“What a strange, incongruous figure I must appear, Mr. Chairman, standing before this august and ancient body to address you on a subject I have spent my whole life studying: sound. I am fascinated by the sound of Big Ben chiming, or a London bus changing gears. Only yesterday I spent a considerable time recording the sound of Bow Bells. You may well ask, how can this have any relevance for the defense of a man accused of insider trading? To answer that, I will need the help of my offspring, Matilda, who like me has never visited London before.”

The professor walked across to a side table on which he had placed a white cube, about two feet square, with what looked like the handset of a telephone attached to one side. On the side facing the committee was a large circular dial with black numbers around its edge that went from 0 to 120. A thick red arrow rested on zero. From the looks on the faces of the committee, Matilda had succeeded in catching their attention.

“Now, with your permission, sir, I shall ask Mr. Bishara to deliver the exact words he was accused of saying to Mr. Buckland. But please don’t look at Mr. Bishara, concentrate on Matilda.”

The committee didn’t take their eyes off the machine as Hakim rose from his place, picked up the handset and said, “Buy Amalgamated Wire, but don’t let anyone know I authorized it, because that would be insider trading. Keep up the good work, Gavin, and I’m sure that it will be reflected in your annual bonus.” Hakim replaced the handset and returned to his seat.

“I should now like to ask you gentlemen,” said the professor politely, “what you observed while you were watching Matilda.”

“While Mr. Bishara was speaking,” said Sir Piers, “the arrow shot up to 76, then fluctuated between 74 and 78 until he put the handset down, when it returned to zero.”

“Thank you, chairman,” said the professor. “The voice of the average male of Mr. Bishara’s age will have a volume level somewhere between 74 and 78. A softly spoken woman will average 67 to 71, while a younger man might reach a high of 85, or even 90. But whatever the individual’s voice level, it remains constant.

“If I may, I would now like to feed Matilda with the tape on which the allegations against Mr. Bishara are based. Once again, I would ask you to watch the arrow carefully.”

By the time the professor had placed the tape into the machine, the committee were leaning forward intently. He pressed Play, and everyone in the room listened to the same words a second time, but this time Matilda registered a very different result.

“How is that possible?” asked Sir Piers.