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Prisoners’ code word caught by software that eavesdrops on calls | New Scientist

The software saw the phrase “three-way” cropping up again and again in the calls – it was one of the most common non-trivial words or phrases used. At first, prison officials were surprised by the overwhelming popularity of what they thought was a sexual reference.

Then they worked out it was code. Prisoners are allowed to call only a few previously agreed numbers. So if an inmate wanted to speak to someone on a number not on the list, they would call their friends or parents and ask for a “three-way” with the person they really wanted to talk to – code for dialling a third party into the call. No one running the phone surveillance at the prison spotted the code until the software started churning through the recordings.

This story illustrates the speed and scale of analysis that machine-learning algorithms are bringing to the world. Intelligent Voice originally developed the software for use by UK banks, which must record their calls to comply with industry regulations. As with prisons, this generates a vast amount of audio data that is hard to search through.

The company’s CEO Nigel Cannings says the breakthrough came when he decided to see what would happen if he pointed a machine-learning system at the waveform of the voice data – its pattern of spikes and troughs – rather than the audio recording directly. It worked brilliantly.

Training his system on this visual representation let him harness powerful existing techniques designed for image classification. “I built this dialect classification system based on pictures of the human voice,” he says.