Digital Audio in the Digital Video Studio, Part 2: What Happened to the Other 4 Bits?
In a previous paper -Digital Audio in the Digital Video Studio-The Disappearing Act?,- an explanation was given on how 20 bits of audio, as conveyed by the AES/EBU data stream, are carried by a combined video plus auxiliary data serial digital interface. This paper describes how the full 24 bit capacity of the AES/EBU data stream can be carried by the same interface. Certain complexities exist when transmitting the 24 bits over a 525 line composite serial digital interface operating at 143 Mb/s. A proposal is put forward to overcome what on the surface appears an impossible task.: In addition to carrying 24 bit signals in the serial digital interface, switching of the signal requires careful controls to be in place, particularly in the case of 525 line signals due to the field rate of 59.94 Hz. The 525 line field rate (59.94 Hz), plus the requirement of the D-1 and D-2 VTRs requiring the audio sampling frequency to be synchronous with the video, produces a five frame audio sequence consisting of 1601 and 1602 samples over a given frame.: The proposals put forward in the paper retains compatibility with current equipment while fully exploring the communication channel capacity of the Serial Digital Interface (SMPTE T14.224 Draft 5-Committee Document).
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