libmusic

libmusic is a powerful C library for spectral analysis, e.g. tone detection. It implements MUSIC algorithm to create a model of the signal that performs well even when the number of samples is limited. libmusic can detect double tones from just 8 samples (and single tones from 4) which makes it useful in VoIP for detection of DTMF which are too short to get detected by standard methods (e.g. Goertzel algorithm). In case of common 8 kHz telephony with PCMA/PCMU codecs, all DTMF fractions down to 1 ms can be detected (and removed)

libmusic was implemented in 2017 and integrated in DTMF fractions remover (FreeSWITCH module), created for VCC Live. Since then, it's been applied to many other applications and used by many companies, including BT

libmusic is available on GitHub