Listening to music is, of course, primarily an audio experience. To complement this experience, however, a volume unit (VU) meter can be added to bounce up and down according to what is sent to the speakers. Taking this one step further, a spectrum analyzer breaks this output down into different frequency ranges, providing yet another way to visualize your music, and even spoken word content.
The Twin Audio Visualizer by Mark Donners (AKA The Electronic Engineer) allows you view two types of visualizations on separate screens at the same time, using a Teensy 4.1 plus a Teensy Audio Shield. A stereo VU meter is permanently shown on one screen, while the second can be switched between different visualization methods.
What makes this even more remarkable is that each of the two stereo spectrum analyzers channel has 69 frequency segments. Added together, along with the two VU meter channels, means that the system is outputting 140 discreet visualizations in real-time. In order to pull this off, even the powerful Teensy 4.1 needed a bit of an upgrade, with external PSRAM soldered onto the board.
The assembly used a custom PCB that is for sale on Tindie, which features accommodations for a microphone and line input/output. The board also includes connections for buttons, potentiometers, and an IR input. Firmware and board info is available on GitHub, this amazing device is demonstrated in the video below.