Digital Audio in the Digital Video Studio-A Disappearing Act 2?
All digital VTRs have the capability of recording at least 4 channels of digital audio with up to 20 bits audio resolution per channel Interfacing such machines in the digital domain was first based on the AES interface for digital audio and the SMPTE 125M parallel interface for digital video. However, the video interface provided a relatively bulky cable and connector arrangement compared to the original analogue video cable and BNC connectors. When the first D1 digital component VTR was introduced, this was not seen as a particularly big problem since the units were installed mainly in productrion houses rather than mainstream studios. However, the introduction of digital video recording to a wider user base needed the implementation of a serial interface using coaxial cable. This implementation is now complete; the interface is widely referred to as SDI and is now enshrined in SMPTE 259M.: The digital video interface offers a significant unused data capacity in the blanking intervals - over 25 Mbits/sec in the component interface. This allows up to 16 digital audio channels to be multiplexed with the video providing greatly simplified cabling requirements. The paper will describe the serial video/audio interface in the light of published standards, and new developments which can offer further leads for the future of the SDI.
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