The songs are encoded in various Bitrates these days which also increases the size of the audio file greatly. Bitrate or Bit Rate is the average number of bits that one second of video or audio data will consume. It is directly proportional to the quality of sound that the audio file produces.
There are a lot of bit rates that are used these days like 128, 144, 160, 192, 256, and 320. Amongst these 128 is the most used bit rate and at this bit rate both the sound quality and file size are balanced. But if you like to convert the audio file from one bitrate to other to reduce the size of the file if quality does not matter much or just convert the file from one format to another like wav to mp3 or other formats, then I recommend the use of Switch.
Switch is an audio file converter for Windows. It can convert wav, mp3, ogg, flac, aac, wma, au, aiff, ogg, msv, dvf, vox, atrac, gsm, dss and other formats to the format of your choice and is a small freeware that can be used any number of times.
It is a great software for not only compressing the song but also for creating ringtones, sound file for presentation and converting the song for listening in the portable audio device.