From the linguistics of bird calls to the military messaging of buglers, sound has a universal role to play in conveying signals and messages. But the messages contained within a piece of audio are not always laid out in clear view.
Concealing hidden messages within audio has been a trend since the earliest days of music, using ciphers and cryptograms to embed secret signals that the casual listener may remain unaware of.
Here are a few of our favourites.
The B.A.C.H. Motif
The musical works of Johann Sebastian Bach are mathematical to the core, characterised by the use of recurring, interlinked musical sequences which are perfect mathematical permutations of each other. Bach’s fascination with musical geometry led him to realise that his own surname could be translated into a musical cryptogram using the notes of “B”, “A”, “C” and “H” — which, in German conventions, corresponds to a B natural.
In the centuries since, composers from Arvo Pärt to Arnold Schoenber have since referenced the B.A.C.H. motif to express their reverence for Bach.
Nokia Morse Code SMS Tones
The Nokia SMS tones were an emblematic part of 90s/00s sound design, marking the days when a ten-message inbox was an accepted part of messaging life. But they were also the carriers of hidden messages: one of the default Nokia SMS tones contains the message “connecting people”.
One of the best-known methods of hiding messages inside sound is by exploiting audio spectrograms: a graphical representation of a sound’s frequency spectrum. By beginning from an image and performing the inverse translation — turning a graphic into sound — a piece of audio can be created that contains a hidden picture.
It doesn’t sound pretty, but dovetails with the abstract works of artists such Aphex Twin and Venetian Snares who have used the technique extensively.
Most recently, a hidden spectrogram appeared in an episode of hacker serial Mr Robot:
There are also pentagrams and other Satanic imagery hidden inside the soundtrack of the recent Doom reboot.
Hidden Voice Commands
Researchers from Berkeley and Georgetown recently published a paper (PDF) detailing how wake-up voice commands like “Alexa” and “Hey, Siri” could be concealed within unintelligible sounds which, though sounding unearthly to a human ear, are interpreted by voice recognition systems as being spoken text.
Though it seems like an amusing curio, there’s huge potential for malicious attackers: imagine broadcasting audio over a shopping centre P.A. system that instructs Siri to call a premium rate number.
Kraftwerk and Musical Morse Code
Resonating with the cold-war era of numbers stations and Geiger counters, Kraftwerk’s Radioactivity opens with a sequence of Morse code pips. Needless to say, there is a message behind the sequence, which one YouTube viewer has passed through a Morse decoder below.
Alexa Easter Eggs
As voice-controlled devices such as Alexa have risen in prevalence, so too has the opportunity for voice-recognition japes:
- Alexa, who let the dogs out?
- Alexa, how much wood could a woodchuck chuck, if a woodchuck could chuck wood?
- Alexa, when is the end of the world?
- Alexa, up, up, down, down, left, right, left, right, B, A, start.
Voice Memo Apple Icon
Apple are fond of concealing Easter eggs within their products. True to form, the icon for the Voice Memo app is a waveform of a single spoken word: “Apple”.
The Wilhelm Scream
The Wilhelm Scream is the movie audio in-joke par excellence. It is a stock recording of an anguished scream that has been taken up as a trope across Hollywood, used in countless movies including most of George Lucas’s works.
Named after the character in The Charge at Feather River (1963) who immortalised the scream, it has since attained cult status and has become the namesake of a popular band and a brand of beer.
In doing so, the Wilhelm Scream has transcended the status of sound effect to become a tiny symbol of communication, a secret nod between filmmakers and their audiences acknowledging a thread of reference that dates back 50 years.
The Modem-Encoded Bonus Track
Bonus tracks are a testing ground for the esoteric and experimental. In 1992, synth-pop band Information Society created a bonus track which, on its surface, is a burbling stream of 2kHz sine-waves. In actuality, it contains a short story passed through the Bell 103 300-N-8–1 modem encoding.
If you’re familiar with a command line terminal, you can decode and read the story by playing the above video through the mini-modem software modem:
minimodem --rx -8 300 -M 2225 -S 2025