I am trying to measure misc. sounds (such as room sounds and other things) w/REW, and I am not sure if I am doing it right or not.
Like bruce wrote, I loaded the software like I was going to do a speaker measurement. But, instead of plugging the line from my soundcard out to my stereo's input, I left that disconnected so no test tone was being played through my speakers.
Just for kicks, to test it out, I hit "start measuring" and unwound a roll of duct tape in front of the mic (~6" away) to try to measure that sound. I got a spectrum that looks somewhat like what I would expect from duct tape (~75 dB peak at ~4 kHz), but it goes <0 dB starting at 70 hz and lower.
What I don't understand is why it goes <0 dB. I would understand if it was dBFS, but this is dB...I didn't think there was such a thing as negative dB.
So, I am wondering...did I set something up wrong, and if not...what's negative dB? Also, I notice that the scale on the graphs bruce shows are in dbfs, but mine are in db...how does one get the data in dbfs vs. frequency in case I wanted to do that?
Mark
Like bruce wrote, I loaded the software like I was going to do a speaker measurement. But, instead of plugging the line from my soundcard out to my stereo's input, I left that disconnected so no test tone was being played through my speakers.
Just for kicks, to test it out, I hit "start measuring" and unwound a roll of duct tape in front of the mic (~6" away) to try to measure that sound. I got a spectrum that looks somewhat like what I would expect from duct tape (~75 dB peak at ~4 kHz), but it goes <0 dB starting at 70 hz and lower.
What I don't understand is why it goes <0 dB. I would understand if it was dBFS, but this is dB...I didn't think there was such a thing as negative dB.
So, I am wondering...did I set something up wrong, and if not...what's negative dB? Also, I notice that the scale on the graphs bruce shows are in dbfs, but mine are in db...how does one get the data in dbfs vs. frequency in case I wanted to do that?
Mark
