Audio (or sound) is created by the vibration of air. These vibrations spread out like ripples from a pool of water when you throw a stone into water. When these vibrations reach your ear, the eardrum changes the vibrations into sounds. Because sound can have a wide range of values, it is known as analogue. Computers though, only have two values (0 and 1) so are known as digital.

One of the tasks of the audio board is to take analogue audio signals and convert them to digital and conversely to take digital audio signals and convert them to analogue. This makes the audio board both an analogue to digital converter (ADC) and a digital to analogue converter (DAC).

There are two common standards for storing audio data, Digital Audio and MIDI.

Digital audio actually stores the sound, while MIDI stores the instructions of how to create the sound. (Compare this with bitmapped and vector drawn graphics).

Digital audio files may be Real Audio files, Wav files, Windows Media Audio (WMA) files or MPEG audio file.

• Search and download three midi files.

• Search and download three digital audio files.

Answer the following questions in your jotter.

1. When inputting sounds via a microphone would an ADC or a DAC be required?

2. When listening to sounds through speakers would an ADC or a DAC be required?

3. Identify two other analogue signals.