We are making progress. Thank you. Thank you Thank you I have a calibration curve - sort of. The top curve is a measurement with the cable connected instead of the SPL meter. The second curve is the calibration curve.
sound card calibration vs loopback measurement.jpg
Two questions.
1. What curve do I look at - Do I use the one tagged "Measured"
2. Any idea about what is going on above 500 Hz.
Thanks for your patience.
Dan