A system comprising a passive headphone and an audio controller, and a method for measuring a sound level of a passive headphone

Abstract

There is provided a method for measuring sound pressure level of a passive headphone, wherein the passive headphone is connected to the audio controller, comprising measuring, by the audio controller, sound pressure level of the headphone in relation to electrical signal inputted to the passive headphone by using sensitivity of the passive headphone.

Description

TITLEA system comprising a passive headphone and an audio controller, and a method for measuring a sound level of a passive headphoneTECHNICAL FIELD

[0001] The present invention relates to a system comprising a passive headphone and an audio controller, and a method for measuring a sound level of a passive headphone.BACKGROUND

[0002] Knowing loudness of a headphone is important for ensuring to listen in a safe volume. In order to find this out, a decibel level of a headphone may be measured. There are accuracy issues in know measurements. One issue is dependency on a microphone in order to pick up the sound to be measured, for example possible calibration or non-calibration of the microphone, and a placement of a microphone at about the same distance as ear could be when using s headphone. In addition, different headphones output different decibel levels.SUMMARY

[0003] Aim is to enable measurement and indication a loudness of a headphone, and thereby enable safe use of the headphone.

[0004] The invention is defined by the features of the independent claims. Some embodiments are defined in the dependent claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] In the following embodiments are discussed in more detail with reference to the attached drawings, of which:

[0006] Figure 1A illustrates, by way of an example, a system comprising a passive headphone and an audio controller.

[0007] Figures IB and 1C illustrate, by way of an example, a system comprising a passive headphone, an audio controller and a computer.

[0008] Figure 2 illustrates, by way of an example, an audio controller.

[0009] Figure 3 illustrates, by way of an example, a computer.

[0010] Figure 4 illustrates, by way of an example, a method for measuring sound level of a passive headphone.

[0011] Figures are presented as illustrative examples and embodiments may not be limited solely to the illustrated parts, but modifications may be made under the scope as defined in the claims. Figures that may not fully present the claimed invention, aim to provide better understanding on the context and relating technical field.DESCRIPTION OF EMBODIMENTS

[0012] There is provided a measurement of a sound level for the sound output from a headphone. Sensitivity of a headphone is known or measured. Sensitivity enables measurement of sound pressure level, SPL, based on electrical input to the headphone. An audio controller is connected to a headphone and it enables measurement the sound level during use of the headphones, without additional or external devices. Sound level measurement and indication enables to gauge exposed sound level of a listener regularly. This enables to avoid unconscious hearing damage and to avoid hearing loss.

[0013] Different headphones are known to output at different sound pressure or decibel levels depending on their sensitivity. Sensitivity describes sound pressure level of outputted sound of a headphone in response to a given electrical input. Sensitivity may be measured per watts or per volts. Sensitivity may be one milliwatt, for example. In case impedance is measured in watts, also impedance of a headphone is needed for measuring sound pressure level. Impedance is a measure of resistance to current, measured in Ohms. Loudness of a headphone is dependent on sensitivity, or sensitivity and impedance, of the headphone, which may vary a lot among different headphones, models and manufacturers.

[0014] Audible sound variation in air pressure at frequencies audible to humans at magnitudes exceeding the human hearing threshold. Audible sound includes frequencies from 20 Hz to 20 kHz. Sound level is measured in decibels of sound pressure, dB SPL (sound pressure level), defines as 20 times the 10-base logarithm of the pressure variation root mean square, RMS, value divided by the pressure threshold value for human hearing, which is agreed to have value of 20 micro-Pascals, uP. RMS refers to amount of continuous poweran amplifier is able to output. Sound can be recorded, stored and played back as an electrical signal proportional to the instantaneous sound pressure. The electrical signal may be turned to a numerical representation. For example, the electrical signal is turned to a digital representation of sound by an analogue-to-digital converter. Such electrical signal may be processed by a signal processor. Audio signal refers to electrical representations of any sound, being typically music and speech. In the headphones, an electrical audio signal is converted into audible sound using transducers.

[0015] SI unit of a sound pressure is pascal, Pa. Decibels, dB, are units for measured sound pressure level, SPL. Decibels describe how loud a sound is using a calculation based on a ratio of two values of sound pressure level: an effective sound pressure and a reference value. The reference value may be a sound pressure in the air, being approximately 0 dB (or 20 uPa), which corresponds to the lowest sound pressure level that a human can hear. The effective value is a sound pressure level of the sound being measured. The ratio is on logarithmic scale: increase of 10 dB corresponds to tenfold increase in power. For example, 20 dB is 100 times more powerful than 1 dB. To a human ear, an increase of somewhere around 6 to 10 dB is sensed as being about twice as loud.

[0016] Although human hearing is very subjective, hearing loss begins at objective decibel levels. For example, the National Institute for Occupational Safety and Health (NIOSH) has recommended maximum of 85 dB in order to prevent hearing damage or loss. Longer durations of exposure to 85 dB, for example maximum of eight hours, are likely to cause hearing damage. There are different standards describing limit values and duration exposures. Laws determine noise exposure levels considered dangerous in terms of the risk of hearing loss. The laws also set limit values for noise exposure, for example for working conditions.

[0017] A passive headphone lacks an amplifier and a power source (battery) needed to drive transducers of a headphone to generate audio output. A passive headphone is therefore connected to an audio controller, which comprises a headphone amplifier and the power source components. The audio controller is configured to pass electrical signals to the passive headphone, where those are output as sound. A sound pressure level, SPL, of the passive headphone be may be measured at an audio controller, which is connected to a headphone. A sensitivity of the passive headphone is first known or measured. Some manufacturers provide information of SPL of their headphones. Sensitivity may bemeasured. The measurement may be implemented using a microphone. An electric signal of certain magnitude, for example frequency of 1 kHz and magnitude of 1 V, is inputted to the headphone by the audio controller. The sound output of the headphone is measured using the microphone, or an SPL meter comprising a microphone. This provides sensitivity of the headphone. Measured value is typically more accurate than information given by the manufacturer. Also, measured value is specific for the passive headphone. A further way to provide sensitivity of a passive headphone is from the factory calibration data of the passive headphone. The factory calibration provides accurate sensitivity value, among other values, for the passive headphone, and for both sides of the passive headphone. The factory calibration is discussed in more detail later in this application.

[0018] SPL describes amount of sound output by the headphone. This is dependent on electrical signal inputted from the audio controller. The relation of the inputted electrical signal and the outputted sound is used for measuring SPL in the audio controller. The electrical signal, or inputted electricity, may be presented in voltage (unit V), or power (unit W). A sensitivity of the passive headphone in dB SPL. It is known how many dB SPL is created per watt or per volt. In case of watts, also impedance of the passive headphone is used in order to provide dB SPL per volts. Magnitude of digital audio (sound sample) data is proportional to volts.

[0019] Sound level measurement may include volume of sound output from a headphone, or also duration of the sound output. Sound level measurement is implemented individually for both sides of the headphone, i.e., to input electric signal of the left and the right earpieces of the headphone separately.

[0020] A measured sound level may be measured constantly, or at certain time intervals. The results may be saved to a memory of the audio controller and / or to a computer connected to the audio controller. Warning may be provided in case a predetermined limit of the sound level is exceeded. A computer and / or the audio controller may display a warning. Warning may comprise displaying results, a light warning and / or a sound warning. This informs the user and thereby enables to avoid at least conscious damaging of hearing. Too loud or too long listening may be avoided. In addition, the saved results may be accessible. For example, an employer, or alike personnel may have access to the measured results. This enables to be aware of possible risks caused by earphones to a specific user.

[0021] The sound level measurement is applied to a passive headphone via an audio controller. Further, factory calibration settings of the headphone are taken into use in the audio controller and applied to electroacoustic signal inputted to the headphone. This enables to provide a predetermined output quality among the headphones. The calibrated headphones enable more accurate measurements for sound level of the headphones, which is dependent on sensitivity and impedance of the headphone.

[0022] An acceptable noise dose may be given by standards, laws or provided values. The audio controller may enable a user to select a noise dose measurement, or reference values, to be used. The used noise dose values vs. SPL provide a cumulative value. Realized vs. acceptable values may be followed up.

[0023] The audio controller comprises ability to measure sound pressure level, SPL. SPL may be measured from outputted sound using a microphone, and the measured value represents information on realized SPL. Measurement may be implemented continuously. In addition, or alternatively, SPL value may be dependent on volume settings, which may be scaled to an SPL reading, in decibels. While volume settings enable to set outputted SPL, the measured value (via microphone) should coincide with it, optionally at least on average, and / or at some tolerance. SPL may be presented to a listener. The audio controller may present SPL, as set and / or as measured, at its user interface, display or screen, for example. Presenting SPL enables the listener to be informed on the used volume level.

[0024] A passive headphone may be connected to an audio controller via a cable. The audio controller may be connected to a computer. The computer enables data transfer to the audio controller, and to view and adjust settings of the audio controller in order to adjust the audio output of the audio controller to the passive headphone. Factory calibration settings have been measured for each passive headphone by a manufacturer. The measured factory calibration settings have been associated to an identifier, like a serial number, of the passive headphone and the factory calibration data is saved, for example to a cloud. The factory calibration settings are accessible by using the identifier of the passive headphone. Each passive headphone has individual factory calibration settings associated with an individual identifier of the passive headphone. The factory calibration may be fetched via the computer, when the passive headphone, which is connected to the audio controller, is taken into use or being used. The factory calibration setting (or data) are used for the passive headphone by the audio controller in order to adjust a frequency response of the passive headphone. Theaudio controller performs signal processing configured to augment the frequency response of the passive headphone. Applying the factory calibration dedicated to the passive headphone has positive effect on characteristics and performance of the passive headphone.

[0025] The factory calibration here refers to data or settings that are determined for left and right sides of each passive headphone individually. The left and right sides refer to the left and right earpieces or earcups. This enables to adjust left and right sides of each passive headphone. This enables to unify the manufactured passive headphones in order to render the sound character neutral, i.e. uncoloured. The same applies between the left and right earcups of the passive headphone. Factory calibration enables reduction or elimination of unwanted left-right balance variation, or to reduce the effects to inaudible level or at least to an acceptable tolerance.

[0026] Factory calibration refers to data, for example settings for filters that are determined collectively or separately for the left and right sides of each individual passive headphone. Left and right sides refer to the left earcup containing the left ear transducers, and the right earcup containing the right ear transducers, correspondingly. Factory calibration enables a manufacturer to unify the manufactured passive headphones in order to render all headphones the same in terms of their acoustical characteristics, for example to set the sound character of a headphone neutral, i.e. subjectively uncoloured. The same may apply also between the left and right earcups, in which case the left side and the right side of the passive headphone will be acoustically similar. Thirdly, factory calibration may render the transduction efficiency, at least substantially, the same across passive headphones and passive headphone earcups. This results in the conversion sensitivity in a passive headphone to the same, i.e. how large sound pressure is generated for a certain magnitude of an electronic drive. Therefore, factory calibration enables reduction or elimination of unwanted left-right balance variation across the frequency as well as render all passive headphones to present the same sound character, or to reduce these effects to inaudible level or to at least an acceptable tolerance.

[0027] A binaural headphone comprises one transducer system for each ear of a user. The transducer system may comprise one or more electro-acoustic transducers configured to reproduce audio as a sound. A headphone may be located in various ways in relation to the ear(s). Over-the-ear, i.e., circumaural, headphone is configured to rest on the head and completely surrounds an external ear (pinna) of a user. On-the-ear (supra-aural) headphoneis configured to rest on the external ear (pinna) of a user. Over-the-concha (supraconcha) headphone is configured to rest on the concha area of an external ear of a user. In-ear (intraconcha) and insert headphone types are configured to deliver audio directly into an ear channel of a user. Resting on the head is typically cushioned in order to make listening comfortable. In addition, it may enable effective and repeatable sealing of the volume inside the headphone, to avoid variations in the headphone frequency response due to leakage of the pressure inside the headphone. Such variations in the headphone frequency response may otherwise be significant, reducing repeatability of the intended headphone frequency response.

[0028] An identifier comprises a unique, headphone-specific identifier of a passive headphone. The identifier may comprise a serial number of a passive headphone, or other identifier, such as an electronic tag, a radio frequency identification, RFID, tag, a memory chip, or a component integrated physically to the headphone, or any such unifier or transponder. An identifier may be attached to, associated with and / or made available in or with each passive headphone. The identifier enables unique identification of a specific headphone. The factory calibration may be fetched based on the identifier associated with the factory calibration. At the factory, the factory calibration of a specific passive headphone is saved to the audio controller paired and shipped with it. In addition, the factory calibration may be stored to a server, to a computer, to a remote device, to an external memory, to a cloud-based service, or alike storage which is accessible, for example, by a computer. The factory calibration may be accessible wirelessly or using a cable connection to a communication network or internet, for example.

[0029] A passive headphone comprises one or more transducers, which are configured to create acoustic pressure in response to an electrical input. Electrical input comprises an audio signal. In addition, a passive headphone may comprise passive electronic components configured to enable connectivity and divide the electrical input into multiple transducers. A passive headphone lacks active amplifier components and power source components, which are configured to generate electrical drive, like voltage or current, in order to drive the transducers and generate the audio output. A passive headphone is configured to be connected to an audio controller, which comprises the active amplifier components and power source components. The audio controller is configured to transmit electrical input (audio signal) to the passive headphone using a wired connection. The audio controller may further comprise a signal processor, analogue-to-digital and / or digital-to-analogueconverters. Since passive headphones do not comprise power sources or power generating amplifiers, running out of battery in the passive headphone is avoided. On the contrary, wireless active headphones, which contain a wireless audio interface, amplifier and power supply components, suffer from audio transfer delay, and may suffer from audio quality deterioration issues. The delay and audio quality change issues are typically created by the fact that the wireless audio signal interface must encode the audio signal into a format that can be effectively transmitted to the active headphone, frequently leading to audio resolution and fidelity changes, particularly considering that the electrical power for such processing, as well as for the amplification, must be supplied by the power supply components and (typically a rechargeable) battery built into the active headphone. Encoding and wirelessly transporting audio signal into the headphone requires time and causes delay to audio signals and output. The passive headphone without electric storage components or a battery, and having a cable connection to an amplifier of an audio controller, is able to avoid all these audio quality degradation and delay issues. For a passive headphone processing of audio data is handled in an external audio controller, and no delay-generating encoding of audio is needed.

[0030] Manufactured headphones typically have some variation between each other due to variations in components used in production. Variations during production may be caused by the manufacturing processes or the components, for example. By nature, mechanical sound reproduction systems, such as headphones, typically vary slightly in their frequency response. This may introduce unwanted variation in a sound colour rendering, as well as the sound balance as a function of frequency between the left and right side of the passive headphone. In order to avoid variations between the headphones, each passive headphone has been calibrated in the factory and possible variations are compensated by factory calibration. The factory calibration provides neutral sound for each headphone, the same sound character across all headphone units, and between the left and the right side of each headphone once the factory calibration is applied. Factory calibration measurements are done after headphone manufacture for each individual passive headphone side before the headphone is shipped. Left and right side of a passive headphone are separately measured. The measured factory calibration enables the frequency response of the passive headphone to be adjusted to a desired frequency response across all manufactured passive headphones. As it is then possible to render similar the left and right side of a headphone may be rendered similar, a monophonic sound image, represented by, at least substantially, the same audio inthe left and right earcups, may be adjusted to correctly appear in the middle of the sound presentation for the listener, and frequency dependent variation of the centre image may be avoided.

[0031] Factory calibration settings are measured at the end of the headphone assembly process, and each passive headphone is measured. Both earcups or both sides of the headphone are measured. The measurements per an earcup may comprise impedance, sensitivity, level and phase of the acoustic output for all frequencies, especially for the midrange frequencies, which may be from 500 Hz to 6 kHz. The measurements may be compared to predetermined target values, which may be determined to yield the desired subjective sound colour and performance. This target may be a neutral uncoloured sensation of the sound output for the listener and correct presentation of the sound image location for given electrical inputs to the left and right ear transducer systems. For example, the sound colour may be adjusted to a shape which delivers neutral sound for a diffuse field sound colour reference loudspeaker arrangement, such as specified in IEC 60268-7 (International Electrotechnical Commission, 2010, and other versions) and / or ITU BS.708 (International Telecommunication Union, Broadcasting Service, approved 1990-06, and other versions). Yet another target is the free-field target, which relates to a listening condition with lack of acoustic reflections and only direct sound from the sound source. In alternative Harman Target Curve variations may be utilized as targets. Harman Target Curve may comprise a headphone target curve being an idealized frequency response that is expected to satisfy the expectations and preferences of the majority of listeners.

[0032] As the headphone eliminates the natural effects of the head, torso, and external ears, the headphone may apply settings configured to emulate such natural effects, collectively referred to as the Head-Related Transfer Function, HRTF. HRTF is known to be personal and specifical for each person. Once the personal HRTF has been determined, binaural processing may use the HRTF information in order to render audio for headphone listening such that the audio signal appears to reside outside of the head and appears to be located in specific directions from the listener. Factory calibration of headphones may yield such binaural audio processing more reliable and accurate.

[0033] Neutral sound refers to reproduced sound not having coloration throughout the audible frequency range. A headphone with a neutral sound character delivers subjectively an even, honest, true and / or pure representation of the original audio data. In other words, atruly neutral headphone reproduces every frequency of sound across the whole range of hearing subjectively in equal measure, with less than three decibels of subjective variation across the frequency range. For example, a neutral frequency response has a balanced bass, mid, and treble frequency ranges, where the bass range may be described as frequencies from 20 to 250 Hz, midrange from 250 Hz to 6 kHz, and treble from 4 to 20 kHz. On the contrary, a non-neutral headphone has regions of excessive or lacking responsiveness. Furthermore, as there may be differences between the left and right side of the headphone, there may be unwanted frequency dependent variations in the left-right balance of the audio presentation. A person mixing or mastering audio data may be aurally misguided by the regions of excessive or lacking responsiveness and an inaccurate frequency-dependent left-right balance.

[0034] Calibration or equalization may be weighed. Weighing refers to frequency weighing, i.e., how different frequency bands are prioritized or adjusted during calibration or measurement. Weighing may refer to applying a frequency weighing curve and this may be done during measurement or equalization. Measurement may include measuring SPL or frequency response, for example. Equalization may include tuning the headphone to sound in a certain way, for example. Standard frequency weighing types are named by letters A, B, C and Z. Weighing types A, B and C have effect on selected frequencies. Thus, those are frequence selective, while Z weighing is non-selective to frequencies.

[0035] Figure 1A illustrates, by way of an example, a system comprising a passive headphone and an audio controller. The passive headphone 101 lacks electrical or power source components. The passive headphone 101 comprises one or more transducers configured to output sound. The passive headphone 101 is connected to an audio controller 102. The connection is a cable connection. In Fig. 1A there are connection cables for both sides of the earphone. In other examples, only one side of the headphone may be connected to the audio controller 102. The audio controller 102 comprises connection ports separately for the left and right sides of the headphone, as well as a single connection port, which is connectable to either of the sides of the headphone. The audio controller 102 comprises a memory, an amplifier, power source components, and an equipment and / or signal processing functions for amplifying, controlling, processing and setting the processing variables or parameters affecting the audio signals, which are passed to the passive headphone 101. The audio controller 102 comprises equipment, or signal processing function(s), configured to measure a sound level of the electroacoustic signal inputted to the headphone 101. Themeasured sound level results may be saved to the memory of the audio controller 102. Factory calibration data may be saved to the memory of the audio controller 102. The audio controller 102 is configured to process and to electrically drive input signal to the one or more transducers of the headphone 101, which are configured to generate audio output. Factory calibration data is applied to the electrical signal, which is inputted to the headphone 101. Sound level measurement is implemented to the electrical signal, before inputting it to the headphone 101.

[0036] Figures IB and 1C illustrates, by way of an example, a system comprising a passive headphone, an audio controller and a computer. Amplification processing and sound control is implemented in the audio controller 102, which is connected to the passive headphone 101. The audio controller 102 is further connected to a computer 103, which may be a desktop, a laptop or a smart phone. Connections may be wired connections. The computer 103 enables connections to internet, external terminals and / or storages 104. The computer 103 is able to fetch or receive pre-stored factory calibration settings from a remote storage 104 using an identifier, like a serial number or other unique identifier, associated with the passive headphone 101. The computer 103 transmits the settings to the audio controller 102, which uses the factor calibration settings to process electric signal for the connected passive headphone 101. Input of the passive headphone 101 is always provided by the audio controller 102. The audio controller 102 comprises equipment or signal processing functions for amplifying, controlling, processing and setting the processing variables or parameters affecting the audio signals passed to the passive headphone 101. In addition, the audio controller 102 comprises equipment or signal processing functions for measuring sound level of the audio signal, before passed to the headphone 101. The computer 103 enables to deliver, download or stream audio data via the audio controller 102 to the headphone 101. The audio controller 102 may comprise inputs to enable audio signal to be directly delivered into the audio controller 102 to be processed and delivered to the headphone 101. The audio controller 102 enables adjusting the sound for the headphonelOl. When sound data is streamed via the computer 103, audio processing is done at the audio controller 102. This leaves the computer 103 also for other use without reserving a significant amount of its processing or bandwidth capacities. The signal processing function of the audio controller 102 may be executed remotely, for example in a cloud computation services, instead of a physical audio controller 102 connected to a headphone 101. Thecomputer 103 may comprise a memory and save the measured sound level results, with possible time indications or durations of those.

[0037] In Fig. 1A, the audio controller 102 amplifier output is connected to a right, R, earcup of the headphone 101. In Fig. IB, the audio controller 102 amplifier output is connected to a left, L, earcup of the headphone 101. The passive headphone may comprise a connection port in both earcups. Thus, the user is able to connect a cable from the audio controller 102 to any one of the earcups of the headphone. This enables to provide improved ergonomics and to support the best connectivity in all usage scenarios. The factory calibration settings have been made separately for both earcups, left and right. The factory calibration may be made separately to all cases that cause the headphone frequency response to change, which may be due to change of cushioning materials and / or surface materials of the headphone. The earcups have been identified in order to separate the two earcups. The audio controller 102 is enabled to identify, or recognise and separate, the left, L, and right, R, sides of the headphone, i.e. earcups. Recognition may be automatic, or take place in response to a user input. The user may input information in order to describe the current configuration of the headphone 101. Recognition enables to select the correct factory calibrations for the left, L, and right, R, side of the headphone. The audio controller 102 is able to use the measured factory calibration settings for both the left, L, and right, R, earcups, correspondingly.

[0038] The passive headphone may be connected to the audio controller via universal serial bus, USB, cable, via an analogue audio cable known as an auxiliary, AUX, cable, via a high- definition multimedia interface, HDMI cable, via an optical or a coaxial cable, or example. When the passive headphone is connected to the audio controller, the audio controller may identify the passive headphone. An identifier of the passive headphone may be transferred to the audio controller via the connection. In addition, the audio controller may receive information on whether it is attached to the right or left side of the headphone. The information may be transferred from the headphone in response to connecting the headphone to the audio controller. Left and right side of the headphone may have identifiers, which is transferred in response to connection to the audio controller. In an alternative, the audio controller may request the information in response to connection of the headphone. The audio controller may receive an identifier of the headphone, in addition to information of the side of the connection of the headphone. The audio controller may have factory calibration data saved in its memory. The factory calibration data of the measured headphonemay be saved after the factory calibration measurements in the factory, to the audio controller which is paired with the headphone. In response to receiving an identifier of the headphone paired to it, the audio controller is able to apply the factory calibration for the electric signal outputted to the headphone. In case a received identifier is not the one paired with the audio controller, the audio controller is able to receive the factory calibration via a computer in response to transmitting the identifier of the headphone to the computer. An identifier of a headphone may be attached to the headphone. The identifier and a side information may be read using radio frequency, or other short-range signalling, by the audio controller. For example, a passive RFID tag may be attached to the headphone and read by the audio controller comprising, or attached to, a reader device. In an embodiment, a user may input an identifier of the headphone, and optionally also a side information, to a computer. The computer has access to a data storage saving factory calibration data associated with a specific headphone identifier. The computer may receive factory calibration settings in response to transmitting the identifier to the data storage. The saved factory calibration comprises factory calibration information for both, left and right, sides of the headphone. The audio controller has information on the side of the headphone, it is connected to. The audio controller is able to apply factory calibration correctly to the both sides of the headphone.

[0039] A passive headphone may be changed or replaced to a new one, while the same audio controller is used. In such case, the new passive headphone is connected to the (already used) audio controller. Factory calibration settings of the new passive headphone are acquired using an identifier, like a serial number, of the new passive headphone. A computer receiving the factory calibration settings transmits those to the audio controller to be used in the signal processing for the new passive headphone. This way, a passive headphone is changeable and / or replaceable with individual factory calibration settings of each individual passive headphone, while the audio controller remains the same, and the resulting headphone sound character is enabled to remain the same, accurate and neutral. Also, multiple passive headphones may be used with a single audio controller, one headphone at a time. For example, in a work environment, a single audio controller may be utilized by several different passive headphones, and their users, at different times.

[0040] Figure 2 illustrates, by way of an example, an audio controller. The audio controller comprises input and output ports configured to input and output audio data, respectively. The audio controller may comprise input ports for left, L, and right, R, analogueaudio data, and similarly output ports for left, L, and right, R, analogue audio data. The sound controller may comprise input and output, I / O, ports for digital audio data. The sound controller may comprise for example input / output, I / O, port for a headphone, a universal serial bus, USB, connection port, or other connection port, for example a cable, an AUX, a HDMI, a coaxial or alike ports. The audio controller comprises a battery, a user interface, UI, and a signal processor, SP. The audio controller comprises an amplifier, Amp, which may be a headphone amplifier integrated into the audio controller. The amplifier may amplify current, voltage or power. The amplifier, Amp, may be a power amplifier, which is configured to convert a low power signal to a high power one by increasing inputted power. A power amplifier may be called a large signal amplifier, which is configured to provide large amount of power to the input audio signal. A power amplifier enables providing more power to the output, while it tends to be larger and heavier compared to a non-power amplifier. However, size and weight are more of an issue for active headphones with integrated audio controller, while those have no effect on a size or weight of the passive headphones. In addition, the audio controller may comprise one or more transducers and a digital-to-analogue converter, DAC. The audio controller is configured to control audio data.

[0041] The audio controller may be a mobile or a portable audio controller. A mobile audio controller differs from a desktop audio controller in size: while a desktop audio controller is fixed in one place, like a studio, a mobile audio controller is portable, being smaller and lighter in weight compared to the desktop audio controller. A mobile audio controller may have limited number of functions and limited adjustment possibilities compared to the desktop version. A desktop audio controller is powered via mains through connected sockets, while a mobile audio controller may use batteries or AC power that can be recharged, in addition to operate using main power.

[0042] The audio controller may be connected to a passive headphone, for example via an I / O port. The audio controller may be connected to a computer via an USB port. Both connections may be wired, cable connections. Wired connections avoid lag or other issues dependent on a wireless network, which may be due to a place and / or a network used. The audio controller is configured to receive factory calibration settings, which have been measured and saved for the specific passive headphone. The factory calibration settings may be stored to the audio controller and / or received from the computer. The audio controller is configured to use the factory calibration settings for any input to the passive headphone.

[0043] Audio signals may be represented in either digital or analogue format, and audio signal processing may be based on either of those. Analog signal processors operate directly on the electrical signal, while digital signal processors operate mathematically on a digital representation of the electrical signal. An audio controller may be used for balancing and adjusting sound sources. The audio controller may comprise an equalizer, EQ, and / or a processor configured to process dynamics, audio effect, mixing, reproduction and reinforcement of sound. Equalization, EQ, comprises adjusting volume of different frequency bands within an audio signal. Audio filter may comprise a frequency dependent circuit, which may amplify (boost), pass, or attenuate (cut) selected frequencies or frequency ranges. Compression or a dynamic range compression, DRC, is configured to reduce volume of loud sounds or to amplify quiet sounds, thus reducing or compressing a dynamic range of an audio signal. Compression may be implemented by a compressor, which may be a dedicated electric hardware unit or an audio software.

[0044] The audio controller comprises equipment or signal processing functions for amplifying, controlling, processing and setting the processing variables or parameters affecting the audio signals passed to the passive headphone. The audio controller comprises equipment or signal processing functions configured to measure sound level of the electric signal, which is to be inputted to the headphone. The computer enables to deliver, download or stream audio data via the audio controller to the headphone. The audio controller may comprise inputs to enable audio signal to be directly delivered into the audio controller to be processed and delivered to the headphone. The audio controller enables adjusting inputted electric signal for providing sound via the passive headphone.

[0045] Figure 4 illustrates, by way of an example, a computer. The computer comprises a processor, which may be a central processing unit of the computer. The processor may comprise a microprocessor, a computer processor or an integrated circuit, IC. The computer comprises a memory, MEM. The memory may comprise a non-volatile memory and / or multiple memory units, which may comprise, for example, a read only memory, ROM, a random access memory, RAM, a flash memory. The memory, MEM, may comprise executable instructions, which are executable by the processor. Memory is configured to store information, executable instructions, and / or at least one application configured to communicate with an audio controller. The computer comprises a battery and a user interface. The user interface may comprise input and output means for a user, for example a display, keys, a touch screen. The computer comprises physical ports for wiredconnections. The ports comprise an input-output, I / O, port, and a universal serial bus, USB, port. The computer may comprise other ports for connecting to external devices and / or terminals. The computer comprises a transmission branch, TX, and a receiving branch, RX. A transmission and receiving branches, TX / RX, may comprise a receiver / a transmitter, a digital-to-analogue converter, an analogue-to-digital converter, an amplifier, and an antenna. The transmission branch, TX, is configured to transmit data and / or signals via a wireless connection. The receiving branch, RX, is configured to receive data and / or signals via a wireless connection. The wireless connection may be a radio frequency network, a cellular network, or a communication network, which may enable exchange of data and information. In addition, the computer may comprise transmission means configured for a short service range wireless communication, like a Bluetooth, an infrared, or alike. The computer may be connected to an internet via a modem, which may be connected via a cable or a wireless connection, like a Wi-Fi according to IEEE 802.11 standard (Institute of Electrical and Electronics Engineers).

[0046] Computer may comprise a mobile computer, a mobile device, a handheld computer, a smart phone, a desktop computer, a laptop, a tablet, or any suitable device. The computer may include means for causing getting factory calibration settings in response to a received identifier of the passive headphone, and means for communicating the factory calibration settings to the audio controller. The computer may comprise a software application configured to communicate with the audio controller. The application may provide a user interface for receiving input from the user and for outputting information to the user. For example, information on sound level measurement, with possible time information or duration of such, may be saved and / or presented by a computer. The computer may further cause saving the sound level measurement results to a remote storage (like 104 in Fig. 1).

[0047] Figure 4 illustrates, by way of an example, a method for measuring a sound level of a passive headphone. Method comprises measuring, by the audio controller, sound pressure level of the headphone in relation to electrical signal inputted to the passive headphone by using sensitivity of the passive headphone.

[0048] In the previous description and figures a passive headphone is made active by its connection to an audio controller, which is further able to get factory calibration settings for the specific passive headphone, for example via a computer. The audio controller isconfigured to measure sound level of the factory calibrated electroacoustic signal before inputting it to the headphone. The system is modular. This enables changing or replacing one of the passive headphone, audio controller and a computer, at a time. For example, replacement of passive headphone has no effect on other modules of the audio controller and the computer, but the system with the new passive headphone may be connected, calibrated using factory calibration settings of the new passive headphone, and used, as well as measured, with the same accuracy and quality, as with the replaced passive headphone.

[0049] A computer may receive a stream or download audio data to be listened via the passive headphone. The audio data is transmitted via the computer to the audio controller. The audio controller is configured process, measure, calibrate and / or equalize audio data. Audio signal processing, or all audio signal processing, is implemented at the audio controller. No further computational or transmission capacity is required from the computer.

[0050] A head related transfer function, HRTF, is used to provide a 3 -dimensional, 3D, audio experience for a headphone user. The HRTF may use images of a head, body and / or a pinnae of a user in order to form a 3D model of the user. The HRTF describes an acoustic filter quantifying the effect of a shape of a head, body, and pinnae on the sound arriving at the entrance of the ear canal. Reference values for the HRTF may have been prepared using loudspeakers in a listening room, for example. Using HRTFs each passive headphone may be aligned with the predetermined hearing experience, for example of several loudspeakers in a listening room. Thereby, a response of the passive headphone may correspond to an acoustic simulation of a room. The factory calibration settings enable providing quality of passive headphone, at a certain tolerance. A personal HRTF may be utilized after the factory calibration in order to provide personal 3D audio experience. This enables a good quality, user-specific audio experience. Without factory calibration settings, any variations among separate headphones might lead to further variations and / or issues with use of HRTFs. Sound level measurement is implemented individually for both sides of the headphone, i.e. to input of left and right earpieces of the headphone separately.

[0051] A listener is able to adjust their headphone. The headphone is factory calibrated in order to produce a natural or flat sound. The play back is predictable. Also, sound level measurements provide comparative and / or corrected results among headphones with applied individual factory calibration. After the factory calibrated natural reproduction, a listener is able to select setting for their headphone. For example, a listener may select so-called warmsound in order to boosts bass frequencies, being low or mid-low frequencies. In warm sound low frequencies dominate over higher frequencies. A warm sound may be called bass-heavy. The opposite of warm sound is so-called bright sound, which boosts high frequencies. In bright sound high frequencies dominate over lower frequencies.

[0052] For most people audible hearing spectrum ranges from about 20 Hz to 20 kHz. In studio environment, full frequency spectrum of different elements, like instruments, may be controlled, adjusted and / or mixed. Frequency response of a signal represents an amount (volume) of every frequency in the human hearing range. The frequency response may be edited in various ways, or example by equalizing and filtering. Equalization is configured to alter parts of a signal frequency response. Filters are configured to attenuate part of the audio spectrum.

[0053] Audio mixing refers to a process for optimizing and combining multitrack recordings into a final sound product. Mixing may include adjusting and balancing relative levels of separate tracks of multitrack recordings, which may include equalization and compression. The described system comprising an audio controller, a passive headphone and a computer may replace a mixer, which may be called a mixing console, a mixing desk, a mixing board or a software mixer. Mixing may be implemented via a software or application, which has been downloaded or added to the computer, and the audio controller configured to handle the signal processing. While mixing consoles may be large and have an exceptional number of controls, the system presented in this application offers a mobile system for mixing. While number of controls of the described system may not be as excessive as in larger local static mixers, mobility enables instant mixing, despite the place. A sound level measurement enables to maintain recommended levels.

[0054] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0055] The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the previous description, numerous specific details are provided, such as examples of structures, lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant artwill recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well- known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0056] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0057] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.

Claims

CLAIMS:

1. A system comprising a passive headphone (101) and an audio controller (102), wherein- the passive headphone (101) is connected to the audio controller (102), wherein factory calibration data has been pre-stored to an audio controller paired with the passive headphone (101) and to a remote storage, and wherein the prestored factory calibration data comprises factory calibration data for both left and right sides of the passive headphone (101), in case the identifier of the passive headphone (101) connected to the audio controller is not the one paired with the audio controller, receiving, by the audio controller, the factory calibration via a computer in response to transmitting the identifier of the passive headphone (101) to the computer, the audio controller (102) is configured to apply the factory calibration data to an electrical signal inputted to the passive headphone (101), and- the audio controller is configured to measure sound pressure level of the headphone in relation to electrical signal inputted to the passive headphone by using sensitivity of the passive headphone, wherein the sensitivity is measured by factory calibration of the passive headphone.

2. A system according to any of the previous claims, wherein the factory calibration is configured to provide neutral sound for the paired passive headphone (101), wherein the neutral sound refers to reproduced sound being uncoloured throughout an audible frequency range.

3. A system according to any of the previous claims, wherein SPL is measured constantly or at certain time intervals, and the results of the measurement are saved to a memory of the audio controller (102) and / or to a computer (103) connected to the audio controller.

4. A system according to any of the previous claim 3 , wherein the audio controller ( 102) and / or the computer (103) are configured to display a warning in case a predetermined limit of the SPL is exceeded.

5. A system according to any of the previous claims, wherein the sound pressure level of the passive headphone is measured using sensitivity of the passive headphone (101), and voltage or power and impedance of the electrical signal inputted by the audio controller to the passive headphone (101).

6. A system according to any of the previous claims, wherein a cumulative noise dose is measured using the measured SPL in view of noise dose.

7. A system according to any of the previous claims, wherein the SPL is constantly measured.

8. A system according to any of the previous claims, wherein the audio controller (102) is configured to get factory calibration data, which is specific for the passive headphone (101) and associated to an identifier of the passive headphone (101), the audio controller (102) is configured to apply the factory calibration data for electroacoustic signal inputted to the passive headphone (101), and- the audio controller is configured to measure a sound level of the electroacoustic signal before inputted to the passive headphone (101).

9. A system according to any of the previous claims, wherein factory calibration comprises data determined individually for the both sides of the headphone (101).

10. A system according to the previous claim 8 or claims 9 and 8, wherein the identifier is dedicated to the passive headphone (101); and / or the identifier is a serial number, a specific identifier, a transponder, an electric tag, or a radio frequency identification, RFID, tag.

11. A system according to any of the previous claims, the audio controller (102) comprises an integrated headphone amplifier configured to amplify electroacoustic signal transmitted to one or more transducers of the passive headphone (101) configured to reproduce the electroacoustic signal to a sound output.

12. A system according to any of the previous claims, wherein the audio controller is a mobile or a portable audio controller.

13. A system according to any of the previous claims, wherein the factory calibration comprises at least one of the following parameters measured for the both sides of the passive headphone (101): impedance, sensitivity, level and phase of the acoustic output as a response to an electrical input for all frequencies.

14. A system according to any of the previous claims, wherein the factory calibration settings of the passive headphone (101), applied by the audio controller (102), are configured to adjust a frequency response of the passive headphone (101).

15. A system according to any of the previous claims, further comprising a computer (103) configured to be connected to the audio controller (102), wherein the audio controller (102) is configured to receive the factory calibration data from the computer (103), which is configured to access a remote storage (104) in order to receive the factory calibration saved to the remote storage (104) in response to provided identifier of the passive headphone (101).

16. A system according to the previous claim 8 or any of the previous claims 9-15 dependent on claim 8, wherein the identifier of the passive headphone (101) is received by the audio controller (102) automatically, in response to connected to the passive headphone (101), and / or read via a short-range signalling from the passive headphone (101).

17. A system according to the previous claim 8 or any of the previous claims 9-16 dependent on claim 8, wherein the identifier of the passive headphone (101) is inputted to the computer (103), received by the computer (103), received via a short- range signalling by the computer (103), and / or received from the audio controller (102) by the computer (103).

18. A system according to any of the previous claims, wherein information on side of the passive headphone (101), to which the audio controller (102) is connected to, isreceived by the audio controller (102) automatically, upon connecting the passive headphone (101) to the audio controller (102), via a connection cable of the passive headphone (101) and the audio controller (102), and / or via short-range signalling.

19. A system according to any of the previous claims, wherein the audio controller (102) is connected to the passive headphone (101) via a wired connection; and / or wherein the audio controller (102) is connected to the computer (103) via a wired connection.

20. A system according to any of the previous claims, wherein the audio controller comprises a processor configured to process dynamics, audio effect, mixing, reproduction and reinforcement of sound.

21. A system according to any of the previous claims, wherein the computer (103) comprises at least a processor and a memory comprising instructions executable by the processor, and wherein the computer (103) has access to a remote storage (104).

22. A method for measuring sound pressure level of a passive headphone, wherein the passive headphone is connected to the audio controller, comprising getting (401), by the audio controller, factory calibration data, which is specific for the passive headphone and associated to an identifier of the passive headphone, wherein factory calibration data has been pre-stored to an audio controller paired with the passive headphone (101) and to a remote storage, and wherein the prestored factory calibration data comprises factory calibration data for both left and right sides of the passive headphone (101), in case the identifier of the passive headphone (101) connected to the audio controller is not the one paired with the audio controller, receiving, by the audio controller, the factory calibration via a computer in response to transmitting the identifier of the passive headphone (101) to the computer, applying (402), by the audio controller, the factory calibration data to an electrical signal inputted to the passive headphone, and- measuring, by the audio controller, sound pressure level of the headphone in relation to electrical signal inputted to the passive headphone by using sensitivityof the passive headphone, wherein the sensitivity is determined by factory calibration of the headphone.

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