I been thinking about mp3 conversion lately. I don’t know exactly how it works. I know the general theory but I don’t know anything else. One of the questions I have always wondered, “Is it necessary to use bit reduction and convert a 24 bit song to 16bits before mp3 conversion?”
After thinking about it, I realized that it probably doesn’t matter. It would most likely depend on the encoder’s ability to deal with 24 bit files. Just going through the simple logic of it, any gains by using dither would be negligible due to the fact that the file is being converted into a lossy format. Which mean any distortion caused by truncation at the 16th bit, would probably not be noticible for two reasons. Reason 1 is that it would mostly likely be masked by the degradation caused through the encoding process. Reason 2, either way the effect of the dither will be un-noticible except in extreme circumstances of bit reduction or in certain listening situations.
My answer to the question of whether a 24bit wav should be converted to 16bits with dithered applied prior to conversion to an mp3 would be, no. Recently I had to make an mp3 out of one of my projects in Logic Studio. The project was a combination of audio and virtual instruments. I do everything in 24bit when I write music. I didn’t even bother to bounce it out and convert to 16, instead iIjust did a straight bounce to mp3 conversion that is in the bounce options. I did not notice any terrible “nasty distortion” from the truncation to 16 bit. All I heard was the usual lossy sound of a 128kbps mp3.