Audacity is an audio recorder, editor and mixer for Windows. You can record live audio through a microphone, mixer or from any external device that outputs an audio signal that can be connected to the line in audio input of the computer.
Furthermore, Audacity can import various sound files (WAV, AIFF, AU, FLAC, Ogg Vorbis, MP3) for editing and can export recordings in different formats.
Audio in Audacity can be edited easily and you can apply various effects to change the audio (alter volume, noise reduction, fade in/out).