231181 ⎘
Details of selecting apparatus or arrangements; Electrical details; Signalling arrangements; Manipulation of signalling currents using alternate current
Sub-classes:Tone, modulated tone, and saturated tone detection in a voice activity detection device
#2Enhanced tone detector including adaptive multi-bandpass filter for tone detection and enhancement
#3Local control of call features in a telephone system
#4Tone, modulated tone, and saturated tone detection in a voice activity detection device