Stereo spatial enhancement system

A stereophonic signal processing system, for enhancing stereo performance of a compact stereo sound system, interposed in left and right stereo signal paths between a source providing a pair of stereo signals, designated L and R, and corresponding input ports of a stereo power amplifier driving stereo loudspeakers, said signal processing system comprising:

• left and right input ports of said system receiving said stereo signals from the source;
• left and right output ports of said system, driving the stereo power amplifier via the input ports thereof;
• left and right low-bass high-pass filter circuits, receiving L and R stereo signals as inputs from the left and right input ports of the system respectively, configured and arranged to provide as outputs the low-bass filtered stereo signals L' and R' wherein low-bass frequency components of the stereo signals are attenuated in a predetermined manner to minimize reproduction distortion by minimizing low frequency signal components in the compact loudspeakers below an effective frequency range thereof;
• a first resistor connected between the output node of said left low-bass high-pass filter circuit and the left output port of said system;
• an inverter circuit having an input node connected to the output node of said right low-bass high-pass filter circuit, and having an output node providing as output an inverted right stereo signal;
• a second resistor connected between the output node of said inverter and the right output port of said system;
• and
• a network of resistors and capacitors including said first and second resistors, configured and arranged to subtract the left and right stereo signals by adding the left signal to the inverted right signal, to thus provide a derived difference signal, to capacitively filter the derived difference signal and thus provide, via a pair of resistive circuit branches, upper-bass high-pass filtered left difference signal and right difference signals, and to separately sum such filtered left and right difference signals correspondingly with a filtered left stereo and an inverted filtered right stereo signals, and to provide a further right channel inversion so as to thus provide at said system output ports a spatially-enhanced right stereo output signal R' and a spatially-enhanced left stereo output signal L'.

A stereophonic signal processing system, for spatial enhancemeeent of reproduced sound in a compact stereo sound system having relatively small stereo loudspeakers driven by a stereo power amplifier, comprising:

• first and second input ports receiving first and second stereo signals from a stereo signal source;
• first and second output ports driving the stereo power amplifier;
• a differential amplifier, receiving the first and second stereo signals as inputs, configured and arranged to subtract the second signal from the first signal so as to derive and provide therefrom a difference signal;
• a difference-signal equalizer circuit configured and arranged to apply frequency-response shaping to the difference signal in accordance with a stepped low-boost equalizer function, providing an equalized difference signal at an equalizer output node;
• an inverter circuit configured and arranged to invert the equalized difference signal and to thus provide an inverted equalized difference signal;
• difference-signal filter means configured and arranged to filter the equalized difference signal and the inverted equalized difference signal in accordance with a high-pass filter function having a designated upper-bass cutoff frequency, thus providing an equalized filtered difference signal and an inverted equalized filtered difference signal;
• stereo-signal filter means constructed and arranged to separately filter the first and second stereo signals in a like manner in accordance with a predetermined stereo high-pass filter transfer function having a cutoff frequency at a designated low-bass frequency that is lower than the upper-bass cutoff frequency by a predetermined amount, the low-bass cutoff frequency being chosen to minimize reproduction distortion by minimizing low frequency signal components below the effective frequency range of the small loudspeakers;
• a first summing circuit configured and arranged to sum the the first stereo signal and the equalized filtered difference signal and to thus provide therefrom a first spatially-enhanced stereo output signal of said processing system;
• and
• a second summing circuit configured and arranged to sum the second stereo signal and the inverted equalized filtered difference signal and to thus provide therefrom a second spatially-enhanced stereo output signal of said processing system.

An audio signal process for enhancing the stereo performance in a compact stereo sound system wherein first and second stereo signals, processed according to the present invention, are delivered to a stereo power amplifier driving stereo loudspeakers that are relatively small and closely spaced, said process comprising the steps of:

• (a) subtracting the second stereo signal from the first stereo signal in a differential amplifier circuit configured and arranged to receive as input the first and second stereo signals, so as to derive therefrom a difference signal wherein rejection of correlated stereo signal content is made to vary with frequency in a predetermined manner;
• (b) applying frequency equalization to the difference signal so as to boost audio frequencies below a designated lower bass frequency region;
• (c) inverting the equalized difference signal by inverter means so as to derive therefrom an inverted equalized difference signal;
• (d) filtering the difference signal and the inverted equalized signal by a difference-signal high-pass filter function with a predetermined upper-bass cutoff frequency so as to provide a filtered equalized difference signal and a filtered inverted equalized difference signal;
• (e) adding the first stereo signal and the filtered non-inverted equalized difference signal in a first summing circuit so as to thus provide, as a first output of said processing system, a first channel modified stereo output signal;
• and
• (f) adding the second stereo signal and the filtered inverted equalized difference signal in a second summing circuit so as to thus derive, as a second output of said processing system, a second channel modified stereo output signal.

An audio signal process for enhancing the stereo performance in a stereo sound system wherein first and second stereo signals, processed according to the present invention, are delivered to a dual stereo power amplifier driving stereo loudspeakers that are relatively small and closely spaced, said process comprising the steps of:

• (a) subtracting the second stereo signal from the first stereo signal in a differential amplifier circuit receiving as input the first and second stereo signals, so as to derive therefrom a difference signal;
• (b) applying frequency equalization to the difference signal so as to boost lower audio frequencies;
• (c) inverting the equalized difference signal in an inverter so as to derive therefrom an inverted equalized difference signal;
• (d) filtering the difference signal and the inverted equalized signal by a difference-signal high-pass filter function with a predetermined upper-bass cutoff frequency so as to provide a filtered equalized difference signal and a filtered inverted equalized difference signal;
• (e) filtering the first and second stereo signals by a predetermined stereo high-pass filter function defining a predetermined low-bass cutoff frequency below an effective frequency range of the small loudspeakers, the low-bass frequency being chosen to minimize reproduction distortion by minimizing low frequency signal components below an effective frequency range of the small loudspeakers;
• (f) adding the first stereo signal and the filtered non-inverted equalized difference signal in a first summing circuit so as to thus provide, as a first output of said processing system, a first channel modified stereo output signal;
• and
• (g) adding the second stereo signal and the filtered inverted equalized difference signal in a second summing circuit so as to thus provide, as a second output of said processing system, a second channel modified stereo output signal.