I need to record vocal mono on the same desk as my 3,1 MP for screencasts. I'm considering an mxl 990 condensor mic as I've read it does a decent job at isolating most external noise. But my internal hard drives and MP fan have that constant idle noise hum. I realize I'll still have to do post noise cancelation filtering for each session. Is there a better condenser USB mic for about the same ~$100 price point that can better isolate the vocal? I'm trying not to use my Mac Book for the audio recording as my MP records the screencast at a much smoother frame rate for things like zoom in/out.