Concertgoers immerse themselves in a pool of sound

When the clock struck midnight here last Saturday, some 160 sophisticated concertgoers floated like jellyfish in the College of the Canyons swimming pool. It looked quite pointless from poolside, because the music they heard was underwater, absorbed as much through the listeners' heads as through their ears.

This was the final concert of the evening at the eighth annual Contemporary Music Festival of the California Institute of the Arts. The festival features composers who are experimenting with new musical ideas.

But none are striking out in a direction as different as Michel Redolfi, composer and conductor of ''Sonic Waters.''

One hears differently in the water. The eardrums play a minimal role. Instead , according to Mr. Redolfi, the sound is picked up largely through the bones of the head. This means that regardless of where the swimmer is or what direction he is facing, the music seems to come from the nape of the neck, where the bones are thin.

The sounds of flutes, harps, synthesizers, and trumpets are crisp and pure underwater. And these are the sounds of ''Sonic Waters.''

On the other hand, bass frequencies are difficult to use in water. They require more voltage than Redolfi feels entirely safe using in the water. It's a problem he is trying to solve.

Percussion doesn't transmit well in the water, either. It's dull and flat, as if heard from behind a wall. But Redolfi claims that sharp rhythms are annoying when one is floating in the water. Rhythm is related to gravity, and in the water, gravity isn't strongly felt. So his music uses rhythm in surges like the surf.

With all the possibilities electronics offers for new kinds of musical performance, he says, ''I think it's a waste of time to concentrate entirely on the concert hall.''

What he says he's found underwater is a very tough set of musical limitations to work within and a new set of demands. He likes that. A style, he says, needs to work against limits in order to mature.

On Monday evening, Redolfi points out two reviews of his concert in that morning's local papers comparing his ''Sonic Waters'' to the mellow style of Muzak.

''Actually,'' he says philosophically, ''Muzak deals with the same problem that I'm dealing with.'' Both kinds of music are for environments where attention is constantly broken and distracted, so shifts in the music must be gradual, easy to follow with attention gaps. He wants to ease people gently into this new kind of music, he says, so he seeks to give pleasure.

Once a part of France's new-music composing establishment, which clusters around various academic institutes, Redolfi has spent the past three years at the Center for Musical Experiment at the University of California at San Diego. Here he has written music to be heard through water, researched underwater acoustics, and developed aquatic sound equipment.

For most of history, he points out, mankind assumed that the ocean was full of sound - whether of mermaids or the songs of mariners lost at sea. In this century, the oceans have been assumed to be silent.

But the oceans are in fact full of the sound of clicking shrimp, barking and whistling fish, the tremulous rumble of huge schools of fish changing direction, and the gnashing of fish teeth.

''I really love the idea that what I'm doing carries as much scientific knowledge as music'' to the public, says Redolfi, a young Frenchman with a winning sincerity and enthusiasm in his manner.

The public has been readier to accept underwater music, he notes, than many of his fellow composers. ''I'm talking about the community that works full-time to try to develop new music,'' he says. ''As soon as you tell them there is no violin, and no chairs, they say it's too new.''

Pioneering a new music medium hasn't been easy. ''I used to be a full-time composer. I couldn't sleep . . . worrying about whether to put this note or that ,'' he explains. But he has had to become part acoustical engineer and part impresario as well, worrying about voltage and the responsibility for ''all those people in the pool.''

He has put on some 40 concerts so far. He has toured the country playing swimming pools, and two concerts have been in the ocean. Last September he held a concert in an underwater park in a cove in La Jolla, Calif. Listeners swam and dove while Redolfi's music was broadcast from a 10-foot-wide float he calls a jellyfish, bobbing in the center of the cove.