Adaptive amplifier voltage with reduced signal chain delay

Abstract

The invention relates to a method for regulating an adaptive supply voltage for one or more audio amplifiers, the method comprising: receiving a first audio signal (V1); processing the first audio signal (V1) thereby providing a processed audio signal (V2) having a first delay (1) relative to the first audio signal (V1); providing a sound preset signal (9) that controls the processing of the first audio signal (V1) such that the processed audio signal (V2) is provided; providing the processed audio signal (V2) to the one or more amplifiers (18); based on the first audio signal (V1) and sound preset signal (9) estimating a supply voltage control signal (13) indicating the lowest supply voltage (19) that is required by the one or more amplifiers (18) to avoid voltage clipping of an audio signal (14) received by the one or more amplifiers, where the supply voltage control signal (13) has a second delay (2) relative to the first audio signal (V1); using the supply voltage control signal (13) to control a supply voltage (19) for the one or more amplifiers; providing the supply voltage (19) to the one or more amplifiers; wherein the first delay (1) is greater than the second delay (2). The invention furthermore relates to devices and systems implementing the method.

Description

[0001] ADAPTIVE AMPLIFIER VOLTAGE WITH REDUCED SIGNAL CHAIN DELAY

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method, device and amplifier in which the supply voltage required by the amplifier is adapted to the input audio signal in order to improve battery play time, reduce power consumption and avoid voltage clipping in the amplifier. These objectives are according to the invention obtained with a minimum of delay in the signal chain of the audio signal.

[0004] BACKGROUND OF THE INVENTION

[0005] When increasing the output voltage of a DC / DC converter generating a supply voltage for an amplifier, capacitors must be charged before the target output voltage is reached. To allow for this process when adapting the supply voltage of an amplifier to the signal content it is amplifying, a delay is normally added to the audio signal chain. Delays in the audio signal chain are rarely desired due to lip-sync, latency and similar requirements, so delay reductions are encouraged.

[0006] OBJECTIVES OF THE INVENTION

[0007] On the above background it is an objective of the present invention to provide a method and corresponding device or system that provides reduced power consumption of amplifiers and increase battery play time on battery powered products without adding unnecessary delay to the audio signal chain.

[0008] DISCLOSURE OF THE INVENTION

[0009] The above objectives and further advantages are obtained by adjustment of the supply voltage used by the amplifier, by controlling a suitable voltage supply. A suitable voltage supply could for instance be a DC / DC converter or an AC / DC converter. The control signal is based on the signal content the amplifier will receive, but estimated using simple filters upstream of the time-consuming signal processing, thereby having enough time to increase the amplifier supply voltage and avoid clipping.

[0010] According to the invention, the signal extraction for calculating the supply voltage takes place before any constant delay contributions, but as late in the audio signal chain as possible, to have as many dynamic and changeable elements act upon the audio signal before calculating the supply voltage. This reduces the bank of filters to change between the supply voltage calculation. If for instance a changeable gain was placed in the speaker processing block (the signal processing located after the signal extraction for the supply voltage calculation), that gain would have to be taken into account when calculating the supply voltage. This problem is solved by the present invention.

[0011] Typically, although not exclusively, the dynamic components in the speaker processing block are only active at loud levels, where the supply voltage calculation is expected to already be in full saturation and therefore have little or no effect on the supply voltage calculation. The user-changeable filters do, however, need to be considered and thus the voltage estimation filters are updated whenever the user changeable filters in the speaker processing block are changed. Fortunately, the number of options for the user changeable filters is limited, and therefore the filters for voltage estimation can be pre-calculated and stored in a filter bank.

[0012] Voltage estimation

[0013] For each set of amplifier channels that share the same supply voltage, the filters estimating their voltage are a combination of each channels’ magnitude response and group delay, resulting in a common maximum voltage and average group delay.

[0014] The voltage estimation filters are calculated as a simplified version of the combined transfer function of the Speaker processing. In the estimation filters, both the frequency response and group delay of the transfer function are considered.

[0015] The voltage estimation filters are modelled as an envelope of the magnitude response of the Speaker processing transfer function, ensuring that the estimated voltage is always at or above the actual voltage for all frequencies.

[0016] Because filters in the Speaker processing block delays some frequencies more than others, the group delay in the voltage estimation filters mimic that of the transfer function, otherwise, the estimated change in voltage for some frequencies would occur too early, resulting in the Supply voltage calculation being out of sync with the output of the amplifiers.

[0017] Envelope calculation

[0018] The result after the voltage estimation filters have been applied is the maximum expected instantaneous voltage for all channels sharing the same supply voltage. Next, the envelope of that voltage is calculated, with a fast attack and slow release. The envelope is then clipped to the minimum and maximum voltage the DC / DC converter and amplifier can safely work with and passed on to the hardware. More details relating to the application of the calculated envelope for controlling the supply voltage of the one or more amplifiers will be given in the detailed description of the invention.

[0019] The above and further objects and advantages are obtained with the following aspects of the invention.

[0020] According to a first aspect of the present invention there is provided a method for regulating an adaptive supply voltage for one or more audio amplifiers, the method comprising:

[0021] - receiving a first audio signal;

[0022] - processing the first audio signal thereby providing a processed audio signal having a first delay relative to the first audio signal;

[0023] - providing a sound preset signal that controls the processing of the first audio signal such that the processed audio signal is provided;

[0024] - providing the processed audio signal to the one or more amplifiers;

[0025] - based on the first audio signal and sound preset signal calculating a supply voltage control signal indicating the lowest supply voltage that is required by the one or more amplifiers to avoid voltage clipping of an audio signal received by the one or more amplifiers, where the supply voltage control signal has a second delay relative to the first audio signal;

[0026] - using the supply voltage control signal to control a supply voltage for the one or more amplifiers;

[0027] - providing the supply voltage to the one or more amplifiers; wherein the first delay is greater than the second delay.

[0028] In an embodiment of the first aspect said calculation of the supply voltage comprises:

[0029] - for each set of amplifiers that share the same supply voltage, where each respective of the amplifiers in the set of amplifiers is part of a corresponding respective signal channel providing a set of filters, where the magnitude and group delay of the respective filter is based on a combination of each channels’ magnitude response and group delay, thereby providing a combined magnitude response and average group delay;

[0030] - providing a maximum expected instantaneous audio signal voltage as the result of processing the first audio signal by the filter having the combined magnitude response and group delay; - calculating the envelope of said maximum expected instantaneous audio signal voltage with a fast attack time and slow release time;

[0031] - clipping the envelope to the minimum and maximum voltage that can be accepted by entities, such as voltage supplies and / or amplifiers, used for implementing the method.

[0032] In an embodiment of the first aspect the processed audio signal and the supply voltage control signal are digital signals.

[0033] In an embodiment of the first aspect the supply voltage control signal is a DC signal.

[0034] In an embodiment of the first aspect the method comprises:

[0035] - receiving a digital audio input signal and optionally processing the digital audio input signal in first processor means thereby providing the first digital audio signal;

[0036] - providing the first digital audio signal to second processor means thereby providing a processed digital audio signal having a first delay relative to the first digital audio signal;

[0037] - converting the processed digital audio signal to a corresponding analogue audio signal and providing this analogue audio signal to one or more of the audio amplifiers;

[0038] - providing a sound preset signal controlling the second processor means;

[0039] - based on the first digital audio signal and the sound preset signal calculating a DC value indicating the lowest supply voltage that is required by the one or more amplifiers to avoid voltage clipping of the analogue audio signal received by the one or more amplifiers, where the DC value has a second delay relative to the first digital audio signal;

[0040] - using the DC value to control a supply voltage supply such that the supply voltage supply provides the one or more amplifiers with the required supply voltage; wherein the first delay is greater than the second delay plus charging time for capacitors in the supply voltage supply.

[0041] It is noted that for supply voltage supply means that either do not comprise capacitors at all or wherein capacitors in such means have very low capacitances, the charging time is either zero or negligible.

[0042] In an embodiment of the first aspect the supply voltage control signal is obtained by providing the first digital audio signal to a set of filters that estimate the output voltage of the amplifiers and calculating the envelope of the estimated output voltage. In an embodiment of the first aspect the transfer function of the set of filters is based on transfer functions of the second processor means.

[0043] In an embodiment of the first aspect the transfer functions and / or parameters of the second processor means are controlled from the sound preset signal.

[0044] According to a second aspect of the present invention there is provided a device for regulating an adaptive supply voltage for one or more audio amplifiers, wherein the device comprises:

[0045] - an input for receiving a first audio signal;

[0046] - a processing means characterized by a first delay which processing means receives the first audio signal and processes this signal to provide a second processed audio signal for use as an input signal to one or more amplifiers which amplifiers iare configured to be driven by an adaptive supply voltage;

[0047] - a supply voltage estimation unit comprising one or more digital filters and envelope calculation means, the supply voltage estimation unit having a first input terminal receiving the first audio signal and a second input terminal configured to receive a sound preset signal and an output terminal that based on the first audio signal and the sound preset signal provides a control signal indicating the needed supply voltage, where the supply voltage estimation unit has a second delay;

[0048] - providing the control signal to a controllable supply voltage supply means, that based on this control signal provides the needed supply voltage; wherein the signal delay associated with the supply voltage estimation filters and envelope calculation plus charging time for capacitors in supply voltage supply is less than the signal delay in the processing means.

[0049] In an embodiment of the second aspect the processed audio signal and the supply voltage control signal are digital signals.

[0050] In an embodiment of the second aspect comprising a D / A converter unit receiving the processed digital audio signal and converting this signal to a corresponding analogue audio signal for provision to one or more audio amplifiers configured to be driven by an adaptive supply voltage.

[0051] In an embodiment of the second aspect the device comprises a D / A converter unit receiving the control signal and converting this signal to a corresponding analogue control signal for provision to the supply voltage supply means that is configured to provide the adaptive supply voltage to the one or more amplifiers.

[0052] In an embodiment of the second aspect the supply voltage control signal is a DC signal.

[0053] In an embodiment of the second aspect the transfer function of the set of filters in the supply voltage estimation unit is based on transfer functions and / or parameters of the processing means.

[0054] In an embodiment of the second aspect the transfer function and / or the parameters of the processing means are controllable by a user via user interface means that are configured to provide the sound preset signal.

[0055] In an embodiment of the second aspect the first audio signal is provided by an input processing means on the reception of an input signal.

[0056] In an embodiment of the second aspect the input processing means have a delay that is much less than the first delay.

[0057] In an embodiment of the second aspect the device comprises means configured to:

[0058] - for each set of amplifiers that share the same supply voltage, where each respective of the amplifiers in the set of amplifiers is part of a corresponding respective signal channel providing a set of filters, where the magnitude and group delay of the respective filter is based on a combination of each channels’ magnitude response and group delay, thereby providing a combined magnitude response and average group delay;

[0059] - providing a maximum expected instantaneous audio signal voltage as the result of processing the first audio signal by the filter having the combined magnitude response and group delay;

[0060] - calculating the envelope of said maximum expected instantaneous audio signal voltage with a fast attack time and slow release time; and

[0061] - clipping the envelope to the minimum and maximum voltage that can be accepted by entities, such as voltage supplies and / or amplifiers.

[0062] According to a third aspect of the present invention there is provided a system comprising a plurality of devices according to the second aspect of the invention, each having a specific input terminal configured to receive respective digital audio input signals such as left and right input audio signals of a stereophonic signal, wherein each input signal after processing in respective first processors is provided to supply voltage estimating units providing respective supply voltage estimates to a supply voltage selection unit that is configured to select a control signal for the supply voltage supply.

[0063] In an embodiment of the third aspect the supply voltage selection unit selects the maximum of the two incoming supply voltage estimates and uses this as the control signal for the supply voltage supply.

[0064] According to a fourth aspect of the present invention there is provided an audio amplifier comprising:

[0065] - a device according to the second aspect;

[0066] - one or more audio amplifiers each having a separate input terminal configured to receive an analogue audio signal and a common supply voltage terminal configured to receive an adaptable supply voltage from the supply voltage supply unit.

[0067] BRIEF DESCRIPTION OF THE DRAWINGS

[0068] One or more embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: figure 1 shows a schematic block diagram illustrating the basic functions of an embodiment of a system according to the invention that provides adaptive amplifier supply voltage without added signal chain delay; figure 2 shows transfer functions of the Speaker processing block, wherein graphs (a) to (d) show the transfer functions from the input to each of the four outputs and graph (e) shows each transfer function and the combined transfer function; figure 3(a) shows the magnitude response of the transfer function of the signal processing after Supply voltage calculation and voltage estimation filter and figure 3(b) shows the group delay of the transfer function of the signal processing after Supply voltage calculation and voltage estimation filter; figure 4(a) shows the calculated envelope signal and figure 4(b) shows the signal after applying voltage estimation filters; figure 5 shows the voltage of each of four amplifier outputs, as well as the supply voltage envelope that determines the shared supply voltage; figure 6 shows an illustrative example of corresponding estimated voltage, envelope signal and supply voltage as a function of time; figure 7 shows oscilloscope measurements of two amplifier outputs sharing the same supply voltage; figure 8 shows oscilloscope measurements of an amplifier output and the supply voltage; figure 9 shows oscilloscope measurements of an amplifier output and the supply voltage; figure 10 shows oscilloscope measurements of an amplifier output and the supply voltage; figure 1 1 shows a block diagram of a non-limiting example of a practical implementation of a system according to the invention; and figure 12 shows a flow chart of an embodiment of a method according to the invention.

[0069] DETAILED DESCRIPTION OF THE INVENTION

[0070] The following detailed description relates to non-limiting embodiments of the invention. It is however understood that other practical implementations than those described below would also fall within the scope of protection as defined by the appended claims. This for instance relates to the signals between the various functional blocks as well as the processing performed by these blocks. Thus, the principle of the invention may be implemented using solely digital signals and processing, a mixture of digital and analogue signals and processing or purely analogue signals and processing. This depends on the specific implementation of the invention.

[0071] With reference to figures 1 (a) and (b) there is shown a schematic block diagram of the main functional blocks of an embodiment 1 of a system according to the invention and the interactions between these blocks comprising two blocks 2 and 3, respectively, but it is understood that this is only an example and that all functional blocks could be integrated in one unit or distributed among several units as desired in any specific implementation of the invention. In the following description of figures 1 (a) and (b) it is assumed that the signals and processing from the input terminal 4 to A and B is digital, but as mentioned, this is not necessarily the case in other implementations of the invention.

[0072] At an input terminal 4 there is received a digital audio input signal Vinthat is provided to a first processor 5 (in the figure termed “Stereo processing”), which first processor could comprise for instance volume setting, bass and treble setting and loudness compensation. The first processor 5 is characterised by having substantially no delay of the signal being processed, i.e. so low delay that it is without importance in the present context. The first processing block 5 provides an output signal Vi that is a processed version of the digital audio input signal Vinat the input terminal 4.

[0073] The output signal Vi is provided to a second processor 10 (in the figure termed “Speaker processing”) that is configured to produce the signals V2that can be used to drive individual loudspeakers in a system, in which the invention is used. The speaker processing block 10 may for instance split the output signal Vi from the first processing block 5 up into a number of driver channels for driving separate loudspeakers. These signals V2are digital signals and each of these are therefore provided to a separate D / A converter, of which only a single D / A converter 12 is shown in the schematic block diagram in figure 1. Each of these D / A converters provide a separate analogue audio signal 14 to a corresponding output amplifier 18, only one of which is shown in figure 1 , that provides the respective loudspeaker with a driver signal 20. In figure 11 is shown an illustrative example of the invention used to drive a stereophonic system with two three-ways loudspeaker units.

[0074] The output signal Vi from the first processor 5 is furthermore provided via line 7 to block 8 comprising supply voltage estimation filters and envelope calculation means. The filters and envelope calculation means herein can be controlled by a user providing a user input at terminal 9. A sound preset signal is provided at terminal 9 which controls the second processor 10. By controlling both the supply voltage estimation filters and envelope calculation in block 8 and the second processor 10 that provides speaker processing, the parameters of block 8 corresponds optimally to the actual speaker processing that is carried out in the second processor 10. By these means, the supply voltage estimation filters and envelope calculation block 8 is brought to contain a model of the speaker processing carried out in block 10 which can estimate the needed supply voltage with much lower delay D2 than the delay D1 of the speaker processing block 10, thus enabling the supply voltage to settle without needing to insert additional delay in the audio signal chain. The more detailed function of these processor blocks 8 and 10 will be described below with reference to figures 2 through 10. The supply voltage estimation filter and envelope calculation block 8 provides an output signal VEon line 13 that in this embodiment is a DC value indicating a needed supply voltage to the output amplifier 18 (or to a number of such amplifiers driven by the same supply voltage). Output signal 13 is a digital signal that in the D / A converter 15 is converted into an analogue DC control signal 16 that controls a supply voltage supply 17 for instance comprising the DC / DC converter circuit shown in figure 1 (b). The output 19 from the supply voltage supply 17 is used for driving the amplifier 18 or a number of such amplifiers, c.f. for instance figure 11 of the detailed description.

[0075] For each set of amplifier channels that share the same supply voltage (it is noted that the set may only consist of a single amplifier, but typically a number of loudspeakers each with its own amplifier channel) the filters that estimate their voltage are a combination of each channel’s magnitude response and group delay, resulting in a common maximum voltage and average group delay. This is illustrated in the following for a system comprising four loudspeakers: a tweeter, a woofer and two full range loudspeakers.

[0076] With reference to figure 2 there is shown transfer functions of the speaker processing block 10, wherein graphs (a) through (d) show the transfer functions from the respective inputs 6 to each of the four outputs 11 , and graph (e) shows the combined transfer function, i.e. the maximum of these four transfer functions. The plots shown in figure 2 relate to an embodiment of the method / system according to the invention in which there are four output channels, one for a LF loudspeaker (woofer) having a magnitude response 21 , one for a HF loudspeaker (Tweeter) having a magnitude response 22 and two channels for full range loudspeakers (Fullrangel and Fullrange2), respectively having magnitude responses 23 and 24, respectively. Each loudspeaker is in this embodiment driven by its own, separate amplifier 18 and all of these four amplifiers share the same supply voltage 19.

[0077] With reference to figure 3(a) there is shown the combined magnitude response of the transfer functions of the signal processing after supply voltage calculation and voltage estimation filter and with reference to figure 3(b) there is shown the combined group delay of the transfer functions of the signal processing after supply voltage calculation and voltage estimation filter.

[0078] The supply voltage estimation filters are calculated as a simplified version of the combined transfer function of the second processor 10 (the speaker processing block). In the estimation filters, both the frequency response and the group deiay of the combined transfer function are considered.

[0079] Figure 3(a) shows the combined transfer function (i) of the four transfer functions shown in figure 2(a) through 2(d) and the transfer function (ii) of the resuiting voltage estimation filters. Figure 3(b) shows the combined group delay (iii) of the four transfer functions shown in figure 2(a) through 2(d) and the group delay (iv) of the resulting voltage estimation filters.

[0080] The supply voltage estimation filters are modelled as an envelope of the magnitude responses of the respective second processing blocks 10, ensuring that the estimated voltage is always at or above the actual voltage for all frequencies.

[0081] Because filters in the second processing block 10 delay some frequencies more than others, the group delay in the voltage estimation filters mimic that of the transfer function of the speaker processing block 10. Otherwise, the estimated change in voltage for some frequencies would occur too early, resulting in the supply voltage calculation being out of sync with the output of the amplifiers.

[0082] In an embodiment of the invention envelope calculation is carried out as follows: The resulting total voltage of all channels after the voltage estimation filters have been applied is the maximum expected instantaneous voltage for all channels (amplifiers) sharing the same supply voltage. An example of this resulting voltage as a function of time is shown in figure 4(b). The envelope of this instantaneous voltage is then calculated. This is shown in figure 4(a). For this calculation it is advantageous that a fast attack (short attack time) and a slow release (long release time) is used. The application of such attack and release times appears clearly from figures 6 through 10.

[0083] With reference to figure 5 there is shown the envelope signal VE of each channel that share the same supply voltage. In figure 5(a) it clearly appears that in the first approximately 10% of the time covered by the plots, the woofer signal is driving the envelope signal (and thereby the supply voltage) up to its maximum level while in the remaining time covered by the plots, it is the full range loudspeaker signals s that drive the envelope signal. Also shown in the plots are the output signals V2from the speaker processing block 10.

[0084] Due to the amplifiers needing a certain overhead in the supply voltage to supply a given amplifier output voltage, the supply voltage should always be at least that overhead above the signal level. This appears clearly from figures 7 through 10. The envelope signal, such as those shown in figures 4 and 5, is after conversion to a corresponding analogue signal (in the D / A converter 15 in the embodiment shown in figure

[0085] I ) used as a control signal 16 for the supply voltage supply 17. The envelope signal occurs in advance of the signals 14 (c.f. figure 1 ) and 49, 50, 51 , 67, 68, 69 (c.f. figure 11 ) because the processing in the "supply voltage calculation block" 8 (c.f. figure 1 ) and 78, 80 (c.f. figure

[0086] I I ) has less delay than the processing in the "speaker processing block" 10 (c.f. figure 1 ) and 42, 60 (c.f. figure 11 ). The time in advance is used for charging up supply voltage capacitance C (c.f. figure 1 ). Also, the supply voltage capacitance C will make the supply voltage drop slower than the envelope signal.

[0087] An illustrative example of corresponding estimated voltage, envelope signal and supply voltage as a function of time is shown in figure 6, wherein figure 6(a) shows an estimated voltage, figure 6(b) shows the corresponding envelope signal, and figure 6(c) shows the resulting supply voltage provided for instance by the supply voltage supply 17 in figure 1. From figure 6(c) it also appears that the supply voltage has a fast attack time and a much slower release time as also indicated by reference numerals 30(1 ) and 30(2) in figure 7.

[0088] With reference to figures 7 through 10 there are shown actual measurements of an amplifier output for a woofer and a full range loudspeaker, as well as the common supply voltage (i.e. the supply voltage on the output of the DC / DC converter 17 and smoothed by the capacitor C shown in figure 1 ). It appears that the supply voltage generally is following the signal level, increasing fast when the magnitude of the signal increases and dropping slowly when the magnitude of the signal decreases.

[0089] With reference to figure 7 there is shown an oscilloscope measurement of two amplifier outputs sharing the same supply voltage 31. The amplifier output signal for the full range loudspeaker is indicated by 32 and the amplifier output signal for the woofer is indicated by 33. The maximum value of the supply voltage is in this example 30 VDC and it appears that the powerful signal peaks 33 in the woofer signal requires the supply voltage being at its maximum value. As indicated by 30(1 ), an increase in the signal level results in a fast increase of the supply voltage (i.e. a fast attack time) whereas, as indicated by 30(2), a reduction of the magnitude of the signal results in a much slower reduction of the supply voltage (i.e. a long release time). In figure 8 and 9 the amplifier outputs for the woofer 33 and full range loudspeakers 37 are separated, to show more clearly which of the two is driving the supply voltage up at a given time.

[0090] Figure 10 shows another example of the woofer channel 39 driving the supply voltage 38 to rise when the signal magnitude increases, and discharging the capacitors C in the supply voltage supply 38 when the supply voltage is at a higher level that what is needed by the amplifiers in order not to clip the signal.

[0091] With reference to figure 1 1 there is shown a block diagram of a non-limiting example of a practical implementation of a system according to the invention. The total system shown in figure 11 comprises a device D according to an embodiment of the invention and the amplifiers 52, 53, 54, 70, 71 , 72 and associated loudspeakers 55, 56, 57, 73, 74, 75.

[0092] It is to be noted that the exact boundaries between “a device” and “a system” can be different from what is shown by the broken line D in figure 1 1. Thus, for instance the amplifiers could each be provided with respective D / A converters, such that the D / A converters shown in figure 11 thereby would not be a part of the device.

[0093] The system shown in figure 1 1 comprises a left and right stereo channel with signal inputs VLand VR, respectively. In the shown embodiment, the left and right signal chains are of identical configuration, but it is understood that this need not necessarily be the case.

[0094] The left channel input signal VL is provided to a first processor 40 (“stereo processing left”) in which for instance gain adjustment, dynamic range compression and / or channel routing and mixing can be carried out. The delay through the first processor 40 can be assumed to be negligible in the present context. The processed audio signal 41 from the first processor 40 is provided to a second processor 42 (“speaker processing left”) that typically comprises both FIR and HR filters having an inherent constant delay of the signal processed by the second processor 42. In the shown embodiment, the second processor 42 splits up the received audio signal 41 into a high-frequency signal 43, a mid-frequency signal 44 and a low-frequency signal 45, which signals - after the required amplification - are provided to a high-frequency loudspeaker (tweeter) 55, a mid-frequency loudspeaker (midrange) 56 and a low-frequency loudspeaker (woofer) 57.

[0095] The signals 43, 44 and 45 are digital audio signals, and these are converted to corresponding analogue audio signals 49, 50, 51 in respective D / A converters 46, 47, 48. The analogue audio signals 49, 50, 51 are provided to corresponding individual amplifiers 52, 53, 54, which are driven by the same supply voltage 84.

[0096] The right channel input signal VRis provided to a first processor 58 (“stereo processing right”) in which for instance gain adjustment, dynamic range compression and / or channel routing and mixing can be carried out. The delay through the first processor 58 can be assumed to be negligible in the present context. The processed audio signal 59 from the first processor 58 is provided to a second processor 60 (“speaker processing right”) that typically comprises both FIR and HR filters having an inherent constant delay of the signal processed by the second processor 60. In the shown embodiment, the second processor 60 splits up the received audio signal 59 into a high-frequency signal 61 , a mid-frequency signal 62 and a low-frequency signal 63, which signals - after the required amplification - are provided to a high-frequency loudspeaker (tweeter) 73, a mid-frequency loudspeaker 74 and a low-frequency loudspeaker (woofer) 75.

[0097] The signals 61 , 62 and 63 are digital audio signals, and these are converted to corresponding analogue audio signals 67, 68, 69 in respective D / A converters 64, 65, 66. The analogue audio signals 67, 68, 69 are provided to corresponding individual amplifiers 70, 71 , 72, which are driven by the same supply voltage 84.

[0098] The common supply voltage 84 is provided by a controllable supply voltage supply 83 which receives a control signal 85. This control signal 85 is derived from the two processed audio signals 41 , 59 and information relating to the sound preset 76 that is chosen by the user via user interface 77. In this manner it is ensured that the estimated supply voltages 79, 81 depends on the sound preset actually chosen by the user (or pre-set in the system). In this example, the sound preset may be different for the left and for the right channel, e.g., one sound preset signal controls the Speaker processing Right 60 and the corresponding supply voltage estimation 80, and a second sound preset signal controls the Speaker processing Left 42 and the corresponding supply voltage estimation 78. It is understood that an alternative embodiment can be contemplated, in which there is only a single sound preset signal controlling both channels and a single supply voltage estimation block.

[0099] In figure 11 two separate supply voltage estimation blocks are shown. It would however also be possible to use separate voltage estimation filters for each channel together with a single envelope calculation means functioning on the maximum signal output from the two voltage estimation filters. This can of course be extended to any number of channels and would also fall within the scope of protection of the invention. In functional block 82 a supply voltage selection is carried out based on the estimated supply voltages 79, 81 . This selection typically consist of taking the maximum of the two incoming supply voltage estimates 79, 81 , but it is understood that other selection criteria could be chosen. The output signal 85 from the supply voltage selection block 82 is used as the control signal for the supply voltage supply 83.

[0100] With reference to figure 12 there is shown a flow chart of the method according to an embodiment of the invention. The method shown in the flow chart relates to a single input audio channel (for instance having input signals V or VRin figure 11 ). The input audio signal (a digital signal) is received in block 85 and provided to the first DSP unit in block 86 that provides a first processed output signal 87. The delay of the processing in block 86 is Δin. This signal 87 is provided (via line 88) to a second DSP unit in block 89 that provides a second processed output signal. The delay in block 89 is Δi. The output signal from block 89 is converted from a digital signal to an analogue signal in a D / A converter in block 90. The analogue signal from the D / A converter in block 90 is in block 91 provided to an amplifier configured to receive a variable supply voltage.

[0101] In block 92 a user can enter a chosen sound preset that in block 93 is converted to corresponding sound preset parameters that are transferred to the processing block 89 and the estimation block 95 via line 94.

[0102] The first processed output signal 87 is provided to the supply voltage estimation in block 95. The signal 99 from the supply voltage estimation is used in block 97 to determine the control signal 102 for a supply voltage supply (not shown). The required supply voltage is finally provided to the audio amplifier in block 100

[0103] In the flow chart, the relationships between the delays in respective functional blocks are also indicated.

[0104] As mentioned above the flow chart shown in figure 12 relates to a single input audio channel. However, the possibility of using the method for a number of amplifiers that share the same supply voltage is shown in the flow chart by lines 96 and 98 and block 101.

Claims

CLAIMS1 . A method for regulating an adaptive supply voltage for one or more audio amplifiers, the method comprising:- receiving a first audio signal (Vi);- processing the first audio signal (Vi) thereby providing a processed audio signal (V2) having a first delay (Δi) relative to the first audio signal (Vi);- providing a sound preset signal (9) that controls the processing of the first audio signal (Vi) such that the processed audio signal (V2) is provided;- providing the processed audio signal (V2) to the one or more amplifiers (18);- based on the first audio signal (Vi) and sound preset signal (9) calculating a supply voltage control signal (13) indicating the lowest supply voltage (19) that is required by the one or more amplifiers (18) to avoid voltage clipping of an audio signal (14) received by the one or more amplifiers, where the supply voltage control signal (13) has a second delay (Δ2) relative to the first audio signal (Vi);- using the supply voltage control signal (13) to control a supply voltage (19) for the one or more amplifiers;- providing the supply voltage (19) to the one or more amplifiers; wherein the first delay (Δi) is greater than the second delay (Δ2).

2. A method according to claim 1 wherein said calculation of the supply voltage comprises:- for each set of amplifiers (18; 52, 53, 54, 70, 71 , 72) that share the same supply voltage (19, 84) ), where each respective of the amplifiers in the set of amplifiers is part of a corresponding respective signal channel (43, 46, 49; 44, 47, 50; 45, 48, 51 ; 61 , 64, 67; 62, 65, 68; 63, 66, 69), providing a set of filters, where the magnitude and group delay of the respective filter is based on a combination of each channels’ magnitude response (21 , 22, 23, 24) and group delay, thereby providing a combined magnitude response (26(ii)) and average group delay (27(iv));- providing a maximum expected instantaneous audio signal voltage as the result of processing the first audio signal (Vi) by the filter having the combined magnitude response (26(ii)) and group delay (27(iv)) ;- calculating the envelope (29) of said maximum expected instantaneous audio signal voltage with a fast attack time and slow release time;clipping the envelope (29) to the minimum and maximum voltage that can be accepted by entities, such as voltage supplies (17) and / or amplifiers (18), used for implementing the method.

3. A method according to claim 1 or 2, wherein the processed audio signal (V2) and the supply voltage control signal (13) are digital signals.

4. A method according to claim 1 , 2 or 3 wherein the supply voltage control signal (13) is a DC signal.

5. A method according to claim 1 ; the method comprising:- receiving a digital audio input signal (Vin) and optionally processing the digital audio input signal (Vin) in first processor means (5) thereby providing the first digital audio signal (Vi);- providing the first digital audio signal (Vi) to second processor means (10) thereby providing a processed digital audio signal (V2) having a first delay (Ai) relative to the first digital audio signal (Vi);- converting the processed digital audio signal (V2) to a corresponding analogue audio signal (14) and providing this analogue audio signal (14) to one or more of the audio amplifiers (18);- providing a sound preset signal (9) controlling the second processor means (10);- based on the first digital audio signal (Vi) and the sound preset signal (9) calculating a DC value (13) indicating the lowest supply voltage (19) that is required by the one or more amplifiers (18) to avoid voltage clipping of the analogue audio signal (14) received by the one or more amplifiers (18), where the DC value (13) has a second delay A2relative to the first digital audio signal (Vi);- using the DC value (13) to control a supply voltage supply (17) such that the supply voltage supply (17) provides the one or more amplifiers (18) with the required supply voltage (19); wherein the first delay Δ1is greater than the second delay A2plus charging time for capacitors in the supply voltage supply (17).

6. A method according to claim 5, wherein the supply voltage control signal (13) is obtained by providing the first digital audio signal (Vi) to a set of filters that estimate the output voltage (20) of the amplifiers (18) and calculating the envelope of the estimated output voltage.

7. A method according to claim 5 or 6, wherein the transfer function of the set of filters is based on transfer functions of the second processor means (10).

8. A method according to claim 5, 6 or 7, wherein the transfer functions and / or parameters of the second processor means (10) are controlled from the sound preset signal (9).

9. A device for regulating an adaptive supply voltage for one or more audio amplifiers, wherein the device comprises:- an input (6) for receiving a first audio signal (Vi);- a processing means (10) characterized by a first delay Δ1which processing means (10) receives the first audio signal (Vi) and processes this signal (Vi) to provide a second processed audio signal (V2) for use as an input signal to one or more amplifiers (18) which amplifiers is / are configured to be driven by an adaptive supply voltage (19);- a supply voltage estimation unit (8) comprising one or more digital filters and envelope calculation means, the supply voltage estimation unit (8) having a first input terminal receiving the first audio signal (Vi) and a second input terminal configured to receive a sound preset signal (9) and an output terminal that based on the first audio signal (Vi) and the sound preset signal (9) provides a control signal (13) indicating the needed supply voltage (19), where the supply voltage estimation unit (8) has a second delay Δ2;- providing the control signal (13) to a controllable supply voltage supply means (17), that based on this control signal (13) provides the needed supply voltage (19); wherein the signal delay Δ2associated with the supply voltage estimation filters and envelope calculation plus charging time for capacitors in supply voltage supply (17) is less than the signal delay Δi in the processing means (10).

10. A device according to claim 9, wherein the processed audio signal (V2) and the supply voltage control signal (13) are digital signals.1 1. A device according to claim 9 or 10 comprising a D / A converter unit (12) receiving the processed digital audio signal (V2) and converting this signal to a corresponding analogue audio signal (14) for provision to one or more audio amplifiers (18) configured to be driven by an adaptive supply voltage (19);12. A device according to any of the preceding claims 9 to 11 comprising a D / A converter unit (15) receiving the control signal (13) and converting this signal to a corresponding analogue control signal (16) for provision to the supply voltage supply means (17) that is configured to provide the adaptive supply voltage (19) to the one or more amplifiers (18).

13. A device according to any of the preceding claims 9 to 12, wherein the supply voltage control signal (13) is a DC signal.

14. A device according to any of the preceding claims 9 to 13, wherein the transfer function of the set of filters in the supply voltage estimation unit (8) is based on transfer functions and / or parameters of the processing means (10).

15. A device according to any of the preceding claims 9 to 14, wherein the transfer function and / or the parameters of the processing means (10) are controllable by a user via user interface means that are configured to provide the sound preset signal (9).

16. A device according to any of the preceding claims 9 to 15 wherein the first audio signal (Vi) is provided by an input processing means (5) on the reception of an input signal (Vin).

17. A device according to claim 16 wherein the input processing means have a delay Δin, where Δin« Δ1.

18. A device according to any of the preceding claims 9 to 17 comprising means configured to:- for each set of amplifiers (18; 52, 53, 54, 70, 71 , 72) that share the same supply voltage (19, 84), where each respective of the amplifiers in the set of amplifiers is part of a corresponding respective signal channel (43, 46, 49; 44, 47, 50; 45, 48, 51 ; 61 , 64, 67; 62, 65, 68; 63, 66, 69), providing a set of filters, where the magnitude and group delay of the respective filter is based on a combination of each channels’ magnitude response (21 , 22, 23, 24) and group delay, thereby providing a combined magnitude response (26(ii)) and average group delay (27(iv));- providing a maximum expected instantaneous audio signal voltage as the result of processing the first audio signal (Vi) by the filter having the combined magnitude response (26(ii)) and group delay (27(iv)) ;- calculating the envelope (29) of said maximum expected instantaneous audio signal voltage with a fast attack time and slow release time; and- clipping the envelope (29) to the minimum and maximum voltage that can be accepted by entities, such as voltage supplies (17) and / or amplifiers (18).

19. A system comprising a plurality of devices according to claims 9 to 18 each having a specific input terminal configured to receive respective digital audio input signals such as left and right input audio signals (V , VR) of a stereophonic signal, wherein each input signal after processing in respective first processors (40, 58) is provided to supply voltage estimating units (78, 80) providing respective supply voltage estimates (79, 81 ) to a supply voltage selection unit (82) that is configured to select a control signal (85) for the supply voltage supply (83).

20. A system according to claim 19, wherein the supply voltage selection unit (82) selects the maximum of the two incoming supply voltage estimates (79, 81 ) and uses this as the control signal (85) for the supply voltage supply (83).

21. An audio amplifier comprising:- a device according to any of the preceding claims 9 to 18;- one or more audio amplifiers (18, 52, 53, 54, 70, 71 , 72) each having a separate input terminal configured to receive an analogue audio signal (14, 49, 50, 51 , 67, 68, 69) and a common supply voltage terminal (19, 84) configured to receive an adaptable supply voltage from the supply voltage supply unit (17, 83).

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