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PostPosted: Tue May 12, 2015 12:47 am 

Joined: Tue May 12, 2015 12:28 am
Posts: 5
Hello all,
If you are using stereo tools in an FM broadcasting Plant how do you setup the pre-emphasis?
Audio chain consist of the following:
Stereo Tools-Analog Composite STL Transmitter-Analog Composite STL Receiver-FM Exciter.(Station Located Processor)
other Setup would be IP Codec Link-Stereo Tools Processor-Analog Composite input to Exciter. (Site Located Processor).
Do you disable all the Pre-emphasis/De-emphasis in the STL's and exciters and enable on Stereo Tools only?
Talked to several other Engineers and non of them had any real answers.
Also, I noticed there are two settings for pre-emp on the processor, one for input and one for output. Mine are setup with Pre-emp on for input only.
From what I've read so far, pre-emp needs to be enabled for input to achieve proper loudness on the stereo signal.
I'd appreciate a little help in my thinking.
Thanks


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PostPosted: Tue May 12, 2015 12:48 pm 
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Joined: Mon Mar 17, 2008 1:40 am
Posts: 11185
1st (composite signal): Send pre-emphasized output from Stereo Tool (there is no other option if you use composite).

2nd: Depends on several things.

Ideally, you would let Stereo Tool generate a pre-emphasized signal and keep it like that. Reason: Pre- and de-emphasis between devices might not be 100% identical (it should be but there might be small differences), and more specifically, they might or might not be phase linear.

However, if you are using for example MPEG2 or MP3 compression in your lines to the transmitter, then the extreme amount of highs will cause your MPEG2 or MP3 compressor to spend too much effort on encoding the highs, which might make the mids/lows sound worse. On the other hand, de-emphasizing and pre-emphasizing afterwards will probably cause much bigger spikes in the audio (lossy compression alters the waveform, and hence causes spikes; they will be bigger if you don't spend the extra effort on encoding the louder highs).

So, I don't have a real answer here either. It also depends on the equipment that you have at the transmitter site.

In short:
- Link without lossy compression: Let Stereo Tool generate pre-emphasized audio and keep it like that
- Link with lossy compression: Test what sounds better.


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