Six-axis surround sound processor with automatic balancing and calibration

• US 5,666,424 A
• Filed: 04/24/1996
• Issued: 09/09/1997
• Est. Priority Date: 06/08/1990
• Status: Expired due to Term

• Current Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Original Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Inventors: Fosgate, James W., Wolfe, Samuel John
• Primary Examiner(s): HARVEY, MINSUN OH
• Application Number:
  US08/637,071
• Time in Patent Office: 503 Days
• Field of Search: 381/18, 381/1, 381/17, 381/19, 381/22, 381/21, 381/23, 381/20, 381/104, 381/107, 381/108
• US Class Current: 381/18
• CPC Class Codes: H04S 3/02 of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other
• CPC Class Codes: H04S 5/005 of the pseudo five- or more-channel type, e.g. virtual surround
• CPC Class Codes: H04S 7/301 Automatic calibration of stereophonic sound system, e.g. with test microphone
• CPC Class Codes: H04S 7/302 Electronic adaptation of stereophonic sound system to listener position or orientation H04S7/301 takes precedence
• CPC Class Codes: H04S 7/40 Visual indication of stereophonic sound image

Abstract

A surround sound processor system for multichannel redistribution of stereophonic signals has digitally controlled gains in each input and each output channel, controlled by a microprocessor, which receives an input signal from a microphone placed at the preferred listening location within the listening area for automatically balancing the input signals and setting both input and output gains during a calibration process so as to provide the listener with the best possible surround sound reproduction of the stereophonic source material. As a visual aid, the microprocessor displays menus and messages on a video screen, and a visual display shows the relative levels of the six axes of control signals within the surround sound processor.

Claims

1. A surround sound processor system including a control unit for multichannel redistribution of sound for reproduction by a plurality of loudspeakers surrounding a listener, comprising;

a plurality of stereo audio inputs for receiving stereo audio signals from one or more source units;

a selection means for selecting one of said plurality of stereo audio signals as a left and a right channel audio input signal;

a digitally controlled gain adjustment circuit in each of said left and right channels for controlling the amplitudes of said left and right audio input signals;

a surround sound processor for combining said left and right audio input signals in fixed and varying proportions according to the directional information contained therein as a result of the instantaneous relative magnitudes and phases of said left and right audio input signals which is detected by a direction detector circuit, said surround sound circuit comprising a a matrix circuit for combining said left and right audio input signals, said matrix circuit including voltage controlled amplifiers which are controlled by a multiplicity of control voltage signals derived from the output signals of said direction detector circuit after said control voltage signals have passed through a detector splitter and a servologic circuit for controlling the attack and decay time constants associated therewith, to provide at the outputs of said surround sound processor a plurality of loudspeaker drive signals;

a plurality of digitally controlled attenuator circuits equal to said plurality of loudspeaker drive signals for adjustment of the output signal level of each of said digitally controlled attenuator circuits;

a calibration signal source;

a microphone for placement at a point in the area surrounded by said plurality of loudspeakers;

a preamplifier and level detector circuit for receiving the input from said microphone and producing therefrom a direct voltage proportional to the sound intensity at the location of said microphone and converting said direct voltage to a digital signal; and

a microprocessor controller so configured in a calibration mode as to receive said digital signal from said microphone and to automatically adjust the gains of each of said plurality of digitally controlled attenuators when the output of said calibration signal is applied thereto so that the sound intensity due to each of said plurality of loudspeakers at the microphone position is the same.

2. The system of claim 1 wherein said microprocessor controller is configured in an input level calibration mode to measure the amplitudes in each of left and right channels of the selected one of said plurality of stereo audio signals from said sources when a reference signal is applied thereto at a standardized level, and to adjust the gains of said digitally controlled gain adjustment circuits so that the levels of said left and right audio signals applied to said surround sound processor are equal to a prescribed reference level.

3. The system of claim 2 wherein the appropriate digital words corresponding to the required gain of each of said digitally controlled gain adjustment circuits for each of said plurality of stereo audio signals are retained in the memory of said microprocessor controller for initial setting of the gain of each of said digitally controlled gain adjustment circuits each time a specific one of said signal sources is selected by said selection means.

4. The system of claim 1 further comprising an automatic balancing detector responsive to the relative magnitudes of left and right signals that are almost equal and in phase and providing therefrom a first logical control signal indicating the presence of nearly equal in-phase signals, a second logical control signal indicating that the left signal is significantly stronger than the right signal, and a third logical control signal indicating that the right signal is significantly stronger than the left signal;

and wherein said microprocessor controller may be configured in a signal playback mode to constantly monitor said first, second and third logical control signals and continually adjust incrementally the gains of said left and right channel digitally controlled gain adjustment circuits according to a predetermined method so as to cause such nearly equal in-phase left and right signals to be brought into balance and maintained in balance.

5. The system of claim 4 wherein said predetermined method comprises the steps of:

determining when said first logical control signal is high;

during a period when said first logical control signal is high corresponding to the presence of nearly equal in-phase left and right audio input signals, determining whether either of said second or third logical control signals is high and remains high for a specified minimum number of sample times;

whenever said second or third logical control signal has remained high for more than the specified number of sample times, first gradually reducing the incremental gain compensation added to the one of the left or right channels which has the higher signal level, if any, and then adding incremental gain compensation to the channel which has the lower signal level, until the one of said second or third logical control signals that was high becomes low, or until said first logical control signal goes low, or until a maximum amount of incremental gain compensation has been added; and

after a balanced condition has been reached, or said first logical control signal has gone low, or said maximum amount of incremental gain compensation has been added, very gradually reducing the incremental gain compensation that has been added until the said second or third logical control signals again begin to go high when said first logical control signal goes high, indicating that sufficient imbalance between the left and right input audio signals exists to recommence automatic balancing of the signals.

6. The system of claim 1 wherein said calibration signal source is a weighted noise source.

7. The system of claim 1 wherein the method for adjustment of each of said plurality of digitally controlled attenuators comprises the steps of:

monitoring the sound intensity at the location of said microphone by comparing the said digital signal representing the sound intensity with a reference value;

if the sound intensity is initially too low, gradually increasing the incremental gain compensation applied to the said digitally controlled attenuator until the sound intensity is higher than the reference value;

otherwise, or when the sound intensity has been made higher than the reference value, gradually decreasing the incremental gain compensation until the sound intensity falls just below the reference value, then increasing the incremental gain compensation until the sound intensity just exceeds the said reference level;

or, if the sound intensity cannot be adjusted to be just above the said reference level, restoring the original incremental gain adjustment settings and indicating to the user that the attenuator cannot be set to the desired level; and

proceeding to the next in sequence of the said plurality of loudspeaker drive signals to adjust its gain in the same manner;

until all the loudspeaker drive signals'"'"' attenuator means have been adjusted to the proper levels.

8. The system of claim 2 wherein the method for adjustment of the digitally controlled gain adjustment circuits in each of the left and right stereo audio inputs comprises the steps of:

monitoring the audio signal level by comparing it with a reference value;

if the audio signal level is initially too low, gradually increasing the incremental gain compensation applied to the said digitally controlled gain adjustment means until the audio signal level is higher than the reference value;

otherwise, or when the audio signal level has been made higher than the reference value, gradually decreasing the incremental gain compensation until the audio signal level falls just below the reference value, then increasing the incremental gain compensation until the audio signal level just exceeds the said reference level;

or, if the audio signal level cannot be adjusted to be just above the said reference level, restoring the original incremental gain adjustment settings and indicating to the user that the digitally controlled gain adjustment means cannot be set to the desired level; and

proceeding to the next in sequence of the said left and right audio input signals to adjust its gain in the same manner;

until both digitally controlled gain adjustment means have been adjusted to the proper levels.

9. The system of claim 8 wherein audio signal level further comprises the average signal level of a varying audio signal as determined by a method comprising the steps of:

comparing samples of the signal level with a reference level in hardware to determine that a certain minimum number of consecutive samples has either exceeded or not exceeded the reference level or that equal numbers have exceeded and have not exceeded the reference level in a given period of time;

but discarding any single samples which greatly exceed or fall below the expected range of values so that a single erroneous sample cannot cause an averaging error; and

if the numbers of high and low samples are equal, adjusting the gain higher after a certain interval has passed.

10. The system of claim 1 further comprising:

a visual display for indicating the relative magnitudes of each of the said multiplicity of control voltage signals therein.

11. The system of claim 10 wherein said visual display comprises:

a plurality of light-emitting diodes equal to said multiplicity of control voltage signals, each in series with a resistor connected to its cathode, the anodes of said light-emitting diodes being connected to a common point;

a like plurality of operational amplifiers whose outputs are each connected to the said series resistor connected to the cathode of a different one of said light-emitting diodes;

a first one of said operational amplifiers being connected as a unity gain buffer having its input connected to the one of said control voltage signals which goes negative in the presence of equal out-of-phase signals in the said left and right audio input channels;

a second one of said operational amplifiers being connected as a unity gain inverter whose input is connected to the output of said first one of said operational amplifiers, such that its output goes negative in the present of equal in-phase signals in said left and right audio input channels;

a third one of said operational amplifiers being connected as a unity gain buffer having its input connected to the one of said control voltage signals which goes negative in the presence of signals exclusively in the said left audio input channel;

a fourth one of said operational amplifiers being connected as a unity gain inverter whose input is connected the output of said third one of said operational amplifiers, such that its output goes negative in the presence of signals exclusively in the said right audio input channel;

a fifth one of said operational amplifiers being connected as a unity gain buffer whose input is connected to the one of said control voltage signals which responds such that its output goes negative to a combination of a larger amplitude left signal in combination with a smaller amplitude out-of-phase right signal; and

a sixth one of said operational amplifiers being connected as a unity gain inverter whose input is connected to the output of said fifth one of said operational amplifiers, such that its output goes negative in response to a combination of a larger amplitude right signal in combination with a smaller amplitude out-of-phase left signal;

said common point being connected to a collector of a transistor which provides a constant total current to said light-emitting diodes that is variable in response to a direct voltage applied to its base for the purpose of adjusting the overall brightness of the light-emitting diodes.

12. The system of claim 10 wherein the input of said third operational amplifier of said visual display may be switched to ground in order to cause the light-emitting diodes connected to the outputs of said third and fourth operational amplifiers to remain unlit.

13. The system of claim 10 wherein the input of said fifth operational amplifier of said visual display and that of said third operational amplifier may be switched to be connected in common to said control voltage signal negatively responsive to the presence of signals only in the left audio input channel.