MP3 files can be split in two different ways. First of all, the audio can be extracted to WAV, split, and compressed back to MP3. Alternatively, it is possible to split MP3 without converting such files to WAV and back. This latter method is often referred to as direct MP3 splitting.
As you know, MP3 is a lossy format. When some audio is converted into this format, certain portions of audio data are discarded (lost). These portions cannot be recovered if you convert the audio back to its original format. While the discarded portions are considered to be unimportant, some people claim they can hear a difference between a high bitrate MP3 file and the same audio compressed with some lossless codec (FLAC, APE, etc.) or uncompressed (WAV PCM).
So, while converting MP3 to WAV and back may look like an acceptable splitting method, you should take into account that the split MP3 files will have slightly worse quality.
Another drawback of this method is the conversion speed. Modern computers can compress and decompress audio data very quickly, but still it takes at least several seconds for each cycle. Furthermore, uncompressed WAV files are typically 10 times bigger than the corresponding MP3 files. Saving them to a HDD and then reading them back will also require some time.
Finally, the MP3 splitting method that requires converting files to WAV and back may hit a limitation of WAV files. A typical WAV file should be smaller than 4 Gb (depending on the program, it may be 2 Gb). Thus a big file (audio book, lecture, or a complete music album) may be cut due to the limitation, with unpredictable parts created from the cut WAV.
The direct MP3 splitting method is free from these drawbacks. A program using this method copies parts of the source MP3 stream exactly as they are, without converting them to WAV and back. For each MP3 part, a proper header and other necessary data are created, which turns it into a correct MP3 file. Thus the audio stream itself is identical to the stream of the source MP3 file.
As no big WAV files are created and no conversion is used, the process of splitting MP3 into parts takes less time. Also the limitation of WAV files has no significance here.
In general, direct MP3 splitting is a far more advanced method that should be preferred, where it is possible.
You can split MP3 files directly with Visual MP3 Splitter & Joiner. The program also supports direct MP3 joining.
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