Program Audio V.S. Monitor Audio Questions

AM Radio discussion. Directional arrays are FUN!
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Program Audio V.S. Monitor Audio Questions

Post by abwdvm »

Currently our program Audio comes from the Rack in engineering. I would expected monitor audio to source from the board.

Is there any difference in Program/monitor audio as far as voltage, impedance? Or i the difference only where it is headed?
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Re: Program Audio V.S. Monitor Audio Questions

Post by TPT »

Most consoles, audio processors (for AM) are specified at +4 DBM (or, 4 DB above a reference power level of 1 milliwatt into a 600 ohm load.

Which, in this modern age, doesn't really mean much anymore. A typical modern console may use a transformerless, balanced output stage--usually a single integrated circuit with an output impedance of around 100 ohms or less. This console may then drive an audio processor with a 10 k-ohm input impedance (e.g., an Omnia One AM). Or a mono STL such as the ubiquitous Marti STL-10, with a 600 ohm transformer input.

Coming back into the board are the monitoring sources. "Program" audio monitoring is usually internally derived--another IC bridged across the console's program feed (for isolation) that sends an unbalanced feed to a selector switch--then to another IC that drives an external amplifier. "Air" or external inputs are likely designed for 10 K-Ohm bridging impedance, and quite often are driven by "IHF" level equipment (a tuner) --10 K-Ohm output at a nominal -10 db level. Thence again to the selector switch and out to the monitor amplifier--nowadays usually a rack mount version of your typical hi-fi amplifier--with the usual -10/10 K unbalanced input, or the more broadcast friendly balanced inputs, which could be 600 ohm, or 10K or???

To make more sense, the crucial questions in stacking together equipment are whether the outputs or inputs are balanced (e.g. 2 wires and shield, often mike connectors) or unbalanced (e.g. an RCA jack); and whether the input is terminating or bridging. Terminating: the impedance of the output more of less matches in input---600 ohms to 600 ohms; Bridging--the input impedance is much higher than the output (a 10 K-ohm device being fed by a low impedance balanced output such as an audio console). Then comes nominal levels--a typical IHF -10 db CD player may not have enough level to drive a console input properly since it is designed to be driven by +4 levels (and that's why the fader always runs wide open).
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