ITU-R BT.656

ITU-R Recommendation BT.656, sometimes also called ITU656, describes a simple digital video protocol for streaming uncompressed PAL or NTSC Standard Definition TV (525 or 625 lines) signals. The protocol builds upon the 4:2:2 digital video encoding parameters defined in ITU-R Recommendation BT.601, which provides interlaced video data, streaming each field separately, and uses the YCbCr color space and a 13.5 MHz sampling frequency for pixels.

The standard can be implemented to transmit either 8-bit values (the standard in consumer electronics) or 10-bit values (sometimes used in studio environments). Both a parallel and a serial transmission format are defined. For the parallel format, a 25-pin Sub-D connector pinout and ECL logic levels are defined. The serial format can be transmitted over 75-ohm coaxial cable with BNC connectors, but there is also a fibre-optical version defined.

The parallel version of the ITU-R BT.656 protocol is also used in many TV sets between chips using CMOS logic levels. Typical applications include the interface between a PAL/NTSC decoder chip and a DAC integrated circuit for driving a CRT in a TV set.

ITU-R

The ITU Radiocommunication Sector (ITU-R) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU) and is responsible for radio communication.

Its role is to manage the international radio-frequency spectrum and satellite orbit resources and to develop standards for radiocommunication systems with the objective of ensuring the effective use of the spectrum.

ITU is required, according to its Constitution, to allocate spectrum and register frequency allocation, orbital positions and other parameters of satellites, “in order to avoid harmful interference between radio stations of different countries”. The international spectrum management system is therefore based on regulatory procedures for frequency coordination, notification and registration.

ITU-R has a permanent secretariat, the Radiocommunication Bureau, based at the ITU HQ in Geneva, Switzerland. The elected Director of the Bureau is Mr. François Rancy of France. First elected by the ITU Membership to the Directorship in 2010.

Rec. 601

ITU-R Recommendation BT.601, more commonly known by the abbreviations Rec. 601 or BT.601 (or its former name, CCIR 601) is a standard originally issued in 1982 by the CCIR (an organization which has since been renamed as the International Telecommunication Union – Radiocommunication sector) for encoding interlaced analog video signals in digital video form. It includes methods of encoding 525-line 60 Hz and 625-line 50 Hz signals, both with an active region covering 720 luminance samples and 360 chrominance samples per line. The color encoding system is known as YCbCr 4:2:2.

The Rec. 601 video raster format has been re-used in a number of later standards, including the ISO/IEC MPEG and ITU-T H.26x compressed formats – although compressed formats for consumer applications usually use vertical as well as horizontal chroma subsampling, thus using 4:2:0 sampling rather than directly using the 4:2:2 sampling used in Rec. 601.

The standard has been revised several times in its history. Its edition 7, referred to as BT.601-7, was approved in March 2011 and was formally published in October 2011.

ITU-R 468 noise weighting

ITU-R 468 (originally defined in CCIR recommendation 468-4; sometimes referred to as CCIR-1k) is a standard relating to noise measurement, widely used when measuring noise in audio systems. The standard, now referred to as ITU-R BS.468-4, defines a weighting filter curve, together with a quasi-peak rectifier having special characteristics as defined by specified tone-burst tests. It is currently maintained by the International Telecommunications Union who took it over from the CCIR.

It is used especially in the UK, Europe, and former countries of the British Empire such as Australia and South Africa. It is less well known in the USA where A-weighting has always been used.

Explanation

While most audio engineers are familiar with the A-weighting curve, which was based on the 40 phon equal-loudness contour derived initially by Fletcher and Munson (1933) the later CCIR-468 weighting curve, now supported as an ITU standard is less well known outside of the UK and Europe. Originally incorporated into an ANSI standard for sound level meters, A-weighting was intended for measurement of the audibility of sounds by themselves. It was never specifically intended for the measurement of the more random (near-white or pink) noise in electronic equipment, though has been used for this purpose by most microphone manufacturers since the 1970s. The human ear responds quite differently to clicks and bursts of random noise, and it is this difference that gave rise to the 468-weighting, which together with quasi-peak measurement (rather than the rms measurement used with A-weighting) became widely used by broadcasters throughout Britain, Europe, and former British Commonwealth countries, where engineers were heavily influenced by BBC test methods. Telephone companies worldwide have also used methods similar to 468 weighting with quasi-peak measurement to describe objectionable interference induced in one telephone circuit by switching transients in another.