MP3 Bit Rate Quality Detection through Frequency Spectrum Analysis

Question

Does exist any program that detects the bitrate of an mp3? I'm not talking about the effective bitrate that the file has been encoded with, but the real bitrate that can be calculated only by frequency spectrum analysis.

For example, to explain more clearly what i mean for the two kinds of bitrates: if i have an mp3 encoded in 128kbps whose size is 1 MB, and then i transcode this mp3 to 320kpbs whose size becomes 3 MB, i will have the same identical audio track, but with different sizes.

But.. if i have a 320kbps mp3 and i transcode it to 128kbps i will lose some quality and therefore some file size.

But still, i have no way to verify that 320kbps is my mp3's real bitrate.

if nobody can understand my lame english, details are explained in this paper: http://www.fileden.com/files/2009/2/14/2321055/My%20Documents/MP3%20Bit%20Rate%20Quality%20Detection%20through%20Frequency.pdf

Answer 1

Only thing that you can easily determine from the frequency spectrum analysis is what is the sampling frequency of the input mp3 file.

For example, if your mp3 is sampled at 44100, you won't have any sound above 22050hz and that will be clearly visible on the spectrum graph.

Since you are crossing into transcendental domain here, try this:

• encode mp3 to 128kbps
• transcode it to say 320kbps
• try RAR-ing or 7Z-ing resulting file and original file. Observe compression ratios.

Their 'entropy' ie. randomness will differ, and maybe that number will tell you something about how much information is 'fabricated' in bitrate expansion during transcoding.