Over the next 40 years, they collaborated on a series of analytical documentaries on the founding fathers of 20th-century music: Schoenberg, Berg, Webern, Bartók, Stravinsky, Ives, Varese, Messiaen and of course Boulez himself.

They made twelve films together: From the 1970s until the end of the 20th century Gavin specialised in portraits of contemporary composers: Roberto Gerhard, Luciano Berio, Luigi Nono, George Benjamin, Karlheinz Stockhausen, John Adams, Sofia Gubaidulina, Aribert Reimann, Toru Takemitsu, Isang Yun, Harrison Birtwistle, Peter Maxwell Davies, Mark-Anthony Turnage, Oliver Knussen, Hans Werner Henze and many others.

In the 1980s, Gavin began a collaboration with Sir Simon Rattle, on a series of productions with the City of Birmingham Symphony Orchestra.

These documentaries included: Whilst much of Gavin's work concentrated on music, he also produced in 1967 a series on classic film directors.

In 2010, he made two short films: A Mind of Winter (George Benjamin) and How Slow the Wind (Toru Takemitsu), using music by these composers.

Copies of many of Gavin's films on contemporary music have been deposited in the archives of the Paul Sacher Foundation in Basel, Switzerland.