1. A speech/silence discriminator comprising first filter means with a very wide band and having an input connected to an input of means of said discriminator and an output connected to a first input of a switch, second and narrow band filter means having an input connected to the input of a discriminator and having an output connected to a second input of the said switch; said narrow band second filter comprising one zero resetting input connected to respond to a "1" output of a two state circuit, a first quantization circuit means, divider means, third filter means with variable bandwidth having an input connected to the input of the discriminator and an output connected to an input of said first quantization circuit means the output of which is connected to the input of said divider means having an output connected to an input of a second switch, said second switch having another input connected to the "0" output of the said two state circuit, first comparator means, the output of the first switch being connected to a first input of said first comparator means and an output of the second switch being connected to a second input of said first comparator means, an output of a said first coparator means being connected to an input for controlling the change of state of said two state circuit, the "1" state output being activated to indicate the silent state in a speech signal, the output of the second filter being connected to the output of the first switch, memory means having an output connected to the output of the second switch, and the "0" state indicating the speech state in a speech signal, means for connecting the output of the first filter means to the output of the first switch and the output of the divider means to the output of the second switch, the bandwidth of the third filter decreasing as a function of time to a minimal bandwidth after it is set to a maximum bandwidth responsive to each activation of the "0" output state.