[2] As characterised by All About Jazz, "He does not fit into any pigeonhole, however, and is also something of a renaissance man: he has long been involved in cognitive psychology and also travels widely, spending extended periods in South Africa, Uganda, Zimbabwe, Nigeria, Morocco, Indonesia and Belize (his parents' homeland).

[5] After beginning to learn classical piano as a young child, also playing euphonium, he went on to study the trumpet in New York in the mid- to late 1980s with Jimmy Owens, Donald Byrd and Jon Faddis.

[4] Wallen graduated from Sussex University with a degree in Psychology, Philosophy and Maths, while developing his music career, recording with Loose Ends and Cleveland Watkiss, and playing trumpet with The Style Council, Charles Earland, Courtney Pine and Jean Toussaint, among others.

[6] Other artists with whom he would later perform include David Murray, Andrew Hill, Butch Morris, Billy Higgins, Hugh Masekela, Manu Dibango, Eddie Henderson, Wynton Marsalis, George Benson, William Orbit, Toumani Diabaté, Ronnie Laws, Chaka Khan and Grand Union Orchestra.

[8] As a composer Wallen has had commissions from such organisations as London's Science Museum, the BBC, Jerwood Foundation, Southbank Centre, National Theatre, Arts Council England, FIFA and Sage Gateshead.