MIDI sucks. This isn't just an opinion, it is a philosophy. It's a decades-old format that has not aged well in many regards. If you are making computer music, I promise more interesting things will happens if you avoid using MIDI.
The MIDI standard was built by keyboardists, for keyboardists. As a result, it is very difficult to not think/sound like a keyboardist while using MIDI. Two very keyboard-y things include polyphony, and blocky chord progressions.
In the computer music world, neither of these are all that interesting to explore.
In other words, using MIDI will force you to think about music in a specific way.
Traditional MIDI is a low-resolution standard. Continuous control is 7-bit, or 128 steps. This can cause an unwanted zipper effect for parameter control. As a result, most synthesizers must employ smoothing to compensenate for this. Smoothing filters introduce a syrupy kind of latency which dulls responsiveness.
With a bit of effort, 14-bit control can be done using pitch the bend parameter. 14-bits is quite decent, but it's a hack on the standard.
The MIDI file format has low temporal resolution. It uses a metric known as pulses-per-quarternote or PPQ. A good typical setting for this is 96.
For how it is used in a modern context, MIDI is a monstrously complex standard, full of legacy cruft that is unused today. For instance, when was the last time a synth properly used polyphonic aftertouch channel voice message?
MIDI makes it too easy for composers to write medicore sounding music. If you've ever heard music that "sounds like MIDI" this is what I mean. This is usually due to a mixture of things. Many composers will generate a MIDI file and use general MIDI soundfonts, which tend to sound cheap and dated. Poorly sequenced MIDI that is keyed in rather than performed often will sound repetitive and fatiguing. This is because it is easy to forget to add humanization and nuance.
MIDI is well suited to think about music in terms of events, notes, and sequences. When composing with MIDI, it is very easy to just get sucked into getting those things right. Continuous events like phrasing and shaping can often get forgotten, and these are crucial to making expressive and compelling performances.
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