Text 1 

Sound travels in waves, but it is not part of the electromagnetic spectrum like light waves and radio waves. Sound is produced when matter vibrates. The frequency of these vibrations is measured in units called hertz (Hz). The term frequency refers to the number of waves produced per second. It is variations in frequency that produce different pitches (high and low sounds). The limits of human hearing are 20 Hz and 20,000 Hz.

Text 2 

A musical note is characterized by regular sound waves of a particular frequency. Different musical instruments may produce notes of the same frequency that sound completely different. This is because additional notes, called harmonics, sound when the instrument is played. Each instrument has its own unique set of harmonics created by the way the instrument is constructed and played. It is the arrangement of these harmonics that enables us to distinguish between different sounds of the same frequency.