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Codex Taught Me How to Play Piano
TL;DR
Codex turned a MIDI piano into a live theory coach — the creator asked Codex to build a simple app that shows pressed keys in real time, then labels and explains what he’s playing instead of leaving him to “play it blindly.”
The breakthrough is going from copying songs to understanding why they work — using Lizzie McAlpine’s “Older” and pianist Taylor Mackall’s walkthrough as an example, he shows how Codex can analyze a favorite flourish and name the chord movement behind it.
Codex doesn’t just transcribe notes; it interprets musical structure — after recording a phrase, it explains details like “A-flat add9 to A-flat sus2” and frames it as a IV-to-I movement, making a dense voicing feel usable rather than mysterious.
That explanation unlocks transfer, not just repetition — once he realizes a fancy passage is basically a G-sharp chord spread across the keyboard, he can reuse the technique in other keys and while improvising.
He frames Codex as a ‘master teacher’ that follows his curiosity — instead of replacing a human instructor, it can open YouTube lessons like Open Studio’s “Root Shell Pretty,” inspect them, and help apply the concept to his own playing.
The Breakdown
A tiny app that makes the piano legible
He opens by showing the setup: Codex on the left, piano plugged into the computer, and a little app Codex made that displays whatever keys he’s pressing. The emotional hook is simple and genuine — for the first time, he can see what he’s doing and connect it to music theory instead of just messing around by feel.
Why this matters to someone who never wanted to grind scales
He tells a quick backstory about learning from an “incredibly cool jazz musician” while being basically the worst possible student, because he didn’t want to do the endless scales and discipline that formal training demands. Now, as an adult who just loves fooling around on piano and guitar, this setup fits how he actually learns: through obsession, taste, and curiosity.
From YouTube tutorials to actual understanding
He uses Lizzie McAlpine’s “Older” as the perfect example of the modern learning stack: any song you love probably has a YouTube breakdown, and in this case pianist Taylor Mackall literally teaches the part on Lizzie McAlpine’s channel. But even when he learns a passage he loves, there’s still a gap — he can play the flourish at the end, but he doesn’t know what it is or how to create more moments like it.
Record a phrase, then ask Codex what’s going on
The new move is dead simple: hit record, play the phrase, then tell Codex to inspect it and explain the theory. He says Codex pulls the saved phrase with time signatures and notes, then comes back with language like “A-flat add9 to A-flat sus2,” plus the functional idea that it’s basically a IV-to-I chord motion.
Making a scary voicing feel usable
The real aha moment is when he translates a fancy-looking shape into something intuitive: it’s “actually a G-sharp chord laid out across the keyboard.” That shift matters because now it’s not magic anymore — it’s a technique he can steal, move to another key, and use while noodling around.
Why theory becomes useful only when it attaches to taste
He says the classic warning from music people is that if you only learn isolated things you like, you never understand why they work, so nothing generalizes. His point is that Codex closes that gap: you can start from a sound you already love, ask “why do I like that?”, and then turn taste into transferable knowledge.
Codex as the always-on teacher who follows rabbit holes
He lights up describing Codex opening an Open Studio exercise called “Root Shell Pretty,” watching it in Atlas, and helping apply the concept wherever he wants. There’s even a funny interruption where Codex starts doing something unexpected and he blurts out, “Oh [__]” — which reinforces the vibe of having a smart, slightly uncanny collaborator using your computer alongside you.
Not a replacement for teachers, but a huge unlock for curious learners
He ends by being clear that this doesn’t replace a real music teacher. But for self-directed people who want to learn through whatever they’re excited about — piano, guitar, or anything else — he thinks this is “the best time in the world” to learn, because you can just fire up Codex and ask it to teach or build the tool you need.
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