Transmission/Technical Information

What is HD?

What is High Definition?
High definition (HD or HDTV) is a different standard of digital television broadcasting which offers sharper, more detailed pictures and surround sound. Only viewers with an "HD Ready" television set, a special HD set top box receiver and reception of a high definition service will experience true HD programming. High definition programmes must also be specially shot.

I want to know more about the High Definition technology.
It requires an entirely separate broadcast stream from current standard definition (SD) broadcasting It has a 16:9 aspect ratio, which is the same as a movie theatre screen, and transmits in either 720 or 1080 formats. The two HD formats currently in use, 720p and 1080i, the number referring to the vertical line resolution of the picture. 1080 has a larger number of displayed lines, and is interlaced as with standard definition TV, whilst 720 is progressively scanned, similar to a PC display. Most channels in the UK are based on 1080i, and Channel 4 will be using only this format. Channel 4 HD will be show a proportion of its acquired programmes with 5.1 surround sound. 5.1 surround sound consists of 6 channels - a front left, center (for dialogue), front right, rear left, rear right and a subwoofer channel for low frequency effects. This is similar to the large number of DVD titles in standard definition which are now available.

Does owning a HDTV mean that I am watching in high definition?
No. As well as an HDTV, you need to have a decoder (set top box) that can receive the HD signals and a TV service offering high-definition programmes, some of which are free and some which you need to subscribe to. The tuner is available as an external set-top box.

What channels are available in HD?

Channel 4 HD is currently available (as at April 2011) on channel 126 on Freesat, channel 230 on Sky HD (UK only), where you will need to have a Sky HD box and viewing card, channel 142 on Virgin and channel 52 on Freeview. E4HD is available on channel 215 on Sky and channel 145 on Virgin, while Film4 HD is on Virgin channel 429.

Will all your programmes be in HD?

Channel 4 HD will be a direct simulcast of the core Channel 4 schedule. A proportion of the programmes will have been originally made in the HD format, these will include some of our well know US series and films as well as some Channel 4 commissioned programmes. The Channel 4 Group is committed to increasing its investment in HD production and acquiring programmes in the HD format. We fully intend to increase the proportion of our schedule which is made in high definition over time. The remaining non-HD programmes will be up-converted from the SD source material.

Will Channel 4 HD have subtitles, signing or audio description?
We currently have subtitles available on Channel 4HD and hope to have other access services available in time.

Will all HD programmes be available with Surround Sound 5.1?
Initially only some acquired programmes will have 5.1 surround sound (Ugly Betty for example). As more programmes are commissioned in HD, that number will increase.

Why are black bars sometimes still visible on a 16x9 HDTV?
Original HDTV programming is made in the 16x9 (1.78) aspect ratio, which fits the dimensions of HDTVs which are Widescreen. However, many theatrically released films are made in either the 1.85 or 2.35 aspect ratio, which is even wider than the 16x9 (1.78) aspect ratios of HDTVs. Therefore, when viewing these films on an HDTV (if presented in their original theatrical aspect ratio) - you will see black bars on your 16x9 screen. However, the bars will be less pronounced than if the same movie is viewed letterboxed on a standard 4x3 set. For upconverted 4x3 programmes , these will be seen with black bars on the left and right.

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