A helpful guide to Audio Visual (AV) connectivity options

Universal rules of connectivity

You will find parts of this guide covering the basics and then more detail for the advanced to cater for differing levels of experience.

Before we start, there are a few universal rules surrounding "connectivity"

Techies can have long debates about the better connector method and there will always be exceptions to rules, so please accept we have had to generalise.
Implementation standards vary. Any recommendations assume your particular equipment has it implemented well. If in doubt seek advice based on the particular equipment/setup you have. For most people, following the general rules will provide satisfactory results.
Using inferior connections can completely undermine the performance of your expensive investment. Steer well clear of budget cables (and that normally includes the cables that came in the box with your equipment). Above budget there is a reasonable spread of options where quality is related to price. Above that the law of dimishing returns applies (the extra benefit you get will not be worth the extra cost). It is not unreasonable to expect 15% of the cost of your system to be cabling costs.
Digital doesnt mean "better" than analog, but since most input sources are 'recieved' digitally nowadays (freeview, Sky, DVD etc), its better to use digital connections rather than analog. As a general rule, once a signal is digital, try to keep it that way.
The physical cable/connector type does not always dictate the signal type. We have described the common types, but this will assume your equipment and settings support them.

A Basic Overview of connecting up your AV equipment

Where to start

All these cables and boxes and socket types. Where do you start if you have little experience. Well, there is no way in a small guide we could cover everything, but lets try to simplify it....

Unless you have equipment with the right number of the required sockets you may have to prioritise and juggle connections around until they're connected as best you can. Identify your priorities for connecting. This may include connecting your main HD sources and your main viewing sources (eg Freeview, Sky) on first to make sure they are connected well.

The connections for most people should aim for is HDMI for Hi-Def sources and RGB Scart for normal def sources as these generally provide the right quality and have audio included (simpler cabling).

NB. While the recommendation would still stand in Components favour vs Scart for enthusiasts, for most people we can assume 'legacy' equipment is best left on a nice simple video and audio connection like RGB Scart. If your chasing quality or features (such as progressive scan) to this level of detail then you'll be upgrading component connected devices to ones that support HDMI soon anyway!!

Freeview and Sky recievers will normally only support audio via digital optical (S/PDIF) or componenent audio.

If you have a Home Cinema system, the HDMI may 'pass-thru' this if it can (one HDMI cable to the amp's HDMI-In, and one from the Amps 'HDMI out' to the TV). If your amp doesnt support HDMI, then you can use HDMI direct to the TV and use S/PDIF (Fibre optic) or Component audio (one per channel) direct to the Home Cinema reciever specifically for audio. Similarly, if you arent using HDMI, directly connect your TV to your player receiver using Component video or RGB-Scart, and use S/PDIF orcomponent audio direct to your amp.

Other input sources such as cameras will probably dictate their connector type (eg S-Video only)

Common connection types (in more detail)

HDMI

Summary : HDMI provides excellent quality and supports HD Digital Video, HD Multichannel Digital Audio (8 Channel)

It is generally accepted to use this is the primary connection method for HD equipment where possible as it supports uncompressed High Defintion Digital Video, multi-channel (8ch) Digital Audio, and (HD Audio in later versions) as well as device control features.

HDMI comes in various 'versions' (eg 1.0 - 1.3), each one exceeding the performance capabilities of the previous version. The latest version (1.3) provides support for the latest and next generation Video and Audio (resolutions, refresh rates, multi-channel HD audio streaming) and in some cases supports levels not yet attainable on consumer equipment. So in the future we will have to watch the version number specified for the HDMI interface. At present, what really gets implemented by a manufacturer is a grey area so dont get hung up on it unless you are chasing a particular feature. HDMI version negotiation is performed by the equipment and is automatically backward compatible with previous versions of HDMI and with DVI-D (single link DVI-D, with the correct cable/adapter) so any HDMI or DVI-D interface can drive any HDMI monitor.

Criticisms of HDMI include that it is often easy to disconnect so securing cables is important. Also it supports HDCP Digital Rights Management technology, so not all media (ie copies) will be allowed to be passed (unlike analog connections which dont care). Also, it has been criticised for its cable reach, but distance limitations are cable and equipment specific as HDMI doesnt specify a distance recommendations, only performance.

Most HDMI cables should support 5m, and up to 15m is possible. If you have a long cable run, seek advice. At the extremes you may get 'sparkle' from missing pixels, Beyond that you will hit the digital cliff where the screens error recovery fails to be able to produce a screen.

DVI-D

Summary: DVD-D provides excellent qualty, supporting HD Digital video (no audio)

DVI-D provides excellent bandwidth and good seperation of signals. DVI colour signal processing is basically the same as the basic HDMI ones (enhanced versions of HDMI such as 1.3 provide more bits for colour encoding and more bandwidth for pixel/re-fresh rates though). But all this is down tto the implementaton of HDMI on your equipment, not the cable. If you have DVI-D, you can think of it as a basic video-only HDMI source as backwards compatibility of HDMI supports DVI-D so a DVI-D output interface can drive a HDMI display.

DVI specification recommends 7.5m max cable distance, but so be careful above 5m, but with the right cables and good DVI-D sockets you can exceed 20m. At the extremes you may start to get 'sparkle' from missing pixels. Beyond that you will hit the digital cliff where suddenly the screens error recovery fails to be able to produce a screen.

VGA (RGB)

Summary: VGA supports good quality HD analog video (no audio)

This is the analog version of DVI and can come with a variety of connector types, some looking similar to the digital connector shown above for DVI-D (different pin pattern). It will normally be presented as DE9 Mini Dsub type (three rows, totallying 15 pins, as shown in picture). Also, check your socket's 'sex' before buying cables (pins means male, holes means female - basic really!!).

VGA is often used in visual display and computer equipment, including LCD screens and projectors, but the emergence of digital screens such as LCD screens has seen more of the digital version. Its rarely seen on DVD players and for HDTV should mainly be considered an extra port for PC connectivity, rather than the primary connection.

Cables limits can be reached as soon as 3-5m depending on equipment and cable (and settings such as refresh rate).

Component Y-Pb-Pr Video

Summary: Component video supports good/excellent quality HD analog video (no audio)

Using three RCA jacks on cables with the ends color coded green, blue, and red, it is used on most quality TVs/HDTVs and DVDs. Widely accepted as a superior quality transmission form, albeit Analog. Also is generally the only analog format that commonly supports progressive scan (assuming your equipment does!). It is gradually being phased out now, as it doesnt support the copy protection that the media giants (some of which are media and electronics giants) are pushing.

The use of quality shielded cables manufactured specifically for video is essential.

Most commonly uses signal type "Y-Pb-Pr" (described later), an sometimes the sockets labelled as that. Also referred to as "component video", "Analog Componenent Video" or "color difference video".

Very useful for extended cable runs as the cable limits can easily extended beyond 20m, and reduction in quality above that will be gradual (no 'digital cliff' where performance drops off instantaneously).

Scart

Summary: Scart provides Good/Adequate Quality and supports SD analog video (no audio)

Using good quality scart cables is normally the recommended method for connecting non-HD sources such as video and set-top boxes with a single simple connection.

Scart does not support hi-def or multi-channel surround audio, but does support 2-channel audio and good quality RGB signals (subject to your equipment). Although RGB-Component in theory supports progressive scan, it is very unlikely your Scart implementtion on your equipment does (see 'Component video' for progressive scan support).

Common in Europe and UK. Comes in Scart-component/RGB (better quality), Scart-S-Video (bi-directional) and Scart-Composite (low quality) form. Generally, check your equipments manual for RGB or S-Video capability and use those sockets as preference (RGB better for quality, S-video requires sometimes for operation with a reciever/recorder).

It has large connectors and chunky cables but chunky doesnt mean quality and they are often made to inferior quality. Each wire should be shielded individually, but this is often ommitted in cheap cables (chunky doesnt mean shielded either). The connectors are non-locking and often fall off or work loose (loosing the audio first as the audio pins are usually the first to work their way off).

Scart is transmitted at a relatively high voltage and supports generous 10m+ cable lengths (on good quality cables)

S-Video

Summary: S-Video provides Good/Adequate Quality and supports SD analog video (no audio)

S-Video is adequate for carrying standard defintion signals from small or compact devices (Camcorders/laptops) or as an alternative to the methods where better video ports are not available (and audio can be sent seperately or is not required)

S-Video carries analog video only. It does not carry audio or high defintion video (HDTV) and doesnt support progressive scan DVD players.

A small connector usually with 4 or 7 small pins (you can connect devices with 7-pin cables, as long as the equipment only requires 4 to be used). The small connectors and thin cables tend to not be of great quality though.

Better than Composite video due to seperation of Luminance and Chrominance signals. Not as good as those supporting RGB which have better colour transport.

Composite Video (RCA or Phono)

Summary: Composite video (RCA) provides adequate quality and supports SD analog video (no audio)

Composite Video cables are RCA cables but are often referred to as 'Phono' cables in this lower quality single cable form. Its better than nothing if you're struggling for connections between your equipment, but isnt great quality, and doesnt support HDTV, or progressive scan DVD players.

In "Composite Video", all the signals are merged and transmitted on one cable, using filtering to prevent interference between signals within the transmission, which loses some of the quality or prevents the full breadth of the signal (bandwidth) to be transported (eg Luminesence).

TOSLINK (S/PDIF Optical)

Summary: S/PDIF Digital Audio provides excellent quality multi-channel audio

S/PDIF optical, commonly known as TOSLINK, is basically the common form of digital audio over fibre optics. It is commonly found in DVD devices and TV set-top boxes to transport audio to amplifiers

TOSLINK was originally developed by Toshiba. S/PDIF was a Sony-Philips steered development. S/PDIF itself can be electrical, and the signalling used for both is the same, the media being the difference (electrical or light pulses). Some devices support electrical S/PDIF, and these should not be considered inferior (having ta least the same bandwidth potential, a more bendable cable, and a more secure connector).

Quality of the fibre optic cable (as well as the optical lens) will define the quality of the signial. Inferior cables will be single plastic fibres (5mhz bandwidth, suitable for simple 2 channel transport). Superior cables will be mutli-fibre quartz cores (>10mhz bandwidth, suitable for HD and multi-channel transport). Multi-fibre cores will also tolerate more bending of the cable without distorting the signal.

Cable limitations are normally 5 metres as the light source in consumer equipment is normally an LED instead of a powerful laser. Bends in cables can reduce quality. Another downside is the connectors disconnect to easily.

Component Audio (RCA)

Summary: Component Audio (RCA) provides good quality 2-channel audio

For Component audio, channel information is seperated and sent along seperate cables. Commonly the 'right' channel is red and the 'left' channel is white. Often it is used for multi-channel, to send each channel on a seperate cable (eg 6 cables). Quality ranges from better than nothing to excellent, depending on the quality of the equipment and quality of the cables.

Another factor is whether you are merely transporting analog signals for amplification, or transporting audio information for re-conversion to digital for further processing or transport. For example, if you are connecting a CD player directly to a 2-channel analog amplifier, this can provide excellent quality transport as the signal can then be amplified simply onto the speaker outputs of the amp. If you are using analog to transport between two digital devices, it is generally lower quality by the time it is output as sound.

In two channel form, a home ciname amp might be able to reproduce a multi-channel effect. Its quality will be dictated by the Home Cinema processors abilities. It is better than nothing but its unlikely compare well to true digital multi-channel audio.

Audio Jack plug

Summary: Jack plug cables provide 'better than nothing' quality 2-channel audio

Jack plugs seperate channel information by using shielded conductors on a single pin. The number of conductors on the pin determines the number of connections, including control and power conductors in some applications.

It is normally only used in low quality applications. Quality is usually further limited by the quality of the cable. Sometimes it may be part of an adapter set, for example Scart at one end, and S-Video and a jack plug at the other (S-Video not being able to support Audio itself)

Comes in different sizes of phono jack, most commonly 3.5mm (mini-jack) and 6.3mm or 1/4 inch (jack). The socket is often refered to as line-in and line-out. The 3.5mm is frequently seen in PC cards and headphones and is most common in three conductor form. Three conductor jacks (identifiable as having two black rings) are the standard stereo jack. Three-conductor jacks are also referred to as TRS (Tip, Ring, Sleeve) plugs, a hand-down from their origins as 'Phone Jacks' from the early phone switchboard era (Ring and Tip).

PAL connector (Coaxial) - supports input RF signal from TV Aerial

Pal coax connector to connect aerial to HDTV or freeview receiver

Analog signal with no separation of signals. Generally now used only for connection from Aerial (can run over long distances)

F-Type connector (Coax) - Supports input RF signal from Satellite Dish

F-type coax connector to connect satellite dish to receiver

Analog signal with no separation of signals. Generally now used only for connection from Satellite dish (can run over long distances)

Video Signal Types (in more detail)

Introduction

Components split signals to improve seperation and quality, whereas Composites by defintion join signals. The reality is that components types will still use some form of composite within certain signal groups or on a particular wire. Therefore, as we run through this list, you will see an increasing use of composite, and a decrease in quality.

Signals that may be required include the (three) colour map groups, luminance, chominance and synchronisation signalling (eg horizontal and vertical sync). In simplistic terms, the more seperation you can provide for each signal, and the more bandwidth available for each signal, then the higher the quality.

Composite

A video stream that combines red, green, blue, and synchronization signals into one signal so that it requires only one connector.

In composite video, the luminance signal is low-pass filtered to prevent crosstalk between high-frequency luminance information and the color subcarrier.

Y/C Component (S-Video / Seperated Video)

Y/C is a component format (barely, and is the lowest quality form) that transmits the signal as two signals, Luminance and Colour, carried on separate synchronized signal/ground pairs. In practice it provides one full luminance signal (most important for a sharp image) and two reduced color signals.

Compared to Composite, S-Video separates the luminance and chrominance, removing the need for low-pass filtering of luminance. This increases bandwidth for the luminance information, and also subdues the color crosstalk problem, reducing dotcrawl and improving the image quality by leaving more information from the original video intact.

YPbBr Component

Typically used in analog video systems and transmitted over three wires. YPbPr is converted from the RGB colour space into components parts; Y, Pr and Pb, over the green, red and blue cable colours respectively.

Y carries the luma information, Pb carries the difference between blue and luma (B - Y) and Pr carries the difference between red and luma (R - Y). Syn information is carried (composite) on the Green Channel (known as SoG). Sync information allows the display to determine when a new line, or a new frame, begins.

Other than being an excellent and efficient seperation of video information, there are many justifications for Analog Video Component pre-existing with HDMI. It has no support for copy protection (DRM/CPRM). It acts as a flexible extra HD capable port on your equipment with easy conversion from other common 'RGB' based interface types (Scart, VGA/DVI-A). The distances you can run over component/rca cables is very flexible (100ft+). And lastly, but not least, in many systems, there are many conversions (framerate conversions and frame insertions, resolution adjustements and upscaling, interlace and progressive scan conversions). YPbPr colour space and a simple analog conversion, transmission, and re-conversion of the video data direct to the TVs optimum capaibility is a useful capability, and will match many 'real world' implementations of HDMI for performance.

YCbCr Component

Similar to YPbPr, it is typially used in digital video systems and transmitted over three wires where Y is Luminance, Cb is Blue Chromanance, and Cr is Red Chromanance.

RGB Component

RGB is the component format used as the base of digital, Scart and VGA cables utilising the multilpe pins available for colour, luminance and sync information.

Using the RGB colour space three pins are used to tramsmit red, green, and blue chroma information. Luminance information may be transmitted on a seperate lead. Sync information may require a further two leads (RGBHV has horzontal and vertial sync leads, RGBS has a single sync lead, SoG composites sync over green).

We hope this guide has been helpful.

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