How a Computer Works (2015)

28. MIDI

Many sound cards incorporate a MIDI interface. MIDI sound was developed to enable musical instruments like keyboards and synthesizers to connect to a computer. The MIDI system enables the computer to save instructions on how to play the sounds but not recordings of the actual sounds this is to conserve disk space.

Wave Table Synthesis

Key being read in

Digital data streaming out of chip

A keyboard or synthesizer issues a MIDI instruction to the digital signal processor (DSP) chip. This instruction tells the DSP which instrument to play and how to play it. If the sound card uses wave table synthesis to reproduce the sound of musical instruments, samples of the actual sounds made by different instruments are stored in a ROM chip. The DSP looks up the sound in the ROMs table. If the instruction is for a keyboard B note the DSP sends the data bits for this to a digital to analogue converter (DAC). The DAC converts the data bits back to an analogue signal.

FM Synthesis

Data being read in.

Sound is produced

When the sound card uses FM synthesis the DSP tells the FM synthesis to produce the note. The chip stores the notes of musical instruments.

The DSP sends the data bits for this to a digital to analogue converter (DAC). The DAC converts the data bits back to an analogue signal. Amplified speakers convert the analogue signal into sound.

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