I found something:
Maybe this will help someone else
If you don't have a sound file with a -12dB 1khz sine wave test tone, Audacity can make one for you, go to the "generate" menu and choose "tone." The generator has an odd control for level, not in dB but in increments between 0 and 1, but you can always make the tone, then go to the "effect" menu, "normalize" it, then reduce the gain by 12 dB with the "amplify" effect. Then export that as a .wav file and keep it to insert in future sessions as a reference.
http://audacity.sourceforge.net/
http://www.transom.org/tools/editing_mixing/200404.audacity.html