Expand description
In-band DTMF: keypad tones found in the call audio itself.
Carriers deliver keypresses in two ways. Out of band, as RFC 4733
telephone-events or a platform’s dtmf message; those are handled by the
SIP and Twilio bridges. Or in band, as the dual tones themselves inside
the audio: a SIP trunk without telephone-events, a transferred call, or a
caller pressing keys while the platform forwards raw media.
DtmfDetector finds in-band tones with the Goertzel algorithm over the
eight DTMF frequencies, in blocks of 25.6 ms (205 samples at 8 kHz), with
the checks ITU-T Q.24 receivers use: both a row and a column tone must be
strong, dominate their groups, sit within 8 dB of each other, and carry
most of the block’s energy, which is what keeps speech and music from
registering as digits.
Structs§
- Dtmf
Detector - Streaming in-band DTMF detector. See the module docs.