Apparatus and method for decoding four channel sound

Apparatus for decoding first, second, third and fourth individual audio signals to the extent they are contained in first and second composite signals, the first composite signals containing the first individual audio signals in dominant proportion and two other individual audio signals in subdominant proportions and the second composite signal containing the second individual audio signal in dominant proportion and two other individual audio signals in subdominant proportions, comprising:

• a. means for measuring the degree of directional predominance of each of said four individual audio signals and for generating control signals which are a measure of such directional predominance;
• b. first, second, third and fourth output terminals;
• c. means responsive to said first and second composite signals for forming first, second, third and fourth partially decoded signals, each of said partially decoded signals including a different one of the individual audio signals in dominant proportion and two other individual audio signals in subdominant proportion;
• d. means for applying said first, second, third and fourth partially decoded signals to said first, second, third and fourth output terminals, respectively, each being applied at a level which depends on the control signal associated with its individual audio signal of dominant proportion;
• e. means responsive to said first and second composite signals for forming first, second, third and fourth enhancement signals, each of said enhancement signals having a different one of said individual audio signals as its principal component;
• and
• f. means for applying each of said enhancement signals to the particular ones of said output terminals at which its principal component is present in subdominant proportion, each of said enchancement signals being applied at a relative phase which is the opposite of said signals present in subdominant proportion and at a level which is a function of the control signal associated with its principal component.

A method of decoding first, second, third and fourth individual audio signals to the extent they are contained in first and second composite signals, the first composite signal containing the first individual audio signal in dominant proportion and two other individual audio signals in subdominant proportions and the second composite signal containing the second individual audio signal in dominant proportion and two other individual audio signals in subdominant proportions, comprising the steps of:

• a. measuring the degree of directional predominance of each of said four individual audio signals;
• b. forming first, second, third and fourth partially decoded signals, each of said partially decoded signals including a different one of the individual audio signals in dominant proportion and two other individual audio signals in subdominant proportion;
• c. applying said first, second, third and fourth partially decoded signals to first, second, third and fourth output terminals, respectively, each being applied at a level which depends on the degree of directional predominance of its principal component;
• d. forming first, second, third and fourth enhancement signals, each of said enhancement signals having a different one of said individual audio signals as its principal component;
• and
• e. applying each of said enhancement signals to the particular ones of said output terminals at which its principal component is present in subdominant proportion, each of said enhancement signals being applied at a relative phase which is the opposite of said signal present in subdominant proportion and at a level which depends on the measured degree of directional predominance of its principal component.

Apparatus for decoding first, second, third and fourth individual audio signals to the extent they are contained in first and second composite signals, the first composite signal containing the first individual audio signal in dominant proportion and two other individual audio signals in subdominant proportions and the second composite signal containing the second individual audio signal in dominant proportion and two other individual audio signals in subdominant proportions, comprising:

• a. means for generating four control signals which are a measure of the degree of directional predominance of the four individual audio signals, respectively;
• b. first, second, third and fourth output terminals;
• c. means for generating eight combination control signals by forming weighted differences between said four control signals;
• d. means responsive to said first and second composite signals for forming first, second, third and fourth partially decoded signals, each of said partially decoded signals including a different one of the individual audio signals in dominant proportion and two other individual audio signals in subdominant proportion;
• e. means for applying said first, second, third and fourth partially decoded signals to the first, second, third and fourth output terminals, respectively;
• f. means responsive to said first and second composite signals for forming eight enhancement signals, two each of said enhancement signals having a different one of said individual audio signals as its principal component;
• and
• g. means for applying each of said enhancement signals to the particular ones of said output terminals at which its principal component is present in subdominant proportion, each of said enhancement signals being applied at a relative phase which is the opposite of said signal present in subdominant proportion and at a level which depends on the measured degree of directional predominance of its principal component;
• said means including eight gain control amplifiers responsive to said eight enhancement signals, the gain of each gain control amplifier being controlled by a different one of said combination control signals.