The EXT MIC input on the Zoom H4N is specified as:
mini stereo phone jack Input impedance = 2 kΩ Input level = −7 dBm _ −47 dBm (0 dBm = 0.755 Vrms) so that's 0.346 Vrms --> equals −7.23 dBu to −47.2 dBu; see discussion
The REC OUT of the Yamaha MG82CX mixing board is specified as:
dual RCA jacks Output Impedance = 600 Ω Appropriate Impedance = 10 kΩ Nominal Level = Lines –10 dBV (0.316 V) Max before clipping = +10 dBV (3.16 V) (where 0dBV = 1 Vrms)
Now −10 dBV is −7.78 dBu. I see the alternate labeling in some places in the documentation, too.
The dBm = 0.755 Vrms might be a typo: “dBm unloaded” commonly noted as dBu and used for this purpose is 0.775 Vrms. But if taken as written, the Input Level would be 0.337 Vrms to 0.00337 Vrms, which is −7.23 dBu to −47.2 dBu.
The nominal level means the highest level that's only occasionally exceeded. So I want to match the nominal levels. 0.316 is lower than either 0.346 or 0.337, so it ought to work.
In fact, before the performance my auto-level decided that “60” was a suitable value. But when someone started talking into the microphone, it pegged the scale and the auto-level turned it all the way down with no relief. The signal was too hot.
Why did it not work?
Related might be my understanding of the specifications.
On the input: does the Input list the available nominal levels I can achieve through using the Level control? Or is it the clipping point at the lowest setting to the quietest discernible sound at the highest setting? Or something else?
On the output: There is no volume control for the REC OUT, as it feeds directly from the Stereo Bus. If the nominal level is the loudest it normally handles with occasional excursions, the clipping level would be only slightly higher voltage. So why is it actually a 10× difference?
The input impedance is lower than the mixer wants, but that would draw more power and drop the voltage if it couldn't handle the current.