If we have an MP3 file and we decode it to an uncompressed WAV file and then later encode it to MP3 again at the same sample rate - why is it that the quality gets degraded?
This is a past exam question that I can't figure out. I know it has something to do with the fact that the MP3 codec uses lossy compression, but I can't figure out at what point it would remove more from it... - can anyone figure this out? Thanks in advance!
When you encode a WAV file to an MP3, some information is irretrievably lost. When you decode the MP3 back to a WAV file, the decoder recreates something close to the original waveform, but not exact due to the lost information. When you re-encode the WAV file back to MP3 once again information is lost. The second MP3 file is of lesser quality than the original MP3 since the WAV file the second MP3 file was encoded from is of lesser quality than the original.
See this answer for an example of what happens to audio and video when you encode a video to a compressed format many times. Information is lost every time it is encoded.
Mp3 discards the frequencies that it believes the listener won't hear but it removes the frequencies that make the music sound the very best and no matter how many times you re-encode a file to .mp3 it will still discard more frequencies that make the music sound the very best.Wav cannot re-create what .mp3 has removed in any case no matter what you do because the data is permanently deleted.