Re: help on card sound
That's getting out of my experience, sorry! I've never shopped for an audio spectrum analyzer (also called RTA or real-time analyzer). I would expect a good instrument to cost many thousands of dollars.
Small PC audio analyzer programs generally don't include a calibrated microphone. If you connect a random microphone, it will have unknown sensitivity, unknown frequency response, and unknown directivity, so you can't directly measure accurate sound levels. However, you could use it to measure the difference in amplitude between two sounds of the same frequency.
I'm guessing the Zelscope program uses a 1024 point FFT for the spectrum display. that may not be enough points to reveal a 0 dB tone above your 40 dB room noise, depending on the frequencies characteristics of your room noise. Most analyzer software provides a selector for increasing or decreasing the number of FFT points. More points lowers the noise floor, but it also slows down the measurement.
In the past, I've seen several free or low-cost audio spectrum analyzer programs on the internet. Keep searching, and try some of them. You should see pretty quickly if your tone is visible above the room noise.
If you have MATLAB, I could show you a few lines of code that uses the microphone or line input of your PC's sound card to display a real-time frequency spectrum.