Modular Digital Control of Audio Analog Function

Abstract

The audio signal processing apparatus includes at least one controllable element 90, 91, 92 for performing an analog audio processing function. The controllable element is operable together with a digital controller 58 that controls the analog audio processing function executed by the controllable elements 90, 91, 92. At least one audio processing module 52, 54 includes a partial audio processing circuit for an audio processing operation. The modules 52, 54 are operable together with the controllable elements 90, 91, 92 to complete the audio processing circuit and thus enable the audio processing operation. In this way, the audio processing operation is controllable by the digital controller. The switching array 96 selectively couples the audio processing modules 52, 54 and the controllable elements 90, 91, 92. The power supply 66 is operable to selectively supply power for the audio processing circuit of the module 52, 54 or each thereof.

Description

Technical Field

[0001] An audio signal processing apparatus, an audio processing module, an audio signal processing system, and a method for processing an analog audio signal.

Background Art

[0002] Audio processing modules are used with various audio signal sources to add acoustic effects to audio. Audio processing modules are used in analog synthesizers and audio mixers or mixing desks. Audio processing modules are used with electric guitars, in which case they are known as fuzz boxes. Fuzz boxes are often used alone. However, fuzz boxes can also be used in multiple combinations.

[0003] Fuzz boxes, and in fact other audio processing modules, are connected in series, in parallel, or in a combination of both to achieve different acoustic effects. Fuzz boxes may be placed on stage prior to a performance and have switches and dials large enough to be operated by foot during the performance. Modules are generally placed in a rack when used with an analog synthesizer, an audio mixer, a mixing desk, etc.

[0004] FIG. 1 is a schematic diagram of the electrical elements in an analog audio processing module 10. There are a number of different ways in which the electrical elements can be configured. Module 10 is shown in FIG. 1 as comprising any selection of elements representative of what can be found in a typical module. These elements include an input connection 11, generally comprising a socket, coupled to an input stage or buffer 12.

[0005] The input connection part 11 enables an audio signal source - for example, a microphone, a pickup in a guitar, or an audio tape - to be coupled to provide an electrical signal as an analog of voice or music. Depending on the intended use of module 10, the input stage 12 can function to provide a specified impedance at the input, isolate the input from subsequent elements in module 10, or condition the signal prior to further processing by the module.

[0006] The signal from the input stage 12 is passed to the processing stage 14, which applies a transfer function fx to process the signal and thereby modify the audio represented by it. The fx stage 14 can comprise elements such as an attenuator, a filter, a delay circuit, a preamplifier, a signal amplifier, a clipping amplifier, etc. In fact, depending on the sophistication or complexity of the audio processing, module 10 can include a combination (not shown) of such elements that together apply the desired processing to the electrical audio signal supplied to it.

[0007] In some modules, one or more control switches, dials, or knobs 15 are provided to enable the user to change the effect fx added to the audio signal. In practice, a rotary switch or a dial is typically provided. The switches and dials enable the user to include or bypass circuit elements (such as the fx stage 14, etc.) in the module to turn the module on or off or to change the processing effect on the input signal.

[0008] The knob 15 can be coupled to a potentiometer or a similar element with a variable impedance that can be used, for example, to attenuate the signal or to control the operation of more active elements such as a filter or an amplifier. The knob is typically included for volume and tone control. However, the knob is also used to change the transfer function of the filter to vary the effect added to the analog audio signal by module 10.

[0009] The processed signal from the fx section 14 is provided to the output stage or buffer 17, which operates in a similar manner to the input buffer 12 to match the impedance or adjust the signal so as to conform to a specified or expected range of output current or voltage. The socket 19 enables the processing module 10 to be coupled to another module for further processing of the signal or, for example, to a power amplifier that drives loudspeakers in an auditorium, theater, or other concert venue. The socket 19 can serve as a connection to a signal storage device, such as a tape recorder, for long-term storage of analog audio signals.

[0010] FIG. 2 shows a processing module 20 with another optional selection of elements. The audio signal is input at a plug 21 coupled to an isolation transformer 22, which outputs a signal for a preamplifier 23. The conditioned signal is applied to a filter 24, which varies the signal according to the filter characteristics and the position of a control knob 25 and outputs a modified signal for another output stage 27. For the sake of diversity - and to show that there is no fixed design for an analog audio processing module - the output stage is shown as a variable preamplifier 27, which operates with another isolation transformer 28 to output the audio signal via a socket 29 for further processing, amplification, or storage. Typically, here the preamplifier will be controlled via a knob similar to the knob 15 in FIG. 1, but this need not be the case, for example, depending on the intended use of the module 20.

[0011] Module 20 includes a tap or connection 26 between filter 24 and preamplifier 27, and the tap or connection 26 can be coupled via a lead wire (not shown) to provide a feedback signal at input 21 or a feedforward signal at output 29. This provides the user with additional control over the effects added to the audio signal by the module. Additional taps (not shown) can be provided between other stages in the module to provide additional user control over the effects.

[0012] Figure 3 shows a series of modules interconnected with each other using feedback path 35 and feedforward path 36 created through the interconnection between taps 26 in the module. This enables the user to modify the effects brought about by the cascade of modules between input connection 37 and output connection 38. The taps can also be coupled to the input and output of individual modules 32 - 34, or, if necessary, to the input 37 or output 38 of the cascade. Such couplings are used in an analog synthesizer (not shown), can be used with a mixing desk (not shown), and may be used as such.

[0013] Figure 4 shows an example of one way these processing modules are used in an audio mixer within a recording studio. In this scenario, as shown in Figure 4, a rack 40 is provided to store several processing modules 42 - 45. If necessary, the rack 40 provides a common power supply (not shown), and the settings in each module can be adjusted via the control knobs and switches 15 on the front of each module 42 - 45. Sockets 26, 29 provided on the front of some of modules 43, 45 provide connections into the module, similar to tap 26 in Figure 2. A similar configuration can also be used for an analog synthesizer.

[0014] Analog audio signal processing modules have been available in numerous and diverse different formats over the decades. As with all products, some models come and go, while others remain popular for years. Analog modules continue to be widely used despite the availability of digital equipment that provides essentially the same functionality.

[0015] Still measured in decades, but more recently, digital signal processing has been widely adopted for audio signals. Analog signals are converted into digital form by taking samples of the analog signal at regular intervals. This results in a sequence of numbers representing the audio signal. These numbers are modified by a digital signal processor in order to modify the audio represented thereby. In this way, equivalent effects can be added to the audio within a digital environment as in the case of an analog environment.

[0016] In fact, many effects created by analog processing modules - such as fuzz boxes - are now available within a digital environment. In some situations, the effects of analog modules are emulated by a computer or digital signal processor. This is inevitable. It is in line with the move from electric-based audio technology to a digital environment.

[0017] However, equivalent digital effects are often said to lack the warmth and pleasantness of their analog originals. This is subjective and difficult to quantify, but nevertheless, it is a real issue in the audio world. The digital versions may be equivalent, but they are not the same as analog. Put simply, musicians, sound engineers, and producers prefer analog modules for the familiarity - many have been available for decades - their sound, and their warmth (however that may be quantified). Users know what to expect from a given module.

[0018] However, when using an audio processing module, it is useful that it is possible to utilize digital control techniques. In a completely analog environment where several modules are combined together to achieve a particular acoustic effect, it is necessary to write down how the modules are connected and what settings are supplied. Failing to do so will make it difficult to reproduce the same sound again in the future.

[0019] During a performance, it takes time to make changes between one set of complex settings and another. Only simple changes - turning a module on or off, adjusting a few dials, and switching a few connections - may be possible between songs. The studio, of course, has the luxury of being able to stop and reset all equipment before continuing recording. However, here too, relying entirely on notes to record various settings takes time to maintain the current or up-to-date state and increases the production cost. Summary of the Invention Means for Solving the Problems

[0020] The present invention provides an audio signal processing apparatus, an audio processing module, an audio signal processing system, and a method for processing an analog audio signal.

[0021] An audio signal processing system includes an audio signal processing apparatus having a digital controller and at least one controllable element for performing an analog audio processing function, the controllable element being operable, together with the digital controller, for controlling the analog audio processing function thereby, and an audio processing module including a partial audio processing circuit for an audio processing operation, the module being connectable to at least one controllable element for completing the audio processing circuit and enabling the audio processing operation.

[0022] The present invention is defined by the claims.

[0023] The above and further features of the present invention will be described in detail in the claims and will become more apparent from the following description given in consideration of the accompanying drawings together with the advantages of the present invention.

Brief Description of the Drawings

[0024]

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Best Mode for Carrying Out the Invention

[0025] Figure 5 is a schematic diagram of an audio processing system 50 having a platform (PFM) 56 and analog audio processing modules 52, 53, 54. The audio processing modules 52, 53, 54 are controlled and connected via the platform 56. The operation of the platform 56 is controlled via a central processing unit (CPU) 58 coupled to the platform via a digital bus 60 that is also coupled to each of the modules 52 - 54.

[0026] The CPU 58 is shown outside the platform PFM 56 for ease of explanation and understanding. In reality, the CPU 58 will typically be included as part of the PFM 56. The operations of the CPU 58 described below can be performed by a dedicated processor in the platform as illustrated. However, there is no technical reason why the CPU cannot be provided as an external unit of the platform. Instead, the operations can be performed, for example, by a personal computer (not shown) coupled to the platform via the bus 60. In either case, the operations are essentially the same.

[0027] The CPU 58 receives commands from a user interface (UI) 62 that enables the user to set the internal operation parameters of each of the modules 52 - 54. The UI 62 can be provided via, for example, a suitable data connection 64, such as USB, Wi-Fi, Bluetooth, or the like, via any of a mobile phone, tablet, or personal computer coupled to the CPU 58.

[0028] The user interface 62 provides a way for a user to input commands into the system 50. Typically, the commands will adjust the operation of the modules 52, 53, 54 in a manner equivalent to the adjustment of the dials and knobs 15, 25 described with respect to FIGS. 1-4. Any form of representation can be used for the modules - including control inputs via a keyboard or mouse - but it is common currently to have a graphical representation displayed on a touch-sensitive screen, such as that seen on a touch tablet device.

[0029] FIG. 6 shows an example of the graphical representation displayed for modules 52', 53', 54' equivalent to modules 52, 53, 54 in FIG. 5. Each module has selector dials 15' and other indicators 25' equivalent to the knobs and dials described and illustrated in FIGS. 1, 2, and 4. The user can operate these visual input elements 15', 25' to change the settings in the corresponding module. The user interface UI62 responds to this operation by generating control data for use by the CPU 58, as will be described in more detail below.

[0030] For reasons that will become apparent later in this specification, the modules 52, 53, 54 can be designed by their current manufacturers directly from existing audio processing modules. Starting from the original modules, the circuitry can be modified and adapted to be suitable for use with the system 50. This allows popular historical models to be included in the system and their operation to be familiar to a number of users. When this is done, the graphical representation displayed on the UI62 can be a reproduction of the front panel of the original module, having the same representation of knobs, buttons, and dials as in the original.

[0031] Returning to FIG. 5, system 50 also includes a power supply (PS) 66 that supplies power to system 50 via power line 68. For purposes of illustration, although shown outside the platform, power supply PS66 will typically be included as part of platform 56. Power supply 66 is coupled to and controlled by processor (CPU) 58 via digital bus 60. Power supply PS66 provides power to various elements on platform 56 and modules 52, 54 via supply lines (not shown in FIG. 5).

[0032] Platform (PFM) 56 includes a switching or coupling arrangement (not shown in FIG. 5) for coupling system analog input and output lines 72 to module analog lines 74. These analog lines 72, 74 are shown as pairs in FIG. 5, but this is done more for purposes of illustration than to imply that the analog lines are necessarily supplied individually or in groups of several lines as needed. Analog line 72 provides points for audio signals to enter system 50 from, for example, a pickup (not shown) in a microphone or musical instrument, and for signals to be output from system 50 to, for example, an amplifier (not shown).

[0033] The platform also includes a digital audio port 77 for receiving and / or outputting audio signals in digital form. This enables the platform to receive signals from digital sources or output digital signals to digital destinations. Thus, for example, the system can convert incoming digital to analog and pass the analog through modules 52, 53, 54 before outputting the resulting processed signal in digital form.

[0034] Figures 7, 8, and 9 show the details of modules 52, 53, and 54 suitable for use in system 50. Modules 52 - 54 are analog devices and are mostly common with the above-described modules 10, 20 shown in FIGS. 1 and 2. In fact, if the modules are based on the original analog design adapted for use with the system, those modules effectively retain access to the popular designs from the past. A module, for example, module 52, still includes an input connector 11' coupled to the input stage 12' and an output stage 17' - here a variable amplifier - coupled to the output connector or socket 19'.

[0035] Each of modules 52 - 54 has an information store or data element 70 coupled to platform 56 via digital bus 60 and thus to CPU 58. The data element 70 holds the operating information characterizing the operation of the module. The operating information is first used to set up the way the module is connected to the platform and to define the way the module and the platform interact during use.

[0036] Thus, the operating information includes the characteristics or functions of one or more parts of the removed module and the required characteristics of the controllable elements CE90, 92 that will replace them. Depending on the details of the module, the information may include the impedances of the input parts 21', 21'' and output parts 29', 29'' to ensure signal balance, signal voltage levels, and power supply requirements between the modules. Generally, the information includes anything necessary to configure the controllable element CE to operate with the module.

[0037] This information is retained in digital form. For this purpose, as shown in detail in the upper left of FIG. 7, the information store or data element 70 includes a memory store (S) and a digital interface circuit (IF) that interfaces with the bus 60 shown in FIG. 5. This enables a platform including the CPU 58 to access the operating information and operate accordingly. The digital interface circuit IF can be a dedicated interface circuit. However, in practice, it is convenient to provide a programmable controller configured to communicate with the CPU 58 via the digital bus 60 and thus operate as a data element 70.

[0038] A microcontroller (μ) generally comprises a memory for storing applications, programs, routines, and for holding operating data. When a module is designed, data defining the various characteristics of the module is held in the memory of the microcontroller, and this data enables the module to be coupled to the platform and operate therein as intended by the designer.

[0039] Therefore, a small microprocessor or microcontroller (μ) 70 is a suitable way to implement the memory S and the interface IF. Depending on the implementation details, the microcontroller μ often provides an efficient way for the module to communicate with the CPU 58 and other parts of the platform 56 and thus operate therein as part of the system 50. Of course, a separate memory can be used together with or instead of the memory of the microcontroller as a matter of design preference. In the following, it is assumed that the information store or data element 70 comprises a microcontroller μ, but it should be noted that this is a matter of design choice.

[0040] As shown in Figure 7, processing stage fx14' and control knob 15' have been removed from module 52. This is represented by the dashed line. Instead of these, the elements are the internal connection lines L from input stage 12' out and internal connection line L to output stage 17' in which are connected to them at terminals 80, 82. As can be seen, these internal connection lines L out and L in are similar to tap 26 that connects inside the modules in Figures 2 and 3. Thus, some of the inside of module 52 (fx) has been removed, and access to the remaining part of the module is made possible via internal connection terminal L out 80 and internal connection terminal L in 82. Thus, modules 52, 53, 54 comprise a partial audio processing circuit for audio processing operations.

[0041] In fact, the platform will typically include a mount such as a rack to which modules 52, 53, 54 can be removably attached. The connectors on the modules corresponding to terminals 11', 19', 80, 82 as shown in Figure 7 connect to corresponding connectors in the rack to couple the electronics and modules in the rack to each other.

[0042] In Figure 8, module 53 is shown coupled to controllable element CE90 via terminals 80, 82. This coupling is done via the above-mentioned connection lines L out and L in Controllable element CE90 is provided in platform PFM56 rather than being part of module 52 and will be described in detail below. As a matter of design choice, controllable element CE90 can be controlled by processor CPU58 or information store 70, or both. When the information store is implemented as microcontroller μ70, it is convenient to place the control with μ70.

[0043] CE90 can be configured by the CPU 58 to perform the same analog functions as the elements removed from the module, such as the processing stage fx14' and the control knob 15'. As will be further described below, CE90 comprises analog components equivalent to those removed from the module, controlled by the CPU 58 based on the operating data for the relevant module from the microcontroller 70. Thus, the controllable element CE90 completes the audio processing circuits of modules 52, 53, 54, thereby enabling the audio processing operations previously performed by the modules to be performed by the remaining elements in the modules combined with the CE.

[0044] In FIG. 9, the variability of the output preamplifier 27'' (see FIG. 7) in module 54 has been moved to a second controllable element CE92 in the output section 29'' of module 54. The output section 29'' is coupled to the second controllable element CE92 via line 94. The controllable element CE92 is within the platform 56 (see FIG. 5), like the controllable element 90. The output (out) of the CE provides a path 95 for the output signal to other parts of the system or to an external connection (not shown).

[0045] In each of the analog audio processing modules 52 - 54 in FIGS. 7 - 9, some of the functions, typically but not necessarily variable functions, are removed from the module and replaced by the controllable elements 90, 92 in the platform 56 by the connectors 80, 82, 94. The reason for this should become clearer from the following explanation. In particular, this approach enables the manufacturer of the analog module to take the existing designs of the manufacturer and modify them by removing a selected part (e.g., the processing stage fx14) in module 52 and providing connectors 80, 82, 94 at those locations to couple to suitably configured controllable elements 90, 92.

[0046] As should be apparent from the following description, placing the controllable element CE90 outside the module and within the platform 56 provides flexibility in the use of the system 50. The module structure is simplified because at least some of the analog functions fx are removed from the module. During use of the system 50, one module can be easily replaced by another, and the operation of one or more associated CEs is adjusted according to the needs of the newly added module. The cost is lower because the system requires only a few CEs in the platform instead of one in each module.

[0047] However, as shown in FIG. 10, it is possible to place the controllable element CE90 inside the module 55. The elements in the module 55 in FIG. 10 are the same as those in the module 54 in FIG. 9 and are marked accordingly. The controllable element 90' is coupled to the bus 60 either directly or via the microcontroller μ70 as shown, and is thus controllable by the CPU 58.

[0048] This approach is advantageous, for example, when the module 55 provides a complex or highly specialized function that cannot be easily performed by a general-purpose controllable element CE. An equalizer that provides separate attenuation over multiple frequency bands requires a large number of filters, one for each band, and thus requires a complex CE with limited appeal to a large number of users. Therefore, using a CE specifically designed for its multi-band function and placing it inside or with the module 55 becomes more cost-effective. The benefits of digital control of the analog functions of the controllable element are still realized even without the same reduction in the cost of the module.

[0049] Figure 11 shows the platform 56 in more detail. In this figure, the CPU 58 is shown as part of the platform, in contrast to the method shown in Figure 5. Similarly, the power supply unit PS66 is included within the platform 56. Here, the bus 60 provides a path for control data between the CPU 58, the microprocessors (μ) 70 in the modules 52, 54, the power supply PS66, and the controllable elements CE90, 91, 92, 94 also in the platform.

[0050] The structure of the bus 60 is implementation-dependent and is affected by issues such as design and cost effectiveness. Although the bus 60 is shown as a single path in Figure 11, it may actually comprise a plurality of different buses. There are a number of available buses suitable for system control and communication. The USB (Universal Serial Bus) standard is widely known and is suitable for systems where the platform may be made by one supplier and the modules by another. USB hardware is widely available and is a cost-effective option for implementing the bus 60. Thus, the bus 60 may comprise USB for data communication between the CPU 58 and the microcontroller 70.

[0051] Of course, other bus standards are available and may be more suitable for the transfer of control data. When the CPU is provided by an externally connected personal computer or the like, the external computer will typically be connected via an external bus such as Ethernet or USB.

[0052] The controlled elements CE90, 91, 92 have a unique identifier, e.g., an address, by which they can be identified by the system control CPU58. Thus, from a design perspective, it is convenient to use a bus based on the Serial Peripheral Interface (SPI) bus standard for transferring information between the CPU58 and the CE90, 91, 92, 94. A number of microcontrollers include General-Purpose Input / Output (GPIO) pins that provide a logical 1 or 0 output that can be used to directly control on / off type operations performed by the controlled elements. This is done in the system shown in the drawings and is further explained below.

[0053] Since the use of a particular bus is an implementation detail, in this description, generally, reference is made to bus 60 in a general sense. When the context requires or permits, particular buses will be identified for their suitability.

[0054] The number of modules 52, 54 in the system is a matter of design choice determined by the user's needs, including in particular the desired processing power of the user and the budget. From a technical perspective, it becomes quite acceptable to provide a system 50 with only a single module 52 coupled to the platform PFM56, but such a system may not utilize all the features of a multi-module system in all cases.

[0055] For example, an entry-level system with two or three modules 52, 54 mounted on the platform with an appropriate number of controllable elements 90, 94 can be made available. If desired, more can be included, and the ellipsis (...) shown between modules 52 and 54 indicates that the system can be increased to more than two modules shown in the figure. These additional elements are omitted in the drawings for clarity. Similarly, the ellipsis (...) between CE92 and CE94 indicates that the platform 56 may include additional control elements (CEs) depending on design-specific needs.

[0056] In larger systems, the platform and modules can be made and sold by separate suppliers. Thus, the platform will come to include a rack (not shown) on which individual modules can be mounted. Suitable connectors in the rack and modules will provide the necessary connections to the data bus 60 and the various analog lines for the modules.

[0057] Referring further to FIG. 11, the switching array 96 controls the movement of analog signals within the platform 56 between the modules 52, 54 and between the modules. The movement of analog signals within the system is effected by the switching array 96 along analog lines, most of which are not shown in this FIG. 11. There are a number of analog audio signal lines between the switching array 96 and the controllable elements 90-94. These too are omitted from the figure for clarity. They include lines 100, 102 coupling the module 52 and the controllable element CE90, and lines 104, 105 between the module 54 and CE94.

[0058] The switching array 96 is identified as the switching matrix MX in this FIG. 11 and in subsequent drawings. The matrix provides flexibility in coupling the modules 52, 53, 54 and the controllable elements 90, 91, 92 to each other. However, in some situations, for example, when the system is relatively small and has only two or three modules, the matrix may not be the optimal solution. A simpler switching array may be more design-effective or cost-effective. Depending on the implementation requirements, the switching array can be provided by CMOS analog switches, multiplexers, relays, etc., as long as they can route signals between different input and output portions on the platform, the controllable elements, and the modules. Nevertheless, for the sake of consistency and clarity, the remaining description will be given with reference to the switching matrix MX.

[0059] The system is designed to maintain the audio signal in its analog form, but to provide computer, i.e., digital control. However, there may be times when the user wishes to receive audio from a digital source or provide audio to a digital system. The analog-to-digital and digital-to-analog converters ADC / DAC 108 provide a path 77 for a digital audio signal to be input to or output from the platform 56. The ADC and DAC are shown as a single unit, but may be provided as separate elements. However configured, the ADC / DAC 108 is coupled to the bus 60 to enable control by the CPU 58. The analog ports of the ADC / DAC 108 are connected or coupled to the switching matrix 96 via the analog lines 109.

[0060] The power supply PS 66 supplies power to the platform 56 and the modules 52, 54 under the control of the CPU 58. In addition to supplying power to the platform and the microcontroller 70 (the digital control part of the system) in the modules, the power supply 66 also separately and selectively supplies power to the analog elements of the modules 52, 54. This is necessary because each manufacturer has, over the years, determined the voltage levels within their devices at their own discretion - there is no uniformity.

[0061] Therefore, the information stored in the microcontroller μ70 also specifies the power characteristics of the modules. This includes information such as how much power the module requires at what voltage. The information is used by the power supply 66 to supply power at the correct level to the analog circuits in the individual modules via the power lines p1, p2, p3... p n This enables the specific power supply of the modules with the required power levels, which is necessary when the system is to support modules of various different designs by different manufacturers.

[0062] Typically, the power supply PS66 is capable of supplying power over a range of voltages, for example, ±48 volts, and a specific voltage is supplied according to the individual requirements of each module. Some of the modules 52-54 may require voltages that exceed the range of the power supply 66. Here, the design of the module will include a voltage booster to take the voltage available from the power supply and increase it to the level required by the analog audio processing part of the module.

[0063] FIG. 12 shows the power supply 66 in more detail. As shown, the power supply 66 is coupled to receive an AC power signal from a multi-tap transformer 120 connectable to a mains power outlet (e.g., 110-240V AC, not shown), and includes two power conversion paths 121 and 121'. The power supply 66 provides a separate power output for each controllable element CE90, 91 (see FIG. 11), and thus includes separate power regulation paths 121, 121' for each CE. However, for clarity, only two power paths 121, 121' are shown. Since both paths 121, 121' operate in essentially the same manner, they will be described together.

[0064] A plurality of taps 122, 122' from the transformer 120 are provided to multiplexers 124, 124'. Each tap provides a different AC power supply voltage to the multiplexers 124, 124'. The taps 122, 122' are shown separately for each power conversion path 121, 121', but the corresponding taps for each path will typically come from the same location in the transformer 120. The AC output from the multiplexers 124, 124' is converted to split rail DC power supplies 126, 126' by regulators R128, 128' that receive a reference voltage V ref from the bridge rectifiers 127, 127' (or similar) and digital-to-analog converters DAC130, 130'.

[0065] The operation of multiplexers 124, 124' is controlled by a controller 132 that is connected to bus 60 and receives control information from a control processor CPU 58 (see FIG. 11). Conveniently, a microcontroller similar to microcontroller 70 in the microcontroller μ-module - is arranged as controller 132. Controller μ132 provides signals for multiplexers 124, 124', and causes multiplexers 124, 124' to select one of the taps input thereto from transformer 120. Controller μ132 also provides signals for DACs 130, 130', and causes DACs 130, 130' to output a reference voltage V ref for use by regulators R128, 128'.

[0066] The selection of the tap and the generation of the reference voltage V ref are determined by the characteristic data for the module. This module data is static (remaining the same for the module in question) and is therefore stored in the microcontroller of the module or in an associated store. As will be described in more detail below in this specification, static data such as this power requirement data is provided from the module to the CPU, and the CPU passes the static data to the microcontroller μ132 in the power supply. Thus, each DC power supply 126, 126' is generated at a level specified by the information passed by CPU 58 from the microcontroller for a given module 52, 54 (see FIG. 11).

[0067] Power is not initially supplied to their respective modules by power conversion paths 121, 121'. Before that can happen, platform 56 must be powered along with the microcontroller 70 in the module, i.e., the digital part of system 50. This is necessary, in particular, so that information about the requirements of each module can be accessed from modules 52, 54 that are used to set the output voltage to the required level for the module.

[0068] Therefore, power supply 66 also includes a further power conversion path 135 for powering the digital part of system 50, which consists of platform 56 and the parts of the modules coupled to the platform via bus 60, i.e., including microcontroller 70. Thus, power conversion path 135 includes a bridge rectifier 137 coupled to receive an AC power signal from transformer 120 and a regulator 138 for providing voltage V dd for the digital part of the system. This part of power supply 66 provides an output when the system is switched on. This part of power supply 66 may, of course, be provided as a separate element when it is convenient to do so, because the power supplied by this part of power supply 66 does not depend on the modules plugged into or otherwise coupled to the platform.

[0069] Before proceeding to FIG. 12, note that a second bus 150 is shown coupled to controller μ132. The purpose of this bus 150 is explained below.

[0070] FIG. 13 shows how parts of the system, specifically modules 52, 54 including CPU 58, PSU 66, and microcontroller 70, are interconnected to enable power to be supplied to the modules. When the system is first switched on, the analog parts of the modules remain unpowered. Similarly, when a module is first added to a powered system, power is applied to microcontroller 70 but not to the analog parts of the module.

[0071] Bus 60 is used for initial communication between CPU 58 and microcontroller 70. As previously described with respect to FIG. 11, this communication can be provided via a USB bus. The USB bus may be made by a supplier where the platform (PFM in FIG. 5) exists, and is suitable for a system such as a system where the modules may be made by another supplier. USB hardware is widely available and is a cost-effective option for implementing bus 60.

[0072] Referring to both FIGS. 13 and 14, the initial data 140 held in store S (FIG. 7) of or coupled to microcontroller μ70 includes a "signature" or "signed certificate" in a known format that serves to identify the module. This signed data 140 is transferred to CPU 58 via bus 60. CPU 58 verifies the signature in handshake 142 between microcontroller μ70 in modules 52, 54 and CPU 58 in the platform.

[0073] The combined platform and modular design allows different manufacturers to contribute to the system, but also creates the risk that parts may be made that are not fully compatible. Modules that do not work, fail immediately, or physically damage the system pose a risk of reputational damage to the product and its supplier. The use of signatures facilitates quality control and reduces the likelihood that low-quality devices can damage the system.

[0074] If the module is rack-mounted, the module can be placed anywhere in the rack. When the initial system data is verified by CPU 58, handshake 142 ends and CPU 58 sends a command to microcontroller μ70 to give a signal identifying its location in system 50. This can be done via USB bus 60. However, there is an easier method.

[0075] As described above with respect to FIG. 11, the microcontroller typically includes GPIO pins (General Purpose Input / Output). These pins are wired to connection pins in the rack-mounted backplane. When the microcontroller 70 receives a command to send an identification signal, it does so by placing a signal (e.g., logic 1) on the associated pin. This action is represented in FIG. 14 by arrow 144 between module M / μ and the CPU. This action is also represented in FIG. 13 by lines 148, 149 that couple the microcontroller 70 in each module 52, 54 to the CPU 58. Thereafter, the microcontroller μ sends power requirement data 147 to the power supply PSU 66. This can, of course, be done via bus 60. However, it is not necessary. The CPU 58 does not need to know this information and thus it is not necessary to pass this information through the CPU.

[0076] An alternative as shown in FIGS. 12 and 13 is for the microcontroller μ to send the power requirement data directly to the PSU 66 via a separate bus. The SPI (Serial Peripheral Interface) buses 150, 151 couple the microcontroller 132 in modules 52, 54, and the PSU 66 and facilitate the transfer of data. Note that this is the bus mentioned towards the end of the description of FIG. 12 above.

[0077] The power data may be encrypted during transfer and provides another check that the module is "valid" in that its structure is known to be compatible with the system, in addition to the signed certificate.

[0078] Before the end of the information exchange shown in FIG. 14, the power supply has all the information necessary to supply power to each module 52, 54 at the correct level. Referring briefly back to FIG. 12, it is confirmed that the microcontroller 132 in the PSU 66 selects the appropriate tap 122 via the multiplexer and drives the regulator R128 to obtain the correct reference voltage V from the DAC 130. ref To set, power requirement data is used. Appropriate power is output from the regulator to module 52 via line 126 (also shown in FIG. 14), thereby powering the analog elements of the module.

[0079] FIG. 15 shows the controllable element CE90 in more detail. The controllable elements are designed to be adjustable so that their functions match the needs of the various individual modules 52. The controllable element 90 includes a microcontroller 160 with a unique identifier, e.g., an address, which enables it to be identified by the system control CPU 58. The microcontroller 160 is coupled to the CPU via the (SPI) bus 60 and controls the elements in CE90 via the internal buses 162, 164, 166, 168.

[0080] To enable control by the CPU 58, the bus 60 can be coupled to the elements in CE90, but the use of one or more internal buses within CE90 enables the CE to be self - contained. In particular, this makes it easier for individual module companies to specify their own CEs for use in the system. As a matter of design choice, the internal buses of the CE are shown in FIG. 15 as these individual connections 162, 164, 166, 168 between the microcontroller 160 and the various elements of the CE controlled by the microcontroller.

[0081] Signals from the module (e.g., connection lines L in FIG. 7) out and L in) is input to the controlled element at the junction 170 and applied to the input of the fixed-gain amplifier 172. The amplifier 172 buffers the signal and adjusts it to a form suitable for CE. This is necessary, for example, when the signal level from a module varies from one module to another. The adjusted signal is passed to a switched passive attenuator (SwA) 174, which provides signal attenuation from 0 to high before the signal is passed to the programmable gain amplifier PGA176.

[0082] A switched passive attenuator typically comprises an array of resistive attenuators (also known as pads) that can be selected individually or in combination to provide the required attenuation of the signal. The switched passive attenuator 174 is controlled by the microcontroller 160 via the bus 162. If the selection is limited to "on / off" or "high / low", a GPIO pin on the microcontroller is suitable for this purpose. If a range is available, a data bus such as an I2C bus (Inter-Integrated Circuit) may be more suitable. The programmable gain amplifier PGA176 is controlled by the microcontroller via the bus 164, which conveniently is an I2C bus capable of transferring data representing different ranges of amplification values. This data is used to select the pads and thus control the operation of the switched passive attenuator SwA174.

[0083] The programmable gain amplifier PGA176 provides variable gain control over a range, and its use in combination with the switched attenuator SwA174 enables a wider range of variable gain than would be possible with the PGA alone. When the microcontroller 160 receives operating data for the SwA174 and PGA176 from the CPU 58 via the bus 60, the microcontroller 160 simply passes it on to the SwA and PGA that operate accordingly. Of course, there are a number of different ways in which the PGA can be constructed. No programmable gain amplifier is more preferable than another. The selection is simply a matter of meeting the design criteria according to the details of the system.

[0084] The audio signal from the PGA176 is applied to the filter 178 and is controlled by a digital potentiometer 179 (also known as a "digital pot"). Typically, a digital pot consists of a series string of resistors with digitally addressable electronic switches that act as a wiper. The digital pot is controlled by the microcontroller 160 via the bus 166, which is a single bus shown as two separate parts simply to avoid cluttering the figure. The bus 166 for the digital pot 179 is conveniently an I2C bus, like the bus 164 for the PGA, which enables data representing a range of resistance values to be sent to the digital potentiometer 179. Again, the microcontroller 160 simply passes the data obtained from the CPU to the digital pot 179, and the digital pot 179 is set accordingly.

[0085] The filter 178 comprises a plurality of filters, typically two that separate high and low frequencies, and corresponding digital pots control the relative amplitude of each filter and thus the frequency response characteristics of the filter 178. The filter 178 provides tone control. As with the PGA, of course, there are a number of different ways in which the filter can be constructed. No filter is more preferable than another. The selection is simply a matter of meeting the design criteria according to the details of the system.

[0086] Cost can be a factor, but there is no technical reason why there cannot be more filters and associated digital pots that provide frequency control of the signal over several frequency bins (ranges or bands of frequencies). Alternative forms such as those described above with respect to FIG. 10 would have the module designer place the CE inside the module to meet the specific needs of that module.

[0087] The filtered signal is applied to output op-amp 180, which functions to buffer the output before the signal is returned to the module via coupling 182. The bypass switch 184 associated with filter 178 is coupled to microcontroller 160 via bus 168, which is conveniently a GPIO pin on microcontroller 160. When switch 184 is closed, it shorts filter 178 and bypasses tone control. This is useful when the module design does not require or requires only minimal changes in the frequency response. Thereby, the audio quality can also be improved, for example, by removing unwanted artifacts from digital pot 179.

[0088] The above description is of one example of the controlled element 90. It should be understood that other circuit configurations are possible depending on the characteristics of modules 52, 54 that will be coupled to CE90 and may actually be desirable. The CE shown in FIG. 15 is a voltage control and voltage sourcing device. Nevertheless, the CE and the module can be modified to accommodate a current control / sourcing module.

[0089] In a current-based circuit, placing a termination resistor at the output of the module provides a path for the output current, and the voltage drop across the resistor serves as the signal input to CE90. This termination resistor (not shown), along with the high dynamic range and low noise of the output buffer amplifier 180, maintains sufficient audio quality for the signal passing through CE. Moreover, the output buffer amplifier 180 has a known impedance, which, together with the input impedance of the current control module, enables the correct output level to be calculated and set accordingly. Also, under the condition that the source has sufficient driving ability and the impedance is known, the input can be modeled as a voltage input in many current control audio systems.

[0090] Other variations may also be desirable. Modules that do not require signal processing but simply require a path to connect the module connection lines L out and L in (see FIG. 7) can be used, and an additional bypass switch (not shown) can be provided. This enables the selective use of the module and can be useful, for example, when all that is required of CE is to maintain a balanced output.

[0091] FIG. 16 shows the switching matrix MX96 in more detail. Matrix 96 is conceptually shown as comprising an array of horizontal and vertical lines, which is a general representation of a switching matrix. These lines are connected via switches 162, as shown in the enlarged cross-section FIG. 160. Closing the switch creates a connection between the horizontal line 164 and the vertical line 166. The operation of the switch 162 is controlled by the CPU. As described above, matrix 96 need not be this complex. A simpler switching array may be more design-effective or cost-effective. Nevertheless, the switching matrix as shown will be continued to be described below.

[0092] Switching matrix 96 connects two modules 52, 54 and their input parts M in (equivalent to connector 11' in FIGS. 7 and 8) and output part M out (equivalent to 19'). The input signal S in is applied to line 170 connected to connection part 172 in matrix 96. To form path 174 to connection part 176, the switch is closed or opened under the command from CPU 58 via bus 60.

[0093] Input part M to the module in is connected to connection part 176 by line 11'. Similarly, the output part M of module 52 out is connected to connector 177 via line 19', and this connection passes through the matrix along path 178 and connects to the input part M of module 54 in . Also, the output part M of module 54 out passes through to the output part S from the system out via path 179.

[0094] In other words, the input signal S in is applied to the input part M of module 52 in . The output part of module 52 is connected to the input part M of module 54 in . Also, the output part M from module 54 out is connected to the system output part S out . This simple example of module connection shows how matrix 96 is used in the system to connect modules to each other without the involvement of CE.

[0095] FIG. 17 shows switching matrix 96 used to connect controllable element CE and module M to each other. The input signal S in is again applied to line 170 connected to connection part 172. To the other lines between modules 52, 54 shown in the figure are internal connection lines L out 80 and internal connection line L in82 is included. Some controllable elements CE181 - 184 are shown connected to the matrix 96. However, the internal paths in the matrix are not shown, because doing so would increase clutter. As already explained with respect to FIG. 16, the CPU 58 activates the switches 162 within the matrix to make the desired connections.

[0096] The controllable elements 181 - 184 are identified by their location - where they are on the bus - and this information is available to the CPU 58. When modules 52, 54 are connected to the platform 56, the data sent to the CPU 58 is used by the CPU to configure the CE181 - 184 and to couple them to their associated connectors (see 11', 21', 19', 11'', 12'', 29'', 80, 82, FIGS. 7 - 9) in order to form the complete circuitry for the modules.

[0097] One way in which modules 52, 54 and the controllable elements 181 - 184 can be coupled via the matrix 96 is shown in FIG. 18. The controllable element CE181 is coupled between the L out connection part of the first module 52 and the L in connection part. Typically, this kind of connection comes to be made in order to replace the internal function fx in module 52 with a controllable element CE in the platform.

[0098] The output part M out from the first module 52 passes through the controllable element 182 and goes to the input part M in of the second module 54. This can be done, in particular, to match the characteristics, such as impedance, of the output part M out and the input part M in of modules 52, 54. The controllable element 183 is similarly connected to CE181 and again typically comes to replace the internal function in the second module 54. Also, CE184, like CE182, is S outBefore being output from the system, signal conditioning - such as amplification, adjustment of the dynamic range or VU level - is carried out.

[0099] The module connections in FIG. 16, as well as the controllable element CE element connections in FIGS. 16 and 17, are shown and described separately in order to avoid overly complex diagrams and to facilitate understanding. Of course, these two types of connections can be made together. Additionally, feedforward paths - such as those shown in FIG. 3 - which may include controllable elements, are also readily achievable.

[0100] Referring to FIG. 19, the information transferred via bus 60 during the above-described handshake (HS) is represented by arrow 190 between the HS on the module side and the HS on the UI side for completeness. As already described above in this specification, the electrical data in the XML file is used by CPU 58 to generate the operating data for the power supply (FIGS. 11 - 13) and the controlled elements 90 (FIG. 15). When there is module connection - where two or more modules 52, 54 are coupled to each other as in the case of FIG. 16 - data from both or all of the modules is used by CPU 58 to control the switching array 96 to establish the desired connection. Similarly, the manner in which modules 52, 54 and controllable elements CE 90, 91, 92 are coupled is included within the XML file and is used by the CPU to establish the required connection by matrix 96.

[0101] In FIG. 19, user control is provided via a user interface UI62 (see FIG. 5). The data from module 52 also comprises an XML file 192 that contains UI information defining the graphics for the display 194 by the UI. This includes the characteristics of the graphical user interface for the modules for the display. The graphics information from modules 52, 54 may provide the full resolution of the graphical image of the modules, but usually it is more efficient to store the graphics for each module 52 in a library in the CPU 58. In fact, the library is stored in an online server (in the cloud) and can be accessed by the CPU 58 via an online connection (not shown) based on the data from each module.

[0102] The CPU 58 operates as a user interface service module UI Srvc that includes a web client Clnt198 and a web-like server SRV196 arranged to generate graphics for a web browser, for example. The web client 198 sends a web request to the web server 196 included in the UI Srvc. The web-like server 196 responds with a web page that the web client 198 receives and uses to display a user interface on the display 194. The web page shows information about the installed modules 52, 54, such as their names, their physical locations, the graphics corresponding to their branding, and their available controls. Using the graphics for the modules displayed on the display 194, the user can change the operation of the system by manipulating the images.

[0103] From the above description of the CPU 58 and the UI 62, it follows that the functions of the CPU or the UI, or both, can be provided by a personal computer (not shown) coupled to the bus 60. Thus, the CPU 58 and the UI 62 shown in the drawings can be implemented via an external computer of the system 50 that is consistent with what is described and illustrated in FIG. 5.

[0104] In FIG. 20, the UI 62 is shown as including a user input I / P 202. When the display 194 has a touch input function, dragging and tapping on the display serves as the user input 202. In a PC-based configuration, the user input I / P 202 can be provided by a mouse (not shown), which drives a cursor on the display, and the movement of the cursor as well as tapping and clicking serve as the user input. In both examples, the user operation of the image is interpreted by the user interface UI 62 as a command to change the operation of the system.

[0105] The command is converted by the UI client Clnt204 into a command web request, and the command web request is sent to the web server 196. The UI Srvc in the CPU 58 converts the command into operation data, and the operation data is sent to the driver DVR206 for each module 52 to change its operation. The driver 206 is provided by the data element 70 of the module. Referring again to FIG. 15, the operation data is used by the microcontroller 160 of the module to generate new data for the switch attenuator 174, the programmable gain amplifier 176, etc., thereby changing the operation of the module.

[0106] In FIG. 21, the user interface 62 is provided by a digital audio workstation DAW running on a personal computer. Since the workstation is digital, the audio data can be in digital format. The digital audio data can be transferred digitally between the system and the DAW via the analog-to-digital converter ADC108 shown in FIG. 11.

[0107] The UI 62 is provided as a plugin within the digital audio workstation DAW. This plugin is client software, and there will be a corresponding DAW plugin server running within the UI service. The DAW plugin includes a graphical user interface P / GUI 210 and a client P / Clnt 212 equivalent to I / P 202 and Clnt 204 in FIG. 20. The DAW plugin P / Clnt 212 is coupled to the UI Srvc in the CPU 58 via a bus 214 that can be provided as an Ethernet connection. The flow of commands between the DAW plugin P / Clnt 212 and the UI Srvc in the CPU 58 is similar to what was previously described with reference to FIGS. 19 and 20.

[0108] Briefly, the audio signal processing apparatus includes at least one controllable element 90, 91, 92 for performing an analog audio processing function. The controllable element is operable with a digital controller 58 that controls the analog audio processing function performed by the controllable elements 90, 91, 92. At least one audio processing module 52, 54 includes a partial audio processing circuit for audio processing operations. Modules 52, 54 are operable with controllable elements 90, 91, 92 to complete the audio processing circuit and thus enable audio processing operations. In this way, the audio processing operation is controllable by the digital controller. The switching array 96 selectively couples the audio processing modules 52, 54 and the controllable elements 90, 91, 92. The power supply 66 is operable to selectively supply power for the audio processing circuit of that or each module 52, 54.

[0109] The present invention has been described with reference to an audio signal processing apparatus, an audio processing module, an audio signal processing system, and a method of processing an analog audio signal, but the same has been described only by way of example, and modifications and variations such as those that would occur to a person having appropriate knowledge and skills can be made without departing from the spirit and scope of the present invention as set forth in the appended claims and their equivalents.

Explanation of Signs

[0110] 10 Analog audio processing module, module, processing module 11 Input connection part 11' Input connector, terminal, connector, wire 12 Input stage or buffer, input stage, input buffer 12' Input stage 14 Processing stage, fx stage, processing stage fx 14' Processing stage fx 15 Control switch, dial, or knob, knob, control knob and switch, dial and knob 15' Selector dial, visual input element, control knob 17 Output stage or buffer 17' Output stage 19 Socket 19' Output connector or socket, terminal, wire 20, 42 - 45 Processing module, module 21 Plug, input part 21', 21'' Input part 22, 28 Insulation transformer 23 Preamplifier 24 Filter 25 Control knob, dial and knob 25' Indicator, visual input element 26 Tap or connection part, tap, socket 27 Output stage, variable preamplifier, preamplifier 27'' Output preamplifier 29 Socket, output part 29', 29'' Output part 32 - 34, 52', 53', 54', 55 Module 35 Feedback path 36 Feedforward path 37 Input connection part, input part 38 Output connection part, output part 40 Rack 50 Audio processing system, system 52 Analog audio processing module, audio processing module, module, first module 53 Analog audio processing module, audio processing module, module 54 Analog audio processing module, audio processing module, module, second module 56 Platform (PFM), platform, platform PFM, PFM 58 Central Processing Unit (CPU), CPU, Processor (CPU), Processor CPU, System Control CPU, Control Processor CPU, Digital Controller 60 Digital Bus, Bus, Data Bus, USB Bus, (SPI) Bus 62 User Interface (UI), UI, User Interface, User Interface UI 64 Suitable Data Connection 66 Power Supply (PS), Power Supply PS, Power Supply, Power Supply Unit PS, PSU, Power Supply PSU 68 Power Line 70 Information Store or Data Element, Data Element, Small Microprocessor or Microcontroller (μ), Information Store, Microcontroller μ, μ, Microcontroller, Microprocessor (μ) 72 System Analog Input and Output Lines, Analog Lines 74 Module Analog Lines, Analog Lines 77 Digital Audio Port, Path 80 Terminals, Internal Connection Terminal L out , Connection Part, Connector, Internal Connection Line L out 82 Terminals, Internal Connection Terminal L in , Connection Part, Connector, Internal Connection Line L in 90 Controllable Element CE, CE, Controllable Element, Controlled Element CE, Controlled Element 90' Controllable Element 91 Controllable Element CE, Controlled Element CE, CE, Controllable Element 92 Controllable Element CE, Second Controllable Element CE, Controllable Element, Controlled Element CE, CE 94 Lines, Connection Parts, Connectors, Controllable Element CE, CE 95 Path 96 Switching Array, Switching Matrix, Switching Matrix MX, Matrix 100, 102, 104, 105, 148, 149 Lines 108 Analog-to-digital and digital-to-analog converters ADC / DAC, ADC / DAC, analog-to-digital converter ADC 109 Analog line 120 Multi-tap transformer, transformer 121, 121' Power conversion path, power regulation path, power path, path 122, 122' Tap 124, 124' Multiplexer 126, 126' Split-rail DC power supply, DC power supply 127, 127', 137 Bridge rectifier 128, 128' Regulator R 130, 130' Digital-to-analog converter DAC, DAC 132 Controller, controller μ, microcontroller μ, microcontroller 135 Further power conversion path, power conversion path 138 Regulator 140 Initial data, signature data 142 Handshake 144, 190 Arrow 147 Power requirement data 150 Second bus, bus, SPI (Serial Peripheral Interface) bus 151 SPI (Serial Peripheral Interface) bus 160 Microcontroller, enlarged cross-sectional view 162 Internal bus, connection, bus, switch 164 Internal bus, connection, bus, horizontal line 166 Internal bus, connection, bus, vertical line 168 Internal bus, connection, bus 170 Connection, line 172 Fixed-gain amplifier, amplifier, connection part 174 Switch passive attenuator (SwA), switch passive attenuator, switch passive attenuator SwA, switch attenuator SwA, SwA, path, switch attenuator 176 Programmable gain amplifier PGA, PGA, connection part, programmable gain amplifier 177 Connector 178 Filter, path 179 Digital potentiometer, digital pot, path 180 Output operational amplifier, output buffer amplifier 181, 183 Controllable element CE, controllable element, CE 182 Coupling, controllable element CE, controllable element, CE 184 Bypass switch, switch, controllable element CE, controllable element, CE 192 XML file 194 Display 196 Web-like server SRV, web server, web-like server 198 Web client Clnt, web client 202 User input I / P, user input, I / P 204 UI client Clnt, Clnt 206 Driver DVR, driver 210 Graphical user interface P / GUI 212 Client P / Clnt, DAW plugin P / Clnt 214 Bus

Claims

1. An audio signal processing apparatus, comprising: a digital controller; at least one controllable element for performing an analog audio processing function, the controllable element being operable, together with the digital controller, for controlling the analog audio processing function thereby, and being operable, together with an audio processing module including a partial audio processing circuit for an audio processing operation, to complete the audio processing circuit and thereby enable the audio processing operation; and at least one controllable element An audio signal processing apparatus comprising the above.

2. The audio signal processing apparatus according to claim 1, wherein the controllable element includes a variable gain amplifier operable to change its gain under digital control, the amplifier being coupled to the digital controller and responsive to a command from the digital controller to change the gain.

3. The audio signal processing apparatus according to claim 2, wherein the controllable element includes an array of attenuators selectable individually or in combination for attenuating a signal, the array being coupled to the variable gain amplifier for passing an audio signal thereto and being coupled to the digital controller, and responsive to a command from the digital controller to change the attenuation.

4. The audio signal processing apparatus according to any one of claims 1 to 3, wherein the controllable element includes a variable filter for filtering a signal in a frequency range, the variable filter being operable to change the filtering thereby.

5. The audio signal processing apparatus according to claim 4, wherein the controllable element includes one or more variable resistors coupled to the variable filter and operable to change its resistance under digital control, the variable resistor being coupled to the digital controller and responsive to a command from the digital controller to change the resistance and thereby the filtering by the variable filter.

6. The audio signal processing apparatus according to claim 4 or 5, wherein the filter has an input and an output, the controllable element includes a switch coupled between the input and the output, the switch is coupled to the digital controller, and in response to a command from the digital controller, bypasses the filter.

7. The audio signal processing apparatus according to any one of claims 1 to 6, further comprising a power supply for selectively supplying power for the or each module.

8. For the power supply for the or each module, a digital-to-analog converter that outputs a reference voltage in response to a command from the digital controller; a regulator for changing a supplied DC voltage to output a DC voltage for the module The audio signal processing apparatus according to claim 7, comprising.

9. The audio signal processing apparatus according to claim 8, wherein the power supply includes a selector that responds to a command from the digital controller for selecting a voltage tap and for outputting a voltage for the regulator.

10. The audio signal processing apparatus according to any one of claims 7 to 9, wherein the power supply includes a microcontroller coupled to the digital controller for receiving commands therefrom and operable to distribute the commands for the operation of the power supply.

11. The audio signal processing apparatus according to any one of claims 1 to 10, further comprising a switching array responsive to the digital controller for selectively coupling the or each audio processing module and the or each controllable element.

12. The audio signal processing apparatus according to any one of claims 1 to 11, wherein when the digital controller is coupled to an audio processing module, in response to operation data from the audio processing module, provides control data for the at least one controllable element.

13. The audio signal processing apparatus according to any one of claims 1 to 12, as long as it depends on claim 7, wherein when the digital controller is coupled to an audio processing module, in response to operation data from the audio processing module, provides control data for the power supply.

14. The audio signal processing apparatus according to any one of claims 1 to 13, insofar as it depends on claim 11, wherein when the digital controller is coupled to the audio processing module, it provides control data for the switching array in response to operation data from the audio processing module.

15. The audio signal processing apparatus according to any one of claims 1 to 14, further comprising a user interface coupled to the digital controller, wherein the user interface provides a command for changing the operation of the controllable element or, insofar as it depends on claim 11, the switching array to the digital controller in response to a user operation.

16. An audio processing module for use with the apparatus according to any one of claims 1 to 15, the module comprising a partial audio processing circuit for audio processing operations, and the module being couplable to at least one controllable element to complete the audio processing circuit and enable the audio processing operations.

17. The audio processing module according to claim 16, wherein the or each audio processing module comprises a signal input for receiving an audio signal to be processed and a signal output for outputting the processed signal, the signal input being couplable to a signal source and the signal output being couplable to a signal destination.

18. The audio processing module according to claim 16 or 17, wherein the or each audio processing module comprises a data element for providing operation data for the module to the digital controller.

19. The audio processing module according to claim 18, wherein the operation data from the data element comprises control data for one or more of the controllable elements, the power supply, and the switching array in the audio signal processing apparatus.

20. The audio processing module according to claim 18 or 19, wherein the data element comprises a microcontroller having at least one input / output pin coupled to the controllable element for providing some of the control data to the controllable element.

21. An audio signal processing apparatus according to any one of claims 1 to 15, and at least one audio processing module according to any one of claims 16 to 20 An audio signal processing system comprising.

22. A method for processing an analog audio signal, comprising: providing at least one controllable element for performing an analog audio processing function; providing at least one analog audio processing module comprising a partial audio processing circuit for an audio processing operation; using the at least one controllable element together with the at least one analog audio processing module to complete the audio processing circuit; controlling the analog audio processing function of the controllable element to enable the audio processing operation of the at least one analog audio processing module A method including.

23. The method according to claim 22, comprising providing a variable gain amplifier in the at least one controllable element and changing its gain to change the analog function of the controllable element.

24. providing an array of attenuators in the at least one controllable element coupled to the variable gain amplifier; selecting the attenuators in the array individually or in combination to change the analog function of the controllable element The method according to claim 23, comprising.

25. providing a variable filter for filtering a signal from the variable gain amplifier in a frequency range; changing the operation of the variable filter to change the analog function of the controllable element The method according to claim 23 or 24, comprising.

26. The method according to claim 25, wherein the filter has an input and an output, and the method comprises coupling a switch coupled between the input and the output and operating the switch to change the analog function of the controllable element.

27. providing a power supply for supplying power to the or each module; selectively supplying power to the or each module individually The method according to any one of claims 22 to 26, further comprising.

28. providing a reference voltage; providing a regulator for varying a supplied DC voltage while referring to the reference voltage; outputting a DC voltage for the or each module; The method according to claim 27, further comprising: **Claim 29** providing a plurality of voltage taps; selecting a voltage tap; generating the supplied DC voltage using the selected voltage tap; The method according to claim 27 or 28, further comprising: **Claim 30** providing a switching array; selectively operating the switching array to couple the or each audio processing module and the or each controllable element; The method according to any one of claims 22 to 29, further comprising:

Images