A digital future from the past (Image: Steve Horrell/SPL))

Digital sound was invented in 1937 – decades before the technology to use it had been developed

THOUGH he didn’t realise it at the time, in 1937 the British engineer Alec Reeves laid the foundation stone of modern digital telecommunications networks. The valve (vacuum tube) was then in its heyday, digital computers were still years in the future, and the transistor a decade away.

In 1927, commercial transatlantic telephone calls were made possible by radio telephones. In the early 1930s, Reeves helped develop higher-frequency radios that could carry several calls at the same time, but these conversations interfered with each other, producing a noisy, hard-to-understand signal.

Then Reeves realised that converting these analogue representations of speech into a series of telegraph-like pulses might avoid the troublesome interference. He designed circuits to measure the strength of each speaker’s voice 8000 times a second and assign that signal strength to one of 32 levels. Each level was then represented by a sequence of five binary digits. As long as the receiver could tell the binary 1s from the 0s, it ought to be able to turn the stream of pulses back into interference-free speech.

That was the theory, at least. “No tools then existed that could make it economic,” he wrote more than 25 years later. His employer, ITT, patented pulse-code modulation, but never earned a penny before the patent expired in the 1950s.

Reeves was something of a visionary, often saying: “I will be right about the things that I say are going to happen, but I will never be right about when.” …