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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 & Laptop).

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

1000Hz test Signal Noise Levels

A few questions:

  1. 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.

  1. 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?

  2. Am I thinking about this in a wrong way being a newbee?

Thanks for your help.

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    $\begingroup$ The practical answer is, you need to get some decent recording equipment, especially if a newbie. You can remove the noise by simply producing that same sine wave, but that defeats the purpose, because in general you don't know what is signal and what is noise. Even top of the line software won't arguably give satisfactory results, so I would abandon the project at this point. $\endgroup$
    – Dole
    Sep 29 '16 at 1:40
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If you know exactly which signal you want to record you could use a bandpass filter for this frequency. Bandpass in Freq Domain, from Wikipedia

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.

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