Digital Audio in the Digital Video Studio-A Disappearing Act?
The D1 and D2 digital VTRs both have the capability of recording four channels of digital audio with up to 20 bits audio resolution per channel. Interfacing such machines in the digital domain has been based mainly on the AES3-1985 interface for digital audio and the parallel 25 way connector approach for digital video. However, the parallel digital video interface requires clumsy connections using large connectors and relatively bulky cable compared with the original analog video cable and BNC connectors. When the D1 digital component machine was introduced, this was not seen as a particularly big problem because the units were installed mainly in production houses rather than mainstream studios; the machines were often operated in self contained areas, and the fact that the machines were component required extra cabling for other surrounding component equipment anyway. There was a desire to implement a serial interface using coaxial cable and with the introduction of the D2 digital composite machine this became even more important. The result is a serial digital video interface which uses coaxial cable with BNC connectors maintaining compatibility with existing studio wiring installations. How does this affect the digital audio connections? The serial digital video interface offers a significant unused data capacity in the blanking intervals - of the order of 25M bits/sec for the D2 serial interface. This allows all four digital audio channels to be multiplexed in the video interface thereby greatly simplifying cabling requirements. This paper will describe the serial video/audio interface and the techniques by which successful integration of audio and video can be achieved.
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