Patent ID: 7457420

Claim:
A method of distinguishing mono, dual mono, and stereo modes in an audio transmission, said method comprising: (a) receiving a current audio signal including a current control signal; (b) filtering the current control signal around a first frequency; (c) filtering the current control signal around a second frequency; (d) comparing the result of step (b) with the result of step (c); (e) predetermining an adjustable upper threshold whose amplitude is used to evaluate the audio transmission modes; (f) predetermining an adjustable lower threshold, whose amplitude is less than that of the upper threshold, which is used to evaluate the audio transmission modes; and (g) determining the current audio transmission mode wherein: (i) the mode is stereo when an amplitude of the result of step (b) is greater than the upper threshold times the amplitude of the result of step (c); (ii) the mode is dual mono when an amplitude of the result of step (c) is greater than the upper threshold times the amplitude of the result of step (b); and (iii) the mode is mono when: the amplitude of the result of step (b) is lower than or equal to the lower threshold times the amplitude of the result of step (c); and the amplitude of the result of step (c) is lower than or equal to the lower threshold times the amplitude of step (b); (iv) the mode is that of the mode of the preceding measurement when: the amplitude of the result of step (b) is lower than or equal to the upper threshold times the amplitude of the result of step (c) and greater then the lower threshold times the amplitude of the result of step (c); or the amplitude of the result of step (c) is lower than or equal to the upper threshold times the amplitude of the result of step (b) and greater then the lower threshold times the amplitude of step (b); and (v) the mode is mono when there is no preceding measurement and: the amplitude of the result of step (b) is lower than or equal to the upper threshold times the amplitude of the result of step (c) and greater then the lower threshold times the amplitude of the result of step (c); or the amplitude of the result of step (c) is lower than or equal to the upper threshold times the amplitude of the result of step (b) and greater then the lower threshold times the amplitude of step (b).