You aren't considering the listening environment. It is possible for ultrasonic sounds to interact with objects in the environment or with other ultrasonic soun

You aren't considering the listening environment. It is possible for ultrasonic sounds to interact with objects in the environment or with other ultrasonic sounds to produce lower frequency sounds that are in the range of normal human hearing. There was an even a creepy ad campaign several years ago that took advantage of this. They had a billboard in New York for A&Es new show "Paranormal State" with the tagline "It's not your imagination". They used an ultrasonic system on the billboard to make audible sounds appear in a small region on the sidewalk but not anywhere else. When people walking along the sidewalk got to that region they would hear a woman whisper "Who's there? Who's there? It's not your imagination". That system worked by making a single ultrasonic beam that somehow as it dispersed became audible. There are other systems that use multiple ultrasonic beams that produce audible sound via interference where the beams meet. Many acoustic instruments do produce significant amounts of sound above normal human hearing range. Cymbals for example have nearly 70% of the sound power above 20 kHz. Trumpets with a mute have almost 2% above 20 kHz. It seems possible then that if you wanted to produce a recording that reproduces the sound you would get if live acoustic instruments were playing in the same environment you might need to include ultrasonics unless you are making a binaural recording. This does raise the question of what we actually want playback of a recording to achieve. Is a recording of a string quartet when played back in my living room supposed to sound like that string quartet is playing in my living room, or is it supposed to sound like what I'd have heard if I was there when the piece was recorded, or is it supposed to be something else? (For those who haven't heard of binaural recordings, they are stereo recordings made by placing microphones inside the ears of a model human head so they record the sounds that actually ends up in each ear when something is recorded live for a listener at a specific location in an environment. This page of headphone tests [2] includes a binaural test if you'd like to such a recording). [2] https://www.audiocheck.net/soundtests_headphones.php https://www.audiocheck.net/soundtests_headphones.php