Audacity (free audio editor and recorder)

Audacity is free software for recording and editing sounds. Downloading Audacity is a great alternative to purchasing expensive audio editing packages such as Sound Forge and Adobe Audition, as well as being easier to use.

Note that if you want to export mp3s you will have to download the LAME MP3 Encoder called Lamenc.dll by doing the following:
1. Go to the LAME download page.
2. Click on any link from the list of links.
3. When you have finished downloading LAME, unzip it and save the file lame_enc.dll anywhere on your computer.
4. The first time you use the "Export as MP3" command, Audacity will ask you where lame_enc.dll is saved.

Audacity's Features

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Editing:
:: Easy editing with Cut, Copy, Paste, and Delete.
:: Use unlimited Undo (and Redo) to go back any number of steps.
:: Very fast editing of large files.
:: Edit and mix an unlimited number of tracks.
:: Use the Drawing tool to alter individual sample points.
:: Fade the volume up or down smoothly with the Envelope tool.

Recording:
:: Record from microphone, line input, or other sources.
:: Dub over existing tracks to create multi-track recordings.
:: Record up to 16 channels at once (requires multi-channel hardware).
:: Level meters can monitor volume levels before, during, and after recording.

Effects:
:: Change the pitch without altering the tempo, or vice-versa.
:: Remove static, hiss, hum, or other constant background noises.
:: Alter frequencies with Equalization, FFT Filter, and Bass Boost effects.
:: Adjust volumes with Compressor, Amplify, and Normalize effects.
:: Other built-in effects include:
:::: Echo
:::: Phaser
:::: Wahwah
:::: Reverse

Plug-ins:
:: Add new effects with LADSPA plugins.
:: Audacity includes some sample plugins by Steve Harris.
:: Load VST plugins for Windows and Mac, with the optional VST Enabler.
:: Write new effects with the built-in Nyquist programming language.

Sound Quality:
:: Record and edit 16-bit, 24-bit, and 32-bit (floating point) samples.
:: Record at up to 96 KHz.
:: Sample rates and formats are converted using high-quality resampling and dithering.
:: Mix tracks with different sample rates or formats, and Audacity will convert them automatically in realtime.

Analysis:
:: Spectrogram mode for visualizing frequencies.
:: "Plot Spectrum" command for detailed frequency analysis.

Import and Export
:: Import and export WAV, AIFF, AU, and Ogg Vorbis files.
:: Import MPEG audio (including MP2 and MP3 files) with libmad.
:: Export MP3s with the optional LAME encoder library.
:: Create WAV or AIFF files suitable for burning to CD.
:: Import and export all file formats supported by libsndfile.
:: Open raw (headerless) audio files using the "Import Raw" command.

Using Audacity as a freeware MIDI to MP3 converter

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I like to convert my MIDI files to mp3 with audacity for use in my SWF files. It works well and is actually a good free way to do it. All you have to basically do is play the .mid file in your audio player then hit the record button in Audacity (for the Web use 22050Hz, at 32-bit float, Mono) then export as mp3.


http://audacity.sourceforge.net/