Amplitude measures how forceful the wave is. It is measured on a Logarithmic scale and reported in decibels or dBA of sound pressure. 0 dBA is the softest level that a person can hear. Normal speaking voices are around 65 dBA. A rock concert can reach about 120 dBA but is often at 100 dB. Sounds that are 82 dBA or above can permanently damage your ears when exposed for a long period of time. The more sound pressure a sound has, the less time it takes to cause damage. For example, a sound at 85 dBA may take as long at 8 hours to cause permanent damage, while a sound at 97 dBA can start damaging hair cells after only 30 minutes of listening. Frequency is measured in the number of sound vibrations in one second. A healthy ear can hear sounds of very low frequency, 20 Hertz (or 20 cycles per second), to a very high frequency of 20,000 Hertz. The lowest A key on the piano is 27 Hertz. The middle C key on a piano creates a 262 Hertz tone. The highest key on the piano is 4186 Hertz.