Universal Transmission Rate of Human Speech – 39 bits per second

A new study of 17 languages suggests humans have a set rate of information transfer in speech.

Researchers estimated the information density of written text as information encoded per syllable. They found that Japanese, which has only 643 syllables, had an information density of about 5 bits per syllable, whereas English, with its 6949 syllables, had a density of just over 7 bits per syllable. Vietnamese, with its complex system of six tones (each of which can further differentiate a syllable), topped the charts at 8 bits per syllable.

They also collected recordings of 170 native adult speakers, each reading 15 semantically identical passages that had been translated into their mother tongue. This was used to calculate an average speech rate, measured in syllables/second.

“Sometimes interesting facts or rules are hidden in plain sight,” says study co-author François Pellegrino. “Although languages differ widely in their encoding strategies, no one language is more efficient than another at delivering information.”

What was surprising was that, no matter how fast or slow, how simple or complex, each language gravitated toward an average information transfer rate of 39.15 bits per second. Moreover, there seems to be a trade off between information density and speech rate, with languages with lower information density being spoken faster.