I have been experimenting with a Soundcard Oscilloscope and I am having some problems understanding what's going on! I have attached a screenshot of my digital scope setup. My hardware setup is simple. I have a male to male TRS jack running from my line out into my mic input. I have been experimenting with a simple sine wave.
When I measure the output voltage of my line out (Stereo plug - TRS) with a voltmeter I get a reading of 26mV for the right channel and 12mV for the left channel (Left and Right speakers not the left and right scope channels). However, the scope is reporting an effective voltage of 508mV rms for the left channel and the right channel (not in the screen shot) is saturated at 783mV rms.
Why do the 26mV and 12mV readings remain constant on the line out when I adjust the signal from my sine wave amplitude or change the volume and balance control of my PC soundcard? The voltmeter reading never changes. The voltage changes on the scope, but not on the voltmeter. What am I missing?
My second question has to do with the soundcard max voltage readings I am getting. When I boost the frequency or amplitude of the wave it saturates at 2 volts. I am guessing +2 and -2 is the max input/output of my soundcard? The research I have done would agree with this conclusion but I would appreciate some input! If this is the case why can't I get a 2 volt reading on the voltmeter instead of this micro volt jitter?
Thanks for your time!