JP5892354B2 - Audio equipment - Google Patents

Description

  The present invention relates to an audio device in which a plurality of types of source devices are connected to input terminals.

  Guitar amps range from high-performance equipment used by professionals to inexpensive equipment used by beginners. Of these, inexpensive ones are provided with only one or a small number of input terminals (jacks) in order to reduce the cost and size (for example, Non-Patent Document 1). On the other hand, the guitar amplifier may be connected not only to the guitar directly but also to various devices. Examples of devices to be connected include an electric guitar, an electric bass, a microphone, and an effector.

“Guitar Amplifier GA15”, [online], Yamaha Corporation, [Search on March 21, 2011], Internet <http://data.yamaha.jp/sdb/local/products/images/18232/99/18232_99_1 .pdf>

  In the case of a high-performance device, each device has an input terminal, and each input terminal is set to an input impedance suitable for the corresponding device. However, since the inexpensive amplifier as described above is provided with only one or a small number of input terminals, a plurality of types of devices are connected to the same input terminal. However, the above-mentioned plural types of devices have different impedances, and there is a problem that sound quality deteriorates due to impedance mismatch when connected to the same input terminal as it is. Also, since the signal level input varies depending on the device, the volume may be too low or too high unless the gain is adjusted.

Inexpensive guitar amplifiers include switches that change the impedance of the input terminals and adjust the gain, but many users who use inexpensive amplifiers are beginners who need to change the impedance and adjust the gain. Many people do not know.
An object of the present invention is to provide an audio device capable of detecting and setting an input impedance and gain in accordance with a device connected to an input terminal.

The audio device of the present invention includes an input terminal to which a source device that outputs an audio signal is connected, an audio amplifier that can change a gain , a test signal generator, a return signal analyzer that detects the impedance of the source device , And a changeover switch. The changeover switch connects an audio amplifier to the input terminal during normal operation. The changeover switch connects the test signal generation unit and the return signal analysis unit to the input terminal when detecting the impedance of the source device. At the time of impedance detection of the source device, the test signal generation unit generates a test signal, and the return signal analysis unit detects the impedance of the source device based on the frequency characteristic of the return signal that is the test signal returned to the input terminal , The input impedance of the audio amplifier is controlled based on the detected impedance .

  A capacitor connected in parallel to the return signal analysis unit may be provided, and the return signal analysis unit may detect the impedance of the source device based on the characteristics of the low pass filter including the source device and the capacitor.

  The capacitor may be a variable element, and the return signal analysis unit may detect the impedance of the source device after controlling the capacitance of the capacitor so that the cutoff frequency of the low-pass filter becomes a predetermined frequency.

  The test signal generation unit may generate white noise as the test signal, and the return signal analysis unit may detect the impedance of the source device based on the frequency characteristic of the return signal.

A variable impedance element connected in parallel to the audio amplifier may be provided, and the return signal analysis unit may control the input impedance of the audio amplifier by controlling the impedance value of the variable impedance element.

  The audio amplifier may be a variable gain amplifier, and the return signal analysis unit may control the gain of the audio amplifier based on the detected impedance of the source device.

  According to the present invention, it is possible to detect the impedance of the source device connected to the input terminal and set the input impedance and gain.

Schematic configuration diagram of an audio amplifier according to an embodiment of the present invention Configuration diagram of impedance switching circuit Diagram explaining the source device impedance detection method Flow chart showing impedance setting operation Flow chart showing gain setting operation

  An audio amplifier according to an embodiment of the present invention will be described with reference to the drawings. This audio amplifier is an amplifier such as a guitar amplifier with a built-in speaker, and has the following characteristics. In order to be compact and inexpensive, only one input terminal (jack) is provided. A plurality of types of source devices are connected to this one input terminal. Examples of the connected source device include an electric guitar, an electric bass, a dynamic microphone, and an effector. Since the impedance and signal level of these source devices are different, this is detected immediately after the input terminal, and the input impedance of the audio amplifier and the gain of the front amplifier are automatically adjusted based on the detection result.

  FIG. 1 is a schematic configuration diagram of an audio amplifier 1. The audio amplifier 1 includes an input terminal 11, an impedance switching circuit 12, a variable gain front amplifier 13, an amplifier body circuit 14, a speaker 15, a signal generation unit 16, and a control unit 10.

  The amplifier body circuit 14 is a circuit that equalizes and amplifies the audio signal and outputs the amplified audio signal to the speaker 15.

  The input terminal 11 is a terminal to which the various source devices 2 described above are connected, and is a two-pole terminal including a hot terminal 11A and a cold terminal 11B. For example, a TS-type phone jack may be used as the input terminal 11, but there is no limitation on the standard and shape as long as an electrical signal with an audio frequency can be input. Note that the cold terminal 11B is not directly connected to the ground (frame ground). The source device 2 is connected to the input terminal 11 via the cable 3. The cable 3 is a so-called single-core shielded cable, and the core wire 3A is connected to the hot terminal 11A, and the shield wire (knitting wire) 3B is connected to the cold terminal 11B. In the present invention, the input terminal 11 is not limited to two poles.

  The impedance switching circuit 12 is a circuit that switches the impedance of the input terminal 11 (the input impedance of the audio amplifier 1). FIG. 2 is a diagram showing a configuration of the impedance switching circuit 12. The impedance switching circuit 12 includes a changeover switch 120, a variable resistor 121, and a variable capacitor 122. The change-over switch 120 connects the input terminal 11 to the variable resistor 121 side during normal operation, and connects the input terminal 11 to the variable capacitor 122 side when detecting input impedance. As the variable resistor 121, for example, a resistor that can obtain a plurality of resistance values by switching connection of a plurality of resistors using an analog switch is used. The variable capacitor 122 is a capacitor in which a plurality of varicaps are connected in parallel via an analog switch, and a plurality of capacitances can be obtained by switching the capacity and connection / disconnection of each varicap. Switching of the change-over switch 120, the resistance value of the variable resistor 121, and the capacitance of the variable capacitor 122 are controlled by the control unit 10.

  FIG. 2 shows a connection form of the impedance switching circuit 12 during normal operation. When performing a normal operation as an audio amplifier, the changeover switch 120 is switched to the variable resistor 121 side, and the resistance value corresponding to the impedance of the source device 2 is parallel to the input terminal 11 (hot terminal 11A, cold terminal 11B). The resistor 121 is connected to perform impedance matching, and the audio signal input from the input terminal 11 is input to the variable gain front amplifier 13 at the subsequent stage.

  In FIG. 2, when the changeover switch 120 is switched, the connection form of the impedance switching circuit 12 is detected when the impedance of the source device 2 connected to the input terminal 11 is detected. When the impedance of the source device 2 is detected, the changeover switch 12 is switched to the variable capacitor 122 side. The variable capacitor 122 and the A / D converter 17 are connected to the hot terminal 11A of the input terminal 11, and the signal generator 16 is connected to the cold terminal 11B. The signal generator 16 is a circuit that generates white noise as a test signal for impedance detection of the source device 2. Thereby, the white noise generated by the signal generator 16 returns to the variable capacitor 122 through the cold terminal 11B, the shield wire 3B, the source device 2, the core wire 3A, and the hot terminal 11A, and this signal is transmitted by the A / D converter 17. The control unit 10 converted into a digital signal is input.

  In the impedance switching circuit 12, the connection of the hot terminal 11A and the cold terminal 11B on the impedance detection side may be reversed. That is, the variable capacitor 122 and the A / D converter 17 may be connected to the cold terminal 11B side of the input terminal 11, and the signal generating unit 16 may be connected to the hot terminal 11A side.

  The control unit 10 is composed of a microcomputer and controls the impedance switching circuit 12 to detect the impedance of the source device 2. Further, the impedance switching circuit 12 and the variable gain front amplifier 13 are controlled according to the detected impedance.

  A method for detecting the impedance of the source device 2 in the audio amplifier 1 will be described with reference to FIG. FIG. 3A is a basic configuration diagram of a low-pass filter. A resistor R is inserted in series on the hot side of the signal line, and a capacitor C is connected in parallel between the hot side and the cold side of the signal line. These R and C determine the filter characteristics, that is, the cutoff frequency Fc. FIG. 3B is a diagram showing basic frequency characteristics of the low-pass filter shown in FIG. There is a passband with a flat gain on the low frequency side, and there is a transient region where the gain gradually decreases from this passband toward the cutoff band. The frequency at which the gain decreases by −3 dB from the pass band in this transient region is called a cutoff frequency Fc.

  In the audio amplifier 1, as shown in FIG. 3C, the impedance of the source device 2 is regarded as R of the low-pass filter, and the variable capacitor 122 of the own device is regarded as C of the low-pass filter, and the cut-off frequency Fc is measured. The impedance Z of the source device 2 is detected based on this Fc.

That is, in FIG. 3C, a signal is input from the cold terminal 11B of the input terminal 11, passed through the source device 2 (impedance Zout), and returned to the hot terminal 11A is converted into a digital signal after the variable capacitor 122. Then, the cut-off frequency Fc is measured by taking it into the control unit 10 and performing FFT. Then, the impedance Zout of the source device 2 is detected based on this Fc and C of the own device (known). Zout (that is, R) is based on the characteristic expression Fc = 1 / 2πRC of the low-pass filter,
Zout = 1 / (2πC · Fc)
Is calculated by

  Here, it is estimated that the source device 2 and the cable 3 include a capacitance component and an inductance component. Ignoring this, the value C of the variable capacitor 122 is set to a sufficiently large value so that the impedance of the source device 2 can be handled as R, and the capacitance of the variable capacitor 122 is dominant in the low-pass filter system. In addition, the cutoff frequency Fc is measured in a state where the cutoff frequency Fc is shifted to a low value.

  FIG. 4 is a flowchart showing impedance setting processing by the control unit 10. First, the changeover switch 120 is switched to the variable capacitor 121 side (S1). Then, the capacitance of the variable capacitor 121 is set to the minimum (S2). Thereafter, a signal (white noise) is injected from the cold terminal 11B (S3). As a result of the signal injection, it is determined whether or not a signal is returned from the source device 2, that is, whether or not a signal is input from the A / D converter 17 to the control unit 10 (S4). If no signal is detected (NO in S4), it is determined that a device having an active drive circuit such as a preamplifier or an effector is connected, and that the impedance (output impedance) is a low value of 1 kΩ or less. (S15), the process proceeds to S12.

  On the other hand, when a signal is detected in S4 (YES in S4), a signal level at a specific frequency Fs (for example, 1 kHz) is detected (S5). Then, the capacitance of the variable capacitor 121 is increased until the signal level at the specific frequency Fs decreases by −3 dB (S6 to S8). As a result, the impedance Z of the source device 2 and the cut-off frequency Fc of the low-pass filter constituted by the variable capacitor 122 become the specific frequency Fs.

  Then, the capacitance C of the variable capacitor 122 is further increased by n (= 10) times (S9). As a result, the cut-off frequency Fc of the low-pass filter is reduced to about 1 / n. However, it is not exactly 1 / n, and the influence of the capacitance component and the inductance component included in the source device 2 is reduced. The signal input in this state is FFT to detect the cutoff frequency Fc (S10), and R, that is, the impedance Zout of the source device 2 is calculated based on the detected cutoff frequency (S11).

  After the above processing, signal injection is stopped (S12), the resistance value of the variable resistor 121 is controlled to match the calculated (determined) impedance Z (S13), and the changeover switch 120 is set to the variable resistor 121. (S14) and the operation is terminated.

  Through the impedance setting process described above, the input impedance of the audio amplifier 1 can be automatically set according to the impedance of the source device 2. Furthermore, as shown in FIG. 5, the gain of the front amplifier 13 can be automatically set by additionally performing signal level estimation processing.

  The detection processing of the cut-off frequency Fc in S9 to S11 is performed a plurality of times while variously changing the capacitance value of the variable capacitor 122 set in S9, R is calculated for each Fc and C, and the average value thereof is calculated. Alternatively, the convergence value may be obtained as the impedance Zout of the source device 2.

  In the above embodiment, white noise is used as a test signal, but the test signal is not limited to white noise. For example, a sweep signal may be used as the test signal, and a level change curve of the return signal may be used as the frequency spectrum. In addition, signals having a plurality of frequencies may be generated sequentially or simultaneously.

  FIG. 5A is a flowchart showing the gain setting process of the control unit 10. FIG. 5B is a diagram illustrating a setting gain table stored in the control unit 10. 5A, first, the impedance setting process of FIG. 4 is executed (S21). Then, it is determined whether or not a signal return is detected from the source device 2 in this process (S22: same as S4 in FIG. 4). If no signal is returned (NO in S22), it is determined that a device such as a preamplifier or an effector classified as D in the table shown in FIG. The gain of the amplifier 13 is set small (S31). If there is a signal return (YES in S22), it is determined whether the calculated impedance Zout is greater than a predetermined value (for example, 1 kΩ) (S23). If impedance Zout is equal to or less than a predetermined value (NO in S23), it is determined that a device such as a dynamic microphone classified as C in the table shown in FIG. 5B is connected (determination C), and the front amplifier The gain of 13 is set small (S32).

  If the calculated impedance Zout is greater than the predetermined value (YES in S23), the source device 2 is assumed to be an electric guitar (pickup) or an electric base (pickup), and the changeover switch 120 is set to a state during normal operation. By switching, the user (performer) is instructed to play a trial (S24). For example, this instruction may be output by voice from the speaker 15. Here, it is instructed to play the opening of the A string (the fifth string of the guitar or the third string of the bass). The frequency of the input performance sound is measured (S25). If A1 (= 110 Hz), the source device 2 is determined to be an electric guitar (determination A). If A0 (= 55 Hz), the source device 2 is determined. It determines with it being an electric base (determination B). In determination A, it is determined that an electric guitar classified as A in the table shown in FIG. 5B is connected, and the gain of the front amplifier 13 is set to a medium level (S34). In the determination B, it is determined that the electric base classified into B in the table shown in FIG. 5B is connected, and the gain of the front amplifier 13 is set large (S33).

  In this example, the string to be played is the open A string, but any string may be used. For example, the lowest E string may be opened. Alternatively, the connected source device 2 may be determined not by the pitch of the input musical sound but by the volume. In that case, the player may perform at a normal volume (for example, mf), and the source device 2 (for example, an electric guitar, an electric bass, etc.) connected at the signal level at that time may be determined.

  4 and 5 may be executed at any time, but when the control unit 10 monitors the state of the input terminal 11 and changes from the open state to the conductive state, that is, some source device 2 is connected. It may be executed at the time.

DESCRIPTION OF SYMBOLS 1 Audio amplifier 2 Source equipment 11 Input terminal 11A Hot terminal 11B Cold terminal 120 Changeover switch 121 Variable resistor 122 Variable capacitor

Claims (6)

An input terminal to which a source device that outputs an audio signal is connected;
An audio amplifier with variable gain ,
A test signal generator;
A return signal analyzer for detecting the impedance of the source device ;
A switch that connects the audio amplifier to the input terminal during normal operation, and connects the test signal generator and the return signal analyzer to the input terminal during impedance detection of the source device;
With
When detecting the impedance of the source device,
The test signal generation unit generates a test signal and inputs the test signal to the source device via the input terminal,
The return signal analysis unit detects an impedance of the source device based on a frequency characteristic of a return signal that is a test signal returned to the input terminal, and controls an input impedance of the audio amplifier based on the detected impedance. Audio equipment to play . A capacitor connected in parallel to the return signal analyzer;
The audio device according to claim 1 , wherein the return signal analysis unit detects an impedance of the source device based on a characteristic of a low-pass filter including the source device and the capacitor. The capacitor is a variable element;
The return signal analysis unit detects the impedance of the source device after controlling the capacitance of the capacitor so that a cutoff frequency of the low-pass filter becomes a predetermined frequency when detecting the impedance of the source device. 2. The audio device according to 2 . The test signal generator generates white noise as the test signal,
The return signal analysis unit, an audio device according to any of claims 1 to 3 for detecting the impedance of the source device based on the frequency characteristics of the return signal. Comprising a variable impedance element connected in parallel to the audio amplifier;
The return signal analysis unit, an audio device according to any of claims 1 to 4 for controlling the input impedance of the audio amplifier by controlling the impedance value of the variable impedance element. The audio amplifier is a variable gain amplifier,
The return signals analysis unit, the detected audio device according to any one of claims 1 to 5 for controlling the gain of the audio amplifier based on the impedance of the source device.

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