I have seen this question come up a lot in the search terms that people use to get to Rooster’s Rail. So much so that I decided to answer the question here.
The short answer is no.
So I guess that deserves an explanation. Mp3 is an audio format that uses complicated compression formula that results in a much smaller file but retaining audio quality based upon what bit rate and sample rate was used to encode the file. Simply put:
Smaller file size = less quality
That is lower bit rate and sample rate.
Bigger file size = better quality
Higher bit rate and sample rate
Then there are mixes of the sample rate and bit rate that produces results that are in-between. There is also a file format called VBR or variable bit rate. I am not going to go into that here but that is basically where the bit rate varies according to the complexity of the music or audio file and results in a file size that can be smaller but retains a higher quality than an otherwise static bit-rate.
This bit rate and sample rate are dictated by the person that encodes the original file. The original file is often a .wav file wich is very large but of high quality. For example The Global Geek Podcast as a .wav file and goes for about one hour is over 500MB. Once encoded to an .mp3 file is between 20 and 25MB. I dictate the bit-rate and sample rate when I encode the file.
So lets say that you get that file which is encoded at 64bit and a sample rate of 44100khz. You want to lower the bit rate to make the file smaller. Sure you could using a program such as RazorLame, decode the file and then re-encode it at a lower bit rate such as 44bps (bit-rate). But the resultant quality would be lower than if I had used the original .wav file and encoded it at 44bps. This is because the best quality that you have is 64bps, that is as good as it gets. The quality can get no better than that. So in conjunction with the fact that .mp3 is a lossy file format and will get worse in quality every time it is opened and closed or encoded you end up with pretty much crap.
Same can be said if you wanted to go up in quality and therefore bit-rate. If you had a file that was encoded at 64bps there is no way on earth to make it better quality than what it is. If anything going up in bit-rate will make it worse because it will very successfully highlight the imperfections that are a result of encoding something as an .mp3 file. When a file is compressed in this way it decreases in quality regardless of the bit-rate. It all has to do with the fact that to make it a smaller file you have to ditch some of the data that the original file contains. That said it would take a very good ear to detect the imperfections in a high bit-rate encoded audio file, but it is there.
Moral of the story is that if you have an .mp3 file leave it as it is. Unless you can get the original source file there is no way to increase or decrease the quality and maintain any sort of standard about the quality of it. I hope this clears up a bit of confusion that there appears to be out there.
I tried to think of a good analogy to use for this post and could not, but this is the lame one that I did come up with:
Trying to change the bit rate of an .mp3 file is like baking a cake and then deciding that you want to know how to make it so it has less sugar in it than what you originally put in it and still have the cake!
Rooster's Rail 