The 65-year-old emeritus professor of composition, conducting, New Zealand music, contemporary music and music theory, will retire next week after 23 years in the music department.
During his prolific career, he has become prominent on the global stage, having composed more than 200 works, including symphonies, operas, concertos, choral works, chamber music and solo works.
And there was still plenty more material locked away, ready to be written, he said.
For a man who had spent most of his life immersed in music, a life without it was inconceivable.
One of the greatest things about working at the university was that it surrounded him with musical inspiration for his compositions, he said.
"I’ve really enjoyed working with my students and seeing where they go.
"It’s particularly satisfying when you can see they’re thinking for themselves and they’re heading off in a direction that’s quite different to my style.
"They spark your own ideas," he said.
"They come at things from a different angle and you think, ‘oh, that’s an interesting idea. I might try that myself’."
For that reason, he said he would miss his students the most when he leaves.
Being a composer can be quite a solitary profession — long hours in a quiet room, away from other people.
So he would also miss his fellow music colleagues, he said.
"Part of the joy of working in a department is the collegiality that you build up over the years.
"I formed a bond with most of my colleagues and collaborated a lot with them on projects.
"So I’ll miss that."
Emeritus Prof Ritchie said he recently turned 65, and felt it was now time to step back from his roles at the university.
"My health hasn’t been that great over the last few years, so I’ve had to slow down a bit — plus I just feel it’s the right time for me.
"I mean, the music industry is changing so rapidly that, in a way, it’s good to have new people coming in if possible, and steering the department in other directions.
"I think I’ve done my time, basically."
He also believed "life’s too short" and there were other things he wanted to go out and do.
"I’ll keep composing and being involved in musical activities, but retirement gives you more time away from the stress, to look after yourself, do a bit of biking or swimming or croquet or whatever it may be."
Even if he wanted to, he said it would be difficult to go cold turkey and cut himself off from the department.
"I’ll probably pop in and do the odd thing — in fact, I was asked the other day to cover for a class.
"So no doubt, I’ll keep doing stuff.
"The expectation is that you’ll still be involved with the university and its activities when you’re an emeritus professor, and I’m more than happy to do that."
Apart from a bit of rest and relaxation, he plans to complete his latest work — his seventh symphony — which he has been working on for the past two years.
"It sort of got interrupted by health and things, but I want to get back and complete that.That’s probably my main project."
As for what comes next?
"Well we’ll just have to see how it goes," he said.
