Audio signal amplifier gain control

Abstract

A system for controlling the gain of an input signal in an audio signal amplifier, the system including a user-operable gain control and analog and digital circuitry that are both configured to modify the gain of the input signal in response to the user-operable gain control.

Description

Technical Field

[0001] The present disclosure relates to controlling gain in an audio signal.

Background Art

[0002] An audio amplifier designed to be used by both consumers and professionals can have an input channel that needs to handle a very wide range of input levels. The input level range can exceed the input range of an analog-to-digital converter (ADC) preceding a digital signal processor (DSP) within the product. This input level mismatch is often addressed by including a separate gain control section or Mic / Line level switch prior to the level or volume control of the channel. These allow the user to control the electronic gain and divide the input level range of the ADC into smaller segments. Then, a normal level or volume control controls the digital gain in the DSP. However, this approach requires the user to recognize that the input level range may be too high and then operate additional controls. These operations can be confusing and unintuitive. Also, if the controls are used inappropriately, the resulting signal quality can degrade. Another approach to this problem is to provide a single analog control that operates multiple analog gain stages together. However, this type of control is not configured to be remotely driven by a mobile application and thus its usefulness is limited.

Summary of the Invention

Means for Solving the Problems

[0003] All examples and features mentioned below can be combined in any technically possible way.

[0004] In one aspect, a system for controlling the gain of an input signal in an audio signal amplifier includes a user-operable gain control, at least one analog circuit element, and at least one digital circuit element. The analog circuit element and the digital circuit element are both configured to modify the gain of the input signal in response to the user-operable gain control.

[0005] Some embodiments include one or more of the above and / or below features, or any combination thereof. In some examples, at least one analog circuit element comprises an analog preamplifier that defines a plurality of first gain steps, each achieving a different gain for the audio signal. In some examples, at least one digital circuit element comprises a digital signal processor (DSP) downstream of the preamplifier configured to define a plurality of second compensation gain steps, each achieving a different gain for the audio signal, to compensate for the gain of the preamplifier. In an example of the DSP, it is further configured to apply a system gain in addition to the compensation gain. In one example, the first gain step and the second compensation gain step are each an individual change in gain. In one example, the second compensation gain step is opposite to the first gain step. In one example, the overall gain achieved by combining the first gain step and the second compensation gain step is constant.

[0006] Some embodiments include one or more of the above and / or below features, or any combination thereof. In one example, the user-operable gain control is a continuous control. In some examples, the user-operable gain control includes a physical control member and a virtual control member, and the physical control member and the virtual control member have a matching appearance. In one example, the physical control member includes a control knob and the virtual control member includes a knob icon. In one example, at least one analog circuit element is configured to reduce the gain of the input signal upon detection of a high input signal level. In one example, at least one digital circuit element is configured to detect a high input signal level and select a gain reduction achieved by at least one analog circuit element.

[0007] Some embodiments include one or more of the above and / or the following features, or any combination thereof. In one example, at least one digital circuit element is further configured to compensate for a time delay between a gain change request and an actual change in the amplitude of the audio data. In some examples, at least one digital circuit element is further configured to remove and replace signal discontinuities in the output signal. In one example, at least one digital circuit element is configured to remove and replace signal discontinuities by zeroing digital data that includes discontinuities. In one example, at least one digital circuit element is further configured to remove and replace signal discontinuities by reconstructing the zeroed digital data from surrounding data. In one example, at least one digital circuit element is configured to remove and replace signal discontinuities by reconstructing the digital data at the signal discontinuity from surrounding data. In one example, the modification of the gain of the input signal is under the control of at least one digital circuit element. In one example, the overall gain applied together by both at least one analog circuit element and at least one digital circuit element matches the target gain from the user-operable gain control.

[0008] In another aspect, a system for controlling the gain of an input signal in an audio signal amplifier, comprising a user-operable gain control, an analog preamplifier that defines a plurality of first individual gain steps, each achieving a different gain for the audio signal, and a digital signal processor (DSP) downstream of the preamplifier configured to define a plurality of second individual compensation gain steps that are opposite to the first gain steps to compensate for the gain of the preamplifier. The DSP is further configured to apply a system gain in addition to the compensation gain. The analog circuit element and the digital circuit element are both configured to modify the gain of the input signal in response to the user-operable gain control. The overall gain achieved by combining the first gain steps and the second compensation gain steps is constant.

[0009] Some embodiments include one of the above and / or below features, or any combination thereof. In one example, at least one analog preamplifier is further configured to reduce the gain of the input signal upon detection of a high input signal level, the DSP is further configured to detect the high input signal level and select the gain reduction achieved by the preamplifier, and the DSP is further configured to remove and replace signal discontinuities in the output signal by reconstructing the digital data at signal discontinuities from the surrounding data.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 5C

Mode for Carrying Out the Invention

[0011] The audio signal amplifier gain control unit is configured to control the signal level with a good signal-to-noise ratio (SNR) over a wide range of input levels using only a single physical or virtual user operation control unit per channel.

[0012] FIG. 1 shows an audio signal amplifier 10 configured to achieve the gain control section of the subject matter. An exemplary input 14 is coupled to the mic / line input connector 12. The amplified signal is output to a speaker. In some examples, the input 14 comes from an instrument being played (e.g., an electric guitar), and the amplifier 10 is configured to amplify the input and provide it to a speaker used to broadcast music in a venue such as a concert hall.

[0013] Exemplary control interfaces for the amplifier are shown in FIGS. 2A and 2B. In some examples, the user-operable control interface of the amplifier includes one or more physical knobs, typically one physical knob per input channel. In some examples, the level control section is additionally or alternatively achieved using one or more virtual knobs, typically one virtual knob per input channel, where the virtual knob can be part of the UI of a mobile application that interfaces with and controls the amplifier. In each case, the knob is preferably arranged along the perimeter of the physical or virtual knob and includes an indication of the selected level using an indicator light (e.g., an LED) that selectively lights up as an indication of the knob position between 0 and 100. For example, when the knob is set to 40%, the first 40% of the light moving from 0 to 100 is lit. In some examples, control types other than knobs, such as sliders, are used.

[0014] In one example, the physical and virtual controls are similar in appearance and operate similarly. In some embodiments, when the physical knob is moved (e.g., rotated or pushed), the control system operates / moves the appropriate functions, on / off, and level indicators of the virtual knob in the same manner so that the physical and virtual controls operate and indicate in unison. For example, in some embodiments, when the virtual knob is rotated up or down, the level indicator associated with the physical knob is similarly changed.

[0015] Figure 2A shows an exemplary physical control panel 20 having knobs used to select and control three input channels. In some examples, two of the three input channels handle a very wide range of input levels, a range that exceeds the input range of the analog-to-digital converter that precedes the amplifier's digital signal processor. One, two, or all three of the knobs 21, 22, and 23 can be used to select from two or more functions such as volume, treble, bass, and reverb functions. In the non-limiting illustrated example, knobs 21 and 22 can each be used to select one of the volume, treble, bass, and reverb functions (via function sets 24 and 25 associated with each knob respectively), and knob 23 can be used to select one of the volume, treble, and bass functions (via function set 26 associated with the knob). In one example, the selection is made by rotating the knob until the selected function lights up and then pressing the knob to enable (turn on) the function. Next, the level is selected by turning the knob, and a series of radial LEDs (such as set 28 of knob 21) are used to indicate the selected level. As shown by knobs 21 and 23, a separate light 27 may be used to indicate whether the knob is currently in use (i.e., has been pressed to turn on).

[0016] Figure 2B shows the same control set 30 as in Figure 2A, but within a digital display (such as a smartphone display). The virtual knobs 31 - 33 can be operated in the same way as the physical knobs 21 - 23, but using the functionality of a touch-sensitive display or otherwise (e.g., using a touch instead of a knob push or knob rotation).

[0017] Functional aspects of amplifier 40 useful for understanding the present disclosure are shown in FIG. 3. Audio input 50 is via any standard connector. In situations where the amplifier is used for a musical performance, the amplifier generally includes one or more input jacks. In some examples, input 50 is an XLR / TRS input jack. In some examples, the input signal is an analog audio signal provided to preamplifier 52. The function of preamplifier 52 is to achieve a first gain stage configured to adjust the gain of the signal in response to the volume selected by the user via physical control knob 42 or virtual control section 43 which is part of a mobile control app. In one example, the gain adjustment is achieved in several individual gain steps. The resulting change in gain is cumulative. In the non-limiting example shown, preamplifier 52 includes four CMOS gain switches, each of which is configured to increase the gain by approximately 10 dB as shown by curve 72 in FIG. 4. In the example shown, there are five overall gain states from 0 to 40 dB. The gain enabled by preamplifier 52 is selected based on the position of the user control. In one example, a physical or virtual control knob (such as those shown in FIGS. 2A and 2B) can be rotated from 0 to 100, and each 20% increment of the knob results in a different gain state as shown by curve 72. The buffered analog signal is then provided to analog-to-digital converter (ADC) 54, which converts the signal into the digital domain and provides it to digital signal processor (DSP) 56.

[0018] The DSP56 receives information regarding the intended channel volume from the system's microcontroller 44 by one of two methods. When the user turns the volume knob of the product, the attached rotary encoder increases or decreases the volume setting stored in the microcontroller. When the user adjusts the volume control in the mobile application, a command is sent to the microcontroller via Bluetooth (through the Bluetooth interface) to increase or decrease the volume setting. In either method, the current volume level is indicated to the user by a circular ring of LEDs around the knob on the product, as shown in Figure 2A, and by a similar indication within the mobile application UI, as shown in Figure 2B.

[0019] The volume control setting is performed in hardware (within the analog front-end preamplifier 52 before the ADC54) and software (within the DSP56). In some examples, the hardware gain control section uses digital control analog (CMOS) switches to select the feedback resistors in the op-amp gain circuit for coarse adjustment (e.g., in 4 steps). In each of these coarse steps, finer adjustment is performed in the DSP to select the appropriate overall gain. By applying only a portion of the gain in the DSP, low-level signals can be amplified in the analog domain without amplifying the noise floor of the ADC, thus maintaining the desired signal-to-noise ratio.

[0020] In some examples, the DSP56 includes a non-transitory computer-readable medium encoded with computer program logic configured to achieve the DSP functions described herein. Within the DSP, in some examples, the overall volume control (i.e., system gain) is represented as a continuous curve mapped to the volume requested by the user. Prior to the application of that curve, a compensation gain, which is the inverse of the analog gain, is inserted. In the example of the four-step analog gain shown by curve 72 in FIG. 4, the opposing compensation gain applied to the second amplifier stage achieved by the DSP56 is shown by curve 74, which also has five overall gain states from 40 to 0 dB achieved over four individual gain steps. In some examples, the analog gain + compensation gain equals a constant non-zero value. By applying the opposing gain in the DSP, the total gain (in the combined analog and digital domains, including the system gain) matches what is requested by the user. The digital output signal is converted to analog by the D / A converter 58. The signal is then amplified by the analog power amplifier 60 and supplied to the speaker.

[0021] The DSP controls the hardware (CMOS) gain applied by the preamplifier 52 via a general-purpose digital output that operates the analog switch. Thus, the overall gain is under the control of the DSP. The overall gain depends on the position of the volume rotary encoder. However, this gain schedule can be automatically adjusted when a larger signal is present at the analog input. This can prevent the ADC from saturating. The DSP has knowledge of the loudness of the input signal via measurement of the signal level at the input to the DSP. If the input signal is too large and there is a possibility that the ADC will saturate, the non-zero hardware gain is stepped down (reduced) by one step at a time under the control of the preamplifier by the DSP, thus reducing the amplitude of the signal present at the input to the ADC. This approach enables the maximum sampling bit resolution and avoids clipping when the rotary encoder is set to a higher volume range. In addition, when the automatic down-step adjustment is active and the audio signal amplitude decreases, the hardware / DSP gain is scheduled to be returned to the schedule one step at a time with an interval via the DSP based on the user interface. In one example, the interval is 4 seconds. This is done to avoid sudden large amplitude changes.

[0022] In some examples, the transition between the hardware gain step and the subsequent DSP compensation gain is synchronized to reduce transient artifacts (i.e., timing inconsistencies in the gain adjustment) that can introduce noise. The time at which the simultaneous gain step and its compensation occur is called a "seam". There are multiple techniques that can be used alone or together to reduce the inconsistent artifacts.

[0023] Latency compensation is one such technique for reducing inconsistent artifacts. Latency compensation takes into account the fixed time delay that occurs (due to ADC latency) between the gain step change request and the actual change in the amplitude of the audio data passed to the DSP. When compensating for this delay, the temporal inconsistency at the seam can be reduced to one sample. In an example of latency compensation, when the DSP instructs the analog hardware to initiate a step change in gain, it takes some time for the new value to appear in the audio signal processed by the DSP. This is due to the buffering of data in the analog / digital conversion hardware. As a result, the portion of the audio signal that requires processing occurs a short time (e.g., about 0.5 ms) after the command start. This time can vary when other hardware is used. A simple delay block (e.g., about 0.5 ms) in the DSP compensation / repair logic ensures that any required signal processing is properly aligned with subsequent changes in the audio signal. In these examples, the delay block time in the compensation / repair logic is aligned with any latency introduced by the analog / digital conversion due to data buffering.

[0024] Even after the ADC latency is compensated, there are often small signal-dependent phase shifts due to the DSP hardware front end. These phase shifts can result in discontinuities that can be heard as noise. An exemplary discontinuity 84 is shown in the audio signal curve 82a of FIG. 5A. Due to the phase shift, it can be difficult to create an inaudible seam. Such inconsistent artifacts can be reduced using the following techniques. See FIGS. 5B - 5C.

[0025] In one example, some samples of data (e.g., about 0.25 ms) are silenced (zeroed) within the audio data centered around the seam (i.e., before and after the seam). The zeroed data is shown as gap 86 in curve 82b of FIG. 5B. The zeroed samples are reconstructed from the surrounding data to interpolate gap 86 and replace it with data 88 of curve 82c in FIG. 5C. In one example, this reconstruction is achieved using a network of sixth-order windowed-sync FIR filters. Since data from both before and after the seam is used, look-ahead is required. This adds a small amount of latency that is practically imperceptible for the overall process. In the illustrated example, the data used is represented by six dots on curve 82c, three before and three after the reconstructed data 88.

[0026] The elements of the drawings are illustrated and described as individual elements of a block diagram. These elements may be implemented as one or more of analog circuits or digital circuits. Alternatively, or additionally, these elements may be implemented such that one or more microprocessors execute software instructions. The software instructions can include digital signal processing instructions. Operations can be performed by analog circuits or by a microprocessor executing software that performs operations equivalent to analog operations. Signal lines may be implemented as individual analog signal lines or digital signal lines, as individual digital signal lines that perform appropriate signal processing to process separate signals, and / or as elements of a wireless communication system.

[0027] When a process is represented or suggested by a block diagram, steps can be performed by one element or multiple elements. These steps may be performed collectively or at different times. The elements performing the activities may be physically the same, close to each other, or physically separated. One element can perform more activities than one block. An audio signal can be encoded or may not be encoded and can be transmitted in either digital or analog format. Conventional audio signal processing devices and audio signal arithmetic processing may be omitted from the drawings.

[0028] Examples of the systems and methods described herein include computer components and computer-implemented steps that will be apparent to those skilled in the art. For example, it should be understood by those skilled in the art that computer-implemented steps can be stored as computer-executable instructions on computer-readable media such as floppy disks, hard disks, optical disks, flash ROMs, non-volatile ROMs, and RAMs. Further, it should be understood by those skilled in the art that computer-executable instructions can be executed on various processors such as microprocessors, digital signal processors, gate arrays, etc. For ease of explanation, not all steps or elements of the above systems and methods are described herein as part of a computer system, but those skilled in the art will recognize that each step or element can have corresponding computer system or software components. Thus, such computer systems and / or software components are enabled by describing their corresponding steps or elements (i.e., their functionality) and are within the scope of the present disclosure.

[0029] Multiple implementations have been described. Nevertheless, additional modifications can be made without departing from the scope of the concepts of the invention described herein, and thus other examples are understood to be within the scope of the following claims.

Description of the Reference Numerals

[0030] 10 Audio signal amplifier 12 mic / line input connector 14 Input 20 Physical control panel 21 Physical knob 22 Physical knob 23 Physical knob 24 Function set 25 Function set 26 Function set 27 Light 28 Set of knob 21 30 Control set 31 Virtual knob 32 Virtual knob 33 Virtual knob 40 Amplifier 42 Physical control knob 43 Virtual control unit 44 Microcontroller 50 Input 50 Audio input 52 Analog front-end preamplifier 54 Analog-to-digital converter (ADC) 56 Digital signal processor (DSP) 58 D / A converter 60 Analog power amplifier

Claims

1. A system for controlling the gain of an input signal in an audio signal amplifier, comprising: a user-operable gain control unit; at least one analog circuit element and at least one digital circuit element, wherein both the analog circuit element and the digital circuit element are configured to modify the gain of the input signal in response to the user-operable gain control unit; The at least one digital circuit element is configured to remove and replace signal discontinuities in an output signal in which a time delay between a gain change request for the at least one analog circuit element for modifying the gain and an actual change in the amplitude of audio data input to the at least one digital circuit element is compensated. The at least one digital circuit element zeros digital data including the signal discontinuity in the output signal and samples before and after the digital data, and uses data on the audio signal curve of the output signal consisting of the zeroed digital data and the zeroed samples. The system is further configured to remove and replace signal discontinuities in the output signal by reconstructing the gap using data on the audio signal curve before and after the gap.

2. The system according to claim 1, wherein the at least one analog circuit element comprises an analog preamplifier that defines a plurality of first gain steps that achieve different gains for an audio signal input as the input signal.

3. The system according to claim 2, wherein the at least one digital circuit element comprises a digital signal processor (DSP) downstream of the analog preamplifier, configured to define a plurality of second compensation gain steps that achieve different gains for the audio signal in order to compensate for the gain of the analog preamplifier.

4. The system according to claim 3, wherein the DSP is further configured to apply a system gain in addition to the compensation gain.

5. The system according to claim 3, wherein each of the first gain step and the second compensation gain step is an individual change in gain.

6. The change in gain in the second compensation gain step is opposite to the change in gain in the first gain step such that the overall gain achieved by combining the first gain step and the second compensation gain step is constant, the system according to claim 5.

7. The user operable gain control unit includes a physical control member and a virtual control member, and the physical control member and the virtual control member have a matching appearance, the system according to claim 1.

8. The physical control member includes a control knob, and the virtual control member includes a knob icon, the system according to claim 7.

9. The at least one analog circuit element is configured to reduce the gain of the input signal upon detection of a high input signal level, the system according to claim 1.

10. The at least one digital circuit element is configured to detect the high input signal level and select a gain reduction achieved by the at least one analog circuit element, the system according to claim 9.

11. The modification of the gain of the input signal is under the control of the at least one digital circuit element, the system according to claim 1.

12. The overall gain applied together by both the at least one analog circuit element and the at least one digital circuit element matches a target gain from the user operable gain control unit, the system according to claim 1.

13. A system for controlling the gain of an input signal in an audio signal amplifier, a user operable gain control unit, an analog preamplifier that defines a plurality of first individual gain steps each achieving a different gain for an audio signal input as the input signal, a digital signal processor (DSP) downstream of the analog preamplifier configured to define a plurality of second individual compensation gain steps that are a change in gain opposite to the change in gain in the first individual gain step such that the overall gain achieved by combining the first individual gain step and the second individual compensation gain step is constant, the DSP being further configured to apply a system gain in addition to the compensation gain, Both the analog preamplifier and the DSP are configured to modify the gain of the input signal in response to the user-operable gain control unit. The DSP is configured to remove and replace signal discontinuities in the output signal in which the time delay between the gain change request for the analog preamplifier to modify the gain and the actual change in the amplitude of the audio data input to the DSP is compensated. The DSP zeros the digital data including the signal discontinuities in the output signal and the samples before and after the digital data, and uses the data on the audio signal curve of the output signal consisting of the zeroed digital data and the zeroed samples to reconstruct the gap on the audio signal curve before and after the gap. By doing so, the DSP is configured to remove and replace signal discontinuities in the output signal. A system. **Claim 14** The analog preamplifier is further configured to reduce the gain of the input signal when a high input signal level is detected, and the DSP is further configured to detect the high input signal level and select the gain reduction achieved by the analog preamplifier. The system according to claim 13.

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