I just received an email from a reader of Practical Electronics magazine in the UK. This reader, who we will call Simon (because that’s his name), had recently run across my old Bodacious Acoustic Diagnostic Astoundingly Superior Spectromatic (BADASS) display project — as illustrated in this video with my chum Ivan pressing the buttons — and was asking for details regarding the use of the MSGEQ7 audio spectrum analyzer IC.  
Just in case you’ve never heard of the MSGEQ7 audio spectrum analyzer, this little beauty is a cheap-and-cheerful 8-pin dual in-line (DIL) integrated circuit that accepts an audio stream as input and splits it into seven different “frequency buckets.” You can then use your microcontroller to read the values in these frequency buckets to see how much base, middle, treble, etc. you have on a moment-by-moment basis, and you can use these values to drive technicolor LED displays. When I created the BADASS display, I took the stereo output from the headphone socket on an iPod (running at about 70% full volume), fed the two channels into two MSGEQ7 devices, and then used an Arduino Mega to loop around reading the frequency values from the MSGEQ7s and displaying them on 16 strips of NeoPixel tricolor LEDs. If you are interested, you can click here to see the code I’m using in the BADASS display. To be honest, it’s been ages since I looked at this, and I have to say that I’m quite impressed how small it is for all the effects I manage to squeeze out of it. More recently, in the case of my Awesome Audio-Reactive Artifact — as illustrated in this video with my chum Ronnie pressing the buttons — I used a single MSGEQ7 being fed by an ADMP401-based INMP401 MEMS Microphone Breakout Board (BOB), which costs $10.95 from the guys and gals at SparkFun.  
Fortunately for Simon, I’ve written quite a few columns on the MSGEQ7 over the past few years, with the following being the most relevant for someone who is just starting to think about experimenting with this little scamp: I also told Simon that, if I were to build a new audio-reactive artifact, then a strong contender would be the decidedly drool-worthy 7-band audio spectrum analyzer shown in this video.  
Actually, it’s been quite a while since I looked at this video, but I just watched it again, and I must admit I feel my creating juices starting to flow…