Provided is a liquid crystal light variable device having a liquid crystal cell, comprising a mixture of a liquid crystal material and one or more dichroic dyes interposed between a first and a second substrate, each substrate having a conductive layer disposed thereon. A speech dialogue system without special hardware for the processing of DTMF in-band signaling is provided and maintains, during the codec negotiation or the fixing of the coding method for application, that only services with DTMF out-of-band signaling, or signaling by means of dedicated data packets are carried out by the speech dialogue system. The fluorophore is usually a cyanine dye with variable substituents. A quantizing scale comparing section outputs the CBRq during constant rate encoding and outputs the larger one of the VBRq and CBRq during variable rate encoding.