Removing noise from Signal captured by Laptop Sound Card using Mic In (4-pole Audio Jack) I am new to Signal Processing and I need a bit of help. I need to capture an Audio signal using the laptop Sound card. But before I captured the actual signal, I tested for the noise levels.

Generated a 1000Hz sine wave from a Mobile App and recorded the Signal using the laptop Sound card using a 4-pole audio cable on both sides (Mobile &amp; Laptop).

After the Recording Audacity's spectrum analysis shows a lot of noise at all other frequencies.



A few questions:


Is there a way I can remove the noise levels from this captured signal since I know that this is a 1000Hz Sine wave?


My ultimate goal is to use the laptop Audio Card to capture the Signal and remove most of the noise.


Since I know the noise levels being introduced by the Sound Card, Can I Subtract a base line noise level from sound Card from the Signal to generate a "Clean" final signal?
Am I thinking about this in a wrong way being a newbee?


Thanks for your help.
If you know exactly which signal you want to record you could use a bandpass filter for this frequency. 


This filter allows only a part of the signal to pass, like the name implies. 
But otherwise, its hard to remove noise because this noise is over the whole spectrum.