Feeding sound to RR
A lot depends on the exact scanner and sound card you are using. However, I would never run a feed with my scanner volume set to full. I strive so that settings are about 50% (12 o'clock).
The first issue has to do with where you get the audio from the scanner, and the model of scanner. Most of the hand-helds I looked at had resistors feeding their headphone jacks, and that played havoc with levels and brought in hum (a ground loop). I am using base scanners (PSR-400, PRO-433, etc) with EXT SP jacks. One side of the signal from the EXT SP jack on my scanners is a true ground.
The next thing I did was to use audio isolation transformers between the scanners and sound card inputs. Because I am using the $1 sound cards from eBay (which work great), and they only have Mic inputs, I also attenuated the signal with the transformer (step-down).
Another error people make is using the PLAYBACK sound mixer settings. You want to use the RECORDING sound mixer settings. You'll need a digital meter to "see" what the true level is when you make the adjustments. There is a thread or two here on RR on the topic (with links to meters people are using).
