Play musical notes from any computer keyboard

I built this crate so that my baby could play multiple notes at the same time just by using a computer keyboard I already had. Basic music toys we had only played one note at a time so it was an excuse for a side project.

Setup

For those new to Rust: download the toolchain here

Run the program: cargo run --release (debug profile can cause lag in generating stream)

Mapping keys to frequencies

Given the scan code of the key pressed, the row and column number are calculated for scan codes less than 64 (mostly the alphabetic keys and numeric keys above). This crate configures the frequencies of neighbouring keys to have strong consonance: neighbour to the right has frequency 4/3 times higher (perfect fourth) and upper right diagonal neighbour has frequency 3/2 higher (perfect fifth).

Use of external crates

• The cpal crate is used to play audio streams which this crate generates based on what keys are pressed.
• The winit crate is used to handle key press and release events.
• An unbounded multi-producer multi-consumer channel from the async-std crate is used to pass messages between winit's EventLoop and dashmap's DashSet to store the set of keys pressed.
• The Lazy wrapper from once_cell is used to arbitrarily construct static variables to satisfy Rust's borrow checker