Created in 1940, it is still found today in most homes. It transmits audio and video signals. The acronym of RCA stands for Radio Corporation of America.

Originally, the RCA plug was designed to replace the old telephone plugs of manual telephone exchanges.
It was launched on the market at a time when cassettes and VCRs were the stars.

RCA connectivity makes it possible to transmit video and audio signals (in mono or stereo) via a cable composed of two strands, according to an analog or digital transmission mode.
Inexpensive to produce, it remains compatible with the majority of video formats offered.

The color of RCA connectors varies depending on their use.
RCA connectors are often sorted by color, yellow for composite video, red for the right audio channel, and white or black for the stereo left channel.
This trio (or pair) of jacks sit on the back of almost all audio and video equipment.

If it is a composite video signal, the connector is yellow. The RCA connector can also transmit component video signals, also known as YUV or YCrCb.
The 3 connectors used for this kind of signal are those of red, green and blue colors.

The YUV standard (also called CCIR 601), previously called YCrCb (Y Cr Cb), is a color representation model dedicated to analog video.

It is based on a separate component video transmission mode using three different cables to transmit luminance (brightness) information and two chrominance (color) components.
This is the format used in the PAL (Phase Alternation Line) and SECAM (Sequential Color with Memory) standards.

Parameter Y represents luminance (i.e. black and white information), while U and V represent chrominance, i.e. information about color.
This model was developed to allow colored information to be transmitted to color TVs, while ensuring that existing black and white TVs continue to display a gray-tone image.

Here are the relationships linking Y to R, G and B, U to R and luminance, and finally V to B and luminance :

      Y = 0.2R + 0.587 G + 0.114 B
U = -0.147R - 0.289 G + 0.436B = 0.492(B - Y)
V = 0.615R -0.515G -0.100B = 0.877(R-Y)


Thus U is sometimes denoted Cr and V denoted Cb, hence the notation YCrCb.
A YUV connection is usually based on the use of three RCA cables of green, blue and red color :

A YUV connection provides optimal video quality by simultaneously sending all 576 lines of the image, without interlacing (in one go).

Admittedly, this connection is very affordable but it has some disadvantages. This is because each cable is used to pass a single signal, which means that a lot of cables are needed on some devices.
Another flaw : its insecure maintenance, it is thus easy to disconnect the cable unintentionally and therefore promote false contacts.
Also : continuous noise may occur if the plug is partially out of the socket.

The S/PDIF format (acronym for Sony/Philips Digital InterFace), or IEC 958, is used to transfer digital audio data.
This standard designed by Sony and Philips can be considered the consumer version of the AES/EBU professional digital audio format. It was defined in 1989.

The S/PDIF standard exists in different forms :

- RCA connector (using a coaxial cable (copper)) with an impedance of 75 Ω.
- Toslink connector (using optical fiber). The main advantage of this format lies in its total immunity to electromagnetic disturbances.
- Mini-Toslink connector (using optical fiber). Identical to the aforementioned technology, only the connector changes, it looks like a standard 3.5mm minijack (0.5mm shorter to prevent making a mistake and touching the LED).

- Resolutions : up to 24 bits
- Sampling frequencies encountered :
96 kHz - Professional and semi-professional applications :
samplers, synthesizers/workstations, interfaces and digital audio recorders...
48 kHz - DAT (Digital Audio Tape)
44.1 kHz - CD