[TZ] [Tech-Assist] Discrete audio feed from 8100A

[Martin Acuff]

Ron,

There are a few things you should be aware of:

First: streaming encoders don't like clipped audio peaks.
Second: depending upon the output bitrate of the encoder, the 15kHz audio bandwidth won't be correct for the encoder's input.
Third: encoders don't like pre-emphasized audio, even if it has been de-emphasized.
Fourth: IIRC, Bob once told me that the load impedance presented at the test jacks needs to be on the order of 1M ohm.

Will it work? Yes.
Will it be optimal? No.
There are better ways to pre-process audio for streaming.

The best-suited de-emphasis circuit schematic is available online: it's the Orban designed de-emphasis for the 8101B. You'll find it here:

<ftp://ftp.orban.com/Bulletins/De-emphasis_Circuit.pdf>

Happy Thanksgiving,
>-- Marty

From: Ron Castro <ronc at sonic.net>

Brain Trust:

I have an 8100A/XT2 feeding composite to an RF STL system and I want to add
a Barix to feed an Aux transmitter site over a digital link.  I would like
to feed de-emphasized discrete audio from the test jacks on the of the 8100A
to the Barix, but I'm not sure how to do that properly.  I know about the
7.5 K Ohm resistor and .01 uf cap used for testing, but will this load down
the internal circuit of the 8100 if used permanently, and will the levels be
right for the Barix?  BTW, the Barix is the inexpensive one with the Hi-Z
(actually 4 K Ohms according to the spec sheet) line input.

--
Ron Castro
Chief Technical Officer
Results Radio, LLC