Abstract:
Apparatus for displaying the frequency spectrum of an audio signal. Multiple filters (20, 24, 25) are employed to divide an audio signal into signals each having a distinct frequency spectrum. The individual signals are combined to provide a composite reference signal. Individual comparators (26, 27, 28) compare each signal with the reference signal and individual light circuits are turned on and off in response thereto. A separation control (32) is provided to alter the magnitude of the reference voltage whereby a variation in separation between lights is achieved.

Description:
TECHNICAL FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to a modulated real time sound display apparatus. Specifically, a multi-channel sound display apparatus is provided which permits display of an audio signal spectrum in discreet frequency bands. 
     Sound display apparatus are known in the art which will visually display the frequency components contained within an audio signal. One such device is shown in U.S. Pat. No. 3,163,077 wherein a single input signal is divided to provide three signals having a different frequency spectrum. Such devices are known to provide a pleasant lighting effect which varies in response to the audio signal. Thus, in addition to listening to the audio signal, a visual impression is given which varies in accordance with the listened-to sound. It is desirable in light display apparatus to provide separation control whereby the individual lights activated in response to individual portions of the audio signal spectrum have a variable and selectable degree of separation between individual lights. For instance, a plurality of lights, each being responsive to a different frequency spectrum, can be controlled such that the lights appear to be distinctly operated independent from each other. 
     By using a preamplifier electrically disconnected from the remainder of the circuit and an amplifier for conveying an isolated audio signal to circuitry connected directly to the main power line an instantaneous sound level is obtained which is completely rectified and averaged. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a light display which is modulated in response to an audio signal. 
     It is a more specific object of this invention to provide for a light display which independently controls separate light circuits in response to different portions of the frequency spectrum of an audio signal. 
     These and other objects are provided by apparatus in accordance with the present invention. 
     An audio signal representing audible information is divided into a plurality of frequency limited signals, each of the plurality of signals representing a different portion of the frequency spectrum of the input audio signal. A portion of each of the plurality of signals is combined to form a reference signal. The reference signal is indicative of the average energy content of the audio signal over the entire frequency spectrum. 
     Comparator means are provided for individually comparing each of the plurality of signals with the reference signal. The comparator means provides an output signal indicating the magnitude of the reference signal with respect to each of the signals contained in the plurality of signals. The Comparator means output signals are used to individually control each of a plurality of light circuits. Thus, each light circuit operates in response to the quantity of energy contained in one of the portions of the frequency spectrum of the audio signal. 
     In a preferred embodiment of the invention, means are provided for supplying a varying signal to the reference signal whereby the reference signal cyclically varies above and below a level indicating the average energy content of the audio signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of an audio signal display apparatus in accordance with the present invention; and 
     FIG. 2 is a schematic diagram illustrating the interconnection between reference levels of a plurality of audio display apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a preferred embodiment of the present invention. The display apparatus of FIG. 1 is supplied with an operating voltage from an AC power line 7, 8. Switch and fuse 10 supply the necessary current through an isolation transformer in a known manner to a preamplifier power supply 11. A separate power supply 12 provides operating voltage for the remaining operational amplifier and comparators used in the apparatus of FIG. 1. Also connected to the AC power line is a radio frequency interference (RFI) network 13 and terminals 50, 51, 52. Terminals 50, 51, 52 provide voltage to one side of individual lighting circuits. Each lighting circuit includes a light source such as an incandescent light bulb. A low wattage bulb provides a fast response time as opposed to a high wattage bulb, which tends to lag behind the input. The return side of the individual lighting circuits 53, 54, 55 is connected to the anode of silicon controlled rectifiers, (SCR) 41, 42, 43. The RFI network 13 suppresses in a known manner any switching transients which may occur upon conduction of individual SCR elements. 
     Shown in FIG. 1 are summing resistors 14a and 14b which receive first and second stereophonically related signals. These signals can be the first and second channels of a standard stereophonic amplifier or pre-amplifier. The signals, when combined, are amplified by amplifier circuit 14. Amplifier circuit 14 having an adjustable gain is coupled through transformer 13 to amplifier 15. Amplifier 15 has an output terminal which supplies a composite audio signal to three bandpass filter circuits, 16, 18 and 19. The bandpass filter circuits 16 through 19 are provided in a known way by combining in tandem low pass and high pass filters. In a preferred embodiment of the invention, the first filter 16 has a passband lying principally between 90 and 400 cycles. Bandpass filter 18 provides a signal having frequency components between 400 and 2,000 cycles. Bandpass filter 19 has a filter characteristic permitting the passage of signal components having a frequency between 2,000 and 10,000 cycles. The foregoing is only one example of how to divide the frequency spectrum. Those skilled in the art will recognize other groups of frequencies which may be utilized, and additional filters may be used to derive signals for operating additional light circuits, as desired. 
     Each bandpass filter is terminated with a potentiometer 16a, 18a, or 19a. The potentiometers serve as channel intensity control devices, the devices selecting the brightness level of an individual lighting circuit for a given energy level of the signal provided by the respective filter. 
     The signals from the potentiometers 16a, 18a, and 19a are applied to a rectifier circuit. The rectifier circuits 21, 22, and 23 comprise an amplifier 21a, 22a, and 23a connected to a diode 21b, 22b or 23b. The amplifiers provide for a minimum loading on the filter circuits, and the rectifiers, as is well known, provide a single polarity voltage. 
     The individual rectified signal voltages are applied to post-rectifying filter circuits 20, 24, and 25. These filter circuits reduce variation of the derived rectified voltage. 
     Three comparators, 26, 27, and 28 are shown which receive as one input the individual rectified signal voltages. Additionally, the individual comparator circuits 26, 27, and 28 receive a common reference voltage. A common comparator input voltage is derived from a potentiometer 32 which serves as a separation control. Potentiometer 32 receives as one input a timed alternating current signal shifted 90° from the voltage applied to terminals 50, 52. The 90° phase shifted current is provided by phase shift network 39 connected to amplifier 35. Amplifier 35 has a DC offset associated with it which is selectable by varying potentiometer 36. Potentiometer 36 receives bias voltage from the bias network comprising resistor 37 and diode 38 connected between a source of DC voltage in a known manner. 
     The second input to potentiometer 32 is a DC voltage level representing the average energy content in the audio signal. This relatively constant average sound level voltage is derived from summing amplifier 30. Summing amplifier 30 combines the three signals from the individual rectifier circuits 21, 22, and 23 in a known manner. 
     Each individual comparator 26, 27, and 28 drives the control gate of one of SCR 41, 42, or 43. When an individual comparator senses the imput voltage to exceed the average sound level voltage, the comparator switches in a known manner thereby activating the respectively connected SCR 41, 42 or 43. The SCR thereby causes current to flow through the light load. 
     As the sound level increases or decreases, the triggering point for the comparator increases or decreases as well. The changing trigger point for the comparator also alters the ON time for a given SCR. Changes in the ON time for each SCR will provide for softer or more brilliant lighting of an associated light circuit. 
     Placing the separation potentiometer 32 in one extreme position will provide for a maximum independent operation between lighting circuits. In this condition, the individual lights display only their relative differences. With separation potentiometer 32 operated in the opposite position, little relative separation is visible. The lights have an intensity proportionate to the magnitude of energy contained in filters 20, 24, 25 supplying the signal to the respective comparators 26, 27, 28. Thus, in this condition, the lights will display the approximate values of energy contained in each filter circuit, and in the opposite condition as selected by separation potentiometer 32, will light only when the energy in a particular associated filter exceeds the total average energy of the three filters 20, 24, 25. 
     Potentiometer 36 provides a DC level for separation potentiometer 32. The potentiometer 36 provides a level adjustment for varying the light level of each channel to a common setting between completely turned off and half-power, corresponding to the time the SCR&#39;s are fully conducting for a full half cycle. 
     The apparatus of FIG. 1 may be used with other display apparatus. An interconection between the two display apparatus will provide for a united functioning of the separation control. Referring now to FIG. 2, there is shown two alternative techniques for providing coordinated separation control between display units. The circuits 201 shown in FIG. 2 are the respective signal generating units of two display units. In the circuit shown in FIG. 2, a four channel display unit 200, which uses 4 filters controlling SCR&#39;s is operated in connection with a three channel display unit 203 of FIG. 1. The alternate positions of each switch 203 provide for one of two different ways for interconnecting the average sound level voltage between two display units. One switch position represents the average sound level voltage provided by the 4 channel averager 200 and the three channel averager. Each summing resistor 202a and 200b are selected to have an equivalent value. Resistors 207 and 209 are selected to weight the 3 channel and 4 channel average respectively to provide a composite average of the 7 channels. In the other positions, each separation control uses the average sound level signal of the other device. 
     Thus, there has been described an apparatus which will display the spectrum of an audio signal by energizing different light circuits at different levels. Those skilled in the art will recognize other embodiments of the invention described more particularly by the claims which follow.