Digital sound level control apparatus

A digital sound level control apparatus for a main unit of a digital key telephone system for receiving signals grow a plurality of telephone circuits, each of said telephone circuits having a classification, said main unit including a circuit control section per telephone circuit for. determining the classification of an employed one of the plurality of telephone circuits, a PCM conversion section having a segment coder for compressing with the .mu.-Law PCM characteristic per telephone circuit, a main control section for designating a pad multiplier which defines an attenuation value corresponding to the determined classification of said employed telephone circuit, a digital sound level control apparatus per telephone circuits and digital time switch means for switching speech paths, said digital sound level control apparatus comprising:

• first discrimination means for discriminating a segment region of a .mu.-Law PCM conversion characteristic polygonal line from a segment region signal of a PCM input data signal which is outputted from said PCM conversion section, said PCM input data including a polarity signal, a segment region signal and a step signal;
• first calculation means for calculating a first level signal which is a data value before compression using an output signal of said first segment region discrimination means and the step signal of the PCM input data signal;
• multiplication means for multiplying said pad multiplier received from said main control section which defines said attenuation value corresponding to said classification of said employed telephone circuit by said first level signal to output a second level signal;
• second segment region discrimination means for discriminating a segment region of said second level signal by comparing the second level signal with the coding threshold values of segment regions based on the segment compression and decompression characteristic;
• second calculation means for calculating a step signal of said second level signal based on said second level signal, the coding threshold signal and intrinsic variation amount per step of the segment region of said second level signal;
• and
• register means for forming a .mu.-Law PCM digital signal combining the original polarity signal, the calculated segment region signal, and the calculated step signal.

A digital sound level control apparatus for a digital key telephone system for receiving signals from a plurality of telephone circuits, each of said telephone circuits having a classification, said apparatus comprising:

• means for decompressing a .mu.-Law PCM compressed digital signal received from a PCM conversion means to generate a decompressed digital signal,
• means for multiplying said decompressed digital signal by a multiplier received from said main control section, said multiplier corresponding to said classification of an employed one of said plurality of telephone circuits,
• means for compressing said multiplied decompressed digital signal to generate a multiplied .mu.-Law PCM digital signal, and
• means for outputting said multiplied .mu.-Law digital PCM signal to a digital time switching means.

A method for digitally controlling a sound level for a digital key telephone system for accessing a plurality of telephone circuits, each of said telephone circuits having a classification, said method comprising the steps of;

• decompressing a .mu.-Law PCM compressed digital signal to generate a decompressed digital signal,
• determining said classification of an employed one of said plurality of telephone lines;
• multiplying said decompressed digital signal by a multiplier, said multiplier corresponding to said classification of said employed one of said plurality of telephone circuits,
• compressing said multiplied decompressed digital signal to generate a multiplied .mu.-Law PCM digital signal, and
• outputting said multiplied .mu.-Law digital PCM signal to a digital time switching means.