WITH innovative German composer Karlheinz Stockhausen for a father, it seems only natural that Markus and Simon would learn their musical craft early - and inherit a taste for the different. It is a legacy the Stockhausen brothers apply to their group Aparis, a progressive jazz trio performing on April 3 and 4 at the Cultural Centre. Although the instrumentation varies, Aparis consists primarily of Markus on trumpet, Simon on synthesisers and Jo Thones on drums. While Markus' playing tends to favour rich jazz and classical scalings, Simon is adept at creating electronic atmospheres - from the ethereal to the aggressive. Thones anchors these disparate styles with solid rhythms and syncopated bursts. The group's compositional duties have always been a creative collaboration between the two Stockhausens. But at age 35 - a decade older than Simon - it is Markus who serves as Aparis' spokesman. ''Of course, words cannot say what music can say,'' he said. ''But I suppose our music is a mixture of improvised and contemporary elements as well as jazz and pop influences - though probably more jazz than pop. We also try to find a balance between composition and improvisation.'' While all three members of Aparis have been involved in a variety of recording projects, the group is about to release what is officially its second album, an ambitious project entitled Despite the Firefighter's Efforts. The new record, while sweeping in its reach, is less contrasted than the first. ''It's more diverse in style,'' Markus said. ''It has more experimental things like sampling techniques and impressions from other musical cultures. ''With each new piece we like to take a step ahead - often with a different process of composition. Sometimes someone comes up with a theme and we build on it; sometimes we look at what we've already done and then we try to go into an area that we haven't explored yet; sometimes we improvise while recording, and then later we make a piece out of it. ''We try to make an amalgam of the music of our time.'' With this in mind, outside of Aparis, the brothers continue to work with their father. It is a reciprocal arrangement: while the elder Stockhausen continues to be a major influence on his sons, so too do the brothers help their father realise his musicalideas. Simon, for instance, is working in the studio on some electronic music for his father's next opera. ''Both my brother and I still work very closely with our father,'' said Markus, ''and 50 per cent of our time we spend collaborating with him. ''Right now, we are helping with the recording of his new opera, Dienstag im Licht [Tuesday in Light]. We've both performed in his earlier operas and we'll also be performing in the premiere of this one in May.'' But, of course, there are always differences between the sensibilities of one generation and those of the next. ''My father is much more of a structural person - like an architect - whereas we capture ideas more spontaneously, less on paper and more in real time,'' Markus said.