If we play two different musical instruments at the same time, the vibrations produced by the musical instruments travel through the same air medium, but we hear different sounds.
A sound has three characteristics. They are
  • Loudness
  • Pitch or shrillness
  • Quality
  • The loudness of a sound is determined by its amplitude.
  • The amplitude of the sound wave depends upon the force with which an object is made to vibrate.
  • If we strike any object lightly, we hear a soft sound because we produce a sound wave of less energy or less amplitude.
  • Similarly, if we strike any object strongly, we hear a loud sound because we produce a sound wave of high energy or high amplitude.
If we strike a bass drum with a stick, the amplitude of the wave is high, so the sound is loud.
Pitch or shrillness:
  • The frequency of a sound determines its pitch or shrillness.
  • Objects of various sizes produce sounds of various pitches vibrating at different frequencies.
  • The higher the frequency and the higher the pitch of the source, the faster it vibrates. As a result, a high pitch sound corresponds to a greater number of compressions and rarefactions per unit time.
  • A sound with a higher pitch is very easy to hear, whereas a sound with a lower pitch is difficult to hear.
If we blow a whistle, the frequency of the wave is high, so the pitch is high. Therefore, the sound of a whistle is very clear.
Fox-40-whistle (1).jpg
Variation of amplitude and pitch
Quality of sound:
  • Sound quality (timbre) is a feature of a sound that allows us to distinguish one sound from another with the same pitch and loudness.
  • The quality of sound depends on the shape of the sound wave.
  • The pleasant sound is said to be a sound of rich quality.
  • A sound of a single frequency is called a tone.
  • The sound produced by a mixture of several frequencies is referred to as a note, and it is enjoyable to listen to.
  • The sound which is unpleasant to hear is called noise.
  • The sound which is pleasant to hear is called music.