Multiphonics refers to.

a. an avant-garde technique of playing two record players at the same time and listening to the aggregate sound
b. a technique of playing more than one note at a time on a wind instrument
c. the sound of multiple horn players improvising at the same time
d. the sound of multiple notes at the same time

b. a technique of playing more than one note at a time on a wind instrument

Explanation:

Multiphonics -

It is one of the technique on the monophonic musical instrument , where various notes are produced at one go , is referred to as multiphonics .

The various notes includes , human voice , brass , reed , wind etc , in this technique .

The method is adapted to make playing the instrument in a very innovative manner , by using many notes .

Hence , from the given scenario of the question ,

The correct answer is b.