What is Reddit's opinion of Yamaha REFACE CP Portable Electric Piano and Vintage Keyboard Sound Engine, Synthesizer?

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Hi! Looks like the perfect place to ask for recommendations.

I'm looking for a small keyboard and I'm a bit lost. My goal is to have something to visualize music theory on, try out some chords progressions and simple melodies, and maybe work the synchronization between the two hands. I'm a guitar player ( trying to learn theory) and I think that could be great to practice some concepts.

Looking at forums, they say 61keys is the minimum to learn piano. But I'd like a smaller keyboard, 60cm length or something, something easy to just sit on my bed or in front of my computer and try out things. What is the minimum amount of keys you'd recommend? Is 37 keys enough to work on synchronization between hands? I saw this one and the size looks nice ( maybe something cheaper though).

I think having built-in sounds would be nice, since having to plug a midi keyboard to my computer will stop me from playing sometimes. However I don't need 150+ sounds, with fancy ding-ding sounds. Just 3-4 nice sounds will be enough. Looks like the one I mentionned previously has that. But it's a bit expensive for me to start on.

Any suggestions?

I'm a curious newb that's been doing my best to soak up as much information as possible researching about synths and keyboards. A lot of this new jargon has been challenging to say the least. I have a question and I suppose I could've made a new thread but I feel like it's a dumb question so didn't want to draw too much attention.

I know it may not be fiscally or practically sensible but lets say that I want to get a Yamaha Reface CP as a mostly on-the-go-jam instrument but I also want to learn how to play keyboard in my room; so I decide that I want to have a master keyboard (lets say something with 49-88 semi-weighted keys w/ touch response) to play the Reface CP. What are my options? What constitutes as a master keyboard?

If I understand my research correctly, a MIDI keyboard controller with a MIDI dim (such as the Alesis Q61) plugged into the Reface CP won't act as Master.

I've seen discussions that mention using a powered MIDI USB host (such as a Hobbytronics MIDI Host) to make digital piano/keyboards with USB MIDI act as Master to the Reface CP but I don't understand which part of that equation makes that possible. Is it the fact that the digital piano has onboard sound or is the powered MIDI host playing some larger role besides merely extending the MIDI out signal from USB to MIDI dim?

Or to put it another way, would using a MIDI host with a MIDI keyboard controller (equipped with either USB or MIDI dim out) cause it to act as Master to the Reface CP when all plugged in together? This is of course assuming all of the components are compliant/compatible.

My instinct is that the device intended to act as Master always needs to have onboard sound and I'm letting the stuff I read about extenders over-complicate what is admittedly a pretty convoluted idea to begin with.