Patent Publication Number: US-2018054690-A1

Title: Single channel sampling for multiple channel vehicle audio correction

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to vehicle audio systems and, more specifically, single channel sampling for multiple channel vehicle audio speaker correction. 
     BACKGROUND 
     Vehicles often include multiple, similar speakers in for example, vehicle doors, covered by door paneling. Modern mass produced commodity vehicle loud speakers can achieve good performance. However, due to material and cost considerations, these speakers have physical limitations on their performance, particularly the linearity of the speaker output. For examples, playing sounds at a high volumes causes listener fatigue, straining, and distortion. 
     SUMMARY 
     The appended claims define this application. The present disclosure summarizes aspects of the embodiments and should not be used to limit the claims. Other implementations are contemplated in accordance with the techniques described herein, as will be apparent to one having ordinary skill in the art upon examination of the following drawings and detailed description, and these implementations are intended to be within the scope of this application. 
     Systems and methods are disclosed for single channel sampling for multiple channel vehicle audio correction. An example disclosed sound system for a vehicle includes a sensing circuit, a channel manager, and a plurality of channel correctors. The example sensing circuit monitors the operational state of only one of a plurality of speakers. The example channel manager generates correction factors based on the operational state and a predicted state of the one of the plurality of speakers. Additionally, the plurality of channel correctors corresponds to the plurality of speakers. The example plurality of channel correctors apply the correction factors to signals driving the plurality of speakers by reading values of the correction factors. 
     An example method includes monitoring, with a sense circuit, an operational state of only one of a plurality of speakers. The example method also includes generating correction factors based on the operational state and a predicted state of the one of the plurality of speakers. Additionally, the example method includes applying the correction factors to signals driving the plurality of speakers. 
     An example sound system includes a plurality of speakers, a sensor, memory, and a circuit. The example sensor may be incorporated into an amplifier. The example sensor monitors an operational state of only one of the plurality of speakers. The example memory includes a virtual speaker table to store operational state and a predicted state of the one of the plurality of speakers. Additionally, the example circuit is communicatively coupled to the memory and the sensor. The example circuit generates correction factors based on the virtual speaker table, and applies the correction factors to signals driving the plurality of speakers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention, reference may be made to embodiments shown in the following drawings. The components in the drawings are not necessarily to scale and related elements may be omitted, or in some instances proportions may have been exaggerated, so as to emphasize and clearly illustrate the novel features described herein. In addition, system components can be variously arranged, as known in the art. Further, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  illustrates a vehicle with a sound system operating in accordance with the teachings of this disclosure. 
         FIG. 2  is a graph depicting speaker linearity. 
         FIG. 3  is a block diagram of electronic components of the multi-channel vehicle audio corrector of  FIG. 1 . 
         FIG. 4  is a flowchart of a method to correct vehicle multi-channel audio with a single channel sample that may be implemented by the electronic components of  FIG. 3 . 
         FIG. 5  is a flowchart of a method to read the virtual speaker table and apply compensation to all audio channels that may be implemented by the electronic components of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     While the invention may be embodied in various forms, there are shown in the drawings, and will hereinafter be described, some exemplary and non-limiting embodiments, with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
     Commodity vehicle sound systems generally include multiples of the same model of speakers. Typically, these speakers are in the vehicle doors. As disclosed below, a multi-channel vehicle audio corrector (sometime referred to herein as an “audio corrector”) determines and applies correction factors to the audio channels to correct for listener fatigue, straining, and distortion caused by non-linearity of the speakers. The multi-channel vehicle audio corrector generates the correction factors that are applied to each of the channels of the sound system based on measurements from one of the speakers (sometimes referred to as the “sampled speaker”). The correction factors are based on a comparison of dynamic current and voltage outputs of the one of the speakers (sometimes referred to as “actual values”) and signal inputs into the sampled speaker (sometime referred to as “predicted values”). Additionally, to generate the correction factors, the multi-channel vehicle audio corrector maintains a virtual speaker table that associates the predicted values with the corresponding actual values. The correction factors are regenerated dynamically to account for aging of the speakers and changes in environmental conditions. In some examples, an event, such as an ignition switch being set to a power position other than off, triggers the multi-channel vehicle audio corrector to regenerate the correction factors by applying a signal to the sample speaker. 
       FIG. 1  illustrates a vehicle  100  with operating in accordance with the teachings of this disclosure. The vehicle  100  may be a standard gasoline powered vehicle, a hybrid vehicle, an electric vehicle, a fuel cell vehicle, and/or any other mobility implement type of vehicle. The vehicle  100  includes parts related to mobility, such as a powertrain with an engine, a transmission, a suspension, a driveshaft, and/or wheels, etc. Additionally, the vehicle  100  may be non-autonomous, semi-autonomous or autonomous. In the illustrated example, the vehicle  100  includes speakers  104  and a sound system  106 . 
     The speakers  104  are vehicle speakers of the same model. While the speakers  104  are the same model, each individual speaker may have slightly different characteristics. The example speakers  104  are built into the doors of the vehicle  100 . Additionally or alternatively, in some examples, the speakers  104  are built into a dashboard and/or a center console of the vehicle  100 . Additionally, the vehicle  100  may also include tweeters (not shown) and a subwoofer (not shown).  FIG. 2  illustrates a graph  200  of a displacement and applied voltage for ideal speakers and actual speakers (e.g. the speakers  104 ). Ideal speakers are speakers that have a proportional, linear relationship between the displacement of the speaker and the voltage applied to the speaker over the expected range of the speaker. The voltage-displacement response of the ideal speaker is illustrated by line  202  on the graph  200 . Non-ideal speakers (e.g., the speakers  104 ), because of manufacturing, design and material limitations, have a non-linear relationship between the displacement of the speaker and the voltage applied to the speaker over portions of the useful range. The voltage-displacement response of the non-ideal speaker is illustrated by line  204  on the graph  200 . For example, at the upper and lower bounds of the non-ideal speaker&#39;s displacement, the voltage-displacement response may not be linear. As a result, for example, when voltage is applied to the non-ideal speaker in the non-linear portion of its voltage-displacement response, the sound produced by the non-ideal speaker may be strained and/or distorted. 
     In the illustrated example of  FIG. 1 , the sound system  106  is coupled to the speakers  104 . The sound system  106 , as part of an infotainment head unit or standalone amplifier, receives inputs from different sources (e.g., a radio tuner, a mobile device communicatively coupled to the infotainment head unit, applications, etc.) and generates an audio signal to play on the speakers  104 . The sound system  106  includes a multi-channel vehicle audio corrector  108 . From time to time, the multi-channel vehicle audio corrector  108  samples dynamic current and voltages from one of the speakers  104 . As discussed in connection with  FIG. 3  below, based on the samples obtained from one of the speakers  104 , the multi-channel vehicle audio corrector  108  determines corrections factors for all of the speakers  104 . The multi-channel vehicle audio corrector  108  alters the audio signal from the sound system  106  to correct for the non-linear portions of the range of the speakers  104 . 
       FIG. 3  is a block diagram of electronic components  300  of the multi-channel vehicle audio corrector  108  of  FIG. 1 . In the illustrated example, the multi-channel vehicle audio corrector  108  includes a volume, balance, and fade controller  302 , equalizers  304 , channel correctors  306 , an amplifier  308 , a sense circuit  310 , and a channel correction manager  312 . In some examples, the multi-channel vehicle audio corrector  108  also includes a digital-to-analog convertor (DAC)  314  and/or an analog-to-digital converter (ADC)  316 . 
     The volume, balance, and fade controller  302  receives an audio signal from the sound system  106 . In the illustrated example, the audio signal is a stereo audio signal that includes a left stereo signal and a right stereo signal. Alternatively, the audio signal may be a mono audio signal or a surround sound audio signal (e.g., 5.1 audio, 7.1 audio, etc.), etc. The volume, balance, and fade controller  302  adjusts the gain of the corresponding audio signals in audio channels  318 . Balance refers to adjusting the gains of the audio channels  318  associated with the speakers  104  on the driver&#39;s side of the vehicle  100  in relation to the audio channels  318  associated with the speaker  104  on the passenger&#39;s side of the vehicle  100 . Fade refers to adjusting the gains of the audio channels  318  associated with the speakers  104  in the front of the vehicle  100  in relation to the audio channels  318  associated with the speaker  104  in the back of the vehicle  100 . Volume refers to adjusting the gains of all the audio channels  318  associated with the speakers  104  of the vehicle  100 . 
     The equalizers  304  are associated with a corresponding audio channel  318 . The equalizers  304  adjust frequency components of the audio signals of the corresponding audio channel  318  according to equalizer settings of the sound system  106 . For example, the equalizer settings of the sound system  106  may be set (e.g. by an occupant of the vehicle  100 ) to emphasize frequencies in a certain frequency band (e.g., 320 Hz to 1280 Hz, etc.). Additionally, in some examples, the equalizer settings are set during the tuning process of the vehicle and not accessible to the end user. 
     The amplifier  308  amplifies the audio signals from the channel correctors  306  to currents and voltages (sometimes referred to as “a drive signal”) to cause displacement of diaphragms of the speakers  104  that converts the audio signal into sound. In some examples, the amplifier  308  accepts an analog input and the volume, balance, and fade controller  302 , the equalizers  304 , and the channel correctors  306  manipulate the audio signal as a digital value. In such examples, the DAC  314  converts the digital output of the channel correctors  306  to an analog input for the amplifier  308 . The sense circuit  310  measures the dynamic voltage and current of one of the speakers  104 . In some examples, the sense circuit  310  may be integrated into the amplifier  308 . In some examples, the sense circuit  310  includes an ADC and is communicatively coupled to the channel correction manager  312  via a digital communication protocol (e.g., RS-232, Inter-Integrated Circuit (I 2 C), SPI, 1-wire, etc.). 
     The channel correction manager  312  determines correction factors for the example channel correctors  306 . The channel correction manager  312  receives the prediction values from the DAC  314  input corresponding to the speaker  104  that is sampled by the sense circuit  310 . The channel correction manager  312  maintains a virtual speaker table  320  that associates predicted values received from the DAC  314  input with the actual values measured by the sense circuit  310 . In some examples, initially, the virtual speaker table  320  is initialized as linear (e.g., the actual values equal the corresponding predicted values. Alternatively, in some examples, the virtual speaker table  320  is initially populated through a testing process performed when the vehicle  100  or speaker  104  are manufactured. 
     From time-to-time, the virtual speaker table  320  is regenerated. In some examples, the channel correction manager  312  continuously updates the virtual speaker table  320  when audio signals are supplied by the sound system  106 . Alternatively, in some examples, the channel correction manager  312  causes a calibration signal to be played on the speaker  104  being monitored in response to a triggering event. In such examples, the calibration signal causes the voltages and currents over the range of the speaker  104  to be applied to the speaker  104 . In some such examples, the channel correction manager  312  updates the virtual speaker table  320  in response to the ignition switch of the vehicle  100  being set to on (e.g., the triggering event). Additionally the calibration signal, which may or may not be audible to the human ear, may be played at other times, such as when the vehicle is locked and parked. 
     In some examples, the volume, balance, and fade controller  302 , the equalizers  304 , the channel correctors  306 , and the channel correction manager  312  are implemented by a processor or controller. The processor or controller may be any suitable processing device or set of processing devices such as, but not limited to: a microprocessor, a digital signal processor, a microcontroller-based platform, a suitable integrated circuit, one or more field programmable gate arrays (FPGAs), and/or one or more application-specific integrated circuits (ASICs). Additionally, the processor or controller includes volatile memory (e.g., RAM, which can include non-volatile RAM, magnetic RAM, ferroelectric RAM, and any other suitable forms) and/or non-volatile memory (e.g., disk memory, FLASH memory, EPROMs, EEPROMs, memristor-based non-volatile solid-state memory, etc.). In some examples, the virtual speaker table  320  is stored in non-volatile memory. 
     The memory is a computer readable medium on which one or more sets of instructions, such as the software for operating the methods of the present disclosure can be embedded. The instructions may embody one or more of the methods or logic as described herein. In a particular embodiment, the instructions may reside completely, or at least partially, within any one or more of the memory, the computer readable medium, and/or within the processor during execution of the instructions. 
     The terms “non-transitory computer-readable medium” and “computer-readable medium” should be understood to include a single medium or multiple media, such as a centralized or distributed database, and/or associated caches and servers that store one or more sets of instructions. The terms “non-transitory computer-readable medium” and “computer-readable medium” also include any tangible medium that is capable of storing, encoding or carrying a set of instructions for execution by a processor or that cause a system to perform any one or more of the methods or operations disclosed herein. As used herein, the term “computer readable medium” is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals. 
       FIG. 4  is a flowchart of a method to populate the virtual speaker table  320 . At block  402  the channel corrector  306  presents a calibration signal(s) (e.g., audio samples or specific test signals, etc.) to the example channel DAC  314  associated with the sampled speaker  104 . At block  404 , the channel corrector  306  sends the calibration signal(s) to the channel correction manager  312 . At block  406 , the DAC  314  converts the calibration signal(s) to an analog signal. At block  408 , the amplifier  308  amplifies the analog signal. At block  410 , the amplified analog signal drives the sampled speaker  104 . At block  412 , the sense circuit  310  measures the resultant current and voltage. At block  414 , the ADC  316  converts the current and voltage to a digital signal. At block  416  the channel correction manager  312  calculates the error between the digital signal received from the ADC  316  and the calibration signal received from the channel corrector  306 . At block  418  the channel correction manager  312  stores the input (e.g. the calibration signal), the output (the digital signal of the current and voltage) and error values in the virtual speaker table  320 . 
       FIG. 5  is a flowchart of a method to read the virtual speaker table  320  based on sampling one audio channel and apply compensation to all audio channels. At block  502  the channel equalizer  304  forwards the audio signal to the channel correction manager  312 . At block  504 , the channel correction manager  312  looks up the error value in the virtual speaker table  320  associated with the audio signal received at block  502  and passes the retrieved error value to the channel corrector  306  associated with the affected channel  318 . This is repeated for all audio channels in channel equalizer  304 . At block  506 , the channel correctors  306  use the corresponding actual audio signal and error value received from the channel correction manager  312  to calculate a corrected signal. At block  508 , the channel correctors  306  pass the corrected signals from the channel correctors  306  to the DAC  314  to be converted so that the amplifier  308  can amplify the corrected signals to drive the speakers  104 . 
     The flowcharts of  FIG. 4  and  FIG. 5  are methods that may be implemented by machine readable instructions that comprise one or more programs that, when executed, implement the multi-channel vehicle audio corrector  108  of  FIGS. 1 and 3 . Further, although the example program(s) is/are described with reference to the flowcharts illustrated in  FIGS. 4 and 5 , many other methods of implementing the example the multi-channel vehicle audio corrector  108  may alternatively be used. For example, the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, or combined. 
     In this application, the use of the disjunctive is intended to include the conjunctive. The use of definite or indefinite articles is not intended to indicate cardinality. In particular, a reference to “the” object or “a” and “an” object is intended to denote also one of a possible plurality of such objects. Further, the conjunction “or” may be used to convey features that are simultaneously present instead of mutually exclusive alternatives. In other words, the conjunction “or” should be understood to include “and/or”. The terms “includes,” “including,” and “include” are inclusive and have the same scope as “comprises,” “comprising,” and “comprise” respectively. 
     The above-described embodiments, and particularly any “preferred” embodiments, are possible examples of implementations and merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) without substantially departing from the spirit and principles of the techniques described herein. All modifications are intended to be included herein within the scope of this disclosure and protected by the following claims.