Would there be a difference in quality converting an mp3 from 128 bitrate to something higher such as 256?

Answer 1

If you have an mp3 encoded at a bit rate of 128, there will be no advantage of converting it into a higher bit rate. Mp3 encoding is "lossy" which is to say, data that is thought to be insignificant is discarded in order to compress the file. Once this data is discarded you cannot recover it. So converting the bit rate of a file encoded at 128 to 256 will do nothing for the sound quality of the file. However if you have the original unecoded music file and encode it at the 256 bit rate you will have a better sounding file.

Answer 2

the higher the original bit rate the better when originally converted to mp3 but to convert or upscale after would probably make little noticable difference