Long before I was old enough to know what it was all about, I loved listening to Alistair Cooke’s Letter from America. Cooke’s opening gambit would always be something like “I was standing on the corner of Lexington Avenue on a Sunday in May waiting for a bus …” and off he would go at a pace that seemed far too leisurely for a mere 14-minute programme, only for him to sidle seamlessly into his main theme just in time. Mostly, it was his voice that kept you listening: beautifully modulated, slightly breathy from chain smoking, with a gentle ascension and declension ideally tailored to his script’s skilful melding of the written and spoken word. It is impossible to read Cooke’s prose now without hearing that voice in your head.

On 1 November, as part of its 90th birthday celebrations, the BBC is releasing 920 editions of Letter from America on the Radio 4 website. It is a fitting choice with which to initiate an intended expansion of the BBC’s online radio archive because what made Letter from America so compelling was really the essence of radio itself – its capacity to draw us in and make us listen intently to the sound of another human voice.

Before radio came along, the ability to hear the voices of absent speakers was seen as the preserve of spiritual mediums or mad people. Early listeners were fascinated by this strange phenomenon, the radio wave, which could carry voices on the air but was itself undetectable without that magical deciphering machine, a wireless. One of the radio wave’s great charms was that, unlike the telephone or the telegraph, it radiated to no one in particular. The early term for the BBC’s audience, “listeners in”, suggested they were eavesdropping on a voice that was not really speaking to them but to the universe. “By enabling a whole country or continent to listen to a disembodied voice, wireless concentrates attention on it – flood-lights it, as it were – bringing out every little trick and peculiarity,” wrote the BBC’s first director of talks, Hilda Matheson, in 1933. “The violence of emotion produced in quite mild people by unfamiliar pronunciation, vowels, accent, is an astonishing proof of this heightened consciousness.”

When listeners get used to a radio voice, though, they become tenaciously attached to it. News of the imminent retirement of the Radio 4 announcers, Harriet Cass and Charlotte Green, has led to a wave of melancholy among the station’s audience because, just by reading the Shipping Forecast and introducing You and Yours in pleasing inflections over thousands of days, their voices have wheedled their way into listeners’ heads. My own favourite radio voices are John Murray, the Northumbrian-accented 5 Live commentator who always sounds as though he is in a musical and is about to break into song; and Clare Runacres, who reads the news on Radio 2 in such an emollient voice that, should the need sadly arise, I would like it to tell me to form an orderly queue for the lifeboats.

The voices coming through the radio mean a lot to us because they wrap themselves around our daily routines. Over 58 years, entering people’s homes at more or less the same time every week, Cooke’s voice came to seem as eternal as the news pips. That is why, although we should all cheer the expansion of the BBC’s digital archive, I hope that one of its rationales for expanding it – that real-time radio and the daily schedule are on the way out and that the listeners of the near future will all be selecting programmes themselves online like picking items off a menu – turns out to be wrong. The Letter from America archive will be a great resource, but it won’t be quite the same as that familiar Friday evening ritual, with that slight pause after the announcer’s introduction and that inimitable voice saying: “Our plane was coming in from San Francisco, nosing in through endless layers of cotton wool …”