While there are so many free audio editor programs available on the internet, many of them cannot edit compressed MP3 files directly. What they do is first convert the MP3 files into WAV files in order to edit them and when you save them, they once again convert the edited WAV files into MP3 files. But all this audio format conversion affects the quality of the audio in general. If you want to edit the compressed MP3 files losslessly, then you can use the free mp3DirectCut software.
mp3DirectCut is a free and portable software for editing the audio files. You can use this program to perform various actions such as copy, paste, cut, crop, adding gain or fades, changing the volume, remove parts, split files, add or copy regions and all this without having to first decompressing the MP3 audio file into the WAV file format.
Using the mp3DirectCut software is very easy. You have to first open one of the MP3 audio files in the mp3DirectCut. Then you can go on and perform all the cut-copy operations on it. You can find all the shortcut icons for selection, cut, copy, edit and other operations in the mp3DirectCut window. It also supports some of the special operations like auto-crop, auto-cue and detection for pauses.
If you need, you can open another mp3DirectCut window by selecting File → New Program Window from the menubar. This way you can copy-paste portions of the audio files from across multiple MP3 files. After having finished with editing the files, you can save the project in form of a CUE file so that you can later continue editing the file. You can also export the edited files and save them as MP3 files.
Conclusion: mp3DirectCut makes editing the MP3 audio files very easy in Windows. It does not decompress the MP3 files into WAV format before editing them and thus preserves the original audio quality.
You can download mp3DirectCut from http://mpesch3.de1.cc/mp3dc.html.