If you have ever recorded video with a DSLR, you may find that setting the audio levels can be a guess. My camera (a Canon 7D) lets you set the levels and see the range with built in VU meters, but during recording, those meters disappear. The issue is if the voice gets louder or softer, you only find out during video editing. While you can buy a cheap mic monitors for a few hundred dollars but they only have simple VU meters for left and right channels. I decided to build a custom unit with a full spectrum display.
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Hence my project, the mic monitor was just completed. If features line in from my powered lapel mic, line out that goes to my camera's input, and a headphone jack for monitoring recording levels. It's built using a Teensy 3.2, an audio board, and a 2.8 inch TFT display. To keep this neat, I printed my own PCB board using thermal transfer paper and H2O2+muriatic acid for the etching solution. I also printed a 3D enclosure. The UI is quite simple and the code is nothing very fancy and is around 1000 lines. It has volume level control that can be dynamically set, a 30 band spectrum graph with option peak indicators, high and low pass filters, control over the background color for indoor/outdoor usage, and brightness control by dragging a finger up/down on the screen.
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It took me a while to get the right audio settings to minimize noise, but I now have the noise as low as my native mic.

The entire project cost around $70 and took several nights to complete. The results are exactly what I was after...full control and display of the mic levels being recorded.

I have a short YouTube video outlining the entire build process, a link to it's free source code, and links to the MCU and audio board.
https://youtu.be/tCUUaf6nYE8

Happy recording