From studio to Transmitter

Where the magic happens...or something...
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From studio to Transmitter

Post by cbugeja » Tue Jul 02, 2013 4:08 pm

I had a radio station broadcast from my church this evening. They took an output from the church's PA and routed it into their mixer as a line input. I didn't like the idea of them sharing a common ground so I inserted a DI box between the PA and their mixer and made them go into their mixer as a mic input (fairly standard procedure till here). The audio output from their mixer was perfect!
They connected their mixer to their transmitter (RF link to their main studio a few KMs away). After the transmission was over, they complained that the audio quality was really poor... they said "It is because of the DI. When you transmit, you cannot have a DI on your input, else it will increase noise, lower sound quality, thin the sound, alter the variation in sound levels, etc."

I had been a broadcast engineer for more than 10 years and for 3 radio stations and always inserted a DI between the source and my mixer, just to lift the ground and isolate the systems... I never had issues... they used to solve issues for me not create them.

For sanity's sake... Does a DI between the source amplification system (eg. the amplification system in my church) and their radio transmission system create all the above stated problems by the time it reaches their studios? Or did they have a fault in their system and wanted to blame it on us instead of facing reality?

Your opinions are greatly appreciated!

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Re: From studio to Transmitter

Post by rockmanac » Tue Jul 02, 2013 5:13 pm

No. This is somewhat of the standard I use when I have bands providing their own mixer and audio person on my shows. I take them as a mic input vs. a line input into my board. Sometimes I can go direct from their mixer (or my outboard mixer) and sometimes I have to go through the DI box. I would suspect it was somewhere between their board and the studio if you say the audio coming from their board sounded ok. My bet is that they screwed up the send bus they were using to send to the station.

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Re: From studio to Transmitter

Post by Deep Thought » Tue Jul 02, 2013 10:28 pm

About 35 years ago the station I worked at ran a lot of live shows from all over town and we used a mic snake splitter with about $1,000 worth of UTC dual secondary transformers doing the heavy lifting. The audio was perfect from a formal auditorium or the worst dive bar. The reason we built the thing was due to one of the engineers almost being electrocuted due to 110 v being on the mic cable shields at a particular hole in the wall, which we didn't know about until he grabbed a mic to tape one of ours to. There was enough current that the spot where the two touched was smoking.

Isolating the two systems is a very good idea.

If they continue to bitch about audio quality, find a quality 600:600 ohm transformer and provide them audio feeds through that. No active electronics and a +20 dBm saturation point. If the radio station can't get that back to their studio in one piece it's their fault. I suspect that in this case they were over-driving their Marti...

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Re: From studio to Transmitter

Post by Baylink » Wed Jul 03, 2013 11:10 am

Gee... I wonder why the broadcaster didn't do a soundcheck before air, to make sure it sounded good...

If you work with them again, insist. Set up as you did this time first, and if they don't like it, then try it without the DI -- though, like everyone else, I can't imagine how that would be the failure point, unless the DI's broken.

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Re: From studio to Transmitter

Post by cbugeja » Thu Jul 04, 2013 1:08 am

Thanks a lot for your replies... You've confirmed my sanity :)

The suggestion to try with and without the DI crossed my mind, but when I test I have to make sure that they do not know when the DI is connected or not... They have to be "blind", else they will spout back the same stuff even if the quality with the DI is the same or better.

I'll try to find an audio transformer in my workshop and hide it in the PA cabinet, lock the cabinet and place an output XLR socket next to it saying "Output". This way they will only focus on finding the fault in their stuff and not try to put the blame on us. We will be working again another time or 2 this year... so I have some time to prepare :)

The sound check is a good suggestion... problem is that when they connected I was not present. Next time I will make sure I will be present.

Thanks again for your feedback!

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