Turn on your computer and open an audio recording program that is capable of loading software effects plug-ins. If you do not already have an application of this type installed, you can download one online. Popular recording programs include GarageBand, Logic, ProTools, Digital Performer, Cubase, Nuendo, Sonar and Reason. While most of these programs must be purchased, there are free alternatives available.
Load the audio file that contains the noise you wish to reduce. Use the "Open" or "Import" option from the menu of your recording program to locate and load the audio file into your audio project. If you do not have any audio file, you can plug in a microphone or musical instrument into your computer via an audio interface to reduce audio noise in real time. Consult the manual of the recording program you are using for specific instructions on importing audio files and setting up audio interfaces.
Apply a noise gate effect and a compressor effect to the audio track containing the unwanted noise. If your recording program does not have a noise gate or compressor plug-in already installed, you can download these types of plug-ins online. Commonly used noise gate plug-ins include GGate and Floorfish. Popular compressors are Blockfish VST and Waves SSL. While some plug-in effects are free, others must be purchased before they can be downloaded and installed. Determine whether your recording program uses VST, DirectX or another plug-in format before downloading or installing anything.
Adjust the levels on your compressor and noise gate. The compressor will make the audio sound more uniform and will remove any "pops" or "cracks" created by volume peaks. Experiment with the Attack, Ratio, Threshold and Release controls until you achieve your desired level of compression. Adjust the noise gate's Threshold, Attack, Release and Hold levels to filter the noise in your recording smoothly.
Playback the audio to which you have applied the noise reduction effects. Make sure that the audio does not sound chopped or overly effected in any way. Compare the new audio file to the original to ensure you have reduced the noise appropriately.