GoKawiilIn 2016, I bought an LED strip and decided to make it react to music in real time. I figured it would take a few weeks, but it ended up being a rabbit hole. Ten years later, the project has 2.8k GitHub stars, has been covered by Hackaday, and is one of the most popular LED strip visualizer projects available. People have built it into nightclubs, integrated it with Amazon Alexa, and used it as their first electronics project.
I'm still not satisfied with it.
The scroll effect. Colors originate from the center and scroll outward, reacting to music in real time.
Volume Is Easy
I started with non-addressable LED strips where I could control the brightness of the red, green, and blue color channels independently, but not the individual LED pixels. I tried the most obvious thing first: read the audio signal, measure the volume, and make the LEDs brighter when it's louder. These were all relatively straightforward time domain processing methods. Read a short chunk of audio around 10-50ms in duration, low pass filter it, map the intensity to brightness.
I assigned each color channel to a different time constant to get a kind of color effect. One color would respond rapidly to changes in volume, one would respond slowly, and one in the middle. You can get something like this working in an afternoon and it looks okay on an LED strip or a lamp with a single RGB LED.
It gets boring fast. All the interesting frequency information is lost and it works best on punchy electronic music. It is terrible on many other kinds of music where volume is not the most interesting feature. There is no understanding of what kind of sound the system is reacting to, just how loud it is.
I also had to implement adaptive gain control almost immediately. If you set a fixed volume threshold, the visualizer either saturates in a loud room or barely flickers in a quiet one. My favorite way to do this was with exponential smoothing a simple and effective filter that I used over and over in various parts of the code.
Although the time domain visualizer was okay, I found the limited output channels made the result unsatisfying. There is only so much information you can display on three color channels. Eventually, I switched to WS2812 addressable LEDs so that I'd have many more output features to work with.
The earliest prototype, 2017. Non-addressable LEDs, controlling only global brightness per color channel. Before I discovered the mel scale, before addressable LEDs. This is where it started.
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