Is there something special about the human voice?

Artificial intelligence-powered speech synthesisers can now hold eerily realistic spoken conversations, putting on accents, whispering and even cloning the voices of others. So how can we tell them apart from the human voice?

These days it’s quite easy to strike up a conversation with AI. Ask a question of some chatbots, and they’ll even provide an engaging response verbally. You can chat with them across multiple languages and request a reply in a particular dialect or accent.
It is now even possible to use AI-powered speech cloning tools to replicate the voices of real humans. One was recently used to copy the voice of the late British broadcaster Sir Michael Parkinson to produce an eight-part podcast series while natural history broadcaster Sir David Attenborough was “profoundly disturbed” to hear his voice has been cloned by AI and used to say things he never uttered.
In some cases the technology is being used in sophisticated scams to trick people into handing over money to criminals.
Not all AI-generated voice are used for nefarious means. They are also being built into chatbots powered by large language models so they can hold respond and converse in a far more natural and convincing way. ChatGPT’s voice function, for example, can now reply using variations of tone and emphasis on certain words in very similar ways that a human would to convey empathy and emotion. It can also pick up non-verbal cues such as sighs and sobs, speak in 50 languages and is able to render accents on the fly. It can even make phone calls on behalf of users to help with tasks. At one demonstration by OpenAI, the system ordered strawberries from a vendor.
These capabilities raise an interesting question: is there anything unique about the human voice to help us distinguish it from robo-speech?
Jonathan Harrington, a professor of phonetics and digital speech processing at the University of Munich, Germany, has spent decades studying the intricacies of how humans talk, produce the sounds of words and accents. Even he is impressed by the capabilities of AI-powered voice synthesisers.