I was thinking the same. From Wikipedia: "The Goertzel algorithm is a technique in digital signal processing (DSP) for efficient evaluation of the individual

I was thinking the same. From Wikipedia: "The Goertzel algorithm is a technique in digital signal processing (DSP) for efficient evaluation of the individual terms of the discrete Fourier transform (DFT). It is useful in certain practical applications, such as recognition of dual-tone multi-frequency signaling (DTMF) tones produced by the push buttons of the keypad of a traditional analog telephone. The algorithm was first described by Gerald Goertzel in 1958." [0] It's also a nice project for an ESP32 with a MEMS microphone. [0] https://en.wikipedia.org/wiki/Goertzel_algorithm https://en.wikipedia.org/wiki/Goertzel_algorithm