Patent Publication Number: US-2023143653-A1

Title: Modular Vehicle Sound System

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of vehicle sound systems. More specifically, the invention comprises a modular amplifier and signal processor whose characteristics can be altered using a plug-in module. 
     2. Description of the Related Art 
     The present invention comprises a modular audio amplifier that can be configured to perform different roles in an existing vehicle sound system or in an aftermarket vehicle sound system.  FIGS.  1 - 3    illustrate three exemplary prior art vehicle sound systems. It is of course impossible to describe the many existing permutations and the three illustrations provided should be viewed as representing a much larger set of possibilities. The present invention can be used with many different types of prior art systems. 
       FIG.  1    illustrates a high-end vehicle sound system as provided by an original equipment manufacturer (“OEM”). OEM systems are typically not designed to function with components from aftermarket manufacturers. As an example, OEM head unit  12  is often made in an irregular shape intended to blend into an overall dash design. The OEM head unit includes a display screen, along with various knobs and buttons. These user-input are employed to select the desired audio source (satellite radio, conventional radio, BLUETOOTH streaming, etc.) and alter the characteristics of the sound produced (volume, tone, etc.). 
     The space available in the dash is often limited. As a result, many OEMs now separate the power amplifier from the head unit. In the example shown, OEM head unit  12  acts as an audio source. OEM amplifier  22  receives the audio signal from OEM head unit  12  and amplifies it to an output level suitable for driving the vehicle&#39;s speakers. 
     The term “amplifier” in this context may be somewhat misleading because OEM amplifiers often include many components in addition to a conventional power amplifier. The OEM amplifier shown is configured to take in two channels (right and left) and drive a seven-speaker sound system. The speakers are: RH dash speaker  24 , LH dash speaker  26 , RH door speaker  28 , LH door speaker  30 , RH rear speaker  32 , LH rear speaker  34 , and woofer  36 . Each of these speakers is configured to efficiently reproduce a particular frequency range. The dash speakers in this example are tweeters. The door and rear speakers are mid-range speakers. The woofer is of course intended to handle only low frequencies. 
     OEM amplifier  22  includes several “crossovers” configured to produce output signals in the proper frequency range for each of the driven frequencies. The term “crossover” can include both active and passive devices. In general, it encompasses a set of high-pass filters (HPFs), band-pass filters (BPFs), and low-pass filters (LPFs). The LPFs pass only the lower frequencies from the left and right input channels. In this example the low frequencies from the left and right input channels are fed into a single output channel that drives woofer  36  (it is common to use a single channel for low frequency sounds since stereo effects are negligible for low frequency sounds). 
     The BPFs pass mid-range frequencies that are suitable for driving the door speakers  28 , 30  and the rear speakers  32 , 34 . The HPFs pass higher frequencies that are suitable for driving the dash speakers  24 , 26 . All these crossover functions are well understood to one skilled in the art. 
     There are two broad approaches used by OEMs when the amplifier is separated form the head unit. In the first approach, volume control remains with the head unit. The user adjusts the volume—typically using a knob—and this adjustment increases or decreases the amplitude of the audio signal sent to the separate amplifier  22 . The amplifier then applies a fixed gain in the power amplification process. 
     In the second approach, OEM head unit  12  sends a fixed level audio signal to the separate power amplifier. The power amplifier then provides a variable gain to set the desired output level for the speakers. This second approach is in fact illustrated in  FIG.  1   . OEM head unit  12  sends fixed level audio  16  to OEM amplifier  22 . The user still sets a desired sound level using OEM head unit  12  (such as by turning a knob). However, rather than varying its audio output level, the OEM head unit transmits a separate signal to the separate amplifier. This separate signal instructs the amplifier to increase or decrease its gain. 
     The separate signal sent from the OEM head unit to the OEM amplifier is usually a digital signal. Since nearly every vehicle now includes a digital data bus, it is convenient to send the signal over the vehicle&#39;s digital data bus. Most vehicle data buses are now some type of “CAN” (Controller Area Network) bus. The first widely-used system implementing the digital CAN paradigm was developed by Robert Bosch. GmbH in the early 1980&#39;s. Bosch called its system the “CAN bus,” and this has now become a generic term. Bosch actually released its protocol to the Society of Automotive Engineers with the initial hope of creating a unified communication platform across all vehicle makes and models, though Bosch did not propose to offer the standard free of licensing fees. 
     The goal of a uniform standard has largely gone unrealized, with the various vehicle manufacturers adopting proprietary systems instead. Even so, the basic characteristics of the original CAN standard are found in most vehicle operating protocols. In general, a CAN network is a “masterless” system in which various microcontrollers communicate without the need for one defined “host” computer. This is a significant feature, as a modern vehicle may contain as many as  70  separate electronic control units. The two most significant control units are typically the Engine Control Unit (“ECU”) and the Body Control Unit (“BCU”). However, there are many other controllers for things such as a blower fan, an air conditioning compressor, power mirrors, air bags, air-inflated suspension “springs,” an automatic transmission, and even small things like the dimming functions of a rear-view mirror. 
     The control of the factory audio equipment is now also done using digital commands over the CAN bus. When the user turns the volume knob on OEM head unit  12 , a digital signal is sent over data link  18  to vehicle data bus  14 . The signal is broadcast generally on the vehicle data bus, but it contains preamble information indicating that it is intended for OEM amplifier  22 . Data link  20  carries the signal to OEM amplifier  22 , where it is decoded and acted upon (to increase or decrease the gain). 
       FIG.  2    shows an alternate version of the system depicted in  FIG.  1   . In the example of  FIG.  2   , a fixed level audio signal  16  is again sent from OEM head unit  12  to OEM amplifier  22 . A digital signal is also sent to instruct the OEM amplifier. However, rather than using the vehicle data bus, direct data link  40  is used between the OEM head unit  12  and OEM amplifier  22 . The direct data link may assume many forms. One commonly used data protocol is the A2B protocol developed by Philips Semiconductor. 
     The examples of  FIGS.  1  and  2    present a problem for the user seeking to upgrade the audio performance of a vehicle. The user often wishes to retain the OEM head unit, since it is an integral part of the dash assembly and replacing it will alter the appearance of the vehicle&#39;s interior. It is still desirable to replace the OEM amplifier, however, since aftermarket units typically have higher output and better overall performance. In addition, aftermarket amplifiers are often highly customizable whereas the OEM amplifiers are not. 
     A well-known disadvantage of the OEM amplifier is that it provides fixed equalization functions. The term equalization refers to selective gain adjustments within discrete bands of frequencies for each channel. The equalization values used in an OEM amplifier are often dictated by the speakers used. Aftermarket speakers are available that vastly outperform OEM speakers. However, the equalization settings of the OEM amplifier cannot be changed. As one example, the OEM amplifier may be set up to attenuate lower frequencies at high volume levels because the woofer used in the OEM system is power-limited. A user seeking to upgrade the sound system can replace the OEM woofer with a larger unit capable of handling much higher sound pressures, However, the potential of the new woofer will go largely unrealized because of the fact that the equalization settings within the OEM amplifier cannot be changed. 
       FIG.  3    presents a known prior art solution to these problems. The OEM amplifier is removed. CAN audio interface  44  receives the fixed level audio  16  from OEM head unit  12 . The CAN audio interface also includes a data link  20  so that it can receive messages from the CAN bus  14  that were originally intended for the OEM amplifier (such as “volume up” or “volume down” commands). CAN audio interface  44  receives fixed level audio signal  16  and produces variable level audio signal  46  — with the output level being changed in response to digital CAN commands the audio interface  44  decodes from the vehicle data bus. There are numerous CAN audio interface products on the market. The one depicted in  FIG.  3    provides six output channels of variable level audio. These would customarily be RH/LH “front” channels, RH/LH “rear” channels, and RH/LH “woofer” channels. 
     In most cases OEM equalization settings will still be present even in variable level audio signals  46 , because the equalization settings are added in the audio source (OEM head unit  12 ). In a few cases the equalization settings are added in the OEM amplifier. In those cases the equalization settings will be removed with the removal of the OEM amplifier. 
     However, the equalization settings are most often added in the OEM head unit and the system depicted in  FIG.  3    is configured to address this problem. Digital signal processor (“DSP”)  48  receives variable level audio signal  46  from CAN audio interface  44 . A set of analog-to-digital converters take the input signals into the digital domain. While the signals are in the digital domain, the DSP applies independent equalization and gain functions to each signal. The functions of the DSP are accessible to a user, who can set the parameters as desired. As one example, the output signals from the OEM head unit may have an increased gain setting in the range from 200 Hz to 5 kHz. The DSP can be set to remove this gain and completely flatten the frequency response. 
     The operation of a DSP is familiar to those skilled in the art. Details as to the operation of such devices are disclosed in U.S. Pat. No. 9,875,078. U.S. Pat. No. 9,875,078 is hereby incorporated by reference for purposes of this disclosure. 
     The “back end” of the DSP has a set of digital-to-analog converters that takes the signal back to the analog domain. The particular DSP shown has seven output channels. The DSP can individually adjust the equalization and gain settings for each of these channels. The DSP output channels are routed to four separate aftermarket amplifiers  50 , 52 , 54 , 56 . Each of these is a two channel power amplifier, though only one of the two channels is used for amplifier  56 . In this prior art configuration amplifier  50  drives speakers  24  and  26 . Amplifier  52  drives speakers  28  and  30 . Amplifier  54  drives speakers  32  and  34 , Amplifier  56  drives speaker  36  (a woofer). 
     The prior art system of  FIG.  3    has the advantage of retaining the OEM head unit and thereby retaining the original look of the dash. it also has the advantage of digital signal processing that can be used to remove unwanted OEM equalization settings and other issues. Unfortunately, the use of a separate CAN audio interface, DSP, and multiple power amplifiers produces an expensive system. It also produces a system that is cumbersome to install, integrate, and tune. It is desirable to provide the functionality of the system of  FIG.  3    in a more integrated system. It is also desirable to provide tis functionality in a system that can be easily upgraded to provide more and more advanced functions. The present invention provides such as system. 
     BRIEF SUMMARY OF THE PRESENT INVENTION 
     The present invention comprises a modular vehicle sound system that can be upgraded or reconfigured by changing a plug-in module, in the advanced-capability embodiments the invention combines the functions of a vehicle data bus interface, a digital signal processor, and an amplifier. In the advanced-capability embodiments the invention provides a wireless interface with a separate digital device that can be used to control the inventive amplifier. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG.  1    is a schematic view, showing a prior art OEM sound system using a separate power amplifier. 
         FIG.  2    is a schematic view, showing a prior art OEM sound system using a separate power amplifier. 
         FIG.  3    is a schematic view, showing the addition of a digital signal processor to a prior art sound system. 
         FIG.  4    is a perspective view, showing an embodiment of the present invention. 
         FIG.  5    is a perspective view, showing a plug-in module such as used in the present invention. 
         FIG.  6    is a schematic view, showing a first operational state of the present invention. 
         FIG.  7    is a schematic view, showing the configuration of  FIG.  6    with an aftermarket head unit. 
         FIG.  8    is a schematic view. showing a second operational state of the present invention. 
         FIG.  9    is a schematic view, showing a third operational state of the present invention. 
         FIG.  10    is a schematic view, showing a fourth operational state of the present invention. 
         FIG.  11    is a schematic view, showing representative internal components of the inventive modular amplifier. 
         FIG.  12    is a schematic view, showing representative internal components of the inventive modular amplifier. 
         FIG.  13    is a perspective view, showing the inventive modular amplifier being paired with an external digital device. 
         FIG.  14    is a graphical view showing a representative graphical user interface. 
         FIG.  15    is a graphical view showing a representative graphical user interface. 
         FIG.  16    is a graphical view showing a representative graphical user interface. 
         FIG.  17    is a perspective view, showing a representative cable assembly configured for use with the present invention. 
         FIG.  18    is an elevation view, showing a jack panel incorporating a modular input board as used in an embodiment of the present invention. 
     
    
    
     REFERENCE NUMFRALS IN THE DRAWINGS 
       10  OEM sound system 
       12  OEM head unit 
       14  vehicle data bus 
       16  fixed level audio 
       18  data link 
       20  data link 
       22  OEM amplifier 
       24  RH dash speaker 
       25  RH rear tweeter 
       26  dash speaker 
       27  LH rear tweeter 
       28  RH door speaker 
       30  LH door speaker 
       32  RH rear speaker 
       34  LH rear speaker 
       36  woofer 
       37  RH woofer 
       38  OEM sound system 
       39  LH woofer 
       40  direct data link 
       42  custom sound system 
       44  CAN audio interface 
       46  variable level audio 
       48  digital signal processor 
       50  aftermarket amplifier 
       52  aftermarket amplifier 
       54  aftermarket amplifier 
       56  aftermarket amplifier 
       58  modular amplifier 
       60  chassis 
       62  plug-in module 
       64  receiver 
       66  contact array 
       68  grip feature 
       70  leading edge 
       72  contact array 
       74  antenna 
       76  aftermarket head unit 
       77  slave amplifier 
       78  variable level audio 
       79  slave amplifier 
       80  audio link 
       82  audio link 
       84  data link 
       86  data link 
       88  inputs 
       90  signal processing 
       92  amplifier section 
       94  outputs 
       96  audio output 
       98  data output 
       100  processor 
       102  on-board memory 
       104  interface 
       106  interface 
       108  processor 
       110  memory 
       112  bluetooth interface 
       114  analog-to-digital converter 
       116  splitter 
       118  equalizer 
       120  delay module 
       122  digital-to-analog converter 
       124  preamplifier 
       126  power amplifier 
       128  digital device 
       130  GUI 
       132  crossover adjustment display 
       134  speaker designation 
       136  filter type designation 
       138  slider 
       140  equalizer display 
       142  delay adjustment display 
       144  connector 
       146  input cable assembly 
       148  power inputs 
       150  power jack 
       152  speaker output jack 
       154  data jack 
       156  data jack 
       158  input board 
       160  input board 
       162  input board 
       164  input board 
       166  input board 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention can be physically realized in a wide variety of ways, and the invention should not be viewed as limited to any particular physical implementation. However, it is beneficial to the reader&#39;s understanding to provide some specific examples. The following descriptions provide these specific examples but should not be viewed as limiting. 
     A desirable feature of the present invention is modular upgradability. A user can purchase and install a limited-capability version of the invention. At a later time the user can upgrade the invention by substituting a new plug-in module.  FIGS.  4  and  5    illustrate this upgradability.  FIG.  4    depicts an embodiment of inventive modular amplifier  58 . Chassis  60  includes a receiver  64 . Receiver  64  is configured to receive a plug-in module  62 . The plug-in module in this example includes lateral rails that slide into slots on the lateral sides of receiver  64 . The plug-in module is pushed into place in the direction indicated by the arrow and then captured by retaining features such as plastic snaps. Contact array  66  on chassis  60  makes electrical contact with a similar contact array on the plug-in module. Grip features  68  allow the user to grasp the plug-in module and pull it free of the chassis in order to substitute a new plug-in module (typically done to upgrade the features of the modular amplifier). 
       FIG.  5    shows the same plug-in module as depicted in  FIG.  4    flipped over to expose its underside. Leading edge  70  is the portion that first slides into the receiver in the chassis. Contact array  72  is configured to provide multiple electrical contacts with contact array  66  in chassis  60 . The contact array preferably includes flexible and resilient contact fingers. The plug-in module can be configured to include a variety of components, including a processor(s), a memory, and external communication devices—such as a BLUETOOTH chipset. 
       FIGS.  6 - 10    illustrate some of the upgrades that are possible by swapping the plug-in module.  FIG.  6    shows a low-capability configuration. A first type of plug-in module  62  (labeled “A”) is plugged into modular amplifier  58 . In this configuration modular amplifier  58  has been substituted for an OEM amplifier (similar to the configuration shown in  FIG.  1   ). The audio source is OEM head unit  12 , which feeds fixed level audio signal  16 . Volume adjustments are made by a signal transmitted from OEM head unit  12  to vehicle data bus  14 . Data link  20  is provided from the vehicle data bus  14  to modular amplifier  58  in  FIG.  1   . 
     Data link  20  is usually just a twisted pair of conductors attached to a vehicle CAN bus. However, as discussed in the introductory section of this application, vehicle CAN busses are not standardized and use a wide variety of transmission formats. In the inventive embodiment of  FIG.  6   , plug-in module “A” includes a memory containing the proper format for the vehicle in which modular amplifier  58  is installed. As an example, if the modular amplifier is installed in a General Motors vehicle, plug-in module A will be programmed with one or more of the varieties of the GMLAN data format used by the CAN buses in General Motors vehicles. The information provided by the plug-in module A allows the modular amplifier to decode messages on vehicle data bus  14  and adjust the gain of the modular amplifier in response to “volume up” or “volume down” data signals. If the user wishes to install the modular amplifier in a different type of vehicle, he or she removes plug-in module A and substitutes a new plug-in module containing the data format information for the new type of vehicle. Thus, the plug-in module provides a vehicle make-specific interface allowing the modular amplifier to decode signals received over its data link  20 . 
       FIG.  7    shows a similar configuration, except that an aftermarket head unit  76  has been substituted for the OEM head unit. The aftermarket head unit is also an audio source. However, it produces variable level audio signal  78 . Thus, the overall gain of the sound system is controlled by the aftermarket head unit with no data messages being used for this purpose. Data link  20  is still provided between the modular amplifier  58  and the vehicle data bus  14  because other signals may still need to be fed into modular amplifier  58 . 
     A good example of non-volume signals is the various warning “chimes” that alert a driver when a door or tailgate is opened. These “chimes” usually originate with the body control unit (“BCU”). The BCU sends a digital signal commanding a chime. OEM amplifiers typically respond to this signal by retrieving the appropriate sound file from memory and then running it through the amplifier and out to the speakers, Modular amplifier  58  is configured to decode these “chime” signals and respond like the OEM amplifier. The modular amplifier retrieves an appropriate sound file from memory, amplifies it, and sends the amplified signal to the speakers. 
       FIG.  8    shows another embodiment in which the capabilities have been altered by substituting plug-in module “B” for plug-in module “A.” Plug-in module B includes a wireless communication chip set that allows modular amplifier  58  to communicate with an external digital device—such as a smart phone. Antenna  74  is used to facilitate wireless communication. This antenna is shown schematically. In most examples the antenna is embedded in the housing of the plug-in module and is not separately visible though a visible version can also be provided. An antenna can also be provided in the chassis of the modular amplifier itself. 
     In the example of  FIG.  8    the wireless chip set is configured to use the BLUETOOTH communication format. As one example, plug-in module B can contain an nRF52840 processor made by Nordic Semiconductor of Trondheim, Norway. This particular processor includes advantageous internal radio frequency communication capability. It can, for example, communicate with other devices using the BLUETOOTH communication protocol. It also includes programmable internal memory allowing it to be customized for the performance of many tasks. 
     In the configuration of  FIG.  8    no audio source that is integral to the vehicle is provided. Instead, a separate phone is used as an audio source, with the data being streamed to modular amplifier  58  via BLEUTOOTH pairing. This configuration is particularly advantageous for off-road vehicles that do not include a head unit. 
       FIG.  9    shows another configuration of the invention having enhanced capabilities. In this version plug-in module “C” has been installed in the receiver in modular amplifier  58 . Plug-in module C adds the functionality of a digital signal processor (“DSP”) to modular amplifier  58 , The DSP is controlled using an application running on an external device, such as a smartphone or tablet. Wireless connectivity is used for the link—such as BLUETOOTH. The chipset for performing the DSP function may actually be contained on plug-in module C. However, the hardware to perform the DSP functions may be included in the modular amplifier  58  itself, with the installation of plug-in module C performing the function of unlocking the use of this hardware. As an example, plug in module C can provide a software key, hardware key, or combination key that unlocks the DSP functionality already found in the modular amplifier. 
     In the example of  FIG.  9   , fixed level audio  16  is fed into the modular amplifier from OEM head unit  12 . The audio signal  16  includes factory-set equalization levels as described previously. The DSP functions provided in modular amplifier  58  are used to remove the factory-set levels and provide equalization that is best suited to drive the speakers being used in an upgraded system. 
       FIG.  10    shows a configuration of the invention having even more enhanced capabilities. In this version plug-in module “D” has been installed in the receiver in modular amplifier  58 . The installation of plug-in module D allows modular amplifier  58  to assume multiple roles in a more advanced system. The system shown includes  10  separate speakers. These are: RH dash speaker  24 , LH dash speaker  26 , RH door speaker  28 , LH door speaker  30 , RH rear tweeter  25 , LH rear tweeter  27 , RH rear speaker  32 , LH rear speaker  34 , RH woofer  38 , and LH woofer  39 . 
     Modular amplifier  58  contains a power amplifier. However, in the case of a powerful and sophisticated sound system, it is often desirable to use multiple power amplifiers. Modular amplifier  58  provides this capability. Th audio source in the example of  FIG.  10    is once again OEM head unit  12  providing fixed level audio  16 . Modular amplifier  58  receives digital data signals over data link  20 . Included in these signals are “volume up” and “volume down” commands sent by the OEM head unit. The modular amplifier responds to these signals by adjusting the system gain. 
     Modular amplifier  58  provides a power output signal to drive RH dash speaker  24 , LH dash speaker  26 , RH door speaker  28 , and LH door speaker  30 . However, the remaining six speakers in the system are driven by other power amplifiers. Slave amplifier  77  drives RH rear tweeter  25 , LH rear tweeter  27 , RH rear speaker  32 , and LH rear speaker  34 . Slave amplifier  79  drives RH woofer  37  and LH woofer  39 . Modular amplifier  58  includes output audio links and output data links. Thee can be “daisy-chained” (connected in parallel) to multiple external amplifiers. Audio link  80  provides an audio signal output from modular amplifier  58  to slave amplifier  77 . Audio link  82  provides the same audio signal to slave amplifier  79 . 
     Data link  84  provides a data signal from modular amplifier  58  to slave amplifier  77 . Data link  86  provides a parallel connection to feed the same data. to slave amplifier  79 . The data links can be bi-directional, depending on the data transmission format used. Modular amplifier  58  provides the only interface needed with the vehicle data bus. Thus, a single-point interface is provided that eliminates the need for this expensive functionality in the slave amplifiers. As for the prior examples, wireless communication is used to link the modular amplifier with a separate controlling device such as a smartphone. BLUETOOTH pairing is the preferred approach. 
     Modular amplifier  58  preferably also provides a single-point for the application of digital signal processing (“DSP”). The audio signals sent to the slave amplifiers on audio links  80 , 82  are post-DSP (meaning that the desired equalization functions have already been applied). Having said that, it is still possible to provide gain functions in the slave amplifiers. Data links  84 , 86  can provide gain adjustment commands that are implemented by slave amplifiers  77 , 79 . The reader should bear in mind that—in some communication formats—the audio and data links can be combined on a single link. 
     While the invention is not limited to any particular data transmission format, the reader&#39;s understanding may benefit from an explanation of some of the possibilities. The MOST format can be used if the links are carried over optical fiber. MOST stands for Media Oriented System Transport. This is a serial communication system for transmitting audio, video, voice, and data signals via plastic optical fiber (POF, as opposed to glass optical fiber). POF is much more robust under bending or flexing than glass. Though POF has a higher signal attenuation than glass, it works well for transmissions over a short distance (such as found in a vehicle like in a car). MOST network can manage multiple devices (up to 64) in a ring configuration (In a ring each node connects to two and only two other nodes—creating a single path around the ring). 
     The IEBus format is another possibility. This standard was originally developed by NEC in Japan, where it became a de facto standard for car audio and navigation systems. IEBus is a master/slave system. A good example (historically) is an OEM head unit being the master and a remote CD changer being the slave. A more recent example is an OEM head unit being the master and a remote NAV system being the slave. IEBus controllers are packaged as chip sets, making them easy to integrate into other systems. 
     Still another example is the A2B format (often written A 2 B). A2B transceivers allow an I2C host to access all transceivers in a system (I2C is a well-known synchronous multi-master, multi-slave communications bus invented by Philips Semiconductor). A2B is ideal for transporting digital audio, with configurable 44.1 kHz or 48 kHz frame rates and a data rate of up to 50 Mbps. 
     The electronics contained within modular amplifier  58  and the plug-in modules  62  can be configured in a wide variety of ways.  FIGS.  11  and  12    provide an illustrative configuration.  FIG.  11    provides a schematic (at a block diagram level) of modular amplifier  58  with plug-in module  62  in place. Power supply and regulation components are not shown for purposes of visual clarity. 
     Input module  88  receives up to six input channels. In the view, a single line is shown for each channel though each channel of course contains two conductors. The six input channels are fed into signal processing module  90 , which is a digital signal processor. Main processor  100  retrieves and runs software from on-board memory  102 . On-board memory  102  includes the program or programs to be run as well as current values for the parameters used in the program or programs. 
     Data output  98  carries digital data from processor  100 . Data output  98  can in some instances be a bi-directional module that allows data to be sent into processor  100  as well. Data link  20  provides communication with the vehicle data bus as explained previously. This data link carries messages into the processor (such as volume up and volume down commands). The processor responds to these messages—such as by altering the gain of amplifier  92 . 
     Signal processing module  90  has  10  output channels feeding into amplifier  92 . Amplifier  92  is a power amplifier that passes  10  amplified channels through output module  94  and on to the speakers being driven. Processor  100  controls signal processing module  90  in addition to amplifier  92 . The control of the signal processing module will be explained in detail subsequently. 
     Plug-in module  62  communicates with processor  100  through interfaces  104 , 106 . The particular plug-in module  62  shown in  FIG.  11    also contains a processor  108  and associated memory  110 . Processor  108  communicates with BLUETOOTH interface  112  (which is typically a set of chips). Additional functionality may be provided to the modular amplifier by processor  108 . Alternatively, the additional functionality can be provided within the modular amplifier, with the use of this added functionality being unlocked by a “software key” found on plug-in module  62 . 
       FIG.  12    provides additional detail as o the components within signal processing module  90  and how they are controlled by processor  100 . The six input channels coming from input module  88  (in  FIG.  11   ) are shown on the left of the view. The processing of one of these six channels is shown in  FIG.  12   . The processing of the other five channels is the same, using additional components. 
     The signals coming in pass through analog-to-digital converter  114 . This converts the signals from the analog domain to the digital domain. Splitter  116  splits the signal into as many separate processing channels as desired. In this example, three separate processing channels are shown. Each processing channel ultimately drives a single speaker in this example. 
     An equalizer function  118  is provided for each processing channel. In this example, each equalizer function splits the signal into  31  distinct frequency bands and allows the user to separately assign a gain to each band. A delay function  120  is provided for each channel as well. This allows the user to assign a time delay to each speaker individually, in order to produce a correct “sound image” for a particular location in the vehicle (typically the position of the driver&#39;s head). 
     Once the equalization and delay functions are applied to each channel, the signal passes through a digital-to-analog converter  122  to return it to the analog domain. A variable gain amplifier  124  is provided for each channel. These are pre-amplifiers under the control of processor  100 . The signal leaving the gain amplifiers  124  are then fed through power amplifiers  126  and out to the speakers. The reader will thereby appreciate how processor  100  controls the digital signal processing in one example. 
       FIGS.  13  through  16    depict a graphical user interface (GUI) configured to control the digital signal processing functions of the present invention. Those skilled in the art will know that a wide variety of GUIs could be provided, and the version shown is therefore properly viewed as being one example among many possibilities. 
       FIG.  13    shows a digital device  128  with a touchscreen display. GUI  130  is provided on the touchscreen display. Digital device  128  is linked via BLUETOOTH to the plug-in module  62  installed in modular amplifier  58 . The devices are shown in close proximity. In actuality the modular amplifier will often be installed behind a vehicle&#39;s dash and the digital device will be some distance away—such as 1 to 2 meters. 
     The digital device will often be a smartphone or a tablet. The tablet is preferred in many cases because of its larger display.  FIG.  14    shows an additional page of the GUI called up on the controlling digital device. This page—designated as crossover adjust display  132 —is used to select filter types and set crossover points for each speaker using nomenclature that is familiar to audio technicians. Speaker designator  134  assigns a processing channel to a speaker. Filter type designator  136  selects a filter type to assign to the channel (low pass filter, band pass filter, or high pass filter). Slider  138  then sets the cross over point for the filter applied. As an example, for the channel applied to the right front speaker, a crossover of  100  is set. Only frequencies at or above 100 Hz are sent through this channel. One advantage of filtering in the digital domain is that the “roll off” can be vertical so that no lower frequencies are passed at all 
       FIG.  15    shows a different page within the GUI—equalizer display  140 . An equalizer display can be called up for each channel. Gain can be set for each frequency band. This example uses  31  discrete frequency bands so  31  adjustable sliders  138  are provided (along with an overall gain slider). Some of the bands can be removed depending on the application of the settings on the crossover page (or greyed out). 
       FIG.  16    shows an additional page within the GUI—delay adjustment display  142 . This page allows the technician to enter a measured distance from the driver&#39;s head position to each individual speaker. The software then uses this information to assign a time delay to a particular channel driving a particular speaker. Thus, rather than having a user enter an actual time delay, the software allows the user to enter a measured distance and the software then calculates the proper time delay. 
     Many other pages and features can be provided within the GUI, These features allow the user to unlock all the capabilities of the modular amplifier. As an example, the GUI could also store different sets of parameters for different users. These could then be called up and loaded as desired. A “sound image” group of settings could be installed in which the speaker delay is set for the position of a passenger. 
       FIGS.  17  and  18    depict exemplary hardware arrangements. It is advantageous to provide cable assemblies that facilitate the installation of the modular amplifier within a particular vehicle or class of vehicles.  FIG.  17    depicts an input cable assembly  146  that is configured for use with the amplifier configuration of  FIG.  6   . In the configuration of  FIG.  6   , modular amplifier  58  requires a fixed level audio  16  input (with two channels), a data link  20  input, and a switched power input. 
       FIG.  17    shows an input cable assembly configured to provide these inputs. Power inputs  148  are simple wires configured to be spliced into the vehicle&#39;s existing wiring harness (one constant +12V, one switched +12V, and one ground). Fixed level audio signal  16  is carried by the two cables having RCA-jack terminations. Data link  20  is carried by two conductors having splice-in terminations allowing them to be spliced into the vehicle&#39;s existing CAN bus wiring. All these conductors lead into connector  144 . A suitable receptacle for connector  144  is provided on the modular amplifier. Thus, the user makes the connections with the individual conductors and then connects these to the modular amplifier by plugging connector  144  into a socket on the modular amplifier. 
       FIG.  18    depicts an exemplary set of connectors that can optionally be provided on the modular amplifier. Chassis  60  in this example includes a detachable input board  158  having a standard receptacle for receiving an input wiring harness. Data jacks  154 , 156  are provided for data links  84 , 85 . Speaker output jack  152  accommodates a wiring harness for the speakers that are driven by the modular amplifier. Power jack  150  accommodates the power inputs. 
     Different input boards can be provided for different jack configurations. Input board  160  is used if the MOST format is employed. Input board  162  is used if the A2B format is employed. Input board  164  is used if the CANBUS, SPDIF, MOST, and IEBUS formats are used. Input board  166  is used if the standard inputs plus BLUTOOTH are present. These input board are preferably made modular so that they can be swapped in chassis  60 . The ability to swap input boards allows the modular amplifier to be easily adapted to different communication formats. 
     The invention can include many features and options, alone or in combination. These include: 
     1. The communication protocol needed for the modular amplifier to decode messages on the vehicle data bus can be stored on the plug-in module; 
     2. The communication protocol needed for the modular amplifier to decode messages on the vehicle data bus can be automatically determined using the methods disclosed in co-owned U.S. Pat. Nos. 8,014,920 and 8,214,105; and 
     3. The input boards ( FIG.  18   ) can be made removable and replaceable by a user in order to alter the configuration of the modular amplifier (in a manner similar to swapping the plug-in module). 
     Although the preceding descriptions contain significant detail, they should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. Those skilled in the art will know that many other variations are possible without departing from the scope of the invention. Accordingly, the scope of the invention should properly be determined with respect to the following claims rather than the examples given.