This year marks the Norfolk Record Office's 50th anniversary - and also the 10th anniversary of the Norfolk Sound Archive, based at the same premises at County Hall.

Jonathan Draper wrests a black wheel anticlockwise and with a creak, the tall grey metal units roll apart to reveal shelf upon shelf lined with slender cardboard boxes.

Here in the cold, dry, carefully controlled atmosphere of the Norfolk Sound Archive are about 10,000 such cases, and within each is a reel of magnetic tape containing hours of recordings.

Put together they amount to a vast oral history, a detailed account of Norfolk life told through the voices of its inhabitants over the past few decades.

There are news reports from BBC Radio Norfolk, conversations with interesting characters, field recordings made by a well known ornithological writer, historic recordings of local folk songs, and interviews with American GIs stationed in the county.

But it also functions at a more humdrum level: all Norfolk life is there, from a recording of an Aylsham parish council meeting in 1978 to the reminiscences of those who worked in Norwich's shoe industry.

While some of it may not seem so exciting, it all amounts to an important resource that will aid future historians by giving a flavour of East Anglian life from the mid-20th century onwards.

The idea of a repository for significant local audio recordings had been mooted for some time, but it was only with the development of the Norfolk Archive Centre beside County Hall at Martineau Lane, Norwich, that it became a reality.

'John Alban realised it was the chance to set up a sound archive,' says Jonathan, 'and soon after that he gave me the opportunity of delivering one.'

April 1, 2003, saw the Sound Archive established with the receipt of its first collection, which came from the BBC.

'At the same time as the Archive Centre was being built, Radio Norfolk moved from Surrey Street to the Forum and had a significant reduction in space, and wanted to deposit their archive with us, which is mainly on magnetic tape,' Jonathan explains.

Since then he has accrued an intriguing and ever-swelling collection of old reel-to-reels, cassettes, gramophone records and acetates, which are aluminium discs coated with lacquer, the high quality format used in the music industry for master pressings of music recordings.

Among Jonathan's own favourites are the conversations with GIs, which were 'very interesting and different from anything else we have – they have some wonderful accents from all over America', a recent radio documentary about Black Anna, the blues-singing landlady of the city's Jolly Butchers pub in the mid-20th century, and a selection of oral history interviews with Ethel George.

She died aged 97 in January 2012, and was already into her 90s when she sat down for a series of reminiscences with local writers Carole and Michael Blackwell. Sitting for hours with a hands-free microphone fitted around her neck, she looked back to a childhood as one of 17 children growing up impoverished in a small house in Norwich, the city where she lived all her life. The authors used her memories as the basis for a book titled The Seventeenth Child.

Some of the recordings can be heard in the Bridewell Museum, but the full collection is preserved at the Norfolk Sound Archive.

'We have the raw interviews that Carole and Michael carried out with her,' says Jonathan. 'It's lovely when the interviewee is so relaxed and forgets they are being recorded.

'Her memory was so clear, and there are 10 to 12 hours of her just talking about her childhood. If you want to know about poverty in the city in that period they are a good resource.'

Anyone interested in accessing the archive should start by visiting the Norfolk Record Office's online catalogue, NROCAT (http://nrocat.norfolk.gov.uk).

'That is the main way we provide access,' he says.

'Because of copyright restrictions we can't put everything on the internet', he adds, but many of the files have been digitised and are available to hear online. With others it is necessary to visit the Archive Centre and sit in a listening booth.

While digital audio formats are standard now, the archive was established at the dawn of the digital era and much has changed in the past decade. 'It was an interesting time to set up a sound archive,' says Jonathan.

'When we started we were given machines by the BBC to play their tapes on, and initially we preserved to tape, but quite quickly we went to digital files.

'It's all reactive – we don't have the resources to chase much. We respond to approaches to us. Very soon after we started, we began receiving requests for help with oral history projects.

'We usually do so on the basis that we can hold copies of the recordings.'

Beneficiaries in recent times include True's Yard Museum in King's Lynn, Gressenhall Workhouse and Farm Museum – whose exhibition on the Land Army and Timber Corps is based on oral history recordings – University of East Anglia students who needed advice on interviewing people regarding care of elderly people, and local oral history groups such as Dragon Hall King Street Community Voices project in Norwich, West Somerton History Group, and others in Happisburgh and Barton Turf, Irstead and Neatishead.

The main criteria for acceptance in the archive are that a recording is not duplicated elsewhere and has a strong Norfolk connection.

The latter can span from someone who has always lived in the county discussing their memories, to recordings made elsewhere in the world by a Norfolk resident: for instance Mark Cocker, the Yare Valley-based writer best known for his expertise on birds, whose recordings from travels around the world are held here.

Those and many more now lie safely preserved in the bunker-like room, where humidity is controlled at approximately 33pc – too much moisture in the atmosphere can degrade the tapes. Just scanning the long rows of boxes reveals the diverse sounds of Norfolk's recent history, which combine to provide an amazing resource – one that will only grow as more people learn of this treasure trove collecting the sounds of Norfolk's past.