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Live broadcast with multi-channel audio

PostPosted: Tue Nov 14, 2017 6:03 am
by Alexander Kinov
Hi, haven't found similar topic, so I'm starting a new one. I hope it's ok.
I think the topic may be useful for other users too.

So, I need to find a solution to send multi-channel audio along with the video signal I'm broadcasting. I know you can embed few audio channels in the SDI.
As far as I know, the ATEM switchers send only stereo audio with the program mix. I think BMD AUDIO to SDI miniconverter is the proper solution in this case. The audio inputs (analog or AES/EBU) allow you to add more channels and decide how to be embedded in the SDI signal (1-4, 5-6 or other channels). I haven't tried this so far, but I think it will work and I hope someone with more experience or someone from BMD can confirm that.

However, my bigger concern is the way the SDI signal will be transmitted from "the field" to the studio.
I've worked many times with mobile broadcasting trucks and we were using SNG (satelite transmitting). Although I never had to deal with the transmitting equipment, I know it is possible to send more audio channels. For example we were doing live broadcast of sports events with two or more different audio feeds. One international audio feed (no comments, just atmosphere sound from the events) and other audio feeds including comments on one or more languages.
Right now I'm working for company that sometimes uses data stream to send (through internet connection) the signal to the studio. I don't know how it works, as we usually hire someone else with the transmitting equipment. I just have to give the guy with the encoder my SDI or HDMI cable with our signal. We were only broadcasting stereo signal so far, but now we might need to send at least one more stereo signal.
I wonder if the encoder can get the different audio signals and send them properly.

Re: Live broadcast with multi-channel audio

PostPosted: Tue Nov 14, 2017 7:14 am
the Audio to SDI units will add either 4 analog audio sources, or 8 AES audio sources to an SDI video signal. You can add to the existing ATEM stereo PGM audio, or completely replace it with the Audio to SDI.

Regardless of transmitting via satellite, fiber, or your internet device-the number of channels sent is completely up to your encoding device used for the medium and how it is setup. Most HD satellite encoders will transmit all 16 embedded audio channels. I have only used VidiU type devices onto the internet which usually only transmit channels 1and2. You will have to check with your internet transmission people to see what they can accommodate.

As an example, we use the OpenGear version of the Audio to SDI to send 4 channel audio on every event we do. Our ATEM PGM is input to the Audio to SDI, along with 4 analog audio channels. The card injects the 4 audio signals on channels 1-4 of the SDI stream. The output of this card becomes our final output to the world, and any internal recordings we make locally. We hand this to our uplink or fiber transmit path, they in turn configure their encoders appropriately, and off it goes to the other end. Once the transmit path is active we ID each audio channel in turn to make sure everything is as expected on the other end. Then it's on with the show!

Re: Live broadcast with multi-channel audio

PostPosted: Tue Nov 14, 2017 8:19 am
by Alexander Kinov
Thank you very much! I appreciate the information.

Let me see if I get it right. As and example - I connect the PGM out of the ATEM switcher into SDI in of the Audio to Sdi converter. I set the converter to receive analog signals from all the 4 inputs and to embed them on channels 1-4. Does this mean the converter will remove the audio coming on channel 1-2 from the ATEM switcher (it is usually sent on 1-2) ?

Re: Live broadcast with multi-channel audio

PostPosted: Tue Nov 14, 2017 1:27 pm
by Xtreemtec
Yes your thinking is right. It will overwrite channels 1&2. If you want to keep 1&2 you can set the Audio embedder to start at channel 3. So you will keep 1&2 en get 3 to 6 for the embedder. ;)

Re: Live broadcast with multi-channel audio

PostPosted: Tue Nov 14, 2017 11:36 pm
by roger.suski
Is that really the case, starting at Ch3? Best I can see (with the BMD audio to SDI) is keeping Group 1 intact (pair 1, skipping 2) then doing embed on Group 2 (pair 1 and 2)

Like Mamba says, coordination between encode and decode is the main thing. Regardless of whether the "datapath" is copper/fiber or through space and back, it is all bits. Most "contribition-level" encoders should handle what you're after.

Re: Live broadcast with multi-channel audio

PostPosted: Wed Nov 15, 2017 7:25 am
by Alexander Kinov
Well, the audio mixer (digital mixer with few different mix layers) stays next to the rack. I have 4 analog audio outputs. Instead of sending two of them into ATEM and two into converter I just have to connect all of them into the converter. I'm not planning to use audio feed from any of the video sources (cameras), so I don't really need to connect 2 of the channels into the ATEM. Simple solution.
As for the encoding. When we send to space and back we usually work with guy who is one of the best, knows what he's doing and has great experience. But when we send the signal by internet, we often use different people with different equipment, so I don't really know what they are doing. So, I prefer to keep everything as simple as possible.