Broadcast Planting Research Articles

PCM Encoded NTSC Color Television Subjective Tests

Digital television may effectively serve as the means to store, process and control color television signals within a broadcast plant. Pulse code modulation (PCM) involves the periodic amplitude sampling of a video signal and the conversion of each sample into a binary number of n bits. The PCM signal bit stream can be in n parallel channels or be time multiplexed into a single channel. In either case the total bit rate equals n times the encoding rate. We desire to minimize the bit rate in order to save circuit elements and bandwidth, consistent of course with acceptable picture quality. — A series of subjective tests was conducted to determine the importance of various parameters when PCM encoding an NTSC, 525-line, 60-field, composite television signal. Among these parameters are: (1) the number of amplitude levels being sampled that, in turn, define the n-bit digital word; (2) the encoding rate, both locked and unlocked with respect to the 3.58-MHz color subcarrier; and (3) the role of dither consisting of coherent square waves and weighted noise. The test setup consisted of a color film camera, encoding rate generators, dither generators, A/D and D/A converters, color and monochrome monitors. A test panel of experienced viewers examined the pictures in a controlled environment and rated each picture on a stepped acceptance scale. We concluded that NTSC television pictures that had been encoded with 6 or more bits per codeword suffered negligible impairment. The encode rate should be phase coherent with the color subcarrier in order to avoid beats in the picture. Dither signals did not make any improvement in picture quality except to mask contours during 4- or 5-bit encoding.

A Pulse Assignment System for Modern Television Broadcast Plants

Modern television plants require not only isolated pulse distribution and an emergency changeover to standby sync pulse generators, but in addition require the facility to flexibly assign varying groups of equipment to different designated pulse sources for independent remote sync lock and VTR operations.

Some Advanced Technical Features of the New WBAL-TV Facilities

This paper describes a new television broadcast plant in which significant improvements have been made in the following areas: 1) Camera control center 2) Sync distribution system 3) Video tape recording and playback system 4) Audio system 5) Control room switcher 6) Transmitter control center 7) Maintenance 8) Studio lighting 9) Automatic switching system

New Broadcast Studio Facilities for the Voice of America

A new and permanent broadcast plant for the Voice of America has been constructed in Washington, D. C. International broadcasts were initiated from these facilities on September 15, 1954. Unique features of this plant include a complete system design for equipment, which was fabricated to specification and requirement and a performance specification for all interior acoustical work. The equipment is comprised in part of a fully presettable, 100 input—50 output Master Control Desk and a 40-channel Recording Console. The Western Electric cross bar system is used for switching, and the recording functions are handled in a ten-cubicle recording room, each cubicle containing four disk or tape machines, the sets being completely interchangeable. Fourteen studios have been built which may be increased in number to thirty-six. A reference recording system of unusual application has been introduced. Five separate air-conditioning systems are used for the facilities area. Both tape and disk playback facilities are provided in every studio control room, all of which are indentical in size and layout to minimize operational problems. The studios are acoustically designed for speech reproduction suitable for the highest intelligibility of thirty-five different languages and are constructed to maintain an operational residual noise level of no greater than twenty-seven decibels. The acoustical performance specification demanded for the prescribed interior acoustical work is described. A variety of acoustical problems posed themselves during the plant design. A discussion is held concerning these problems and their practical solution.

Maintenance of Broadcast Operations in Wartime

This paper deals with the technical measures which have been taken in Canada by the Canadian Broadcasting Corporation to meet the daily increasing difficulties of maintenance of broadcast operations in war time. After a brief description of the facilities involved in these plans the paper outlines the steps that have been taken in the physical protection and guarding of broadcast plants. The problem of conservation of equipment in the face of acute shortages is then discussed with the measures that have been applied to prolong the life of tubes, microphones, and other equipment. In treating the final aspect of the problem, that is, the maintenance or resumption of essential operations after destruction of regular facilities, the paper describes the setting up of emergency and stand-by facilities such as secondary control centers, stand-by transmitters, frequency-modulation links, and other equipment designed to insure continuity of service.

A New Standard Volume Indicator and Reference Level*

In recent years it has become increasingly difficult to correlate readings of volume level made by various groups because of differences in the characteristics and calibrations of the volume indicators used. This paper describes a joint development by the Columbia Broadcasting System, National Broadcasting Company, and Bell Telephone Laboratories which resulted in agreement upon, and standardization in the respective broadcast and Bell System plants, of: a new copper-oxide rectifier type of volume indicator having prescribed dynamic and electrical characteristics; a new reference level based on the calibration of the new instrument with a single frequency power of one milliwatt; and a new terminology, the readings being described in “vu.” It if hoped that other users of volume indicators will join in the adoption of these new standards.

A New Standard Volume Indicator and Reference Level

In recent years it has become increasingly difficult to correlate readings of volume level made by various groups because of differences in the characteristics and calibrations of the volume indicators used. This paper describes a joint development by the Columbia Broadcasting System, National Broadcasting Company, and Bell Telephone Laboratories which resulted in agreement upon, and standardization in the respective broadcast and telephone plants of a new copper-oxide-rectifier type of volume indicator having prescribed dynamic and electric characteristics; a new reference level based on the calibration of the new instrument with a single-frequency power of 1 milliwatt; and a new terminology, the readings being described in vu. It is hoped that other users of volume indicators will join in the adoption of these new standards. The paper gives in considerable detail the technical data and considerations on which was based the choice of the characteristics of the new volume indicator and the other features of the new standards. Particular attention is paid to the technical data supporting the decision to make the new volume indicator approximately a root-meansquare rather than a peak-reading type of instrument.