Audacity Forum

Is there a way (using audacity) to test if a .wav file was ever an mp3?

TIA

Given that MP3 works on psycho-acoustical phenomena, not electrical, I'm going with no. You can obviously tell if somebody overdid it and the show is bubbling and honky, but if they did a good job in encoding and used a high enough bitrate, you should not be able to tell. The only other way to tell would be if the MP3 encoding left artifacts behind in the WAV header, but Audacity is a supremely bad tool for getting INFO.

Koz

There are some tools that TRY to do that, but without the original uncompressed data there's no way to know for sure if there's a difference between the original and the copy you have. Tau Analyzer is one such tool.

Of course, if you buy the CD (or download a FLAC) from a legitimate source you are getting the best possible quality and if it's a CD (or FLAC) from a "big" record company it's very unlikely that it was produced from MP3s. If you download illegally from torrent sites, you often get what you pay...

I have seen an option on a program i have "somewhere" that purports to be able to tell. I don't remember where. I was looking around audacity to see if that was it. there is anj option in traders little helper that says "test wave files for mpeg". the file i'm concerned with returns " track looks like CDDA with probability 92%.". I'm not sure what that means........

If there are frequencies above 20kHz present in the file then it is likely that it has never been compressed.
The very highest quality MP3s (320 kbps) are limited to a maximum frequency of 20 kHz.
Lower quality MP3s are generally limited with a lower cut-off.

You can also use the "Spectrogram"-view; zoom out to look at the range between 15khz and 20khz. A mp3 will have holes when the high frequency content is masked by lower frequency content. Here's an example (original wav, 320kbps mp3, 160kbps mp3):

I don't understand. What is the purpose of finding this out? It's not like you can somehow revert it into .wav again, what you get is what you get.

As for the replies above, the methods can tell whether the a file labelled as .mp3 contains a lossy-compressed audio, they do not tell whether the .mp3 was compressed from a .wav source (which is what I understand the TS to be asking).

Unless there is some tag/header information that specifies the source, I'm gonna go with "no".

youTookMyNickname wrote:What is the purpose of finding this out?

I too was wondering that.

youTookMyNickname wrote:the methods can tell whether the a file labelled as .mp3 contains a lossy-compressed audio, they do not tell whether the .mp3 was compressed from a .wav source

Yes. As I wrote in my reply "If there are frequencies above 20kHz present in the file then it is likely that it has never been compressed.". Other lossy compression formats are likely to have similar characteristics to MP3.

rocko wrote:A mp3 will have holes when the high frequency content is masked by lower frequency content. Here's an example

Nice

the purpose is to try to see if a file i have on a CD was converted to a .wav from an MP3 before I burned it to disk - it's been over a decade since i burned the disk and years of free thinking has rendered some memories incomplete. I have a CD of a very rare performance of a band calling themselves "Acoustic Allstars" (Tony Rice, Sam Bush, Bela Fleck, Mark Schatz, and Tim O'Brien) performing at Red Rocks Amphitheater in 1999. This is an audience recording and is pretty high quality - i'm thinking about building a torrent and sharing. Some folks are very particular about the source of their recordings. I agree that what you have is what you have....in my opinion, fretting about the provenance of the recording is about as useful as fretting about what my motivation was in gathering the info, pilgrim..

"Test if .wav file was ever an mp3"

The word "test" implies a computer-based test - run some audio through a program, and get back a Yes or a No. I don't think that's possible (yet), but I'm willing to be proven wrong.

Meanwhile, though, there's a pair of web pages on the topic which are quite instructive:
Detecting MP3-Sourced and Mini-Disc Audio (Frequency Analysis)
Detecting MP3-Sourced and Mini-Disc Audio - Part 2: Spectral Analysis

These date from 2002 (!), and I think they come from the folks who like to record live shows by musical performers, then produce and distribute recordings without the assistance of the artists or their record companies. (Back in my day, we called these "b00tleggers") The good news is, these people are actually advancing the state of the art, and requiring high-quality lossless recordings. Check out The Trader's Den.