[brucek]

Not sure how to calibrate sound card, but C weighting checked on REW, including C weighting SLOW on Radioshack digital SPL.

I wouldn't take any measurements until the soundcard had been calibrated and you have downloaded the proper meter calibration file. They will be quite inaccurate until you do so.

Read REW Help Files on calibrating the soundcard.

Download the meter calibration files from our download page.

Once that's complete and you've checked the soundcard calibration file for accuracy - take some measurements.

brucek

 

[brucek]

I have a question is if I use use the left channel as reference, do I still need to calibrate the sound card?

No, but I highly recommend you don't use the "Left Channel as Reference" method and switch back to using the soundcard calibration file method.

brucek