Two-Tone Doorbell Using IC 555
https://maker.pro/arduino/projects/two-tone-doorbell-using-ic-555
Learn how to build a two-tone doorbell using an IC 555 for around $3.
ECH83 Guitar Preamplifier with Tone Control on 12V DC
https://maker.pro/analog/projects/ech83-guitar-preamplifier-with-tone-control-on-12v-dc
Simple single tube preamplifier with tone control that includes options for adjusting the bass, midrange, and treble frequencies. It also has gain, volume, and input sensitivity controls.
DIY Electronic Horn for a Bicycle or Car
https://maker.pro/arduino/projects/diy-electronic-horn-for-a-bicycle-or-car
Learn step by step how you can build a bicycle horn with variable tone and volume.
Guide On Implementing Audio Signal Detector
https://maker.pro/custom/projects/guide-on-implementing-audio-signal-detector
The guide describes the implementation of an audio signal detector with the GreenPAK SLG47512. This design can detect human speech or music and can ignore single tone noise or flat random noise. The audio signal detector can be used in safety services or to save energy in audio decks.
5.1 channel analog audio processor
https://maker.pro/arduino/projects/51-channel-analog-audio-processor
This project is a 5.1-channel, USB analog audio processor based on PT2322 and Arduino Nano. This inexpensive audio processor contains 6-channel individual channel attenuators, a 3-way tone control system for front-end speakers, and a 3D audio simulation system.