Method for processing and reproducing audio signal at desired sound quality, reduced data volume or adjusted output level, apparatus for processing audio signal with sound quality control information or test tone signal or at reduced data volume, recording medium for recording audio signal with sound quality control information or test tone signal or at reduced data volume, and apparatus for reproducing audio signal at desired sound quality, reduced data volume or adjusted output level

An audio signal processing and reproducing method, comprising the steps of:

• converting analog audio signals of multiple channels into multiple digital data streams corresponding to the multiple channels, the multiple digital data streams having original maximum levels which are different from each other;
• producing level-shift control data responsive to a highest level among the original maximum levels of the multiple digital data streams;
• shifting levels of all the multiple digital data streams by a determined amount determined by the level-shift control data and resulting level-shifted data streams corresponding to the multiple channels;
• coding the level-shifted data streams and the level-shift control data to produce a packed data stream in a predetermined format to be transmitted or recorded;
• transmitting or recording the level-shifted data streams and the level-shift control data on a recording medium in a disc shape;
• decoding the packed data stream in a predetermined format to reproduce the level-shifted data streams and the level-shift control data;
• recovering the original maximum levels of the multiple digital data streams by adjusting levels thereof responsive to the level-shift control data transmitted or recorded;
• and
• outputting the multiple digital data streams having the original maximum levels thus recovered.