29 dB 4. Marginal (snow somewhat objectionable) 25 dB 16.4.3 Other Parameters For black and white video systems there are four critical transmission parameters: 1. Amplitude-frequency response (see Figure 16.5) 2. Group delay (EDD, envelope delay distortion) 3. Transient response 4. Noise (thermal, intermodulation (IM), crosstalk and impulse) TELEVISION TRANSMISSION REFERENCE FREQUENCY 200 KHZ VIDEO AMPLITUDE VS. FREQUENCY RESPONSE FREQUENCY IN MHZ Industries Figure 16.5 Video amplitude-frequency response. (From Ref. 6, EIA/TIA-250C, Courtesy of Electronic Association/Telecommunication Industry Association, reprinted with permission.) Color transmission requires the consideration of two additional parameters: 5. Differential gain 6. Differential phase A description of amplitude-frequency response (attenuation distortion) be found the in Section 3.3.1. Because video transmission involves such wide bandwidths may compared requirements are much more stringent. voice channel and because of the very nature of video itself, both phase and amplitude to Transient response is the ability of a system to "follow" sudden, impulsive in signal waveform. It usually can be said that if the amplitude-frequency and changes phase good. characteristics are kept within design limits, the transient response will be sufficiently Noise and signal-to-noise ratio are primary parameters for video transmission. Of course, noise is an impairment and is described in Section 3.3.3. Signal-to-noise ratio is principal measure of video signal quality. Signal-to-noise ratio is defined in Section 3.2.1. the Differential gain is a parameter especially critical for the transmission of color tele- vision. It describes how system gain varies as the video signal level varies (i.e., which it traverses the extremes from black to white). Differential phase is another as of is also critical for the transmission of color television. It is any variation parameter in phase the the color subcarrier5 as a result of changes in luminance level. Ideally, variation 