Blackmagic Forum

Hi,
I'm planning a new setup where pgm audio will come from an A&H mixer to a Constellation 8K via MADI. I won't do any MADI out from the Constellation.
MADI is new to me, so I'm wondering if this should be plug and play as long as sample rate is the same on a point to point setup like this, or do I need to think about external sync ect?
Thanks!

I would expect so. You would just need to do your mix outputs or tielines from your A&H console to the appropriate slot with the MADI card in it. I am not sure how the routing would work on the BMD side but I do believe it treats every input as a stereo input so you will have to take that into account on both the A&H & BMD side of it.

Digital audio always needs to be synchronized. The Constellation cannot be synchronized to audio word clock or MADI, it has to be the master clock or slave to a video reference. Two ways to do this:

Either you connect the MADI out from the Constellation to your audio console, even if you don't use any of the channels, and sync your audio console to MADI, thus making the Constellation the master clock or you get an external master clock that provides frequency locked tri level video sync, like the Tascam CG-1800 and sync your audio console (via word clock) and the Constellation (via tri level sync) to it.

Cybershadow wrote:Digital audio always needs to be synchronized. The Constellation cannot be synchronized to audio word clock or MADI, it has to be the master clock or slave to a video reference. Two ways to do this:

Either you connect the MADI out from the Constellation to your audio console, even if you don't use any of the channels, and sync your audio console to MADI, thus making the Constellation the master clock or you get an external master clock that provides frequency locked tri level video sync, like the Tascam CG-1800 and sync your audio console (via word clock) and the Constellation (via tri level sync) to it.

Euhhmm The Constellation 8K does a fine job without ANY synchronization.. We are doing festivals and an external company does the Audio mixing for us. Getting ONLY Madi output from him which we plug into the Atem and we have not had ANY issues with audio. So the Atem is capable of syncing on the Madi input it gets without external reference if you ask me.. Works for 2 years without issues now.. Done like 20+ jobs..

That's ... interesting.

So the Constellation resynchronizes the MADI inputs? I've read of regular clicking noises when running unsychronized, but maybe that was MADI out from the constellation to a console.

Anyhow, it's still good practice to run digital audio equipment on a common word clock and that additional BNC cable from the Constellation to the audio console sure doesn't hurt.

Oh for sure.. But since the Constellation has no Word clock in.. It might introduce more issues by syncing the audio desk to the constellation, compared to let the constellation free sync to the Madi.

And honestly i would not know why an Atem would not be capable of retrieving a clock from a rather slow audio digital audio protocol ( Slow compared to 12G-SDI clocking as Madi is 125Mbit/s )

Interesting. Reclocking Madi !? That would very much surprise me as you usually have to pay a lot of money for a sample rate converter that can handle MADI or similar multichannel interfaces. Look at the optional SRC card for the Appsys Multiverter for instance ( which I have two of , one at work and one in my private system ),

To bad that BMD´s manuals are so lacking about these issues.

You can't just resync audio by doubling or dropping a sample like you drop or double a video frame to resync, that's why it amazes me that the Constellation obviously does it. But thinking further it does have to have that logic to resynchronize audio together with the video on the SDI inputs, so applying the same logic to the 64 MADI channels should be possible. For me as an audio guy who came to doing video during the pandemic it's still amazing.

Cybershadow wrote:So the Constellation resynchronizes the MADI inputs? I've read of regular clicking noises when running unsychronized, but maybe that was MADI out from the constellation to a console.

YEs .. I was used MADI from Constelation 8K into Multiverter , to convert channels to AES50 .. There was clicks .. I was added SRC board and insertet it on input from Constelation and everything was fine ..

Well basically the Atem can buffer a Full 4K frame of each of the 40 inputs at the same time.. So why would it not be able to buffer a few audio frames at 125mb/s

Those FPGA's can do Awesome things by pushing the Madi input into a FIFO buffer too, Determining the start of the Madi stream packet. And based on the internal Frame clock pull data from the FIFO buffer at the correct point.

Audio gear need a SRC converter / beefy DSP to do something similar.. As normal audio gear does not have FPGA's that cost 1K each and handle anywhere between 12 and 20x 12G differential inputs per FPGA..

The Constellation 4ME / 8K has about 6 FPGA's inside if not mistaken..

Could not find the actual picture i have in my head.. But here is some indication:

Thanks for the replies!
My conclusion is that I'll just have to try and see what works when I get the equipment. I at least know what might cause issues if I have any. Using the Constellation as sync master for audio might cause some issues since there will actually be two A&H's, one for FOH and one for streaming, linked with fibreACE's. The FOH mixer would be the preferred master since it is always active.

Thanks again!

I actually asked BMD support this question and got a reply today :

Enquiry: Hi ! Does the Constellation 8K re-clock the incoming the MADI signal and synchronize it to the internal video ?

Reply:
Thank you for contacting Blackmagic support with your query. I can tell you that the MADI input will synchronise to the video reference applied to the Constellation. If reference is not present, then the MADI will freerun.

Best regards,

Steven Hemsley
Senior Broadcast Specialist

We’re using a Prodigy MC to send 64 Madi channels into an Ultrix over fibre. It’s freerunning with no issues thus far.

Good Luck

That's really nice. Standalone devices that do asynchronous sample rate conversion are really expensive, let alone 64 channels of ASRC.

Also add, if running at 48khz then the Madi card in the A&H will be doing sample rate conversion so that should help with any sync issues.