Digital Audio / Visual Signals

Stands for Digital Visual Interface and is an industry standard for Digitally transmitting RGB signals to digital displays such as LCD monitors, Plasma screens and projectors. There are two basic forms – 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 take Digital information from a DVD, convert 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 analogue to digital conversions.

The DVI standard is defined as either dual-link of single link. Single link uses 12 of 24 pins in the cable giving a bandwidth of 165MHZ which will transfer resolutions up to 1920 x 1080 @ 60Hz and 1280 x 1024 @ 85Hz. Dual-Link will use 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!!

Essentially, iLink is the computer IEEE 1394 or Firewire standard. A Digital data transmission medium that is capable of transferring data at up to 400Mbps. In the 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, or for the transfer of Advanced Resolution Audio – 6 channels of uncompressed 192Kbps digital audio (notably useful for high-resolution audio formats such as SACD or DVD-Audio in addition to transferring Dolby Digital and DTS).

HDMI brings the relative advantages of DVI and iLink into one industry-supported, consumer interface. In it's basic sense a HDMI lead is essentially a cable that carries DVI style video and high-bandwidth style audio. Unlike standard DVI implementations, HDMI can also send interlaced images, and is capable of running over longer cable lengths to DVI due to built in error-correction. With higher gauage and/or amplified HDMI leads we are able to reach cable runs of 30m or more sending a 1080p signal!

HDMI 1.2 brings some new features to the standard most relevant for us is support to send SACDs 1-bit format (DSD) in it's native format from source to amp/processor. Previously devices which were capable (e.g. Arcam DV139), would convert to multi-channel PCM instead. Which to be fair would have been required at the processing stage anyway for bass management.

HDMI 1.3 available late 2007 will bring more advances in bandwidth and hence support the latest high definition audio and video formats without conversion or compression. Deep Colour will allow 30/36/48-bit colour depths where previously only 24-bit max was supported. On the audio side, Dolby TrueHD and DTS-HD lossless audio formats will be supported, as will a handy Lip Sync adjustment feature to keep video and audio perfectly in sync.

Typical applications are from DVD to plasma/projector, and soon this will run via your AV amp which will pick up the audio stream. For more information see http://www.hdmi.org/faq/faq.asp