"You assume a lot about your readers."
I suppose so, I didn't think anyone except maybe those more than familiar with Python would go through it. 😅
"What is a MIDI keyboard? The only keyboard I have is my computer keyboard."
A MIDI keyboard/controller is something that sends MIDI signals used to control software instruments.
It's under the first heading: https://python.plainenglish.io/build-your-own-python-synthesizer-part-3-162796b7d351#b8e9
And like I mentioned in the note in the intro section of this post, in case you don't have a MIDI keyboard you may have to install VMPK (https://vmpk.sourceforge.io/) which replicates one using your computer keyboard.
"Also, the code you provided, in all the three parts, leave out a lot."
Sorry about that.
The code snippets were meant to be purely illustrative, not all encompassing, for that I have added links to the Jupyter notebooks containing the code at the end of each of the posts in the final section.
"Even in the third part, which you claim to be simple, does not run."
Install the libraries and give it a go, it should work, I spent time ensuring it runs (well, at least on my system).
Let me know if it throws any errors, I'll help you out.
"Also, in the first part, I am unable to produce the series of sine curves. How too do them?"
It's a Colab notebook containing all the code from the first post. So it contains the code for generating the curves and the audio samples too, it should run in your browser without any additional setup.