ST was the first silicon vendor to introduce a Cortex-M7 chip.  Like the M4, the M7 has a floating point processor, and a specialized I2S peripheral called the SAI (Serial Audio Interface, I guess).

Floating point is a big help in computing envelopes for audio outputs.

The M7 also runs twice as fast as the M4.

The STM32F7-DISCO board includes an audio codec, the wm8994, and an audio output that works either for headphones or powered speakers.  In addition it has a 420 x 272 touchscreen, and a TFT color LCD.

So the hardware needed for the theremin is already in place.

All that was needed was the code, which this book provides.

Writing code for modern ARM processors is sometimes a challenging activity.  There are a great many modern peripherals on chip.  So many in fact that there are seldom enough processor pins to accommodate all the peripherals on the chip.  So only certain combinations of peripherals can be used at the same time.  Each peripheral must have its clock individually configured, and there are multiple layers to the chip libraries.  It is a good idea to have a completed project to use as a model.

Every detail of the development, from requirements through testing and validation is documented in the chapters of this book.  All of the code included in the final product is included in this book.  It is also available as source code, and in digital form as an extra you can download when you purchase the book. Just go to your leanpub library, click the XY Theremin icon there, and then click the extras entry in the menu that appears in the bottom half of the Library screen.

One of several free development environments is described, along with links to the silicon vendor's design and debugging tools.

There are several possibilities for expansion of the program.  One might add a capability of recording and playing back tracks played on the device using a micro-sdcard slot on the board.  It should be possible to add a 24dB per octave, variable cutoff, resonant filter to replace the simple smoothing filter supplied.

I wasn't interested in recording, and wasn't able to get the fancy filter working.