Hack 38. Search Audio for Hidden Messages
Use a simple effect from the SoX play tool to check audio for hidden messages.
Backward messages in music (or "backmasking") have provided quite a bit of controversy over the years. Music from the Beatles in particular has been popular to listen to backward in hopes of discovering hidden messages (one of the most famous being the phrase "Paul is Dead" at the end of "I'm So Tired" from the White Album). Since the Beatles, there have been numerous claims that music from a number of musicians contains hidden messages that are heard when played backwardmessages that contain references to Satan, other evil things or, most commonly, drug use.
Of course, back in the days when most people listened to music on records, it was relatively easy to listen to a song backwardyou just rotated the record on the turntable in reverse. This method won't exactly work (or at least not easily) for tapes or CDs, but for digital content, Linux has just the tool to aid you in your search for backmaskingthe SoX tool and its frontend called play.
SoX is a universal sound sample translator and allows you to format audio with a number of interesting effects. SoX provides two frontend applications, play and rec, that make it easier to play and record audio, respectively (the rec frontend is discussed in [Hack #33]).
SoX is a popular program and should already be packaged, and possibly even installed, by your distribution. If not, you should be able to install it using your distribution's package manager. If for some reason you don't have a SoX package available, download the source from the official page at http://sox.sourceforge.net and compile it according to the included installation instructions.
With SoX installed, pick the track you want to play backward, and test it by playing it forward:
$ play file.mp3
The play tool will start playing the audio file back to your speakers. Make any mixer adjustments you need at this point. To play the file backward, just add the reverse argument to play:
$ play file.mp3 reverse
Keep in mind that the reverse sound filter will require some drive space to store the temporary sound file it uses, so it might take some time for play to finish processing large files, particularly on a slow system. Once play is finished processing the file, it will start to play it back backward. Listen to the file all the way through, jot down all the English-sounding words you hear, and then hit Ctrl-C to exit play.