Apparatus equipped with a transmitting and receiving station for generating, converting and transmitting signals

A transmitting and a receiving station for generating, converting and transmitting and receiving speech signals are disclosed. The transmitting station includes a transducer for converting an acoustical signal into an analogue electrical signal and a band limiting filter for filtering out those components of the analogue electrical signal which have frequencies falling above or below a predetermined frequency band. An emphasizing circuit adjusts the amplitude of those frequency components of the band limited analogue electrical signal falling within the predetermined frequency band such that the power of each of the components is substantially equal. A syllabic amplitude compressor having a forward acting regulation time constant which is greater than its backward acting regulation time constant regulates the amplitude of the adjusted, band limited, analogue electrical signal. An analogue-to-digital converter samples the regulated, adjusted, band limited electrical analogue signal at a sampling rate which is less than twice the maximum of frequency of the predetermined frequency band. The analogue-to-digital converter has a non-linear quantization characteristic with smaller quantizing steps at signal input levels of smaller magnitude and larger quantizing steps at signal input levels of higher value.