JP2010226329A - Portable terminal device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a portable terminal device capable of measuring the characteristics of an earphone connected to the portable terminal device by itself and correcting the characteristics. <P>SOLUTION: In the portable terminal device 100, switching means (switches 113-116) for selectively intervening resistors 121, 122 for impedance measurement on a signal channel having capacitors 117, 118 for DC cut-off between an amplifier part 112 and an output terminal 130. An audio signal for test is output from a signal processing part 111 in a state that the resistors 121, 122 are intervened in the signal channel, and a voltage of an intermediate point of a voltage dividing circuit configured by the earphone connected to the output terminal and the resistors is detected. The impedance of the earphone is measured based on the detected voltage of the intermediate point. Based on a result of measurement, low band boost correction of the output audio signal is executed so as to compensate the characteristics of a high pass band filter configured by the impedance of the earphone and the capacitors. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a portable terminal device to which an earphone can be connected.

  In recent years, various devices and models such as mobile phone terminals, PHS, and music terminals are commercially available as mobile terminal devices having earphone connection terminals. The earphone connection terminal allows a user to freely connect various types and characteristics of earphones. However, sound characteristics such as frequency characteristics are heard differently depending on the connected earphone.

  There are various types of earphones on the market, such as an impedance of 16Ω, 32Ω, and 64Ω. Recently, there is a GND bias type earphone amplifier that generates a negative power source using a charge pump or the like, but the output of a general earphone amplifier is biased by a DC power source. For this reason, a DC cut (DC blocking) capacitor (about 47 μF-220 μF) is used.

  As shown in FIG. 1, when the earphone 200 is connected to the earphone connection terminal of the terminal 100, the audio signal output from the signal processing unit 10 is amplified by the amplification unit (earphone amplifier) 11, and the DC cut capacitor 12 Is output to the earphone 200 via. In this case, a CR high-pass filter (HPF) is formed by the capacitor 12 and the impedance 13 of the earphone 200.

  FIGS. 2A and 2B are graphs showing the HPF characteristics when the impedance of the connected earphone 200 is 16Ω and 64Ω when the capacitance of the capacitor 12 for DC cut is 220 μF. Show. The horizontal axis of the graph represents frequency (Hz) and the vertical axis represents signal intensity (dB). As can be seen from both graphs, when earphones having different impedances are connected to the same capacitor 12, both frequency characteristics are different in the audible band of 20-20000 Hz.

  Also, the earphone itself has frequency sensitivity characteristics. FIG. 3 is a graph showing an example of frequency sensitivity characteristics of the earphone. The horizontal axis of this graph represents frequency (Hz), and the vertical axis represents sensitivity (dB). Thus, it can be seen that the earphone is not flat in the audible band of 20-20000 Hz.

  HPF is formed by these two factors: (1) DC cut capacitor and earphone impedance (when using a DC bias type earphone amplifier), and (2) Frequency sensitivity characteristics of the earphone itself. As a result, the sound output from the terminal is not reproduced with the earphone faithfully to the original sound.

  Patent Document 1 proposes an audio device that can adjust the state of an audio signal to be output in accordance with the impedance of a connection destination device and reduce the trouble of changing the connection device.

JP-A-9-148861

  The technique described in Patent Document 1 has a circuit and a control configuration for determining whether a connection destination device is an earphone or a line output cable and automatically adjusting an audio signal. However, it does not consider the detection of different types of earphones and the automatic correction of sound quality based on the detection.

  The present invention has been made in such a background, and allows the characteristics of an earphone connected to a mobile terminal device to be measured and corrected by the mobile terminal device itself.

  A portable terminal device according to the present invention includes a signal processing unit that processes an audio signal, an amplification unit that amplifies the output audio signal of the signal processing unit, an output terminal of the audio signal, and between the amplification unit and the output terminal. A signal path having a DC blocking capacitor, a switching means for selectively inserting a resistance for impedance measurement in the signal path from the amplifying unit to the output terminal, and a control means. The control means outputs a test audio signal from the signal processing unit in a state where the resistor is inserted in the signal path, and a voltage dividing circuit configured by the resistor and an earphone connected to the output terminal. An operation mode for detecting the voltage of the intermediate point and measuring the impedance of the earphone based on the detected voltage of the intermediate point is provided.

  The “earphone” in this specification is a means that is detachably connected to the mobile terminal device and converts an electrical audio signal into audio, regardless of whether it is stereo or monaural. In addition, so-called headphones are included.

  The control means controls the signal processing unit according to the impedance of the earphone measured by the measurement means, so as to compensate for the characteristics of the high-pass filter configured by the impedance of the earphone and the capacitor. Low frequency boost correction of the output audio signal can be performed.

  The control means further includes a microphone for converting sound into an electric signal, and outputs a test sound signal swept within an audible frequency range from the signal processing unit to the earphone, and the output sound is collected by the microphone. You may have the 2nd measurement mode which measures the frequency characteristic of the said earphone based on the input audio | voice signal obtained by sounding. In this case, the control means obtains characteristic correction data for correcting the frequency characteristic based on the frequency characteristic of the earphone measured in the second measurement mode, and determines the signal processing unit based on the characteristic correction data. It is possible to control and correct the frequency characteristic of the output audio signal.

  According to the present invention, in the mobile terminal device to which the earphone connection terminal is attached, the characteristics of the earphone connected by the user are measured by the mobile terminal device itself, and the characteristics of the output sound are corrected corresponding to each earphone. It becomes possible.

It is the figure which showed the structure of the output circuit to the earphone of the conventional terminal. 2 is a graph showing HPF characteristics constituted by a DC cut capacitor and an earphone shown in FIG. 1. It is the graph which showed the example of the frequency sensitivity characteristic of an earphone. It is the figure which showed the circuit structure of the principal part of the portable terminal device in embodiment of this invention. FIG. 5 is a diagram illustrating an extracted part of a measurement circuit for measuring the impedance of an earphone in the circuit of FIG. 4. It is the graph which showed the example of the pattern of the right-and-left impedance of the earphone measured at all the set frequencies. It is explanatory drawing of user operation at the time of the measurement of the frequency characteristic of the earphone in embodiment of this invention. It is the figure which showed the structural example of the principal part of the terminal utilized for the frequency characteristic measurement of the earphone in embodiment of this invention. It is the figure which showed the earphone data in embodiment of this invention typically in the table format. It is the figure which showed the example of the user interface screen in the terminal in embodiment of this invention. The flowchart of the process which unifies the 1st and 2nd measurement and correct | amends the acoustic characteristic of an earphone is shown. It is a flowchart which shows the additional process with respect to the process of embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

  FIG. 4 shows a circuit configuration of a main part of the mobile terminal device 100 according to the present embodiment. Hereinafter, the mobile terminal device is also simply referred to as “mobile terminal” or “terminal”.

  Stereo audio data (R audio and L audio) is output from the control unit 110, converted into analog signals by the signal processing unit 111, and amplified by the amplification unit 112. Both the left and right outputs of the amplifying unit 112 pass through the switches 113, 114, 115, and 116, and are output to the earphone jack 130 via the DC-cut capacitors 117 and 118. The switches 113, 114, 115, and 116 are linked under the control of the control unit 110 (that is, according to the control signal CNT1 from the control unit 110) to switch the signal path. That is, the switches 113, 114, 115, 116 constitute switching means for selectively inserting a resistance for impedance measurement in the signal path from the amplifying unit 112 to the earphone jack 130 that is an audio output terminal. This switching means switches whether the output of the amplifying unit 112 is directly passed to the capacitors 115 and 116, or is connected to the capacitors 117 and 118 via the resistors (R1) 121 and 122, respectively.

  When the signal processing unit 111 and the amplification unit 112 process a stereo signal, a pair of left and right audio signal paths, resistors, and output terminals are provided as shown in the figure. The controller 110 selectively detects the voltage at the left and right intermediate points. Therefore, the signal at the switch 115 side end of the resistor 121 and the signal at the switch 116 side of the resistor 122 are selectively input as digital signals to the control unit 110 via the ADC 119 by the switch 120. The switch 120 is switch-controlled by a control signal CNT2 from the control unit 110.

  Earphone jack 130 has an earphone detection terminal 131 (connection detection means) that is grounded when an earphone plug is inserted. Thus, the earphone connection detection signal is input to the control unit 110 when the earphone is connected. The control unit 110 controls the switches 113, 114, 115, and 116 to insert a measurement resistor in the signal path according to the detection output of the connection detection unit, and shifts to an operation mode for measuring the impedance of the earphone. This measurement is referred to as the first measurement.

  Connected to the control unit 110 are a CPU, other processors, a storage unit 151 including a memory such as a ROM and a RAM, a display unit 152 that displays information on a display screen, and an operation unit 153 that receives an information input operation from a user. The The control unit 110 may be in charge of reproduction processing of music data (music data) stored in the recording medium, or another dedicated reproduction processing unit (not shown) may be in charge.

  FIG. 5 shows an excerpt of the main part of the measurement circuit for measuring the impedance of the earphone connected to the earphone jack 130 in the circuit of FIG. In the operation mode in which the impedance of the earphone is measured, a test audio signal is output from the signal processing unit 111 with the impedance measurement resistor (R1) inserted in the signal path. Further, the voltage at the intermediate point of the voltage dividing circuit constituted by the resistor and the earphone connected to the audio output terminal is detected, and the impedance of the earphone is calculated based on the detected voltage at the intermediate point. For this purpose, in the measurement circuit, the test signal StR of the right audio with a predetermined frequency passes through the capacitor 117 and is grounded via the resistor 201 of the earphone. Therefore, a signal obtained by dividing the test signal StR by the resistors 121 and 201 appears at a point A which is an intermediate point between the resistors 121 and 201. Similarly, a test signal StL of a predetermined frequency of the left sound passes through the capacitor 118 and is grounded via the earphone resistor 202. Therefore, a signal obtained by dividing the test signal StL by the resistors 122 and 202 appears at a point B which is an intermediate point between the resistors 122 and 202. The signal at point A and the signal at point B are selectively input to the ADC 119 via the switch 120.

Here, the procedure of impedance measurement (first measurement) of the earphone 200 in the present embodiment will be described. Here, the impedance (right or left) of the earphone is R2. However, the left and right impedance values are not necessarily the same.
(1) When the control unit 110 detects that the plug of the earphone 200 is connected to the earphone jack 130, the impedance measurement mode which is the first measurement mode as one of the operation modes of the present embodiment is entered. In response to this, the control unit 110 switches the signal path switches 113, 114, 115, and 116 to the resistor R1 side.
(2) The control unit 110 outputs an audio signal of a sine wave set at a certain frequency (f1).
(3) The ADC 119 measures the voltage value divided by the resistor R1 and the earphone resistance value R2.
(4) By inputting the output data of the ADC 119 to the control unit 110, the control unit 110 measures the voltage at the midpoint at the f1 frequency of the earphone. This voltage can be obtained from the effective value, peak value, etc. of the sine wave.
(5) The impedance of the earphone is measured by changing the sound output frequency in (2) and performing the measurement in the same procedures (3) and (4).
(6) Determine the impedance of the earphone from the result of the frequency characteristics of all the set frequencies.
(7) The switch 120 is switched to execute (2) to (6).
(8) After the impedance of the earphone is determined, the impedance measurement mode is terminated, the signal path switches 113, 114, 115, and 116 are controlled, and the voice path is switched to return to the original state.

  FIG. 6 is a graph illustrating the left and right impedance patterns of the earphones measured at all the set frequencies. As the measured representative impedance (representative value) of the earphone, an average value of impedances of all frequencies can be taken. However, as shown in FIG. 2, in the HPF characteristics of the DC cut capacitor, signal degradation on the low frequency side becomes a problem. Therefore, in the present embodiment, the impedance measured in the low band is used as the representative impedance of the earphone.

  Note that (7) can be omitted by assuming that the left and right impedances of the earphones are the same. Further, the frequency for measuring the impedance may not be the entire frequency range, but only a part of the frequency range (for example, a low frequency range).

  The HPF characteristics are corrected according to the representative impedance of the earphone obtained in this way. For example, as shown in FIGS. 2A and 2B, the lower the impedance, the greater the attenuation in the low band. Therefore, the control unit controls the signal processing unit 111 according to the measured impedance of the earphone, and reduces the output audio signal so as to compensate for the characteristics of the high-pass filter formed by the impedance of the earphone and the capacitor. Perform band boost correction. For example, the low frequency boost correction of the audio signal output by the signal processing unit 111 is performed as follows according to the impedance value.

Impedance (16Ω) → Low frequency boost correction: Strong impedance (32Ω) → Low frequency boost correction: Medium impedance (64Ω) → Low frequency boost correction: None

  Since these depend on the DC cut capacitor, the correction amount can be changed depending on the capacitance.

  Next, a method for measuring the frequency characteristic (sensitivity frequency characteristic) of the earphone according to the present embodiment will be described. This measurement is called the second measurement, and the operation mode is called the second measurement mode.

  FIG. 7 is an explanatory diagram of a user operation when measuring the frequency characteristic of the earphone 200 in the present embodiment. In this example, a mobile phone terminal is shown as the mobile terminal. As illustrated, a test audio signal having a predetermined frequency is output from the terminal 100 to the earphone 200. The speaker unit is held or arranged close to the microphone 140 so that the sound generated from the left or right speaker unit to be measured can be picked up by the microphone 140 of the terminal 100. As is well known, the speaker unit is a device that converts an electric signal into sound, and the microphone 140 is a device that converts sound into an electric signal.

  FIG. 8 shows a configuration example of a main part of the terminal 100 used for this measurement. As described above, the earphone 200 is supplied with the test audio signal from the signal processing unit 111 and the amplification unit 112. The sound generated from the left or right measurement target speaker unit is collected by the microphone 140 of the terminal 100, and the output signal of the microphone 140 is converted into a digital value by the ADC 150 and input to the control unit 110. In this way, the level of the signal output from the microphone 140 is measured. The level of the test audio signal given to the earphone 200 is constant, and a frequency SWEEP (sweep) signal whose frequency is continuously converted in a predetermined frequency range is output, and the level of the output signal of the microphone 140 is measured. The frequency characteristic of the earphone 200 can be measured.

  The specific measurement procedure of the frequency sensitivity characteristic of the earphone is as follows.

(1) Press the sound output part of the earphone against the microphone.
(2) Set the transfer function of the earphone.
In general, there are open types of earphones with a sponge cover attached to the ears and canal types with a silicon cover attached to the ears. The low frequency sound is more likely to leak outside with the open type, and the low frequency sound is less likely to leak outside with the canal type. Therefore, a transfer function difference depending on the type of the earphone is absorbed by having a representative value of a transfer function that absorbs these differences before measuring inside the terminal and setting it before measurement.
(3) Measure external noise.
At this time, the output signal of the microphone 140 is measured without giving a test sound signal to the earphone 200. By subtracting the external noise thus obtained from the subsequent measurement data, the influence of environmental noise can be reduced.
(4) A frequency SWEEP signal is output from the control unit 110, measured by the ADC 150, and frequency analysis calculation is performed by the control unit 110. Thereby, the frequency sensitivity characteristic of the earphone can be obtained.

  In order to reduce the influence of external noise, it is considered that the same measurement is repeated a plurality of times.

  FIG. 9 schematically shows the earphone data stored in a memory (not shown) in the terminal 100 as a result of the measurement of the impedance of the earphone in a table format.

  Each time a new earphone is connected to the terminal, the impedance is measured, and the measurement data and characteristic correction data determined based on the measurement data are saved as earphone data for each earphone. In the illustrated example, each earphone data includes “earphone name”, “representative impedance”, “impedance pattern”, and “characteristic correction data”. The “earphone name” is a name of the earphone that can be given by the user as will be described later. As described above, “representative impedance” is a representative impedance value of the earphone obtained as a result of measurement. The “impedance pattern” is a pattern indicating the frequency characteristics of the measured impedance. This impedance pattern is a data group indicating a relationship between a frequency in a specific frequency range and a measured impedance value, or a pattern name representing the data group. “Characteristic correction data” is data for correcting an audio output characteristic (acoustic characteristic) determined for the earphone.

  FIG. 10 shows an example of a user interface screen on the terminal in the present embodiment. FIG. 10 (a) shows the case where the earphone is determined to be a new earphone for the terminal after the impedance measurement of the earphone is performed when the earphone is connected to the terminal. The screen example which requests | requires giving arbitrary names with respect to it is shown. That is, when it is determined that a new type of earphone is connected, the user is prompted to input the name of the earphone. In response, the earphone name input by the user is stored in the storage unit together with the measured representative impedance value, impedance pattern, and characteristic correction data. FIG. 10B shows the result of the measurement after the impedance measurement, when the earphone is measured in the past and is assumed to be a specific earphone holding data, the earphone name is presented to the user for confirmation. An example of a screen to be obtained is shown. That is, when it is determined that a stored earphone is connected, the name of the earphone is displayed on the display screen to prompt the user to confirm whether the connected earphone is the earphone. If the user's confirmation is “No”, the process proceeds to the second measurement mode, and if “Yes”, the characteristic correction data of the earphone with the earphone name is used.

  FIG. 11 shows a flowchart of a process for correcting the sound output characteristic of the earphone by integrating the first and second measurements described above. This process is a process executed by each unit of the mobile terminal 100 under the control of the control unit 110 (FIG. 4).

  “Earphone connection”, that is, whether or not the earphone 200 (plug) is inserted into the earphone jack 130 is monitored (S1). When the earphone connection is detected, it is checked whether or not the amplification unit of this terminal is a DC bias amplifier (S2). If it is a DC bias amplifier (Yes “Yes”), the process proceeds to Step S3. If not (No “No”), the process proceeds to Step S13. Note that step S2 may be omitted when this process is applied only to a terminal equipped with a DC bias amplifier.

  In step S3, the operation mode is switched to the impedance measurement mode. In this operation mode, a frequency for determining impedance is set (S4), and an audio output signal (sine wave) of that frequency is output (S5). Therefore, the voltage at the intermediate point is measured (S6). The impedance is calculated based on the measurement result (S7). Until the measurement for all the frequencies to be measured is completed, the process returns to step S4 to repeat the measurement.

  When measurement for all frequencies is completed (S8, Yes), the earphone impedance (representative value) is specified, and the frequency characteristic (impedance pattern) is stored (S9).

  When this impedance pattern is compared with the stored impedance pattern, when there is a matching impedance pattern, that is, when it is confirmed that this earphone is the earphone that has been measured in the past (S10, No), The past correction data is read (S22), and the process proceeds to step S21.

  For the earphones that have not been measured in the past, the voice path frequency characteristics are corrected according to the measured earphone impedance (S11), and the impedance measurement mode is terminated (S12).

  Next, the measurement mode of the earphone frequency characteristic which is the second measurement mode of the present embodiment is entered, and the measurement is started (S13). In the measurement of the earphone frequency characteristics, a test sound signal swept within the audible frequency range is output from the signal processing unit 111 to the earphone 200, and the output sound is obtained by collecting the output sound with the microphone. Based on the above, the frequency characteristics of the earphone are measured.

  Specifically, first, a transfer function between the earphone and the microphone is set (S14). This is because, even if the positional relationship between the earphone and the microphone is constant, for example, the transfer characteristic from the earphone to the microphone differs depending on the type of the earphone (open type, canal type, etc.). The transfer function is selected by specifying the earphone type.

  Next, environmental noise is measured (S15). This is a process for detecting an audio signal obtained from a microphone in a state where no audio signal is output to the earphone and estimating environmental noise. The environmental noise obtained in this way is used to cancel out the results of subsequent frequency measurements.

  Therefore, the determination sound frequency is set (S16). For example, a sweep start frequency, a frequency interval, and a transmission end frequency are set, and based on these, a frequency sweep signal of a sine wave in a predetermined frequency range is output as “determination voice output” (S17). The microphone sound is analyzed for such a determination sound output (S18). Steps S16 to S18 are repeatedly executed until the measurement of the set frequency range is completed. When completed (S19, Yes), the process returns to step S15, and such measurement processing is repeated N-1 times (N is a plurality). As a result, N measurement results are obtained, and the measurement results for each frequency are calculated from the average value and the like.

  Based on the measurement result thus obtained, the earphone frequency characteristic is corrected (S21). That is, based on the frequency characteristic of the earphone measured in the second measurement mode, characteristic correction data for correcting the frequency characteristic is obtained, the signal processing unit 111 is controlled based on the characteristic correction data, and the output audio signal Correct the frequency characteristics. For example, when the sensitivity frequency characteristic of the earphone is as shown in FIG. 3, low-frequency boost correction and mid-range (1-4 KHz) attenuation correction are performed on the output audio signal, and the frequency sensitivity is included up to the earphone. Correct so that it becomes flat in the route. It also sets the overall volume control. Such correction data of the frequency characteristic of the earphone can be added to or stored as “characteristic correction data” in the table shown in FIG.

  In steps S15 to S20, in the case of stereo output, measurement may be performed separately on the right and left, or only one of them may be performed as a representative.

  By correcting the audio signal as described above, it is possible to absorb a difference in acoustic characteristics depending on the type of the earphone connected to the terminal and provide a reproduction environment faithful to the audio output from the terminal. Of course, after performing this correction, the user can set the sound quality as desired by setting the equalizer and changing the audio output parameter.

  Next, an additional process to the process of the above embodiment will be described with reference to FIG. This process further corrects the earphone frequency characteristics in accordance with the usage status / environment of the mobile terminal. Mobile terminals in recent years are equipped with devices for realizing various functions. Such functions include, for example, a GPS (Global Positioning System) function as a current position detection unit, an acceleration detection function by an acceleration sensor that detects the acceleration of the terminal, and the like in addition to the music playback function. The process of FIG. 12 is intended to provide an earphone frequency characteristic suitable for the use state and environment of such various functions.

  First, mobile terminal information, that is, the usage status / environment of the terminal is determined (S31). Here, it is terminal position information, acceleration information, attribute information of music (reproduced music) data, ambient noise level, and the like.

  Next, an optimum audio output parameter is obtained (S32). Although not shown in the drawing, a data table or the like in which appropriate audio output parameters are determined according to the contents of various types of portable terminal information as described above is prepared so that it can be referred to in the terminal or an external server. The earphone frequency characteristic is corrected based on the obtained audio output parameter (S33). Specific examples are shown below.

(1) Use of location information When the music playback function is used when going out, it is difficult to listen to music due to ambient noise in certain places such as downtowns and urban areas. Therefore, the current location is detected by the GPS function, and it is determined whether or not the current location belongs to the specific location by using a map database or the like in the terminal or an external server. If it belongs to a specific place, a predetermined audio output parameter is acquired correspondingly, and the earphone frequency characteristic is corrected based on this audio output parameter. More specifically, for example, the output sound can be easily heard by changing the frequency characteristics without changing the volume (emphasizing the output in the middle and high frequency bands, for example, the range of about 100 Hz to 10 KHz).

(2) Use of acceleration information It is possible to determine from the acceleration sensor built in the mobile terminal whether the user carrying the mobile terminal is walking or stationary. Therefore, for example, if the user is walking, the volume is reduced as a whole in consideration of the increased risk of traffic accidents if he cannot hear surrounding noise.

(3) Use of attribute information of music data When the attribute information, for example, the type of music (Pops, Rock, Classic, etc.), the singer's gender, etc. can be recognized from the music data, the audio output parameter suitable for the attribute information Is selected. For example, measures such as emphasizing the low frequency (100 Hz or less) and high frequency (5 KHz or more) if it is a lock, and emphasizing the voice band (1-4 KHz) if it is Pops. Further, for example, if the singer is male, the voice range (100 Hz-8000 Hz) is emphasized, and if the singer is female, measures such as highlighting the voice range (150 Hz-10000 Hz) are taken.

(4) Use of ambient noise level The noise level is determined with a microphone to improve the ease of listening to the output voice. For example, it is easier to hear by changing the frequency characteristics (emphasizing the mid-high range) instead of noise cancellation.

  The above processing is merely an example, and after obtaining a plurality of types of mobile terminal information, it is possible to comprehensively determine and set the audio output parameters.

  The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made.

  For example, the first and second measurement operations described above and the use of the measurement results are not necessarily used together as described above, and only one of them can be executed independently.

  The mobile terminal device is not limited to a mobile phone terminal, and the present invention can be applied to any portable terminal device having a DC cut capacitor in an audio output signal path.

  The process illustrated in FIG. 12 has been described as an additional process to the process illustrated in FIG. 11, but can be executed independently of the process illustrated in FIG. 11.

DESCRIPTION OF SYMBOLS 100 ... Portable terminal device, 110 ... Control part, 111 ... Signal processing part, 112 ... Amplification part, 113, 114, 115, 116 ... Switch, 117, 118 ... Capacitor, 120 ... Switch, 121, 122 ... Resistance, 130 ... Earphone jack, 131 ... Earphone detection terminal, 140 ... Microphone, 200 ... Earphone, 201, 202 ... Resistance

Claims (11)

A signal processing unit for processing an audio signal;
An amplifying unit for amplifying the output audio signal of the signal processing unit;
An audio signal output terminal;
A signal path having a DC blocking capacitor between the amplification unit and the output terminal;
Switching means for selectively interposing a resistor for impedance measurement in a signal path from the amplification unit to the output terminal;
A voltage at an intermediate point of a voltage dividing circuit configured to output a test audio signal from the signal processing unit in a state where the resistor is inserted in the signal path and is configured by the resistor and an earphone connected to the output terminal. And a control means having an operation mode for measuring the impedance of the earphone based on the detected voltage at the intermediate point.   Connection detecting means for detecting that an earphone is connected to the output terminal, and the control means inserts the measuring resistor in the signal path in accordance with a detection output of the connection detecting means. The portable terminal device according to claim 1, wherein the mobile terminal device shifts to an operation mode in which switching means is controlled to measure impedance of the earphone.   The signal processing unit and the amplifying unit process a stereo signal, and the signal path, the resistor, and the output terminal are provided in one set on each of the left and right sides, and the control unit selectively selects the voltage at the left and right intermediate points. The mobile terminal device according to claim 2, wherein the mobile terminal device is detected.   The control means controls the signal processing unit according to the impedance of the earphone measured by the measurement means, so as to compensate for the characteristics of the high-pass filter configured by the impedance of the earphone and the capacitor. The portable terminal device according to claim 1, wherein low-frequency boost correction is performed on the output audio signal.   The control means further includes a microphone for converting sound into an electric signal, and outputs a test sound signal swept within an audible frequency range from the signal processing unit to the earphone, and the output sound is collected by the microphone. The mobile terminal device according to claim 1, further comprising a second measurement mode for measuring a frequency characteristic of the earphone based on an input audio signal obtained by sound.   The control means obtains characteristic correction data for correcting the frequency characteristic based on the frequency characteristic of the earphone measured in the second measurement mode, and controls the signal processing unit based on the characteristic correction data. The portable terminal device according to claim 5, wherein the frequency characteristic of the output audio signal is corrected.   Storage means for storing characteristic correction data obtained in the second measurement mode for each earphone is further provided, and the control means has impedance of the earphone at a plurality of frequencies within an audible frequency range when the earphone is connected. Is stored in the storage means, and when the earphone is newly connected, the impedance of the earphone is measured and the impedance pattern is stored in the memory. 7. The portable terminal device according to claim 6, wherein when a matching impedance pattern exists in the means, the characteristic correction data for the earphone of the impedance pattern is read from the storage means and used when there is a matching impedance pattern.   A display unit that displays information on the display screen and an operation unit that receives an information input operation from the user, and prompts the user to input the earphone name when it is determined that a new type of earphone is connected. The portable terminal device according to claim 7, wherein the input earphone name is stored in the storage unit together with the measured representative impedance value, impedance pattern, and characteristic correction data.   When it is determined that the stored earphone is connected, the name of the earphone is displayed on the display screen and the user is prompted to confirm whether the connected earphone is the earphone. The mobile terminal device according to claim 7 or 8, wherein the mobile terminal device shifts to the second measurement mode if "", and uses the characteristic correction data of the earphone with the earphone name if "positive".   The mobile terminal information includes at least one of terminal position information, acceleration information, music (playback music) data attribute information, and ambient noise level, and the control means is based on the detected mobile terminal information. The mobile terminal device according to claim 1, wherein the earphone frequency characteristics are corrected. A signal processing unit for processing an audio signal;
An amplifying unit for amplifying the output audio signal of the signal processing unit;
An audio signal output terminal;
A microphone that converts audio into electrical signals;
Based on the input sound signal obtained by outputting a test sound signal swept within the audible frequency range from the signal processing unit to the earphone and collecting the output sound by the microphone, the frequency of the earphone Control means for measuring the characteristics;
A mobile terminal device.

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