You might have heard of MIDI before; typically, people associate it with old synthesizers and cheesy drum sounds. The truth is, MIDI doesn’t sound like anything. MIDI stands for Musical Instrument Digital Interface. It is a specific protocol for sending “events” and these events do not contain any sound, or any sound files. An event might be “the volume knob has been increased one point” or “the key G3 on the keyboard has been triggered”. The receiver of the MIDI message can interpret that message anyway it wants. For example, “the key G3 on the keyboard has been triggered” might be transformed by the receiver into “play snare sound in bank 4″ or even “trigger flange effect”; it can be anything.
It is common for someone to misunderstand what MIDI really is and say, “That track sounds cheap. It has MIDI drums!”. While the producer may have used MIDI to trigger the drums sounds in his sampler, what actually sounds cheap are the drum samples he used. As we have already learned, MIDI has no sound, it just transmits information. If the producer had used more robust drum samples, it wouldn’t sound as “cheap”.
The most common usage of MIDI is to use a keyboard to trigger a sampler. When you use your 1990′s Casio keyboard to play the piano in your computer software, the keyboard is translating your input into MIDI events. Those are then traveling through a MIDI cable (nowadays, USB cables can transmit MIDI as well), and into your computer. The software you’re using likely incorporates a sampler which then routes your keyboard’s MIDI signal into a user-defined output, for example a grand piano sound.
Almost any instrument or piece of “audio” gear that interfaces directly with your computer uses the MIDI protocol. Such items might include, keyboards, MIDI guitars, drum pads, or digital mixers. While some of this equipment uses MIDI cable, most will use USB cables to transfer the MIDI information. So whether you are plugging MIDI cable into an audio interface, or plugging USB cable directly into your computer’s USB port, the equipment you use will still be transferring data via the MIDI protocol.
Within the last few years, advances have been made such that MIDI information can be gleaned directly from real audio. Advanced software scans the audio and figures out pitch, timing, velocity and other parameters. Engineers and producers are able to leverage this powerful functionality in many exciting ways. Some engineers extract MIDI information from live drum tracks. They are then able to manipulate that MIDI information anyway they see fit, as if they were played with a keyboard. They can fix timing, remove mistakes completely, or use completely different drum sounds. The possibilities are endless! Learning how MIDI works has always been the key to working with samplers, but now it’s powerful enough to manipulate real audio. It’s an extremely exciting time!