Actual Customer Question:
If I need a microphone level output to feed to a mic level input, can I just decrease the output gain of the RIU channel? I need a signal level of 10-200 mV p-p; the mic impedance is 600 ohms.

Actual ASTi Answer:
The RIU outputs are nominal line level, with very low impedance; connecting an RIU output directly to a 600 ohm input is perfect.

Concerning output levels, we'll assume that you are connecting a mic to the RIU, then using Model Builder to loop this mic signal back out the RIU output. Here's the procedure:

First, make sure that the RIU input is set up correctly. The mic input signal strength should register peaks of about 0.2 to 0.5 on the Vox object meter in Model Builder. Adjust the input gain (either RIU jumper or external analog amp) as needed.

Second, set up your model such that all of the signal and feeder objects (vox, buffer, input and output RIU feeders, outputs) have gains of 1.00.

At this point, if you want to be cautious, tie a 600 ohm resistor across the RIU output, and measure the peak-peak signal to see if it's in your range.

If the output signal is close to being in range, but you would like to adjust it up or down by 6 dB or so, adjust the buffer gain. The signal quality should be OK if you keep the buffer gain between about 0.1 and 3.0.

Also, be aware that some computer mic interfaces provide mic bias. One one particular project, this was the case with an SGI mic input. It was designed to work with an SGI microphone that requires bias voltage. The SGI mic input had a hefty DC voltage that we had to block using a cap. Check the PC input to see if it has a bias level.

Note: The output line of the new version RIU can either be DC-coupled or capacitor-coupled. If the PC audio input is providing bias voltage, you should set the outputs to capacitor coupling. To do this, remove jumpers J5 through J8. Note that this places a capacitor in-line with the output audio output + line. If there is DC bias on both sides of the PC mic line, you will need to connect caps outside the RIU. This is an unlikely scenario; we've never encountered it, at least.