"The first performance is always nerve-racking for me. Of course I want it to go well, but funny things usually happen in first performances," he said.
"It's a half-hour work for full orchestra in two large movements. The first is subtitled Up and the second Down and the music it evokes is concerned with moods and psychological states.
"The symphony is a portrayal of two sides of human personality, represented by the two sides of the work; Up and Down. The music depicts the constant struggle to find balance in one's life, in terms of mood and relationships with people.
"The first movement is almost hyperactive. It's very full-on, fast and furious and it's actually quite a challenge to sustain that for 14 or 15 minutes.
"The second movement is slower and more brooding."
The 30-minute symphony was recorded by the New Zealand Symphony Orchestra in May under the baton of Dunedin conductor Tecwyn Evans.
"This is very unusual, to have the work recorded before a performance, but the opportunity arose to make a CD with the orchestra including older works of mine and I wanted to include the symphony. I have heard it in lots of small bits which is tantalising but, ultimately, unsatisfying compared to a live performance.
"It was useful, however, for sorting out the errors in the score. It's hard to avoid errors when there are more than 100 pages of orchestral music."
Dr Ritchie grew up in Christchurch and has lived in Dunedin since he was University of Otago Mozart Fellow in 1988 and 1989.
For the past 10 years, he has taught composition at the University of Otago.
He was the Dunedin Sinfonia [now Southern Sinfonia] composer-in-residence when he wrote his first symphony, Boum, in 1994. The sinfonia also performed his second symphony, The Widening Gyre, in 1999.
Tonight's performance will have an added resonance, for he will share the spotlight with his father, Canterbury University emeritus professor of music John Ritchie, whose Papanui Road overture also features.
"I thought that was a lovely idea. Dad's coming up to 89 now, so he's getting on a bit. Our music has not been paired together very often in a concert - probably more so on recordings, such as Alexa Still's Kiwi Flute CD."
Dr Ritchie develops his ideas at the piano, before translating the sounds into orchestral instruments.
"I spend a lot of time thinking about the piece before starting on sketches. I start with non-musical ideas - such as the idea of opposites, or polarity in personality. From there, I gather sketches and ideas that relate to the general theme. At some stage, I'll settle on an overall structure for the ideas, but it usually changes as I create the specific musical passages. There are pre-set musical structures that can be used, such as 'sonata form', but these don't play a big role in Symphony No 3.
"Percussion plays an important role rhythmically; especially the combination of log drum and tom-toms. Eventually, the lively character of the music loses control, leading to a riotous climax involving the percussion and full orchestra in unison," he said.
"The music disintegrates into a short oasis of calm, before the busy mood is gradually re-established and brings the movement to a bright end on a D Lydian chord.
"Broadly speaking, Up is active, busy, bright in mood. Musical motifs and themes emphasise upward progressions. Down, by contrast, is melancholic, slow and mournful in mood. If Up is associated with the Sun, then Down is associated with Saturn. Structurally, Up has elements of sonata form, which become increasingly loose as the movement progresses. Down is symmetrical in arrangement," he says.
Dr Ritchie will also play a keyboard composition before the three screenings of Dunedin dance choreographer Daniel Belton's Line Dances film at the Otago Festival of the Arts.
"I want to express ideas I can share with people. That's important to me; to feel I can say something that other people may find interesting or thought-provoking."
The concert will open with Papanui Road overture by John Ritchie.
Bulgarian violinist and 2007 Michael Hill International Violin Competition winner Bella Hristova will conclude the concert with Beethoven's Violin Concerto.
The Southern Sinfonia performs the world premiere of Anthony Ritchie's Symphony No 3 at 8pm today, in the Dunedin Town Hall.
