequency aliases. In such cases, burst
frequencies that increase with each burst of the input signal may contain burst
frequencies in nearly any order in the output of the device under test.
For example, in the 480p rendering of an ATSC 1080i multiburst signal, 5 MHz
is rescaled to 4.85 MHz, 10 MHz to 9.71, but 15 MHz, 20 MHz, 25 MHz, and
30 MHz become any number of frequencies (including 12.44 MHz, 7.58 MHz,
2.73 MHz, and 2.12 MHz respectively). These frequency aliases and respective
amplitudes are measured and displayed in order: 2.12 MHz, 2.73 MHz,
4.85 MHz, 7.58 MHz, 9.71 MHz, 12.44 MHz.
How Results are
Calculated
The six largest peaks are found in the spectrum of signal on the pedestal. These
frequencies are displayed in order from lowest to highest. For each of these
frequencies, the maximum magnitude of the cross-correlation between the signal
within the pedestal area and a windowed complex sinusoid is found. This gives
the amplitude.
Noise
The unweighted noise within the nominal bandwidth of the video signal is
measured to ensure that the video quality is not reduced by random errors such
as those that cause ‘snow’.
Signal Source
You can use the matrix signal, or you can use any flat line or line pedestal signal.
Interpreting Results
As a rule of thumb, errors generally become visible when the signal-to-noise dB
measurement ranges in the low 40s. However, the degree of visibility depends on
many factors, including spectral distribution of the noise. In standard definition
television, noise weighting filters such as the CCIR Recommendation (Rec)
576 -2 unified weighting filter are used to weight the noise spectrum to better
match the visibility of noise in typical viewing conditions. The unified weighting
filter has been modified to exactly match the ‘visibility of noise characteristics’
of 576 -2 on the screen for each selected video format.
How Results are
Calculated
After line tilt and other low frequency distortions are removed from the signal,
all AC signal content is spectrally weighted by the selected filter, if any, and the
resulting RMS voltage is calculated along with the signal-to-noise ratio in dB
using a 700 mV peak signal value.
3-34 VM5000 Automatic Video Measurement Set User Manual