Understanding the transmission of audio across SDI

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Andy Agnew

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  • Joined: Sat Dec 02, 2017 10:45 am

Understanding the transmission of audio across SDI

PostSat Dec 02, 2017 11:34 am

Hi, I wonder if someone could help me understand how audio is sent across SDI using the converters available? My apologies if this has already been covered in the forum?

My understanding is that there are16 audio channels available, the channels used is dependant upon the jumper settings e.g. 1-4, 5-8, 9-12, 13-16 using the Audio to SDI and SDI to Audio converters?

What is confusing me is that the SDI to HDMI converter can also access audio from the 16 channels albeit that there are only two channels available to this converter (two external ports) rather than the 4 that the Audio/SDI converters can access? But looking at the HDMI to SDI converter, there is no option to choose which of the two channels to use of the 16 that I think exist, only an option to choose either the external inputs or the HDMI feed. My understanding from the manual is that the HDMI to SDI converter is using channels 1 and 2? Why is there not an option to choose the channels used which the SDI to HDMI converter has?

If this is indeed correct? if then an Audio to SDI converter was included in the chain, would channels 1-4 then be unavailable to use for an Audio to SDI converter is in the chain? Lastly, if there are SDI to Audio converters daisy chained together, can more than one converter access the same audio?

Hopefully I haven't understood things all wrong, would really appreciate getting a better understanding of how the audio transportation across SDI works both standalone and with a video signal using the converters available.

Thanks for your help in advance
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Gary Adams

Blackmagic Design

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  • Joined: Sat Aug 25, 2012 6:14 am

Re: Understanding the transmission of audio across SDI

PostTue Dec 05, 2017 5:29 pm

Hello Andy. SDI and HDMI signals are similar in that they have ancillary space to carry digital audio. We have lots of converters and you didn't specify exactly which ones you were looking at. But generally most of our SDI devices will carry 16 channels of audio embedded. The HDMI counterparts will carry 8 channels of embedded audio. Any device that extracts audio is non destructive to the original signal so you may have several converters in the chain to extract what you want. Some have 2 channels and are generally the Stereo 1 and 2. Others allow access to groups of 2, 4, or 8 in chain. Audio embedders will replace audio on the specific channels you select. This may not answer every question but I hope it helps.

Regards, Gary
Gary Adams
Blackmagic Design
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Andy Agnew

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  • Joined: Sat Dec 02, 2017 10:45 am

Re: Understanding the transmission of audio across SDI

PostWed Dec 06, 2017 8:28 am

Hi Gary, thank you for the very informative reply to my question, I now understand a lot more :-)

If I may ask another question...

Is it possible to interconnect both micro converters and mini 4K converters together to transmit video and audio. I now have a selection of both and would like to utilise as many of them in transporting video and audio around a large room? I have normally kept them separate

Scenario... Television Studio HD (1080i 50 output) to Audio-to-SDI 4K (ch5-8) to micro SDI-to-HDMI to mini SDI-to-HDMI 4K to SDI-to-Audio 4K (ch5-8) to micro SDI-to-HDMI... I beleieve all converters can handle 1080i 50... would this work?

Again thank you for your reply

Best regards, Andy

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