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LostInParadise's avatar

Can we recognize recorded sounds when played backwards?

Asked by LostInParadise (28559points) June 19th, 2011

I am guessing no, for the simple reason that you never find examples of it. It does seem though that the sound of a tuning fork played backwards should be recognizable. What about a single note on a musical instrument? There are certain letter sounds like vowels and some consonant sounds like l, r, m and n that can be held. Would they be recognizable if played backwards? I have the feeling that entire words played backwards would not sound anything like human speech.

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4 Answers

krrazypassions's avatar

The best way to know is to play different sounds backwards and ask volunteers to try to recognise.
But for now, from just a thought-experiment, i feel the following:-
It depends on the complexity of the sound. Is the sound spoken words? Or singing words (i.e. with a tune)? Or only an instrumental track? Or a full-fledged song with vocals and instruments? Does the track contain a peculiar rhythm?
If it is spoken word, it generally sounds like a new language. Its more difficult to recognize the words. But reversing words of a sentence one by one and playing them in the correct order in which they appear in the sentence is different from playing the entire sentence backwards
If it is a song, there is more probability that you will recognize it from its beats and peculiar notes. Also, from the voice of the singers. Recognizing whose voice it is is easier than what the sentence was.

TV and Radio game shows based on music have a section in which a part of the song is played backwards and the teams have to recognize it correctly. Its tricky but a lot of people can recognize the song correctly.

Kayak8's avatar

Any single note played backward has similarities and significant differences from the same sound played forward. This because there are several parts of a sound that we don’t consider. A sound is considered to have an envelope (you can actually graph them). They start with the attack, there is a peak, there is some amount of sustain and then there is decay.

If you were to play a single note on the guitar and record it and play it backwards you would hear decay, sustain, the peak and the attack (which sounds very abrupt played backward). Only the “sustain” part of the note (steady state without a lot of dynamics) sounds the same forward and backward for most people.

This is completely different from reading the notes on a piece of music from bottom to top and right to left and playing them that way. The sound envelope for each note remains the same and it might be possible (for some) to recognize.

This technique is called backmasking and you can find some information on Wikipedia. There is also a website here that will allow you to select a segment of familiar songs and hear them forward and backward.

Some of what helps in the identification is a familiar voice or orchestration (listen to Eagles Hotel California) at the link above for example. The new rhythm introduced into the clip by playing it backward is hearing the attack segment of the sound backward with a sudden end.

gasman's avatar

Sustained notes on any instrument should sound about the same forwards or backwards. It’s the attack and decay envelopes of the sounds—how they begin and end—that would sound unnatural.

As for speech, that’s a whole different thing. Outlandish claims that recordings contain “subliminal messages” encoded as backwards sounds, explicitly audible by playing in reverse, are urban legend, no doubt a case of pareidolia—same as hearing voices in static. Your cerebral cortex doing what it evolved best to do: Find patterns in complex stimuli—even if there aren’t any.

Backwards English sounds vaguely Swedish to me!

josie's avatar

The only acceptable answer is here at 2:35
http://www.youtube.com/watch?v=MPjDMZiuhbQ

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