Abstract: An analysis system for accurately measuring the time-of-flight of an audio signal generated in response to a stimulus signal by an electro-acoustic transducer of an electro-acoustic system, such as an audio loudspeaker, to a point of measurement. The measurement is made by correlating the audio signal to a second signal having the same characteristics as the stimulus signal, but is delayed with respect to the stimulus signal. The measurement identifies the total overall delay from the time the stimulus signal is generated to the time the resulting audio signal is detected. Thus, any system delays, such as those due to signal processing, have already been accounted for by the measurement. Some or all of the measurement process may be automated through software programming in order to minimize measurement time. The time-of-flight is the delay time corresponding to when the stimulus signal, or the delayed second signal, and the resulting audio signal reach peak correlation.

Abstract: A method and apparatus for analyzing performance parameters of an electro-acoustic system. The bandwidth of the electro-acoustic system is determined by applying a broad band stimulus signal to its input, and picking up the resulting acoustic signal with a microphone. The microphone output is then applied to a state variable filter having a low-pass filter output, a high-pass filter output, and a band-pass filter output. The operating frequency of the state variable filter is changed incrementally through each of a plurality of frequencies. The high and low frequency responses of the electro-acoustic system is determined on the basis of the operating frequencies of the state variable filter at which accumulated values of the outputs of the state variable filter bear certain relationships to each other.

Abstract: An audio system having an improved sound field by generating a center audio channel from left and right stereo channels. The center channel is preferably generated by summing the left and right channels, and then filtering the resulting output. The center channel signal is also combined with the left and right channel signals to remove a portion of the monophonic information from the left and right channels thereby maintaining a constant level of monophonic information in the sound field.

Abstract: An audio processing system for injecting left and right channel audio signals with a signal having a fundamental frequency component that is half the frequency of the highest amplitude low frequency component in the left and right channel audio signals. The left and right channel audio signals are combined to form a monaural signal that is low pass filtered and applied to a demodulator circuit. The demodulator circuit generates a control signal having a frequency that is half the frequency of the highest amplitude frequency component in the signal at the output of the band pass filter. The control signal varies the phase of the signal at the output of the band pass filter according to the polarity of the control signal. The resulting signal is selectively added to the left and right input signals.