CIRCUMSTANCES could hardly have been worse for the dawn of the world’s largest arts festival. Britain was two years out of war, the economy was crippled, rations were still in place, relationships around Europe were dismal. Maybe circumstances could hardly have been better.

It’s an old story but it’s worth telling again. Rudolf Bing, general manager of the young Glyndebourne opera, was strolling through Edinburgh one night in 1942 when he looked up at the castle, spotted a resemblance to Salzburg – one of the great music centres of Europe – and had an inkling that Edinburgh would make the right place for a festival. It had the grand beauty, the historic tourist industry, the centuries-old links with Europe. Bing also knew that music could provide hope and unity even at the most broken of political times.

It took him five years and some deft haranguing of the British Council and the Edinburgh City Council, but by 1947 he had himself a festival. German, Austrian and Italian conductors and orchestras were invited for the very first editions – the aim here was explicitly internationalist, determinedly non-partisan despite prevailing politics of the time, and the city was declared a "platform for the flowering of the human spirit". Just last week the acclaimed Iranian children’s book illustrator Ehsan Abdollahi was denied a UK visa to attend the Edinburgh International Book Festival. How easily we forget the lessons of the past.

Revisiting that brave founding vision is just one of the joys of listening back. Over the past few weeks, I’ve been involved in putting together Edinburgh 70 – a special archive series for BBC Radio 3 Lunchtime Concert featuring vintage broadcasts and recordings from the very earliest years of the Edinburgh festival. Actually it’s a double birthday, marking 70 years of both the festival and of Radio 3’s involvement with it: the station was here, as the Third Programme, right from 1947.

That didn’t make for straightforward archive digging, though. Over the decades things have been lost, taped over, mislabelled, forgotten. Thanks to the expert rummaging skills of Lindsay Pell, Senior Producer for Music at BBC Scotland, what we’ve emerged with is genuinely exciting. It’s one thing knowing that Edinburgh hosted epoch-defining performances by towering artists of the 20th; it’s another thing actually hearing the grainy, potent proof.

We start the series with Kathleen Ferrier – who else? – that great Lancastrian contralto who visited the festival every year for the first six editions and whose voice, for me, is utterly matched with the era. Even her voice type seems like it’s from a bygone age (today we talk about "mezzo-sopranos", but for Ferrier the term "contralto" was absolutely right: the immense warmth and weight of that low register).

Ferrier performed at the festival most regularly with Bruno Walter – the conductor/pianist who himself had reason to love Edinburgh. He had worked with the Vienna Philharmonic since 1907, but as a Jew that relationship had fallen apart in the early 1940s and it was only on 8 September 1947, at the Usher Hall, that Walter and the Vienna Phil were reunited. One of the pieces they performed was Mahler's Song of the Earth. The singers? Tenor Peter Pears and Kathleen Ferrier.

Lindsay unearthed several other epic voices from the archive. There’s Fritz Wunderlich, the German lyric tenor whom we hear singing Schumann’s Dichterliebe at the age of 36 in early September 1966. What makes this performance so heartbreaking – apart from its intense musicality and immense, ringing tone – is that only two weeks later Wunderlich would be dead: he fell down the stairs at a friend’s hunting lodge, apparently something to do with badly tied shoelaces. He was only a fortnight away from his Metropolitan Opera debut and his voice was in stunning form. His pianist, Hubert Giesen, wrote that “he was a man of everything-or-nothing, a man who always tried to make the best of what nature had given him. It was not only his voice of unspeakable clearness that distinguished him, not only the intelligence and the earnestness of his work, but something that is best described by the term ‘aggressiveness’ – every note came from his entire body; he stuck to every note; his heart was with every single note.” The latent potential in that last Edinburgh performance is devastating.

Another thrilling find was a recital by a young Jessye Norman, 34 years old in 1979 and already on her fifth visit to the festival. This was the year Norman moved to London from the US and did no staged opera but decided to concentrate on recitals, and the plush-velvet hues of her voice are utterly gorgeous in the Brahms songs we’ve programmed. Her concert that year also included some starry guest chamber partners: anyone heard of James Galway?

Charting the past seven decades of festival performances also meant charting seven decades of political history. We hear Rostropovich playing Bach at St Cuthbert’s Church in 1975 – only a year after he and his wife left the Soviet Union for good. The support they had given to the subversive author Alexander Solzhenitsyn had raised the suspicions of Soviet authorities, and a fierce open letter Rostropovich wrote to Pravda attacking cultural oppression hadn’t earned him any lenience. In the early 1970s the couple were restricted to touring inside the country but eventually they were exiled in 1974 and declared "un-persons". When we hear him playing Bach’s cello suites in Edinburgh the following summer – and remember this is the same music he would play all night long when the Berlin Wall fell in 1989 – the warmth and tenderness is profoundly moving.

There’s so much more. Poulenc playing Poulenc, Dohnanyi playing Dohnanyi, composer-performers from a time when the festival really championed new music. Jorge Bolet, the Cuban pianist whose lineage goes straight back to Liszt via his teacher Moriz Rosenthal – you’d be hard-put to find that kind of huge romantic sweep delivered today with such dignified authority. Clara Haskil, a tremendous Romanian Mozart interpreter of the mid 20th century, playing Mozart with supreme elegance in 1957.

Even the original Third Programme announcer’s voice is brilliantly atmospheric: meet David Cleghorn Thomson – Scottish journalist, playwright and politician – who describes in impeccable tones how the New Town audience reacts to a performance of Bartok’s Piano Suite Opus 14 by the great (and today shamefully undervalued) Hungarian pianist Geza Anda.

For me, growing up in Edinburgh, the festival was an education, a horizon-widener, an ear-opener. Until now I had only really experienced its past two decades. Hearing the mighty voices of Ferrier and Wunderlich from our familiar streets, the grandeur of Norman, the great flourish of Bolet, the dignity of Anda and Haskil – all this has been a reminder of the clout and dogged creative ambition on which the festival built its legacy.

The Edinburgh 70 archive series begins on August 8 at 1pm on BBC Radio 3.