Quantifying an audio file?

I have several hundred classical orchestral audio files. Some are flac or wave that I edited in Audacity & saved as high BR mp3. Others are original mp3, which require editing & exporting in Audacity.

Among those are numerous duplicates. For the sake of this discussion, assume I have two 320BR mp3 from different sources of the same piece.

Perhaps one of those originated as a flac,was edited & then saved as 320br. The other could have been originally a 200br mp3, edited & exported to 320br…I just don’t know.

I’m familiar with computer & photo graphics, terms such as dpi or ppi, where a higher number usually indicates a better quality graphic/photo.

I’m looking for something in Audacity that could provide a similiar number to thati. I could than distinguish between the two (or more) 320br files & keep & edit the better quality one, ie, the one that has the most bits/samples(?) of music.

I don’t know how to read a spectrogram. Reading the manual, it didn’t mention that it could provide that number.

I know I’m probably missing something obvious, but the brain cells have run into a road block.

Really, the only way to know is by listening. Some people use the spectrum but “better looking” doesn’t always mean better sounding. MP3 usually throws-away the highest frequencies (and you can usually see the difference from the uncompressed original) but if you hear a compression artifact it’s usually not the loss of high frequencies that you hear (especially with higher bitrates).

Even if you can hear up to 20kHz in a hearing test, in the context of music the highest frequencies are usually masked (drowned-out) by other not-quite so high frequencies. MP3 mostly works by analyzing the file and throwing-away sounds that are masked. You can tweak MP3 to keep more of the high frequencies (and the spectrum would look better) but then it will have to throw-away something else instead (that may not show-up on the spectrum) and it might be worse.

Note that when you edit an MP3 in Audacity (or any regular audio editor) it gets decompressed. If you re-export as MP3 you are going through another generation of lossy compression and some “damage” accumulates. You may not notice the quality loss but it’s something you should be aware of.

There are special-purpose programs like mp3DirectCut that can do some limiting editing without decoding.

Since MP3 is lossy compression it’s more like high-low JPEG compression. You can have a high dpi JPEG with low-quality. With video you can have high resolution but high compression (low bitrate) and you can get “pixelization”, especially when there is lots of movement.

Higher bitrates (less compression and bigger files) tends to indicate higher quality. But it’s not really straightforward… CDs are 1411kbps. FLAC is lossless compression and it can be almost half of that with no loss of quality (no loss of data).

With lossy compression you have to throw-away more data to get a lower bitrate. But a high-bitrate MP3 can often sound identical to the uncompressed original (in a proper blind listening test) and a 256kbps MP3 may sound identical to the original and identical to a 320kbps MP3. It’s unpredictable because some sounds compress easier than others. Or, VBR (variable bitrate) adjusts the bitrate moment-to-moment because you don’t need 320kbps for silence or simple sounds.

To make matters worse, a high-bitrate MP3 could have been created from a low-bitrate MP3. I have some high-bitrate MP3s (256kbps+) that sound as bad as a '90s 64kbps MP3. Someone probably took low-bitrate MP3s or ripped them from a CD that was originally created from low-bitrate MP3s and re-encoded them at a high bitrate. At least they probably didn’t lose any more perceptible quality with that re-encoding!

Thanks for the detailed explanation…informative.

Seems like the magic number I’m looking for isn’t easily attainable.

With my classical music, & I’m stuck with only a mp3 as the source I usually save the result of any editing as flac. My home system (Sonos) plays those. My car doesn’t, which is OK as cars ain’t the best for enjoying that genre.

I usually toss any very low BR mp3 I get…I may like a tune, but I do have my standards!*

*I seem to remember a girl saying that to me, in a Land & Time Far Away…sigh…