There was a time when any hi-fi worth its salt had a little row of sliders on its front panel, a graphic equalizer. On a hi-fi these arrays of variable gain notch filters were little more than a fancy version of a tone control, but in professional audio and PA systems they are used with many more bands to precisely equalise a venue and remove any unwanted resonances.
On modern hi-fi the task is performed in software, but [Grant Giesbrecht] wanted an analogue equalizer more in the scheme of those fancy tone controls than the professional devices. His project makes for a fascinating foray into analogue filter design, as well as an understanding of how an equalizer combines multiple filters. Unexpectedly their outputs are not mixed because it proves surprisingly difficult to ensure all the filters have the same gain, instead they are in series with the signal path passing through all filters.
The resulting equalizer is neatly built upon a PCB with a 4-AA-cell power supply, and makes for a self-contained audio component. Unexpectedly such analogue equalizer have been few and far between here at Hackaday so it’s particularly pleasing to see. We’re more used to graphical displays for off-the-shelf devices.
There are a lot of tinkerers out there who got their start in electronics with musical hacks. Surprisingly though, we don’t see many submissions to our tip line covering boost circuits for electric basses, rewiring guitar electronics, or even more complex effect pedals. [Deadbird], though, is bucking that trend with an EQ display stomp box that fits neatly on his pedal board.
[Deadbird]’s build isn’t a graphic equalizer that can change the volume of different frequency bands; instead, he used the MSGEQ7 chip to listen in on the signal his guitar is producing and display that on a 128×64 graphic backlit display.
The entire project was prototyped on a breadboard with an Arduino. After he got all the components working – a momentary switch to turn the pedal on and off, 1/4″ jacks for the input and output, and a power supply – [Deadbird] took an Arduino prototyping shield and made everything more permanent. Now he’s got an attractive pedal on his board that shows the signal coming from his guitar in seven neat bands.
[Taichi Inoue] put together this beautiful visualization system called Yukikaze, japanese for “snow wind”. Basically a spectrum analyzer, Yukikaze is delightful to watch. We would love to see what kind of response he gets, as most of the footage shows very slowly changing smooth jazz. While we don’t think he gets crisp EQ visualizations out of this since it is a single large chamber, we still think it is amazing to watch.