Questions & Answers:
Digital and Analogue Audio & Video signals |
| Digital and Analogue Audio/Video Signals |
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| The Basics |
| The following is an attempt to simplify some of the issues surrounding the items that connect all of your electronics together – cables! They connect your equipment to power, each other, for visuals and audio. We hope this is helpful. |
| The Vision: |
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| Composite, S-Video, Component, DVI, HDMI, iLink, SDI, Firewire |
| A video signal, no matter what type, must contain the colour detail and a synchronisation signal (to tell the display how to put the colours together). In some cases the picture signal is split; brightness (Luminance) plus the colour streams for the signal (Chrominance), again the synchronisation tells the display how to put all this together. To achieve this, different types of video formats are used to primarily get the video signal from one component (DVD player) to another (Plasma screen). In terms of quality the cables can be rated as follows: |
| RF Video – Very Basic |
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| Composite – Quite Good |
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| S-Video – Good |
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| RGB Video – Very Good |
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| Component, DVI, HDMI, iLink, SDI, Firewire – Excellent |
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| However as with all cables there are implications, which are outlined below |
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| What is – RF Video? |
| RF Video is the basic video feed associated with older televisions and Video Recorders (VCRs). Hardly used in most Home Cinema set ups as Composite video is catered for on most video equipment produced nowadays. The audio output is Mono. The coaxial cable from your TV aerial feeds the signal. |
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| What is - Composite Video? |
| Composite Video is the basic form of video used with VCRs, Laserdisc and Camcorders. This format is cheap and easy and almost every piece of video equipment has a composite signal connection facility. As the name implies all the various video signal components (luminance – brightness and chrominance -colour), are combined and sent down one single cable. Composite signals can run over long distances – however, because a composite video signal combines transmission through a single coaxial cable, (i.e. the signals interfering with each other); the signal’s ability to convey fine detail is reduced. Although convenient, composite video signals are the least desirable in a high quality home cinema system. These cables have RCA connectors – one each end – normally colour coded Yellow. |
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| What is - S-Video (SVHS, Super VHS & Separated Video)? |
| S-Video is an upgrade to Composite video. A S-Video signal separates the luminance (brightness) and chrominance (colour) parts of the signal. This split is achieved by running the separate signals along two coaxial cables within the larger sheath, resulting in improved detail and resolution. However, this advantage can be lost if the signal has to travel long distances. Most video equipment has an S-Video connection. These cables have 4-pin DIN connectors – one each end. A good alternative if the DVD player has no SCART facility. |
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| What is - Component Video (YUV, YpbPr & YcbCr)? |
| Component video is a further upgrade on the video path (i.e. better than Composite & S-Video). The signal is carried down three separate coaxial cables, one carrying Luminance, with the Chrominance colour elements divided into the other 2 cores – Red & Blue. The sync signal is sent with the Luminance. Component video signals are similar to RGB (i.e. three signal paths - red, green, blue) used by video professionals. This is deemed as the best option to take as long as you have video sources and a TV/Monitor/Screen that accepts this format. It is capable of sending progressive interlaced signals as well. Like Composite these cables have RCA connectors – only in this case, three each end normally coloured Red, Blue & Green. |
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| What is - RGB Video (SCART)? |
| RGB also sends a signal in separate components and offers similar quality to Component video. The three basic colours (Red, Green & Blue) plus a sync are run along the green component, or as a separate sync (most common) or two separate syncs; one for horizontal, one for vertical (PC display systems use this). “SCART” is a signal transfer format popular in Europe, and the name stands for Syndicat des Constructeurs d’Appareils Radiorecepteurs et Televiseurs. A computer style 25-pin connector terminates a single cable. SCART is a convenient way to connect a source (DVD, VCR, Satellite) to a TV, however quality varies depending on the exact cable used. If you are considering use of a receiver or surround sound processor, SCART sockets are unlikely to be found! |
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| What is - DVI? |
| DVI stands for Digital Visual Interface and is an industry standard for transmitting RGB signals from a PC to digital displays such as LCD monitors, Plasma screens or projectors. There are two versions – DVI-D and DVI-I; DVI-D is only capable of carrying digital signals, whereas DVI-I has several extra connections within the cable that gives it the ability to carry standard analogue RGB signals too. In the context of Home Cinema, DVD players normally take digital information from DVD software (disc) converts it to an analogue signal for transmission, then have the display convert the signal back to digital again in order to reproduce the image. When using a DVI connection the signal remains digital throughout and as such doesn’t suffer loss incurred through the analogue to digital conversions. The DVI standard is defined as either dual link or single link. Single link uses 12 out of 24 pins in a cable giving a bandwidth of 165Mhz which will transfer resolutions up to 1920 x 1080 @ 60Hz and 1280 x 1024 @ 85Hz. Dual link uses all 24 pins, doubling up the bandwidth to two 165Mhz channels. This is capable of transferring resolutions up to 2048 x 1536 @ 60Hz and 1920 x 1080 @ 85Hz. As this was developed for PC’s cable length in computer usage was not an issue. However, signal quality over 4 metres can degrade – so use in home cinema where large distances are covered in some installations, should be carefully considered. |
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| What is – HDMI? |
| The next generation of connection of digital connection is considered to be HDMI. Think of it as a High Tech SCART. HDMI brings the relative advantages of DVI and iLink into one industry supported, consumer product. It transfers both uncompressed digital audio and digital video to give the highest level of sound and vision available from digital sources, essentially a marriage of HDMI style video to iLink style audio. Video signals transferred by this format remain in the digital domain and the loss of data encountered with digital to analogue conversion is removed. HDMI currently transfers2 channel audio, whereas v.2 will carry full multi-channel (8 channels in fact) surround sound codes such as DD & DTS. Another benefit is that this format allows other sources to communicate with each other, allowing two-way functionality. All this is achieved with one cable link between units, compared to say 6 separate cables for SACD/DVD-A. This format also allows transmission of interlaced images. All of this is can be achieved over longer cable lengths than DVI. The end of spaghetti junction behind the TV or HiFi, perhaps? |
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| What is - Ilink (Firewire IEEE 1394)? |
| Essentially, iLink is the computer IEEE1394 or Firewire standard. A digital data transmission medium that is capable of transferring data at up to 400Mbps. Firewire IEE1394 sends an MPEG data stream and is available for devices such as VCRs, Camcorders etc. However, the display unit (e.g. Plasma, Projector) has to have an MPEG decoder built in to it to convert this data and produce an image. In Home Cinema context it is limited to 100 or 200 Mbps and is commonly used either for transfer of Digital Video (DV) material from Camcorders to DVD recorders and PCs. Additionally transfer of Advanced Resolution Audio – 6 channels of uncompressed 192 Kbps digital audio (notably useful for high resolution formats such as SACD or DVD-Audio in addition to transferring Dolby Digital and DTS). ILink has been designed along similar lines to HDMI, mainly to eradicate the need for multiple cabling (e.g. DVD-A/SACD). Digital cables that send signals from a CD player to a DAC or Dolby Digital, DTS sound formats from a DVD/Satellite to a Processor/Receiver are not iLink. |
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| What is – SDI? |
| SDI stands for Serial Digital Interface, which is a broadcast standard. As this type of signal carries no form of copy protection, for obvious reasons it is rarely found on DVD players or Satellite/Freeview receivers. Modifications to allow some components to utilise this "raw" signal have entered the market (Japan/USA - plus these components are also highly priced at present). However, compatibility to other elements of your home cinema kit may not accept/recognise SDI. When components do match excellent picture quality can be achieved. Watch this space? |
| The Sound... |
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| What is – Coaxial Interconnect cable? |
| Coaxial is on of two types of cable to connect a CD/DVD player to an amplifier/AV receiver, using electrical signals to feed data e.g. Dolby Digital/DTS sound to the Home Cinema amp/receiver. |
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| What is – Optical (TOSLink) Digital Interconnect Cable? |
| This type of Digital interconnect utilises pulses of light to pass the information e.g. Dolby Digital/DTS sound to the Home Cinema amp/receiver. |
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| What is - Speaker Cable? |
| In order to hear your music or surround sound you will have to connect your amplifier / AV receiver to your speakers. Speaker cable comes in many forms – some are even flat to so they disappear under carpets. Good quality cable will retain the quality of the signal, especially over long distances. |
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| The Ends... |
| The right connectors are as important as the cables they are attached to. The connection should be where possible of similar metals (Gold preferably because of it’s conductivity properties) and airtight. If the connection is not airtight it will break down at a molecular level over time and begin to rectify or produce a diode effect on the signal. It will also determine what you can connect to each unit, e.g. most Receivers/Processors do not accept SCART Connectors, whereas TVs, DVD’s, Satellite & VCRs do. Below are examples of the connectors to be aware of: - |
| What is a Phono (RCA) connector? |
| Phono (RCA) connectors are for interconnect cable connection to a device. This includes coaxial cables carrying digital audio signals. These are the connections you normally find on interconnect cables used between a source (e.g. CD, Tuner, Satellite) and an Amplifier. Most products are supplied with these, but upgrades will help to improve sound quality. |
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| What is a BNC connector? |
| SDI stands for Serial Digital Interface, which is a broadcast standard. As this type of signal carries no form of copy protection, for obvious reasons it is rarely found on DVD players or Satellite/Freeview receivers. Modifications to allow some components to utilise this "raw" signal have entered the market (Japan/USA - plus these components are also highly priced at present). However, compatibility to other elements of your home cinema kit may not accept/recognise SDI. When components do match excellent picture quality can be achieved. Watch this space? |
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| What is a DIN connector? |
| DIN connectors are used on interconnect cable connections to a device with this type of input sockets. They are German standard multi-pin (between 3 – 8 pins) inside circular connectors. Usually used to connect pre and power amps for companies such as Quad & Naim whose products use this type of connector. A similar type of connector is also used for S-Video. |
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| What are XLR/NEUTRIK connections? |
| XLR/Neutrik connectors are for interconnect cables connecting to a device, normally found on ‘High End’ equipment using ‘Balanced’ inputs/outputs. These are three pin connectors that lock on to the sockets of a preamplifier, amplifier, CD/DVD player. |
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| What’s a Banana Plug? |
| Banana plugs are an efficient way of ensuring that your speaker cable connection from amplifier to speaker is secure. They plug into the amplifier and speaker terminals where available and subject to fitting. They are usually colour coded Red & Black/White to differentiate between +ve & -ve termination. |
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| What is a (TOSLink) Connector? |
| This type of Digital connector is distinctive in shape, (squarish) with a small point that is clear - to allow the light to travel through the fibre optics cable |
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| What is a Spade Plug? |
| Similar to the Banana plug, Spades are for speaker cable connection from amplifier to speaker. Rather than plug into the terminals, they attach to the binding posts on the amplifier and / or speaker terminals where fitted. |
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| What is a VGA / HDMI connector? |
| VGA/HDMI connectors are for connection of cables that stream video information to a display. Multi-pin connector with locking screws. Commonplace in the computer world, these connectors are just entering the fray in the Audio Visual world. Digital information direct from DVD’s to suitable screens (Plasma, Projection) without analogue conversion is now being pushed by major manufacturers. |
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| What is a DVI connector? |
| Similar to VGA/HDMI connectors this type of connector is for connection of cables that stream video information to a display. Multi-pin connector, almost like a "mini" SCART. |
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| What is a SCART connector? |
| SCART connectors are for connection of cables streaming video and audio information to a display. This connector is another multi-pin connector that carries audio, visual and switching data. This allows the sound and picture of your TV to work through one cable and also helps to switch different screen aspect ratios e.g. 4:3 to 16:9 automatically. |
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| What are IEC / Fig 8 Connectors? |
| There are two main connectors for connection of mains power to units that have removable power cables. One is known as IEC or “Kettle” plug which fits to 3 pin sockets designed for this style of power input.The other type of power connector is known as “Figure 8” as one end appears to look like an ‘8’ face on. This fits the power input socket on units with two round pins. |
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