Although it is generally accepted that humans cannot perceive frequencies above 20kHz, recent research has shown that it is possible through bone conduction. It has been shown that frequencies above the audible range of hearing do have an affect on the brain. When compared with audible frequencies affect on the brain, the results are almost equal. Professor James Boyk of the Californian Institute of Technology, has shown that "one member of each instrument family Strings, Woodwinds, Brass and Percussion produces energy up to 40kHz or above". Conventional audio equipment generally limits the frequencies which they can record and reproduce, from 20Hz to 20kHz. This stems from the 70's when the compact disk was being created and storage mediums were very small. Limiting the frequencies saved space. The question asked in this book is "Do we prefer music with ultrasonic content?" This stemmed from the idea that possibly, the reason we prefer going to a concert more than listening to the cd of said concert is because in the live setting we also have ultrasonic content, affecting our brain and perception of the music presented.