Patent Publication Number: US-2003223596-A1

Title: Audio multi-channel equalizer

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to an audio multi-channel equalizer with a plurality of bandpass filters for subdividing an audio signal into a plurality of channels. There are also level controllers associated with the channels and an optical level-indicating means, which contain semiconductor switches connected to the outputs of the bandpass filters for activation of optical indications.  
       [0003] These equalizers, which are used in the form, of graphic equalizers, enable a user to adjust the channels and to balance them relative to one another on the basis of optical indications of the respective channel level. Various means are conceivable as optical indications. Some examples of optical indicators are measuring instruments or LEDs. Optical monitoring of the channel levels is also referred to as visual feedback or closed-loop indication.  
       [0004] 2. The Prior Art  
       [0005] An audio multi-channel equalizer, of the type mentioned in the introduction, with optical indication of the channel level is known, for example, from U.S. Pat. No. 5,737,428. To activate the respective optical indications, this equalizer provides peak-value detectors, each of which comprise a sensing diode and a storage capacitor. These peak-value detectors are connected between the output of the respective bandpass filter and the semiconductor switch for activation of the associated optical indication, and are designed to discriminate the relative maximum of the signal of the respective channel from the many other signals. Regarding the optical channel-level indications, this known equalizer unfortunately has a large component expense which then discriminates the respective signals from one another for the purpose of optical indication.  
       SUMMARY OF THEE INVENTION  
       [0006] One object of the present invention is to provide an audio multi-channel equalizer which has a simpler optical level-indicating means than the prior art. This design results in a less costly configuration, while ensuring reliably of the intended optical indication.  
       [0007] Accordingly, the invention is a device for generation of a reference voltage which corresponds substantially to the average signal level of the channels and which is connected commonly to all semiconductor switches.  
       [0008] Thus, the inventive equalizer avoids the use of complex peak-value detectors and directly exploits the actual audio input signal in combination with the semiconductor switches for optical channel-level indication. These switches are used as comparators and are activated whenever the actual input-signal level exceeds the average signal level or a common signal-level threshold. The comparator effect creates an indicator of when the actual input signal exceeds the average signal level, by the fact that the longer the semiconductor switch is activated (by comparison with one period of the input signals), so also is the optical indication more intense or, brighter, whereby a reliable indication of the signal level of the individual channels relative to one another is available to the user.  
       [0009] There can also be a power source which acts as a device for generating a reference voltage, corresponding substantially to the average signal level of the channels. To achieve automatic adjustment of the reference voltage to the average signal level of the channels, this power source is preferably designed as a slow-response power source. To configure the optical indications of the inventive equalizer universally, the power source can be designed to be adjustable, meaning that its supply voltage can be appropriately adjusted so that it can be matched to the level of the audio input signal.  
       [0010] The semiconductor switch can be a transistor or any other known type switch.  
       [0011] The optical indications can also be of any desired intensity indications in the form of light-emitting diodes, but these indications can also be of any desired type. Furthermore, the inventive equalizer is preferably designed as a graphic equalizer. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawing. It is to be understood, however, that the drawing is designed as an illustration only and not as a definition of the limits of the invention.  
     [0013] In the drawing, wherein similar reference characters denote similar elements throughout the view:  
     [0014]FIG. 1 shows a schematic circuit diagram of an audio multi-channel equalizer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0015] As FIG. 1 shows, the audio multi-channel equalizer contains an amplifier  12  with an input  14  and an output  16 . Amplifier  12  has a first amplifier control stage  18  having an operational amplifier  20  and an amplifier controller  22  in the form of a potentiometer in the feedback loop. Amplifier control stage  18  feeds a two-stage amplifier  24 , which contains first and second operational amplifiers  26 ,  28  respectively. First stage  26  has an output  27 , which is connected to an inverting feedback amplifier  30 . Bridge circuit  36  includes amplifier  24  disposed in bridge circuit  36  between an input  32  of first stage  26  and an input  34  of second stage  28 . Amplifier  30  or bridge circuit  36  generates an output signal for bridge circuit  36  on line  38 .  
     [0016] Bridge circuit  36  contains a plurality of level controllers  40 A to  40 N, a corresponding plurality of filter networks  42 A to  42 N, or in other words one for each of a plurality of frequency bands, and RC-coupled control lines  44 A to  44 N, which are connected to center tap  46  of level controller  40  and to the corresponding outputs  47 A to  47 N of filters  42 A to  42 N.  
     [0017] Bridge  36  also contains a plurality of driver amplifiers  48 A to  48 N, which are connected to light-emitting diodes  50 A to  50 N respectively. Driver amplifiers  48 A to  48 N are based on semiconductor switches, which can be three-lead elements in the form of transistors. Each driver amplifier  48 A to  48 N or semiconductor switch is connected via a resistor to the output of a filter network  42 A to  42 N respectively.  
     [0018] All driver amplifiers  48 A to  48 N are connected via one lead such as the emitter electrode to a common line  56 , to which there is applied to common line  56  reference voltage whose magnitude is substantially the average signal level of the channels of the equalizer. This reference voltage, which is used as the threshold voltage, is supplied by a generating device in the form of a power source  70 , whose voltage supply can be toggled between a voltage minus V 1  and V 2 , specifically via switch  71 .  
     [0019] Power source  70  is preferably designed as a slow-response power source, so that the reference voltage can be automatically matched to the average signal level of the channels. In turn, the average number of active driver amplifiers  48 A to  48 N and of LEDs  50 A to  50 N activated thereby are limited at any time to a small number thereof corresponding to the channels with the highest average signal levels.  
     [0020] Because the semiconductor switches or driver amplifiers, which work as comparators, are connected to a common threshold level or to a common pulling voltage, the respective semiconductor switch is activated whenever the actual input signal level exceeds the common threshold level. The higher the actual input signal level lies above the common threshold, the longer the corresponding switch is activated compared with one period of the input signals and thus the greater is the perceptible brightness of the associated optical indicating means, or LED.  
     [0021] Accordingly, while at least one embodiment of the present invention has been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention as defined in the appended claims.