Help Understanding Signal Cal.

[hoofenshnoz]

Hey guys,
Here is my first test of Rew using standard laptop soundcard with the RS 4050 meter. I calibrated soundcard/spl meter and then i put pink noise in the system to -18db under speaker cal. but once i got my signals to ok and did my sweep it gave me a distortion alert. I read about this and it told me to lower my sweep volume which is default to -18dB. Well, I ended up having to lower this to -30dB before the distortion alert went away. So now, isnt my signal cal mest up if the -18dB calibration distorts? Because i had to record the sweep 12dB lower? Anyways some clearity on this would be great help. Here is the graph i did with the sweep calibrated to -18dB with a -30dB sweep.

[brucek]

Rew using standard laptop soundcard with the RS 4050 meter

Laptop internal soundcard mic inputs are not allowed for use with REW. You require a proper line-in interface. Most people use external USB soundcards with laptops.

brucek

[hoofenshnoz]

ok! got it, i have a soundcard im going to be using i just thought it was possible to try it out with the internal soundcard.

[brucek]

i just thought it was possible to try it out with the internal soundcard

The microphone input jack offers quite high gain since actual inexpensive computer microphone signals are quite low in relation to a line level signal. This extra gain at the mic inputs front end usually results in increased noise.

Mic inputs usually enjoy a very limited bandwidth that is designed to comply with a narrow voice frequency range that a cheap microphone would supply. The port often supplies a 5 volts bias signal also.

Note when posting graphs: For subwoofer plots, always use the standard Vertical graph axis of (45dB - 105dB) and the Horizontal graph axis of (15Hz - 200Hz) using the Graph Limits button in the top right corner of REW. Use a measurement start frequency of 0Hz and an end frequency of 200Hz with a 75dB target. Use the appropriate target line that matches your crossover.

brucek