Abstract:
An audio signal processing system for a vehicle is disclosed. The vehicle has a plurality of audio output producing devices. The system includes an audio input circuit, a processor, an audio output circuit, and at lease one speaker. The audio input circuit receives a plurality of audio signals from the plurality audio output producing devices. The processor is in communication with the audio input circuit for combining the plurality of audio signals. The audio output circuit is in communication with the audio input circuit for receiving the combined plurality of audio output signals. The audio output circuit conditions the plurality of audio signals for output. The at least one speaker broadcasts the conditioned plurality of audio signals to a vehicle occupant.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present invention claims priority to U.S. Provisional Serial No. 60/341,095, filed Oct. 29, 2001, entitled “Audio Routing For An Automobile.” 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates to systems and methods for routing audio signals in an automobile and for allowing multiple audio signals to be broadcasted over a single set of speakers.  
         BACKGROUND  
         [0003]    A typical emergency services vehicle today has numerous devices that use audio inputs and generate audio outputs. They include two-way radios, scanners, AM/FM radios, PA systems, Doppler radar tones, computer input and output, etc. In most cases each piece of equipment that generates output will have its own speakers and each piece of equipment that requires input will have its own microphone.  
           [0004]    The proliferation of speakers and microphones (and often the equipment to which they are attached) in the passenger compartment leads to clutter and confusion. The audio outputs are not coordinated with each other, so a low priority output might drown out a high priority output. Similarly, it may be difficult to locate the correct microphone for a particular device.  
           [0005]    One of the reasons that vehicles may have multiple two-way radios is that different emergency services may communicate on different bands, thus requiring a separate radio for each service. A consequence of this is that when several emergency services arrive at a site, they may not all be able to talk to each other. The situation is exacerbated when the workers leave their vehicles and carry handheld radios, which typically service a single band each.  
           [0006]    Large agencies have command vehicles that contain specialized equipment (repeaters) to receive signals on one band and retransmit them on another. These vehicles are deployed to sites as needed, to allow the different services to communicate with each other.  
           [0007]    Therefore, what is needed is a system and method for an automobile that integrates all of the audio signaling, and eliminates redundant speakers and microphones. The system and method should also allow any vehicle to become a repeater using two-way radios already present.  
         SUMMARY  
         [0008]    In an aspect of the present invention an audio signal processing system for a vehicle is provided. The vehicle has a plurality of audio output producing devices. The system includes an audio input circuit, a processor, an audio output circuit, and at lease one speaker. The audio input circuit receives a plurality of audio signals from the plurality audio output producing devices. The processor is in communication with the audio input circuit for combining the plurality of audio signals. The audio output circuit is in communication with the audio input circuit for receiving the combined plurality of audio output signals. The audio output circuit conditions the plurality of audio signals for output. The at least one speaker broadcasts the conditioned plurality of audio signals to a vehicle occupant.  
           [0009]    In another aspect of the present invention the audio input circuit further comprises a plurality of analog to digital converters.  
           [0010]    In yet another aspect of the present invention the audio input circuit further comprises a plurality of CODECS.  
           [0011]    In yet another aspect of the present invention the audio input circuit comprises twenty CODECS.  
           [0012]    In still another aspect of the present invention the processor further comprises a digital signal processor.  
           [0013]    In still another aspect of the present invention the system further comprises four speakers.  
           [0014]    In still another aspect of the present invention the system further comprises at least one microphone.  
           [0015]    In yet another aspect of the present invention the audio output circuit further comprises an audio amplifier.  
           [0016]    In yet another aspect of the present invention the audio input circuit further comprises a microphone router circuit for directing a plurality of microphone inputs to a plurality of audio equipment.  
           [0017]    In still another aspect of the present invention the audio output circuit further comprises an audio mixer for receiving the plurality of audio signals and directing the plurality of audio signals to the proper output device. In yet another embodiment of the present invention, the audio mixer functions is a repeater by receiving audio signals having different frequencies and outputting an audio output signal having a single frequency.  
           [0018]    In yet another aspect of the present invention an audio signal processing system for a vehicle is provided. The vehicle has a plurality of audio output producing devices. The system includes an audio input circuit, a processor, a voice activated control circuit, an audio output circuit, and at lease one speaker. The audio input circuit receives a plurality of audio signals from the plurality audio output producing devices. The processor is in communication with the audio input circuit for combining the plurality of audio signals. The voice activated control circuit in communication with the processor for controlling a processor operation. The audio output circuit is in communication with the audio input circuit for receiving the combined plurality of audio output signals. The audio output circuit conditions the plurality of audio signals for output. The at least one speaker broadcasts the conditioned plurality of audio signals to a vehicle occupant.  
           [0019]    In yet another aspect of the present invention a method for processing audio signals for broadcasting in a vehicle is provided. The vehicle has a plurality of audio output producing devices. The method includes receiving a plurality of audio signals from the plurality of audio output producing devices, combining the plurality of audio signals using a processor, receiving the combined plurality of audio output signals using an audio output circuit, wherein the audio output circuit conditions the signals for output, and broadcasting the conditioned plurality of audio signals to a vehicle occupant using at lease one speaker.  
           [0020]    These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description of the invention in combination with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0021]    [0021]FIG. 1 is a schematic diagram illustrating a vehicle having an audio board for mixing and broadcasting audio signals, in accordance with the present invention;  
         [0022]    [0022]FIG. 2 is a schematic diagram illustrating the connection of a microphone (not shown) to the mixer busses, in accordance with the present invention;  
         [0023]    [0023]FIG. 3 is a schematic diagram illustrating the connection of a monaural input to the mixer busses, in accordance with the present invention;  
         [0024]    [0024]FIG. 4 is a schematic diagram illustrating the connection of the stereo input to the mixer busses, in accordance with the present invention;  
         [0025]    [0025]FIG. 5 is a block diagram illustrating the microphone router, in accordance with the present invention;  
         [0026]    [0026]FIG. 6 is a schematic diagram illustrating a microphone input circuit, in accordance with the present invention;  
         [0027]    [0027]FIG. 7 is a schematic diagram illustrating a microphone router circuit for matching router and output circuits, in accordance with the present invention;  
         [0028]    [0028]FIG. 8 is a block diagram illustrating an embodiment of the audio board, in accordance with the present invention;  
         [0029]    [0029]FIG. 9 is an alternate embodiment illustrating an in vehicle audio system for processing a plurality of audio input signals, in accordance with the present invention;  
         [0030]    [0030]FIG. 10 is a block diagram illustrating a general purpose input channel, in accordance with the present invention;  
         [0031]    [0031]FIG. 11 is a block diagram illustrating an audio routing logic for an output channel, in accordance with the present invention;  
         [0032]    [0032]FIG. 12 is a block diagram illustrating how the PTT signal for each output is generated, in accordance with the present invention; and  
         [0033]    [0033]FIG. 13 is a block diagram illustrating an audio routing for a single output channel, in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0034]    With reference to FIG. 1, a vehicle  10  having an audio board  12  for mixing and broadcasting audio signals is provided, in accordance with the present invention. The audio board  12  includes an audio mixer  14  for combining audio signals for delivery to the user and other equipment, and a microphone router for directing the microphone inputs to the equipment that uses them.  
         [0035]    The audio board  12  further includes a microphone router  16 . Microphone router  16  and audio mixer  14  are both under the control of a processor  17  such as a MPC-565. The microphone router directs microphone input from either an array microphone or the hand-held microphone to the appropriate piece of equipment (e.g., a radio transmitter or the voice recognition system (VACM)  20 ). The audio mixer  14  takes all of the available audio signals (radios  22 , microphones, voice feedback, etc.) and directs them to the proper output devices (e.g., speakers  24  in the vehicle or the PA speaker (not shown)). Additionally an application&#39;s processor  19  in communication with audio mixer  14  is a source of audio signals and communicates the audio signals to audio mixer  14 . AP  19  is a Windows&#39; based computer system for hosting Windows&#39; applications.  
         [0036]    Further, the audio mixer  14  receives audio from a variety of devices in the vehicle and routes them to speaker  24 , PA, and an optional recording device  26 . The audio mixer  14  is, in an embodiment of the present invention, a 15 input×3 output switch. In principle it could route any mix of input signals to any combination of output ports.  
         [0037]    The mixer handles three kinds of inputs: monaural microphones with push-to-talk (PTT) signal, other monaural inputs (without PTT), and stereo inputs. The monaural and stereo inputs can be either line level or speaker level signals.  
                                     TABLE 1                       Signal   Purpose   Type                                1   Output from radio (AM/FM tuner, voice feedback   stereo           from VACM, etc.)       2   AP sound/voice   stereo       3   general purpose (two-way radio, scanner, etc.)   monaural       4   general purpose   monaural       5   general purpose   monaural       6   general purpose   monaural       7   general purpose   monaural       8   general purpose   monaural       9   general purpose   monaural       10   general purpose   monaural       11   general purpose   monaural       12   general purpose   monaural       13   microphone 1   microphone       14   microphone 2   microphone       15   microphone 3   microphone                  
 
         [0038]    The mixer  14  delivers three outputs: (1) for a stereo speaker amplifier  28 , (2) for the PA amplifier, and (3) for an optional recording device  26 . Table 2, below, shows an assignment of the output signals, in accordance with an embodiment of the present invention.  
                       TABLE 2                       Signal   Purpose   Type                   1   power amplifier to vehicle speakers   stereo       2   PA system   monaural with PTT       3   optional recording system   monaural                  
 
         [0039]    Internally mixer  14  in an embodiment of the present invention, has three output busses: (1) a Stereo bus—a left and a right audio channel, (2) Aux (auxiliary) bus—a monaural audio channel, (3) PA (public address) bus—a monaural audio channel and a push-to-talk signal.  
         [0040]    There are 15 input lines that connect to the busses, under computer control. The input lines are partitioned into three microphone inputs, ten monaural inputs, and two stereo inputs. Each of the three kinds of input connects to the busses differently, and delivers a slightly different set of capabilities.  
         [0041]    As shown in FIG. 1, note that the audio outputs of the radios feed back into the microphone router, so that output from one radio can be fed back into another radio, thus accomplishing the repeater function.  
         [0042]    With reference to FIG. 2, the connection of a microphone  18  (shown in FIG. 1) to mixer  14  busses is illustrated, in accordance with the present invention. Microphone  30  can be routed to the Aux  32  and PA  34  busses. The microphone should not be routed to stereo bus  36 . Further, the PTT signal routing is shown as a relay  38  in FIG. 2. However, the PTT signal routing could equally well be implemented as a solid-state switch.  
         [0043]    With reference to FIG. 3, the connection of a monaural input  33  to the mixer busses is illustrated, in accordance with the present invention. The monaural signal can be routed to all three busses  32 ,  34  and  36 . By changing the relative volume of the signal on the left and right stereo channels, the mixer can pan the signal from left to right.  
         [0044]    Each monaural input has two mechanically configured settings. First the input signal can be either line level  35  or speaker level  37 . Second, a push-to-talk signal  41  can either be supplied directly by the input device or a computer controlled squelch circuit in the mixer can generate it. The settings are implemented as either a DIP switch or a jumper. A computer controlled solid-state switch may also be used.  
         [0045]    With reference to FIG. 4, the connection of the stereo input  40  to the mixer busses  32 ,  34 ,  36  is illustrated, in accordance with the present invention. The stereo input  40  can be routed to the stereo  36  and aux  32  busses. The stereo inputs are intended for a vehicle entertainment system (i.e. an AM/FM tuner) which are not required to be routed to the PA bus  24 .  
         [0046]    The mixer can change the balance of the stereo output, and can mix the right and left channel inputs together on both the right and left channel outputs. This allows both reducing the channel separation and steering the apparent location of the signal.  
         [0047]    Each stereo input  40  has a configuration setting  42  to switch between speaker  44  and line level  46  inputs. It is implemented similarly to the settings for a monaural input.  
         [0048]    The microphone router occupies three microphone inputs and sends the audio and PTT signals to the VACM (for voice recognition) and up to five radios or other devices. The router routes both audio and PTT signals. The PTT enables the microphone and the appropriate output devices.  
         [0049]    The microphone router can send any input to one of the six outputs. Any inputs not being used are disabled. Multiple microphones can be routed to the same output. Routing more than one microphone to the same output causes them to mix (i.e., the audio is mixed and the PTT signals are OR&#39;d together) and both can talk at the same time.  
         [0050]    The three microphones are preferably configured as follows:  
         [0051]    1. a hands free microphone for the driver;  
         [0052]    2. an optional handheld microphone for driver or passenger; and  
         [0053]    3. an optional auxiliary microphone (possibly a wireless microphone).  
         [0054]    In addition to the switched output, the router provides an unswitched buffered output from each microphone that is sent as an input to the audio mixer.  
         [0055]    With reference to FIG. 5, a block diagram of the microphone router  50  is illustrated, in accordance with the present invention. The switch is implemented using 1:8 demultiplexers  52  of which one output is “unused” (as differentiated from “off”). The microphone router includes two main circuits: a microphone input circuit  54 , replicated three times and a microphone output circuit  56 , replicated six times. A bus  58  connects the circuits. In addition, a latch  60  interfaces to the MPC-565 (not shown) to hold the routing information.  
         [0056]    With reference to FIG. 6, a schematic diagram of a microphone input circuit  70  is illustrated, in accordance with the present invention. For purposes of illustration, the drawing shows switches and relays where an alternative embodiment of the router may use solid-state components. The input circuit  70  supports both transistorized microphones and condenser microphones. The microphone selection is made during system configuration, including setting the phantom power to the microphone (0-12vdc) and setting the gain. Each microphone  72  can be individually configured. Moreover, the present invention contemplates setting the configuration in hardware and/or software. A pair of 1-to-8 demultiplexers  74  switches the microphone  72  to the desired output bus. One demultiplexer  74  routes the audio signal  76  onto the internal bus and the other routes the PTT signal  78  onto the internal bus. The demultiplexers are ganged together so that the audio and PTT inputs from a microphone are routed as a pair.  
         [0057]    With reference to FIG. 7, a schematic diagram of a microphone router circuit  80  is illustrated for matching router and output circuits, in accordance with the present invention. The circuit  80  connects to the internal bus and provides a microphone level output  82  that can be connected to the VACM or to a two-way radio. The output circuit provides both a PTT signal  84  and a balanced and isolated audio signal  86 .  
         [0058]    The audio board requires connectors for power/ground, communication with processor, and audio input and output signals.  
         [0059]    With reference to FIG. 8, a block diagram of an embodiment of the audio board  14  is illustrated, in accordance with the present invention. The audio board  14  includes of four major subsystems. The only subsystem not discussed previously is the optional processor block  92 . When board  14  is used as an internal interface module block  92  is depopulated since those functions are incorporated into the main processor board. When board  14  is used as an external interface module, block  92  includes a 68HC12 micro-controller or similar device and CAN interface. Together, they drive a (Serial Peripheral Interface) SPI interface to the audio mixer and microphone router. The interface looks just like the interface that the main processor board drives when the audio board is used as an internal interface module.  
         [0060]    With reference to FIG. 9, an alternate embodiment of an in vehicle audio system  100  for processing a plurality of audio input signals  112  is illustrated, in accordance with the present invention. System  100  includes an audio board  114 , a processor board  16 , and an audio output board  118 . The audio board  114  includes twenty CODECs and supporting circuitry (e.g. control logic and microphone power). Board  114  receives twenty analog inputs and combines the inputs into a 32 kHz by 16 bit digital audio stream that is passed to processor board  116 . Further, board  114  receives a 32 kHz by 16 bit digital audio stream from processor board  116  and generates 20 analog outputs. Generally, all the inputs are identical and all the outputs are identical.  
         [0061]    Processor board  116  includes a central processor (CP)  124  and a digital signal processor (DSP)  126 . The DSP  126  does all the audio processing, including: mixing, routing, and array microphone signal processing. The processing executed by DSP  126  is controlled by configuration settings that CP  124  passes to DSP  126  via a host processor interface (HPI). Further, CP  124  uses the HPI to download firmware to DSP  126  each time the system powers up. Further, CP  124  sends commands to DSP  126  during normal system operation. DSP  126  controls audio board  114  (i.e. input levels, CODEC gain levels, etc.) through a serial peripheral interface (SPI). The SPI is a standard interface supported by many micro-controllers and micro computers, including an MPC565 and 68HC112 micro controllers. Output board  118  includes an audio amplifier  128  in communication with audio board  114  and a plurality of speakers  130 . Audio amplifier  128  amplifies the data signals received from audio board  114  and then communicates those signals to the plurality of speakers  130 . Speakers  130  then broadcast the signal to a vehicle&#39;s passenger compartment. Preferably, system  100  includes at least four speakers  130  and accordingly, audio amplifier  128  is a four-channel audio amplifier. Further, system  100  provides enable inputs and outputs for most of the audio channels. The enable input and output information is passed between DSP  126  and audio board  114  via the SPI. For example, the enable inputs are typically connected to push-to-talk (PTT) signals from microphones or to the squelch outputs for radios. System  100  generates the enable outputs using the enable inputs, internally generated voice operated transmitter (VOX) signals, and input from CP  124  as directed.  
         [0062]    DSP  126  implements a seventeen by twenty mixer/router through control logic. Sixteen of the physical inputs are routed to the mixer. The seventeenth mixer input is reserved for a future processed audio input that will be generated from a four array microphone inputs.  
         [0063]    Advantageously, there are no inherent restrictions on routing, all inputs to the mixer/router can be routed to any of the outputs, along with the accompanying enable signals. Of course, a high level control software has the option of limiting certain routing combinations but the hardware does not enforce these restrictions.  
         [0064]    In addition to routing audio signals to various outputs, the mixer/router routes the enable signals to the appropriate enable outputs to be used for keying radios, enabling voice recognition, activating log recording, etc. The enable signals are also used to modify the internal behavior of the mixer, for example, prioritizing certain inputs, changing the gain of an input, or modifying the audio routing. The mixer routes the enable signals in a similar manner to and with the same flexibility as it routes the audio signals. Any input enable signal can be used anywhere in the mixer.  
         [0065]    Devices such as a two-way radio  132  have both inputs  134  and outputs  136  associated with them, however, from an internal routing perspective, the inputs  134  and outputs  136  are treated as separate entities. Although the connector strategy may imply that certain pairs of inputs  134  and outputs  136  belong to the same device, the actual relationship of input  134  to output  136  is totally under the direction of the high level software.  
         [0066]    In embodiment of the present invention, multiple inputs are assigned to a signal output. In this case, control software is provided for designating one or more inputs as priority inputs which would result in a dimming (reduction in volume) or completely turning off the other inputs. Further, some devices require a signal at all times. For example, a voice recognition system continuously tracks the ambient noise levels. However, other devices only require noise signal to be present when a corresponding enable signal is active. The mixing/router of the present invention support both functions.  
         [0067]    Further, the present invention provides a mixer/router implemented by DSP  126  and designed to support the functions shown below. Processor  124  sets up the following functions when required by changing DSP&#39;s low level control information. After the low level control information is set by processor  124 , DSP  126  will perform the following functions without processor  124  interaction. By keeping processing  124  out of the loop, the mixer/router of DSP  126  responds more quickly to changes in the audio inputs. Some of the functions supported by DSP&#39;s mixer/router are:  
         [0068]    a) Routes two-way radio audio to a public address speaker;  
         [0069]    b) Create a cross-band mobile repeater to assist communication between hand-held radio and dispatch (for example, by interconnecting 150 mHz radio and a 450 mHz radio to the mixer to function as a mobile repeater);  
         [0070]    c) Provide a mobile command post function by using a multiple radios to connect different agencies or sources on different radio bands;  
         [0071]    d) Use a single hands-free microphone to work with both a voice recognition and two-way radio by selecting the appropriate PTT switch (i.e. one switch for voice recognition, another for the radio);  
         [0072]    e) Log conversations and other communication using the vehicle&#39;s recorder system;  
         [0073]    f) Set the apparent spatial location of each radio within the vehicle compartment using speakers  130 ; and  
         [0074]    g) Use a hands-free microphone operating in VOX mode with the dispatch two-way radio while the vehicle is operating.  
         [0075]    Audio inputs  136  are specific as to their function. Microphone input and line and speaker inputs are provided, and because of electrical differences, six different types of input circuits are provided. For example, a general purpose input having an input voltage ranging from 80 mV to 5 volts RMS with a PTT is provided. Input impedance is at least 10 K Ohms. A swamping resister may be placed across a line to function as a speaker load.  
         [0076]    General purpose high level inputs work from 400 mV to 25 volts RMS without PTT. Input impedance is at least 10 K Ohms. This input is for exceptionally high level input signals such as a siren driver amplifier.  
         [0077]    Speaker inputs work from 160 mV to 10 volts RMS, no PTT. Input impedance is at least 10 K Ohms. Again, a swamping resister may be placed across the line to function as a speaker load. Speaker inputs are designed to handle high output signals that would overpower a general purpose input.  
         [0078]    A hand-held microphone input is provided to work with standard transistorized carbon microphone and having a 12 volt bias voltage. The microphone input supports PTT. The microphone&#39;s impedance is 600 Ohms. A hand-held microphone is 16 mV to 1 volt with PTT; a wireless microphone is 80 mV to 5 volts with PTT and a hands-free microphone is 80 mV to 5 volts but with no PTT. Input impedance is at least 10 K Ohms. Array element microphone inputs work identical to standard microphone input except that they do not support PTT.  
         [0079]    Each input  136  has a gain control that may be set by processor  124 . Processor  124  sets the overall input sensitivity range which may be either a positive or negative gain value (using a db scale). The gain is achieved using a programmable gain feature of the CODEC, and analog gain section before the CODEC and the digital gain applied to the DSP. Table 3 below shows an assignment of physical input signals along with the properties of the individual inputs, in accordance with an embodiment of the present invention.  
                                     TABLE 3                       Channel   Purpose   Type                                1   Radio 1   GP       2   Radio 2   GP       3   Radio 3   GP       4   Radio 4   GP       5   Radio 5   GP       6   Radar (Doppler signal)   GP       7   Spare   GP       8   Spare   GP       9   AP   GP       10   Wireless Microphone   GP       11   Handheld Microphone   Mic.       12   Handsfree Microphone   GP       13   VACM Responses   GP       14   Reserved for siren driver signal for noise   GPH           cancellation       15   AM/FM Tuner Left Channel   Speaker       16   AM/FM Tuner Right Channel   Speaker       17   Reserved for array microphone element 1   Array Mic. Element       18   Reserved for array microphone element 2   Array Mic. Element       19   Reserved for array microphone element 3   Array Mic. Element       20   Reserved for array microphone element 4   Array Mic. Element                  
 
         [0080]    The mixer implemented in DSP  126  has an input  138  which carries the digital information from the CODEC&#39;s  120  to DSP  126 . Each of the mixer inputs  138  have a gain control that is used to fine tune and normalize the input signal. The mixer normalizes the inputs to minimize distortion and to avoid overdriving a radio transmitter which would cause it to operate incorrectly. Each input  138  is capable of generating an enable signal. The enable signal can be generated using any combination of the following inputs:  
         [0081]    1) An external enable input, usually generated by the attached device using a “dry contact” such as a microphone push-to-talk switch or a radio generated squelch open signal;  
         [0082]    2) An internal voice operated transmitter (VOX) signal generated by DSP  126  to indicate the presence of audio on the input channel; or  
         [0083]    3) A processor enable is generated by software running on processor  24 .  
         [0084]    Each mixer input  138  is configured to use any or none of the enable signals. If multiple enable signals are selected, then they are logically or&#39;ed together (any one of the enable signals will activate the enable output).  
         [0085]    With the exception of the four speaker outputs, all audio outputs have an associated output enable signal which is in the form of a dry contact. The outputs specified for the two-way radios each have a hardware timer on the PTT output that times out after four minutes. The monaural outputs are settable from microphone output levels up through a 600 Ω 0 dB ceiling at line level. DC blocking is required on all monaural outputs. Table 4 below shows an assignment of the output signals, in an embodiment of the present invention.  
                                     TABLE 4                       Signal   Purpose   Type                                1   Two-way radio 1   Monaural with PTT + HW timer       2   Two-way radio 2   Monaural with PTT + HW Timer       3   Two-way radio 3   Monaural with PTT + HW Timer       4   Two-way radio 4   Monaural with PTT + HW Timer       5   Two-way radio 5   Monaural with PTT + HW Timer       6   Spare   Monaural with PTT       7   Spare   Monaural with PTT       8   VCR   Monaural with PTT       9   Spare   Monaural with PTT       10   Spare   Routed to internal expansion connector       11   Spare   Routed to internal expansion connector       12   Spare   Routed to internal expansion connector       13   VACM   Monaural with PTT       14   PA system (siren   Monaural with PTT           amplifier)       15   Spare   Routed to internal expansion connector       16   Spare   Routed to internal expansion connector       17   Stereo Left Front   To internal Amplifier       18   Stereo Right Front   To internal Amplifier       19   Stereo Left Rear   To internal Amplifier       20   Stereo Right Rear   To internal Amplifier                  
 
         [0086]    Referring now to FIG. 10, a general purpose input channel  150  is illustrated, in accordance with the present invention. Input channel  150  includes an audio input (analog)  152  and an enable input (discrete)  154 . Two outputs, audio and enable are generated and used internally within the mixer/router of DSP  126 . Both outputs  156  and  158  are digital. Audio input signal  152  may be either line level or speaker level. Further, the audio input signal  152  is processed by a gain control stage  160  in CODEC  20  which is reflected in the digitized output  156 . Enable input  154  may come from for example a microphone pushed-to-talk switch or a squelch open indication from a two-way radio. Further, an input enable signal may be generated by the input channel and configured to come from any combination of: an external device, an internally generated VOX signal, a combination of a VOX signal and an external device, or directly driven by processor  124 .  
         [0087]    All the switches shown in FIG. 10 are, in an embodiment, registers in DSP  126  or latches on audio board  114 . Processor  124  sets the DSP registers directly via the HPI interface. Processor  124  sets the latches on audio board  114  by setting registers in DSP  126 . DSP  126  then propagates the audio board  114  via the SPI interface. Gain and level settings  162  and  164  (i.e. the CODEC gain setting or VOX threshold setting) are also registers. Processor  124  controls gain and level settings  162  and  164  in a like manner as switches.  
         [0088]    Mixer of DSP  126  provides  20  outputs. Any input  138  can be routed to any output. Multiple inputs may be assigned to a single output in which case they will be mixed accordingly to their gain settings. System  100  automatically calculates gain settings so that multiple inputs do not override an output. System  100  further provides an automatic compression system so that the output level can be set to be heard when only one channel is active and not be driven into distortion when the remaining inputs go active at the same time. Using the enable signals one or more inputs may be assigned a priority allowing an input to take over a channel when the enable signal becomes active. For example, each output can be assigned its own set of priority inputs. The priority inputs may enable the other inputs on an input by input basis. Generally, no more than one input will be designated a priority input for each output channel. For example, the input enable signal may be used internally to disable the output even when the input audio is not enabled for that output.  
         [0089]    Each output has for example, all seventeen enable signals available with the ability to ignore or mask out enable signals that are not related to the output. Additionally, each output has a processor  124  controlled enable signal. The processor controlled enable signal has a higher priority than the other enable signals, such that when the processor enable signal is commanding the output on, the output is on regardless of the other enable signal. Each output enable has the configurable setting that permits it to be in one of the following states: always on, always off, follow the input enable signals, and follow only the processor enable signal. The enable signal for example, may be sent to an output device to activate a transmitter, start a log in device, or enable voice recognition.  
         [0090]    In an embodiment of the present invention microphone inputs are provided. The microphone inputs are general-purpose inputs with different initial gain settings. In addition, a handheld microphone input (a specially designated channel) supports a powered microphone with a +12V power signal imposed on the microphone audio input signal. The handheld microphone input supports both standard dynamic microphones and standard “transistorized” amplified microphones that mimic carbon microphones. The hands free microphone input is also specialized in that it supplies a DC voltage of at least 9.0V at a current of at least 100 mA for powering the external hands free microphone electronics.  
         [0091]    Of the twenty physical inputs, sixteen are directly connected to the mixer. The remaining four inputs, the array microphone elements, are made available for future array microphone processing. The 17 th  input of the mixer is reserved for the output of the array microphone algorithm. The mixer/router mixes and routes both audio signals and enable signals (PTT output).  
         [0092]    Advantageously, the audio portion of the mixer/router can mix any combination of the input audio channels into each output channel. Processor  24  is responsible for communicating to DSP  126  what level of each input signal should be mixed into each output signal. If the mix level is set to zero, the corresponding input channel is not included in the output signal.  
         [0093]    Processor  124  is capable of specifying two sets of mixing levels for each output channel. The two levels can be used in various ways. For example, the speaker output channels can be set up with one setting for normal listening and a second setting that dims the AM/FM tuner, etc. when the user presses the push to talk switch for a microphone.  
         [0094]    With reference to FIG. 11, there is illustrated an audio routing logic  200  for an output channel. The audio routing logic determines which of two sets of mixer levels to use at any moment in time. Each output channel has its own copy of this logic with the associated configuration switches. Output  202  of circuit  200  determines which of the two sets of mixer levels will be used to generate an audio output.  
         [0095]    The input configuration switches  204  determine which inputs are used to calculate the Audio Routing Enable signal for a given output channel. CP Enable logic  206  determines whether the CP  124  controls the output, overriding the enable calculation. Force control logic  208  allows a second level of override, which is used primarily for debugging purposes.  
         [0096]    With reference to FIG. 112, a PTT Enable Signal Logic  300  is illustrated. PTT signal for each output is generated. Each output has its own copy of logic  300  along with the associated configuration switches  302  and controls.  
         [0097]    PTT Enable Signal Logic  300  is similar to its audio counterpart, with the addition of a watchdog timer  304  and the ability to completely disable the output.  
         [0098]    Input configuration switches  302  (implemented as a register in DSP  126 ) selects which inputs are part of the calculation that generates the enable signal output. The next logic section  306  selects whether the CP or the Input Enables controls the PTT logic. It is followed by force logic  308  to hold the PTT on or off always. Then the PTT watchdog timer  304 , mandated by the FCC, makes it impossible to hold a radio in key on condition for more than three minutes. The watchdog timer section  304  is only present on outputs that act as microphone inputs to two-way radios. Then the PTT output can optionally be disabled or inverted.  
         [0099]    The PTT watchdog timer may need to be implemented in hardware as a separate device if FCC requirements dictate hardware-based fail-safe devices.  
         [0100]    The mixer/router supports two kinds of outputs: monaural and speaker. The monaural outputs drive two-way radios, logging devices, etc. The speaker outputs drive the four speakers in the vehicle passenger compartment.  
         [0101]    With reference to FIG. 13, an audio routing  350  for a single output channel is illustrated. Each output has its own Audio Routing Enable Signal Logic (see FIG. 11). Seventeen pairs of gains  352 , an enabled and a disabled setting  354  for each input  356   
         [0102]    Each output has an automatic gain control circuit (AGC)  358  that limits the level passed on to the external device. The primary function of the AGC circuit  358  is to allow the system to have multiple outputs active at the same time and to maintain the average audio output level, regardless of how many outputs are producing audio at a given time. Although the AGC does, in fact, compress the audio signal, it is not intended to be used as a full-fledged compressor because that would require running the normalized signals “hot”, which in turn will cause the mixer to distort the output.  
         [0103]    The final step in the output processing is to be able to set the output level. Speaker outputs have the same audio processing capability as monaural outputs (see FIG. 13), but they serve a particular purpose. By including four speaker outputs it is possible to assign both the level of an input channel in the vehicle, and where in the passenger compartment the signal appears to originate. The ability to assign input signals to different spatial locations eases the listeners&#39; auditory burden when multiple audio sources are present simultaneously.  
         [0104]    As any person skilled in the art of systems and methods for routing audio signals in automobiles will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.