The Leviathan wrote:

-Download and use Audacity for your commentary.

-Make sure that your input device is your microphone of choice.

-Record about 6 seconds of dead air(sounds you don't want in your commentary(typing,fan,computer humming,etc)
afterwards go to effects>noise removal>get noise profile. (This will remember the noise you don't want in your commentary.

-Open a new file and record your commentary track as you would.

-After you've finished go to effects>noise removal.

Make sure to have these parameters set:

Noise Reduction: 25db

Sensitivity: 3.09

Frequency Smoothing: 400

Attack/Delay Time: 0.15

Click ok(make sure it's on remove and not isolate)

Afterwards go to Effects>Compressor(makes loud noises louder and softer noise quieter)

Make sure these parameters are set:

Threshold: -10db

Noise Floor: -30db

Ratio: 6:1

Attack Time: 0.5secs

Decay Time: 1.0secs

Click ok.

Next go to Effects>Treble and Bass

Set the bass to 3.0db

Voila, you now have perfect audio.

After that, go to file>export and export the file as an mp3.

Most editing software has a "ducking" option for audio tracks meaning that when a certain track has ducking enabled, the other tracks will go down in volume.