Does converting an mp3 format audio file to m4a format makes audio quality better ? I was just wondering if mp3 is lossy. How it can generate lossless m4a file after conversion. I know mp3 can be converted to m4a but will this m4a file will give the same audio quality as compared to an originally created m4a file.
It is mathematically impossible to improve any digital audio stream to a "Better Quality" by a simple conversion to said file type. A poor quality mp3 can be "converted" to any format you like but the poor quality will remain and, as mentioned, you may even lose a bit in the conversion.
There seems to be some misconceptions floating around out there about stepping up quality as many programs allow you to import lossy or low quality audio into a workspace that may be set at a high quality/resolution. That being said the lossy or low quality audio does not get any "better" in doing so. The fundamental problem is that you cant insert samples into a track. you can estimate them (although aliasing can be an issue) but you can't fundamentally insert them.
Just to add & clarify that
m4a is a container format, actually the same spec as
mp4, merely a different file extension, and therefore can contain either
AAC (lossy) or
ALAC (lossless) formats -- or even
mp3! -- so the question as stated doesn't make sense (same with many of the answers & comments).
Regardless, the simple answer to the intended question is that converting a lossy format to a non-lossy format inherently can't make audio quality "better" (literally: no new information can be added to the data via this transformation). In theory, the very best you can do is achieve the same quality; in practice, you'll probably lose a little quality, but carefully selecting the right conversion & format options you might not notice the degradation.
I think it's important to understand: Rakesh, what is your motivation for converting? Also, within M4A, are you specifically referring to http://en.wikipedia.org/wiki/Apple_Lossless ?
Clarifying this will help with useful answers.