FIELD OF THE APPLICATION
[0001] This application relates to the field of wireless devices, and more specifically,
to a method and system for controlling a maximum signal level output to headphones
coupled to a wireless device.
BACKGROUND
[0002] Current wireless mobile communication devices include microprocessors, memory, soundcards,
speakers, headphones, and run one or more software applications in addition to providing
for voice communications. Examples of software applications used in these wireless
devices include micro-browsers, address books, email clients, instant messaging ("IM")
clients, and wavetable instruments. Additionally, wireless devices have access to
a plurality of services via the Internet. A wireless device may, for example, be used
to browse web sites on the Internet, to transmit and receive graphics, and to execute
streaming audio and/or video applications. Such wireless devices may operate on a
cellular network, on a wireless local area network ("WLAN"), or on both of these types
of networks.
[0003] One problem with current wireless devices pertains to the adjustment of maximum output
sound pressure levels for headphones coupled to such devices. Headphones are typically
used to listen to voice calls, radio programs, audio programs (e.g., music), etc.,
stored on or accessed by the wireless device. In particular, the maximum output sound
pressure level for headphones for wireless devices and handheld products is legally
constrained in several jurisdictions in order to protect users from hearing loss.
For example, European Standard EN 50332-1:2000, dated March 2000 and entitled "Sound
System Equipment: Headphones And Earphones Associated With Portable Audio Equipment
- Maximum Sound Pressure Level Measurement Methodology And Limit Considerations -
Part 1: General Method For 'One Package Equipment"', and which is incorporated herein
by reference, restricts maximum sound pressure level at the headphones (i.e., for
headphones provided with the portable audio equipment and from the same manufacturer)
to 100 dB. In addition, European Standard EN 50332-2:2003, dated October 2003 and
entitled "Sound System Equipment: Headphones And Earphones Associated With Portable
Audio Equipment - Maximum Sound Pressure Level Measurement Methodology And Limit Considerations
- Part 2: Matching Of Sets With Headphones If Either Or Both Are Offered Separately",
and which is incorporated herein by reference, restricts maximum sound pressure level
at the headphones (i.e., for headphones provided separately from the portable audio
equipment by a different manufacturer) to 94 dB. Measurement of maximum sound pressure
levels according to these standards is specified with respect to headphones having
an impedance of 32 Ohms. One problem relating to such standards is that in order to
set the output signal level (e.g., in mV RMS) appropriately at the output jack of
the wireless device in order to meet the maximum sound pressure level specified, the
impedance of the headphones must be known. This is especially problematic if the headphones
are not provided by the manufacturer as a package with the wireless device.
[0004] A need therefore exists for an improved method and system for controlling a maximum
signal level output to headphones coupled to a wireless device. Accordingly, a solution
that addresses, at least in part, the above and other shortcomings is desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Features and advantages of the embodiments of the present application will become
apparent from the following detailed description, taken in combination with the appended
drawings, in which:
[0006] FIG. 1 is a front view illustrating a wireless device coupled to headphones and adapted
for implementing an embodiment of the application;
[0007] FIG. 2 is a block diagram illustrating the wireless device of FIG. 1 and a wireless
network adapted for implementing an embodiment of the application;
[0008] FIG. 3 is a block diagram illustrating a memory of the wireless device of FIGS. 1
and 2;
[0009] FIG. 4 is a block diagram illustrating a headphones subsystem in accordance with
an embodiment of the application;
[0010] FIG. 5 is a block diagram illustrating an alternate headphones subsystem in accordance
with an embodiment of the application; and,
[0011] FIG. 6 is a flow chart illustrating operations of modules within the memory of a
wireless device for controlling maximum signal level output to headphones of the wireless
device, in accordance with an embodiment of the application.
[0012] It will be noted that throughout the appended drawings, like features are identified
by like reference numerals.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0013] In the following description, details are set forth to provide an understanding of
the application. In some instances, certain software, circuits, structures and techniques
have not been described or shown in detail in order not to obscure the application.
Embodiments of the present application may be implemented in any computer programming
language provided that the operating system of the wireless device or data processing
system provides the facilities that may support the requirements of the application.
Any limitations presented would be a result of a particular type of operating system
or computer programming language and would not be a limitation of the present application.
Embodiments of the preset application may also be implemented in hardware or in a
combination of hardware and software.
[0014] According to one embodiment of the application, there is provided a method for controlling
a maximum signal level output to headphones of a wireless device. The method includes:
determining an impedance of the headphones; determining a carrier specific maximum
signal level for headphones having the impedance; and, adjusting an audio amplifier
of the wireless device coupled to the headphones to restrict the maximum signal level
output to the headphones to the carrier specific maximum signal level.
[0015] FIG. 1 is a front view illustrating a wireless device
100 coupled to headphones
105 (a.k.a., headphone set, headphone, headset, earphone, earphones, etc.) and adapted
for implementing an embodiment of the application. The wireless device
100 includes a casing
150, a display screen
122, a graphical user interface ("GUI")
180 displayed on the display screen
122, a keyboard (or keypad)
132, a trackball (or thumbwheel)
110, various select buttons
120, various inputs/outputs (e.g., power connector jack, data interface ports, etc.)
160, and a headphones jack
106. Internally, the wireless device
100 includes one or more circuit boards (not shown), a CPU
138, memory
124, 126, 200, a battery
156, an antenna (not shown), etc., which are operatively coupled to the various inputs/outputs
160, the keyboard
132, the display screen
122, the headphones jack
106, etc., as will be described below.
[0016] The headphones
105 are coupled to the wireless device
100 by a headphones cable or lead
107 which is inserted into the headphones jack
106. The headphones
105 include a speaker assembly which is inserted into or placed over a user's ear. According
to one embodiment, the headphones
105 include two speaker assemblies, one for each of the user's ears. Each speaker assembly
includes a speaker having an impedance (referred to as the impedance of the headphones
in the following). The headphones
105, headphones jack
106, and headphones cable
107 may be configured for stereo and/or mono operation. When the headphones cable
107 is inserted into the headphones jack
106, audio output signals may be switched from the internal speaker
134 (see FIG. 2) to the headphones
105. Control of audio signal level (e.g., in mV RMS) output to the headphones
105 is performed by a headphones subsystem
400 as described below. According to one embodiment, the headphones jack
106 is a 3.5 mm headset jack adapted to support both a stereo headphones output and a
mono microphone input.
[0017] FIG. 2 is a block diagram illustrating the wireless device
100 of FIG. 1 and a wireless network
220 adapted for implementing an embodiment of the application. The wireless network
220 may include antenna, base stations, access points, transceivers, supporting radio
equipment, etc., as known to those of ordinary skill in the art, for supporting wireless
communications between the wireless device
100 and other devices (not shown).
[0018] The wireless device
100 may be a two-way communication device having at least voice and advanced data communication
capabilities, including the capability to communicate with other devices. Depending
on the functionality provided by the device
100, it may be referred to as a data messaging device, a two-way pager, a cellular telephone
with data messaging capabilities, a wireless Internet appliance, a data communication
device (with or without telephony capabilities), a Wi-Fi device, a WLAN device, a
dual-mode (i.e., Wi-Fi and cellular) device, or a portable audio device.
[0019] The wireless device
100 has a communication subsystem
111, which includes a RF receiver, a RF transmitter, and associated components. As will
be apparent to those skilled in the field of communications, the particular design
of the communication subsystem
111 depends on the communication network
220 in which the device
100 is intended to operate.
[0020] The device
100 may be capable of cellular network access and hence the device
100 may have a subscriber identity module (or "SIM" card)
162 for inserting into a SIM interface ("IF")
164 in order to operate on the cellular network (e.g., a global system for mobile communication
("GSM") network).
[0021] The device
100 may be a battery-powered device and so it may also include a battery IF
154 for receiving one or more rechargeable batteries
156. The battery (or batteries)
156 provides electrical power to most if not all electrical circuitry in the device
100, and the battery IF
154 provides for a mechanical and electrical connection for it.
[0022] The wireless device
100 includes a microprocessor
138, also called a processor, which controls overall operation of the device
100. The microprocessor
138 interacts with device subsystems such as the display
122, a flash memory
124 or other persistent store, a random access memory ("RAM")
126, auxiliary input/output ("I/O") subsystems
128, a serial port (e.g., a universal serial bus ("USB") port)
131, the keyboard
132, the trackball or thumbwheel
110, the headphones
105, an internal speaker
134, a microphone
136, a short-range communications subsystem
141, and other device subsystems
142. The microprocessor
138, in addition to performing operating system functions, preferably enables execution
of software applications on the device
100.
[0023] FIG. 3 is a block diagram illustrating a memory
200 of the wireless device
100 of FIGS. 1 and 2. The microprocessor 138 is coupled to the memory
200. The memory
200 has various hardware and software components for storing information (e.g., instructions,
data, database tables, test parameters, etc.) for enabling operation of the device
100 and may include flash memory
124, RAM
126, ROM (not shown), disk drives (not shown), etc. In general, the memory
200 may include a variety of storage devices typically arranged in a hierarchy of storage
as understood to those skilled in the art.
[0024] Operating system ("O/S") software modules
202 used by the microprocessor
138 may be stored in a persistent store such as the flash memory
124, which may alternatively be a read-only memory ("ROM") or similar storage element
(not shown). Those skilled in the art will appreciate that the operating system, specific
device applications, or parts thereof, may be temporarily loaded into a volatile store
such as RAM
126.
[0025] To provide a user-friendly environment to control the operation of the device
100, operating system ("O/S") software modules
202 resident on the device
100 provide a basic set of operations for supporting various applications typically operable
through the GUI
180 and supporting GUI software modules
204. For example, the O/S
202 provides basic input/output system features to obtain input from the auxiliary I/O
128, the keyboard
132, the trackball or thumbwheel
110, and the like, and for facilitating output to the user through the display
122, the speaker
134, the headphones
105, etc. According to one embodiment, the wireless device
100 is provided with hardware and/or software modules 206 for facilitating and implementing
the method of the application as will be described below.
[0026] A user may interact with the wireless device
100 and its various software modules
202, 204, 206, using the GUI
180. GUIs are supported by common operating systems and provide a display format which
enables a user to choose commands, execute application programs, manage computer files,
and perform other functions by selecting pictorial representations known as icons,
or items from a menu through use of an input or pointing device such as a trackball
or thumbwheel
110 and keyboard
132. The GUI
180 may include a cursor
190, various selectable objects and icons
191, and various windows
192.
[0027] Thus, the wireless device
100 includes computer executable programmed instructions for directing the device
100 to implement the embodiments of the present application. The programmed instructions
may be embodied in one or more hardware or software modules
206 which may be resident in the memory
200 of the wireless device
100. Alternatively, the programmed instructions may be embodied on a computer readable
medium (such as a CD disk or floppy disk) which may be used for transporting the programmed
instructions to the memory of the wireless device
100. Alternatively, the programmed instructions may be embedded in a computer-readable
signal or signal-bearing medium that may be uploaded to a network
220 by a vendor or supplier of the programmed instructions, and this signal or signal-bearing
medium may be downloaded through an interface
111, 131, 141 to the wireless device
100 from the network
220 by end users or potential buyers.
[0028] FIG. 4 is a block diagram illustrating a headphones subsystem
400 in accordance with an embodiment of the application. Components of the headphones
subsystem
400 are generally contained in the wireless device
100 and are used to determine the impedance of the headphones
105 in order to adjust the maximum signal level (e.g., in mV RMS) output to the headphones
105 (and hence the maximum sound pressure level output by the headphones
105).
[0029] According to one embodiment, the headphones system
400 includes a signal generator
410, a digital to analog converter ("DAC")
440, and an audio amplifier
430 for generating an inaudible high frequency signal (e.g., 25 kHz). The signal generator
410, DAC
440, and audio amplifier
430 are controlled by the microprocessor
138. The audio amplifier
430 is coupled to the headphones
105 through a series resistor
R. The series resistor
R may have a low value (e.g., 5 Ohms). A voltage
V produced across the resistor
R when the high frequency signal is applied to the resistor
R and headphones
105 is indicative of the impedance
Z of the headphones
105. The signal may be applied to the resistor
R and headphones
105 whenever the headphones
105 are connected to the headphones jack
106 via the headphones cable
107. The voltage
V is amplified by a microphone pre-amplifier
450 which is coupled to an analog to digital converter ("ADC")
420. The ADC
420 monitors the voltage
V and provides a digital signal indicative of the voltage
V and hence the impedance
Z of the headphones
105 to the microprocessor
138. The ADC
420 may also be used by the microphone
136 of the wireless device
100 in order to reduce component count. The microprocessor
138 receives the digital signal from the ADC
420 and determines the impedance
Z of the headphones
105 from it (e.g., by voltage divider principles, etc.). The microprocessor
138 may do this by accessing a table that stores voltage values (or digital signal values)
and corresponding headphones impedance values.
[0030] Having determined the impedance
Z for the headphones
105, the microprocessor
138 controls the audio amplifier
430 to restrict the maximum signal level (e.g., in mV RMS) output to the headphones
105. In this way, the sound pressure level output by the headphones
105 may be restricted to a maximum sound pressure level for the determined impedance
Z. The microprocessor
138 may do this by accessing a table (e.g., included in or associated with modules
206) that stores headphones impedance values, corresponding maximum signal level values
for the audio amplifier
430, and/or corresponding maximum sound pressure values for the headphones
105. For example, for a headphones impedance value of approximately 32 Ohms, the table
406 may indicate that the maximum sound pressure level for the headphones
105 is 100 dB.
[0031] According to one embodiment, if a headphone impedance value corresponding to the
determined headphone impedance
Z is not listed in the table
406, no maximum signal level for the audio amplifier
430 and no maximum sound pressure level for the headphones
105 is prescribed and hence the maximum signal level of the audio amplifier
430 and the maximum sound pressure level for the headphones
105 are not restricted for that value of determined headphones impedance
Z.
[0032] Now, the maximum signal level (e.g., in mV RMS) and/or the maximum sound pressure
level (e.g., in dB) for a given headphones impedance may be set by government regulation
which may change depending on the carrier or the location in which the wireless device
100 is operating or is sold. As is known to those skilled in the art, the wireless device
100 has means for determining its carrier and/or location and hence the government regulations
that may apply to set maximum signal levels and/or maximum sound pressure levels.
Thus, according to one embodiment, the microprocessor
138 receives a signal indicative of the carrier and/or location of the wireless device
100 and determines whether a maximum signal level value and/or a maximum sound pressure
level value has been prescribed for the carrier and/or location and for the determined
headphones impedance
Z. The microprocessor
138 may do this by accessing a table
406 that stores wireless device location, corresponding headphones impedance values,
corresponding carrier (or location) specific maximum signal level values (if any)
for the audio amplifier
430, and/or corresponding carrier (or location) specific maximum sound pressure level
values (if any) for the headphones
105. For example, the table may indicate that if the wireless device
100 is associated with a carrier based in Great Britain and if the headphones impedance
is 32 Ohms (i.e., +/- 20%), then the maximum sound pressure level should be restricted
to 100 dB (i.e., if the headphones
105 and wireless device
100 are sold as a package). As another example, the table
406 may indicate that if the wireless device
100 is associated with a carrier based in Great Britain and if the headphones impedance
is 32 Ohms (i.e., +/- 20%), then the maximum sound pressure level should be restricted
to 94 dB (i.e., if the headphones
105 and wireless device
100 are not sold as a package).
[0033] Similarly, the maximum signal level (e.g., in mV RMS) and/or the maximum sound pressure
level (e.g., in dB) may be set by government regulation which may change depending
on the carrier or the location in which the wireless device
100 is operating or is sold (i.e., irrespective of the impendence of the headphones
105). Again, as is known to those skilled in the art, the wireless device
100 has means for determining its carrier and/or location and hence the government regulations
that may apply to set maximum signal levels and/or maximum sound pressure levels.
Thus, according to one embodiment, the microprocessor
138 receives a signal indicative of the carrier and/or location of the wireless device
100 and determines whether a maximum signal level value and/or a maximum sound pressure
level value has been prescribed for the carrier and/or location. The microprocessor
138 may do this by accessing a table
406 that stores wireless device carrier (or location), corresponding headphones impedance
values, corresponding carrier specific maximum signal level values (if any) for the
audio amplifier
430, and/or corresponding carrier specific maximum sound pressure level values (if any)
for the headphones
105. For example, the table
406 may indicate that if the wireless device
100 is associated with a carrier based in Great Britain, then the maximum sound pressure
level should be restricted to
100 dB (i.e., if the headphones
105 and wireless device
100 are sold as a package). As another example, the table
406 may indicate that if the wireless device
100 is associated with a carrier based in Great Britain, then the maximum sound pressure
level should be restricted to 94 dB (i.e., if the headphones
105 and wireless device
100 are not sold as a package).
[0034] According to one embodiment, updates to the table
406 storing carrier (or wireless device location), corresponding headphones impedance
values, corresponding carrier specific maximum signal level values (if any) for the
audio amplifier
430, and corresponding carrier specific maximum sound pressure level values (if any)
for the headphones
105 may be periodically downloaded to the wireless device
100 (e.g., over the network
220).
[0035] According to one embodiment, the carrier associated with the wireless device
100 may be determined from messages delivered to the wireless device
100 over the network
220. According to another embodiment, the carrier may be determined from information stored
in the wireless device's SIM card
162.
[0036] According to one embodiment, the location of the wireless device
100 may be determined from messages delivered to the wireless device
100 over the network
220. According to another embodiment, the location of the wireless device
100 may be determined by a global positioning system ("GPS") receiver (not shown) optionally
provided for the device
100. According to another embodiment, the location of the wireless device
100 may be determined from the location of antennae towers associated with the network
220 on which the wireless device
100 operates.
[0037] FIG. 5 is a block diagram illustrating an alternate headphones subsystem
400 in accordance with an embodiment of the application. In FIG. 5, a signal source
510 (e.g., microprocessor
138) generates a signal (e.g., an audio signal, an inaudible audio signal, etc.) that
is applied to a digital to analog converter ("DAC")
540. The output of the DAC
540 is conditioned
530 (e.g., amplified
430, etc.) to allow for impendence measurement
520 (e.g., via a resistor
R, etc.) of the headphones
105 connected to the headphones jack
506.
[0038] The application may provide several advantages. For example, the method of the present
application allows wireless devices
100 to restrict maximum signal levels and maximum sound pressure levels to prescribed
legal limits when necessary.
[0039] Aspects of the above described method may be illustrated with the aid of a flowchart.
FIG. 6 is a flow chart illustrating operations
600 of modules
206 within the memory
200 of a wireless device
210 for controlling maximum signal level output to headphones
105 of the wireless device
100, in accordance with an embodiment of the application.
[0040] At step
601, the operations
600 start.
[0041] At step
602, an impedance
Z of the headphones
105 is determined.
[0042] At step
603, a carrier specific maximum signal level for headphones having the impedance
Z is determined.
[0043] At step
604, an audio amplifier
430 of the wireless device
100 coupled to the headphones
105 is adjusted to restrict the maximum signal level output to the headphones
105 to the carrier specific maximum signal level.
[0044] At step
605, the operations
600 end.
[0045] The above described method is generally performed by the wireless device
100. However, according to one embodiment, the method can be performed by, or in combination
with, a data processing system (not shown) such a personal computer ("PC") or server,
a stereo system, a television system, etc.
[0046] While embodiments of this application are primarily discussed as a method, a person
of ordinary skill in the art will understand that the apparatus discussed above with
reference to a wireless device
100 and a data processing system, may be programmed to enable the practice of the method
of these embodiments. Moreover, an article of manufacture for use with a wireless
device
100 or data processing system, such as a pre-recorded storage device or other similar
computer readable medium including program instructions recorded thereon, may direct
the wireless device
100 or data processing system to facilitate the practice of the method of these embodiments.
It is understood that such apparatus and articles of manufacture also come within
the scope of the application.
[0047] The embodiments of the application described above are intended to be exemplary only.
Those skilled in this art will understand that various modifications of detail may
be made to these embodiments, all of which come within the scope of the application.