From series 4 of The Avengers, when Diana Rigg joined the cast as Mrs Emma Peel, the programme had ceased to be television in the classic Doctor Who style. "These were movies, made on 35mm film with the best of talent," said Brian Clemens in comment on the first of these episodes.

These 'films' comprise the most popular era of the programme and the scrutiny they've received has proved invaluable as they've come to disc.

The Avengers was filmed and recorded at feature film's 24 frames per second speed, despite the 25 FPS of British television being slightly faster. The film speed and early use of colour in these episodes optimised them for overseas sale.

Certain DVDs of The Avengers operate at 25 FPS with an accompanying increase in audio pitch. Cinema films were routinely screened on UK and European television in this way but coming out of modern speakers, the slight changes to the sound are more pronounced:

• the famous theme tune in the wrong key
• all other music equally out of tune
• actors' voices pitched high, like oddly-recorded actors in early 'talkies'

As with the 'stretching' of old television episodes to HDTV width, some in The Avengers' audience are simply not bothered by the difference.

Only certain discs in the DVD sets have been affected and chasing down just which can be tricky. The Avengers Forever! team have assembled a nice guide describing the problems and offering details on how to get problem discs replaced by the vendor, Canal+.

Contrary to the guide however, the Complete Series DVD set may not be immune to the audio problems; the Series 5 portion of the set I own certainly isn't, as illustrated in the video above. Please note I'm speaking of DVD region 2, which includes the United Kingdom. Releases in other regions may have all, some or none of the problems described here and in the guide.

Happy ending: with the blu-ray release in the UK, the vendor has at last delivered a product that accurately documents this much-loved piece of Western popular culture. This is a huge win for fans, film historians, the artists involved and Canal+.