In this topic you will learn about differences in sound.

A sound can be high or low, depending on the pitch. The higher the pitch, the more "squeezed together" the sound waves are. Higher pitched waves have a greater frequency. Frequency is the number of times an object vibrates per second. The higher the frequency, the higher the pitch. Frequency describes vibrations and waves. Pitch describes how your brain interprets a sound.

A unit for measuring frequency is the hertz. One hertz (Hz) has a frequency of one vibration per second. Humans hear sounds from about 20 Hz to about 20,000 Hz. Some animals hear sounds above 20,000 Hz.

Sounds can be loud or soft. A loud sound has more energy than a soft sound. A unit for measuring loudness is the decibel (dB).

Music and noise are both sounds. In music the sounds are arranged in a pattern that can include rhythm, melody, and harmony. Notes are arranged in an eight-note musical scale called an octave. In other cultures, the number of notes between the bottom and top of the scale is different. Noise is a jumble of sounds that don't make a pattern. Noise is often unpleasant.

Sounds can be recorded by changing the sound into an electric current using a microphone. The sound waves make the diaphragm in the microphone vibrate, which makes a wire coil vibrate, sending an electrical current to an amplifier. The current is then changed to a magnetic particle pattern on a blank tape. When a recording is played, the process is reversed.

Compact discs do not store sound in magnetic patterns. During CD recording, a computer turns the sound waves into a code. A laser beam uses the code to cut millions of tiny pits into a blank compact disc. When you play a CD, a laser beam shines on it. The flat parts of the CD reflect light back into a small computer, which changes the patterns of these reflections into sound.