Listening to the needs of the Audio Engineers

Taken from latest edition of The Audiofile Magazine. Article by Alan Wheable FISTC, MITOL – Communications Manager at Omnitek

SDI video monitoring within an installation can be straight forward. You plug the signal into a monitor and the picture appears. This, however, is not necessarily the case for metadata and especially not for audio.

If a SMPTE 352 payload packet is present on the SDI signal, this metadata determines how the video content should be viewed, the data structure, the colour space, closed caption, parental control, timecode information, audio information, etc.

The audio embedded in the SDI data stream could be AES/EBU, Dolby E, Dolby D or Dolby D+, depending on where you are in the production chain. Monitoring AES/EBU audio content is straightforward, but requires it being de-embedded from the SDI data stream. Dolby on the other hand is a little bit more challenging because you not only have to de-embed it, but you then must decode it to ensure it is correct.

The monitoring challenges also become a bit more complicated when you are working with SMPTE 2110 content as the video, audio and ancillary metadata are separated into elemental streams so that they can be accessed and processed independently or all together. You need to be able to monitor these elemental streams independently during processing and when they recombined before transmission.

You also need to monitor the audio in whatever form it is transmitted. This includes its channel configuration, PPM levels and its programme loudness and ideally you need to able to hear it to be sure it is free from pops and clicks.

With more mixed SDI / IP and ‘all IP’ installations being designed and implemented it raises a few additional challenges for audio engineering. The Omnitek Ultra TQ can analyse and decode Dolby E, Dolby D and Dolby D+ audio for monitoring and quality checking using a new Audio board. This board decodes the Dolby from the selected SDI/IP stream, it accepts native AES/EBU input/output as well as providing an analogue audio monitor output of the selected audio channels. 

The demand for this additional audio functionality comes from broadcasters who need to be able to ensure the quality of all aspects of their content before server ingest and broadcast. This has been complicated due to the adoption of IP standards such as SMPTE 2110 which has made it essential to check that all the elemental streams (video, audio and ancillary) are correct.

The Ultra TQ uses a SMPTE 2110 SFP module that can be configured from within the Ultra user interface. This allows IP addresses to be setup for video, audio and ancillary elemental streams. The user can then select how to analyse the video, audio and ancillary data.

The Ultra TQ’s audio instruments include the Audio Status and Audio Errors tiles to ensure that the data structure is correct, the Audio Meters to ensure that channel assignment and levels are correct, the Loudness tile to ensure that program loudness is within the required limits and the AV Delay tile to allow the relative measurement of each audio channel with respect to video. These instruments can monitor the SDI embedded audio, the decoded Dolby audio and the AES/EBU input audio. 

Dolby Metadata, Dolby audio channel assignments, Dolby programme loudness can be analysed and decoded Dolby output via AES/EBU and headphone outputs.

The Ultra TQ is fully configurable and allows any audio channels to be assigned to the headphone output and up to 8 channels to be assigned to the AES/EBU outputs available on the back panel via a ‘break-out’ connector.