Glossary

audio signals

XLR connectors provide dual-channel audio signals. The left channel can be set to click as a means of easily distinguishing the left channel from the right channel in audio tests.

average picture level (APL)

The average signal level with respect to blanking during the active picture time. APL is expressed as a percentage of the difference between the blanking and reference white levels.

chrominance

The color information in a television picture. Chrominance affects two properties of color: hue and saturation. Also called chroma.

chrominance-to-burst phase

The difference between the expected phase and the actual phase of the chrominance portion of the video signal relative to burst phase.

chrominance-to-luminance delay

The difference in time that it takes for the chrominance portion of the video signal to pass through a system relative to the time it takes for the luminance portion. Also called relative chroma time.

chrominance-to-luminance gain

The difference between the gain of the chrominance portion of the video signal and the gain of the luminance portion as they pass through a system.

color burst

The burst of color subcarrier added to the back porch of the composite video signal. It serves as a frequency and phase reference for the chrominance signal.

composite video

A single video signal containing all of the necessary information to reproduce a color picture.

convergence

Used for adjusting convergence of the green, blue and red beams on picture monitors.

decibel

A logarithmic unit that expresses the ratio between a signal and a reference signal. For voltages, dB = 20 log (V_measured/V_nominal).

differential gain

Variation in the gain of the chrominance signal as the luminance signal on which it rides is varied from blanking to white level.

differential phase

Variation in the phase of the chrominance subcarrier as the luminance signal on which it rides is varied from blanking to white level.

frequency response

A system's gain characteristic versus frequency. Frequency response is often stated as a range of signal frequencies over which gain varies by less than a specified amount.

graticule

The calibrated scale for quantifying information on a waveform monitor or vectorscope screen. The graticule can be silk-screened onto the CRT face plate (internal graticule), silk-screened onto a piece of glass or plastic that fits in front of the CRT (external graticule), or it can be electronically generated as part of the display.

horizontal blanking interval

(See artwork below.)

 

Figure 8-1. Horizontal blanking interval.

insertion gain

The gain (or loss) in overall signal amplitude introduced by a piece of equipment in the signal path. Insertion gain is expressed as a percent (V_out - V_in)/V_in x 100.

IRE

A relative unit of measure (named for the Institute of Radio Engineers). One IRE equals 1/140th of the composite video signal's peak-to-peak voltage.

low-frequency amplitude distortion

A variation in amplitude level that occurs as a function of frequencies below 1 MHz.

luminance

The brightness information in the television picture. The luminance signal amplitude varies in proportion to the brightness of the televised scene and is therefore capable of producing a complete monochrome picture.

luminance nonlinearity

The degree to which the luminance signal gain is affected by changes in luminance level.

multiburst

This signal is commonly used in making system frequency response measurements.

NTC 7 Composite

Often specified as the reference signal for various tests. Also contains the 12.5T modulated sine-squared pulse used in measuring chroma-luma gain and delay errors.

NTSC

National Television System Committee. The organization that developed the television standard currently in use in the United States, Canada, and Japan. Now generally used to refer to that standard.

relative chroma level

See chrominance-to-luminance gain.

safe area

This allows the material positioning of video images to be checked. Both safe title and safe action boundaries are included. This signal can be keyed by any switcher or special effects generator that incorporates the luminance keying function.

saturation

The variable property of color that is determined by its purity, or its lack of dilution by white light. Highly saturated colors are vivid, while less saturated colors appear pastel.

signal-to-noise ratio (SNR)

The ratio in decibels of the maximum peak-to-peak voltage of the television signal (sometimes including sync) to the rms voltage of the noise at any point. The higher the ratio, the better.

5-Step Staircase

This signal is commonly used to check luminance gain linearity.

subcarrier

The 3.58 MHz signal that is modulated by color information to form a chrominance signal.

sweep signal

A signal whose frequency is varied through a given frequency range.

sync

A 40 IRE pulse used to ensure correct timing relationships throughout the system.

VITS (Vertical Interval Test Signal)

A signal that can be used for in-service testing by inserting it on a specific line, or lines, in the vertical interval.