KR20010110799A - Centralizing of a spatially expanded stereophonic audio image - Google Patents

Abstract

In stereo systems with sum and difference signals with extended spatial imaging, the concentration of the central audio component in the more central direction is achieved by equalization of the (L + R) sum signal. Equalization involves increasing the treble response of the sum signal through the desired bass reduction achieved by using the gyrator to economically synthesize inductance while reducing bass response. In addition, the equalization in the (L + R) sum signal to reduce the low frequency signal and increase the high frequency signal is switchable between "on" and "off" modes, either alone or in concert.

Description

Centralization of spatially extended stereo audio images {CENTRALIZING OF A SPATIALLY EXPANDED STEREOPHONIC AUDIO IMAGE}

Stereo enhanced audio systems typically handle sum (L + R) and difference (LR) signal components, which sum (L + R) and difference (LR) signal components, if not otherwise available, It can be generated from the left (L) and right (R) signals of the pair. The difference signal can be used to produce a spatially extended stereo image when played through a pair of left and right speakers or through a surround system.

Boosting the level of the difference signal relative to the sum signal can widen such perceived sound image. Such processing of the difference signal involves equalization, including boosting of both bass and treble. However, increasing the level in the difference signal may have an undesirable effect on human perception of sound. In one example, boosting the difference signal at midrange audio frequencies may undesirably cause sound perception that is very sensitive to the listener's physical location relative to the left and right speakers. In addition, spatially expanded stereoimages do not preferably localize sound that would normally be emitted from the center, such as voices from people visually focused on the display of television or moving image programming. This is the case whether the sound system has one center speaker or just the left and right speakers.

In a system that increases the level of the (LR) difference signal with respect to the (L + R) sum signal to produce a spatially extended stereo image, (L + R) increases the treble response of the sum signal with (L + R). It has been found that reducing the bass response of the + R) sum signal helps the listener better concentrate the center audio component in the center direction.

The present invention claims priority from US Provisional Application No. 60 / 134,005, filed May 13, 1999.

1 is a graph showing the desired frequency response of a (L + R) sum signal to provide a desired centralized positioning effect on a central audio component.

2 is a block diagram for equalization in the (L + R) sum signal path and spatial image expansion equalization in the (L-R) difference signal path.

3 is a schematic diagram of the block of FIG. 2 providing equalization in the (L + R) sum signal path.

4 illustrates switching of the bass and treble equalization circuit of FIG.

5 illustrates an alternative embodiment to the switching of FIG.

For consumer products, it is necessary to keep costs low. In the present invention, in order to help the listener to concentrate the central audio component more centrally, the desired bass reduction in the (L + R) sum signal of the audio system can be achieved by using a gyrator to economically synthesize the inductance. It is recognized that it can. The inductance produced by the gyrator, in cooperation with the resistance in the (L + R) sum signal path, provides such a reduced bass frequency response economically while at the same time more expensive, bulky, hum and other electromagnetic / It avoids defects in the wound inductance that will be affected by the heterogeneous noise of static electricity and the pick-up of the signal. Thus, the inductance synthesized by the gyrator is more economical and can be used for the lower signal level portion of the audio system.

In addition, the equalization (s) of the (L + R) sum signal to reduce the low frequency signal and increase the high frequency signal is switchable alone or in concert between the "on" and "off" modes, and And / or variably adjustable alone or in concert. This switch capability / adjustment capability allows for greater flexibility in tailoring the system's response to the listener's satisfaction.

The drawings are now described.

Referring to the drawings in which like elements are given the same numerical designations, FIG. 1 is a nominal graph of the desired frequency response 10 of a (L + R) sum signal to provide a desired centralized positioning effect on a central audio component. Indicates. This frequency response varies the level of the bass response reduced between the maximum bass (14) and minimum bass (12) dotted lines starting at 580 Hz, the minimum response between 250 Hz and 300 Hz, and then at 100 Hz. It is represented by an increased bass response to 1 dB of gain. The nominal treble response increases from 580 Hz to a maximum gain of approximately 4 dB above about 2,000 Hz, within the minimum treble 16 and maximum treble 18 limits shown by dashed lines.

2 shows, in block diagram form, the equalizer 20 in the (L + R) sum signal path and the spatial image expansion equalizer 22 in the (L-R) difference signal path. Spatial image extension equalization 22 using (L-R) difference signals is known in the art.

2 shows (L + R) and (LR) signal formation from L and R signals, but this indicates that the detected signal is already in (L + R) and (LR) forms and provides separate L and R signals. It does not need to be the case for an FM or television stereo program in the United States, which must be matrix decoded in order to do so. Thus, as an example a matrixing encoder / decoder 24/26 is shown for the case where the difference (L-R) and sum (L + R) signals must be both encoded and decoded.

FIG. 3 shows a schematic diagram of block 20 of FIG. 2 providing equalization in the (L + R) sum signal path which helps the listener to concentrate the central audio component more centrally. The LC network 30 is a divider with a resistor 32 that effectively implements the bass frequency response of FIG. Simulated gyrator inductance 34 has a reduced impedance at lower frequencies, taking over the impedance of capacitor 36 in series with inductance 34 and raising the response at lower frequencies. Reduce the bass response through the divider resistor 32 up to. This divider can be placed at the input of the op-amp stage 38 which allows a simple serial RC network that buffers the signal and uses feedback around the op-amp 40 to provide the high frequency boost shown in FIG. have.

More specifically, gyrator 34 includes a general purpose transistor 42 having an emitter electrode connected to ground through resistor 44 and a base electrode biased through resistor 46. Capacitor 48 connected to the base electrode, in cooperation with the feedback resistor 50 in an emitter follower amplifier configuration with a gain of nearly one, provides an effective inductance of approximately 1.5 H (Henries) simulated with the gyrator. . There are other circuit configurations for providing a gyrator circuit, most of which can be used in the present invention. The configuration of the illustrated gyrator 34 is merely illustrative and is chosen to provide the required operation with minimal component cost.

Capacitor 36 connects gyrator 34 to resistor 32 to increase the gain at lower bass frequencies, i.e. to have a 1 dB gain at 100 Hz, as described above. Provides increased impedance at frequency. The bias provided through the resistor 46 places the transistor 42 in a linear operating range.

The high pass filter 38 includes an op-amp 40 having a feedback resistor 52 connected to its negative terminal, and a capacitor and resistor 54 connected to a bias source that also provides AC ground from the negative terminal. 56) and a serial RC network. To increase the frequency, the impedance of capacitor 54 drops and the feedback decreases, thereby increasing the gain of op-amp 40. The bias is adjusted to place the op-amp 40 in a linear operating range.

4 shows the switching of the bass and treble equalization (s) circuit of FIG. The equalization portion can be switched to the "on" or "off" mode alone or in concert. This allows great flexibility to tailor the system's response to the listener's satisfaction.

Such switching may be provided in response to each control signal provided by a microprocessor (not shown), which switching may suitably be discrete or provided to a monolithic integrated circuit. Achieved by commonly available devices such as relays, bipolar transistors, MOS / CMOS FETs, and the like. A control signal is applied to each transistor to saturate or cut off transistors 60, 62 in each gyrator and treble boost circuit. In addition, the control signal applied to the transistors 60 and 62 and the bias provided by the transistor 58 are variably adjustable, respectively, for the transistors 60 and 62 to " on " and " off " It can be adjusted within the limits of the control signal needed to switch between.

FIG. 5 shows an alternative embodiment to the switching device of FIG. 4, where switches for the gyrator 34 and the LC network 30 are removed from ground, so that the general switch 64 responds to each control signal. The high pass filter circuit 38 is shown as being switched by a general switch 66 in response to its respective control signal.

Exemplary values of the elements shown in the various figures are: resistor 32 is 3.3 kV, capacitor 36 is 0.22 kV, resistor 46 is 68 kV, resistor 44 is 1 kV, and resistor 50 is 2.2 kV, resistors 52 and 56 are 15 kV, and capacitor 54 is 0.01 kV. Transistors 42, 58, 60, and 62 may be, for example, 2N2222, which is a non-critical signal type, and op-amp 40 is a non-critical general purpose MC3404 op-amp.

As mentioned above, the present invention is used for the centralization of spatially extended stereo audio images.

Claims (18)

Means for providing (L + R) and (L-R) signals and respective signal paths; Means for providing spatially extended stereo audio effects in said (L-R) signal; Means for processing the (L + R) signal to focus the clear position of the center sound closer to the center between the left and right sound emitting speakers, Means for reducing a signal level at a bass frequency; Means for increasing the signal level of the high frequency, Said means for reducing the signal level of the bass frequency comprises a gyrator; Included, stereo audio system. 2. The stereo audio system of claim 1, wherein the gyrator is shunt for the (L + R) signal path. 2. The stereo audio system of claim 1, wherein the means for increasing the signal level of the high frequency comprises a high pass filter in series with the (L + R) signal path. 2. The stereo audio system of claim 1, wherein the bass signal reduction comprises a frequency within a band of 100 Hz to 580 Hz. 2. The stereo audio system of claim 1, wherein the treble signal increase comprises a frequency of at least 580 Hz. 2. The stereo audio system of claim 1, wherein reducing the signal level of the low frequency and increasing the signal level of the high frequency is switchable between " on " and " off " 7. The stereo audio system of claim 6, wherein the switching is in response to a control signal. 8. The stereo audio system of claim 7, wherein the control signal is provided by a microprocessor. Means for providing (L + R) and (L-R) signals and respective signal paths; Means for providing spatially extended stereo audio effects in said (L-R) signal; Means for processing the (L + R) signal to focus the clear position of the center sound closer to the center between the left and right sound emitting speakers, Means for reducing a signal level at a bass frequency; Means for increasing the signal level of the high frequency, The means for reducing the signal level to the bass frequency and the means for increasing the signal level of the high frequency may independently or cooperatively switch the processing means between the "on" and "off" modes. Included, stereo audio system. 10. The stereo audio system of claim 9, wherein the switching is in response to a control signal. 11. The stereo audio system of claim 10, wherein the control signal is provided by a microprocessor. Means for providing (L + R) and (L-R) signals and respective signal paths; Means for providing spatially extended stereo audio effects in said (L-R) signal; Means for processing the (L + R) signal to focus the clear position of the center sound closer to the center between the left and right sound emitting speakers, Means for reducing a signal level at a bass frequency; Means for increasing the signal level of the high frequency, Said means for reducing the signal level of the bass frequency comprises a gyrator, The reduction of the signal level of the low frequency and the increase of the signal level of the high frequency can be accomplished either independently or in concert to switch between the "on" and "off" modes. Included, stereo audio system. 13. The stereo audio system of claim 12, wherein the gyrator is in a shunt state for the (L + R) signal path. 13. The stereo audio system of claim 12, wherein the means for increasing the signal level of the high frequency comprises a high pass filter in series with the (L + R) signal path. 13. The stereo audio system of claim 12, wherein the bass signal reduction comprises a frequency within a band of 100 Hz to 580 Hz. 13. The stereo audio system of claim 12, wherein the treble signal increase comprises a frequency of at least 580 Hz. 13. The stereo audio system of claim 12, wherein the switching is in response to a control signal. 18. The stereo audio system of claim 17, wherein the control signal is provided by a microprocessor.