Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:
The invention will now be described based on preferred embodiments which do not intend to limit the scope of the present invention but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention.
The electronic apparatus 1000 includes the electronic volume apparatus 100, a reproducing unit 10, a volume control unit 12, and a sound output unit 14. The reproducing unit 10 is a block which converts sound data which is stored in a disk media, memory or a hard disk or wiredly or wirelessly input from the outside into an analog audio signal S1 to reproduce the audio signal. The volume control unit 12 is an input apparatus arranged to change a volume by a user, and a volume value VOL is designated through the volume control unit 12.
The electronic volume apparatus 100 amplifies the audio signal S1 output from the reproducing unit 10 depending on the volume value VOL input to the volume control unit 12. The electronic volume apparatus 100, as will be described below, includes an amplifier which amplifies or attenuates the audio signal S1. The electronic volume apparatus 100 changes a gain of an internal amplifier depending on the volume value designated by a user.
A configuration of the electronic volume apparatus 100 will be described below in detail.
The electronic volume apparatus 100 includes an amplifier 20 and a gain control unit 30. The amplifier 20 is amplifier which amplifies an input audio signal S1 to change the amplitude. The amplitude is a concept which includes not only a gain more than 1 but also an attenuation equal to or less than 1. Therefore, the amplitude is a concept including an attenuator and means a circuit to widely change an amplitude of an electronic signal. As a gain of the amplifier 20, a plurality of gains discretely set is switchably set.
The gain control unit 30 outputs a gain control signal CNT to the amplifier 20. The gain control signal CNT corresponds to a control function g(t) (will be described later). The gain of the amplifier 20 moderately changes from an initial value g1 to a target value g2 according to a control function g(t) (will be described later).
For example, the amplifier 20 is constituted by using a variable resistor.
In another example, as shown in
In still another example, as shown in
In this manner, in the embodiment, the configuration of the amplifier 20 is not limited to a specific type. The configuration of the amplifier 20 may be constituted such that a plurality of discretely set gains are switchably arranged.
The digital control unit 32 outputs a digital value DIG depending on the input volume value VOL. A decode circuit 34 ON/OFF-controls a plurality of switches in the amplifier 20 depending on the digital value DIG to set a gain corresponding to the volume value. More specifically, the gain control signal CNT is a signal to ON/OFF-control the plurality of switches in the amplifier 20.
When a user changes a gain having an initial value VOL1 in a certain state into a volume value VOL2, the gain control unit 30 changes the gain of the amplifier 20 from an initial value g1 corresponding to the volume value VOL1 to a target value g2 corresponding to the volume value VOL2. A method of controlling a gain by using the gain control unit 30 will be described below.
In the embodiment, the gain control unit 30 transits a gain of the amplifier 20 depending on the control function g(t) by using time as a parameter. The gain control unit 30 sets a transition period Tp depending on a combination of the initial value g1 and the target value g2 and transits a gain having the initial value g1 at time t=0 to the target value g2 at time t=Tp after the transition period Tp elapses.
The gain control unit 30 controls a gain of the amplifier 20 depending on a control function g(t) which satisfies the following conditions (1) to (3):
g(0)=g1, g(Tp)=g2 (1)
g′(Tp/2)>g′(0) (2)
g′(Tp/2)>g′(Tp) (3)
where g′(t) is time differentiation.
At the start and end of transition, when a variation in inclination of a gain, that is, a variation in amplitude (envelope) of an audio signal S1 is large, the audio signal S1 is easily sensed as noise. Therefore, when the control function g(t) which satisfies the condition (1) to (3) is set, inclinations of a gain at the start and end of transition are smaller than an inclination of a gain at a halfway point set between the start and the end of transition. As a result, noise can be preferably reduced.
For example, the control function g(t) maybe regulated depending on a target function f(t) defined as a trigonometric function which passes through points (0,g1) and (Tp,g2) and has a cycle of 2Tp. For example, the control function g(t) may be regulated depending on the target function f(t) defined by the following equations. The transition period Tp is preferably set within the range of 10 ms to 100 ms.
f(t)=A×cos(π×t/Tp)+B
A=(g1−g2)/2
B=(g1+g2)/2
As the control function g(t), the target function f(t) itself may be used. The control function g(t) may be a function obtained by quantizing the target function f(t). A method of setting the control function g(t) will be described below.
In a first setting example, as the control function g(t), the target function f(t) itself is defined. In this case, in the digital control unit 32 in
In a second setting example, as the control function g(t), a function by quantizing the target function f(t) is defined. The target function f(t) is divided by N (N is an integer which is not less than three) in a range of time t=0 to t=Tp. A division point obtained by the division is linearly interpolated.
Even though the control function g(t) is regulated by any one of the first to third setting examples, the above conditions (1) to (3) are satisfied. In the examples in
An operation of the electronic volume apparatus 100 having the above configuration will be described below. A user changes a volume of the electronic volume apparatus 100 with reproducing audio data at a certain volume value of VOL1 by the volume control unit 12 when a certain initial value VOL1 is set. As a result, from the volume control unit 12, a changed volume value VOL2 is sent to the electronic volume apparatus 100.
The gain control unit 30 of the electronic volume apparatus 100 which receives the changed volume value VOL2 generates a control function g(t) regulated depending on the target function f(t) from the initial value g1 and the target value g2 of the gain of the amplifier 20 in the digital control unit 32. From transition start time t=0, a digital value DIG depending on the control function g(t) is output to the decode circuit 34. The decode circuit 34 turns on or off the switches in the amplifier 20 depending on the digital value DIG to change gains.
The gain control unit 30 may set the length of the transition period Tp depending on a combination of the initial value g1 and the target value g2 of the gain. For example, as the difference between the initial value g1 and the target value g2 decreases, the gain control unit 30 may set the transition period Tp to be short. Since a small difference between the initial value g1 and the target value g2 means a small volume difference, noise is not easily sensed by the human ear. Therefore, when the transition period Tp is regulated depending on the combination between the initial value g1 and the target value g2, the volume can be changed within a short period of time while suppressing audible noise.
As described above, in the electronic volume apparatus 100 according to the embodiment, audible noise generated by a change in volume value of an audio signal can be reduced. In particular, a triangular wave is defined as the target function f(t), so that noise can be preferably reduced.
When the control function g(t) is generated by dividing the target function f(t) by N and linearly interpolating the division points, affinity to a digital signal processing circuit using a counter or the like is improved. For this reason, the digital value DIG can be easily generated. Furthermore, it is advantageously unnecessary that a control function is held in a memory such as a table.
The settings of the control function g(t) and the target function f(t) by the gain control unit 30 described above and the gain control method can be recognized as follows.
More specifically, when a gain of the amplifier having the initial value g1 at time t0 in the initial state is transited to the target value g2 after a certain transition period Tp elapses, the gain control unit 30 linearly changes the gain in M steps (M is an integer which is three or more). The gain control unit 30 changes the gain of the amplifier 20 depending on the control function g(t) which satisfies the following conditions (4) to (7):
t
M
=t
0
+Tp Condition (4)
g(t0)=g1, g(tM)=g2 Condition (5 )
g′(ti)>g′(t0) Condition (6)
g′(ti)>g′(tM−1) Condition (7)
where i is an integer which satisfies 1≦i≦M−2, ti is time at an ith division point, and g′(ti) is an inclination of g(t) at time ti to ti+1.
A trigonometric function having a cycle of 2Tp is defined as a target function f(t). The control function g(t) is regulated depending on the target function f(t). For example, the target function f(t) is defined by the following equations:
f(t)=A×cos(π×t/Tp)+B
A=(g1−g2)/2
B=(g1+g2)/2
where t=0 corresponds to transition start time t0.
Furthermore, the control function g(t) is regulated as a function obtained by dividing the target function f(t) by M and linearly interpolating division points.
The control function g(t) regulated by the design method recognized as described above is equivalent to control functions shown in
The embodiment according to the present invention has been described. The above embodiment is an exemplification. It is understood by a person skilled in the art that combinations of the constituent elements and the processing processes can be variably modified and that the modifications are included in the spirit and scope of the invention.
In the embodiment, the target function f(t) is mainly set as a trigonometric function, and the control function g(t) is regulated depending on the target function. However, the present invention is not limited to the embodiment. For example, the target function f(t) maybe regulated as a part of a trigonometric function the cycle of which is set to be longer than 2Tp. The control function g(t) is not necessarily regulated after the target function f(t) is set. The control function g(t) can be directly regulated to satisfy the above conditions (1) to (3).
In the explanation of the embodiment, volume is changed. However, the application of the electronic volume apparatus 100 is not limited to the change in volume. The electronic volume apparatus 100 may be applied to an equalizer or the like which controls gains for every certain frequency. In the explanation of the embodiment, volume is changed. However, the present invention can also be applied to a mute process in stopping of reproduction.
While the preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing form the spirit or scope of the appended claims.
Number | Date | Country | Kind |
---|---|---|---|
JP2006-154321 | Jun 2006 | JP | national |