In the case of amplification the transistor is used to amplify a signal. One example of such a signal can be a sound. To the left is an example of a circuit that is used to amplify sound signals. The sound entering the microphone is converted to an electrical signal that is amplified in the transistor. This amplified sound signal then travels through the circuit until it reaches the loudspeaker. This speaker converts the electrical sound signal back into a sound. The sound leaving the speaker is the same as the sound that entered the microphone, only much louder. This is called amplification – the sound is being amplified.