Patent Application
20100150378
This application claims priority to an application entitled “METHOD AND APPARATUS FOR AUDIO SIGNAL CONTROL” filed in the Korean Intellectual Property Office on Dec. 17, 2008 and assigned Serial No. 10-2008-0128239, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to audio signal control protocol and, more particularly, to an audio signal control method and apparatus for providing a hearing protection.
2. Description of the Related Art
With advances in technologies, many portable devices such as mobile terminals support playback of multimedia files such as audio and video files. While in motion, many users enjoy the replay of music from their mobile terminals through headsets or earphones. During a replay of music via an earphone, the users tend to raise the sound volume to enhance their enjoyment of vivid or dynamic sounds. However, an audio signal (such as music sound) at a high sound pitch delivered to the ear may cause serious damage to hearing ability.
Many countries including South Korea, the United States of America, England, and Japan have similar regulations on occupational safety related to noise exposure. For example, the U.S. Department of Labor's Occupational Safety and Health Administration (OSHA) requires the employer to implement a special hearing conservation program whenever employee noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 decibels measured on the A scale (85 dBA).
Efforts are made to provide portable devices with mechanisms to comply with the noise exposure regulation and to protect worker's hearing from excessive noise level that lasts longer than a recommended time duration.
A similar protection is desirable to portable device users as many started to experience hearing problems. As such, there is a need to develop a means to control the output audio signal of a portable device so that the user is not exposed to a too high-level of sound that may cause hearing degradation.
The present invention has been made in view of the above problems and provides additional advantages, by providing an audio signal control method and apparatus when a fatigue index (=“exposure time”/“permissible time”) is accumulated for a preset time duration, a warning message is produced when the cumulative fatigue index exceeds a preset permissible value.
In accordance with an exemplary embodiment of the present invention, there is provided an audio signal control method including: producing an output level of an audio signal being input; determining whether the ratio of an output time of the audio signal within a preset time duration to a permissible time corresponding to the produced output level is greater than or equal to a limit reference value; and limiting, when the ratio of the output time to the permissible time is greater than or equal to the limit reference value, the output level of the audio signal to a preset level.
In accordance with another exemplary embodiment of the present invention, there is provided an audio signal control apparatus including: a sound level producer producing an output level of an audio signal being input; a signal control unit determining whether the ratio of an output time of the audio signal within a preset time duration to a permissible time corresponding to the produced output level is greater than or equal to a limit reference value; and an audio output unit limiting, when the ratio of the output time to the permissible time is greater than or equal to the limit reference value, the output level of the audio signal to a preset level.
Hereinabove, the features and advantages of the present invention are described in a relatively broad perspective to help those skilled in the art understand the present invention. Other features and advantages constituting the subject matter of the present invention will be more apparent from the following detailed description.
The features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which:
Hereinafter, exemplary embodiments of the present invention are described in detail with reference to the accompanying drawings. The same reference symbols are used throughout the drawings to refer to the same or like parts. For the purposes of clarity and simplicity, detailed descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present invention.
The present invention relates to an audio signal control scheme that enables a user not to be exposed to a harmful noise that may damage hearing ability by controlling an output audio signal generated via an earphone, a headset, or other head phones that enable audio signals. Briefly, this is achieved by preventing audio sound at a level higher than or equal to a preset level within a predetermined time period. A detailed description will be explained hereinafter with reference to figures.
As shown in
As known by artisians, the sound pressure level, in the unit of dBA, represents a local pressure deviation from the ambient pressure caused by a sound wave.
In graph A, a threshold value 101 indicates the lowest sound pressure level triggering a hearing conservation program specified in the noise exposure regulation in many countries, and may be 90 dBA as illustrated later in Table 1. As the criterion time duration in such a noise exposure regulation is 24 hours, the audio signal is controlled through measuring the sound pressure level higher than or equal to the threshold 101 for 24 hours. In graph B, a maximum value 151 indicates the maximum permissible exposure time limit specified in the noise exposure regulation. When the audio signal carries sounds of higher than or equal to the threshold value 101, the exposure time relative to the corresponding permissible time duration is accumulated. If the cumulative exposure time reaches the maximum value 151 at a time (in graph B, a point in time indicated by a reference numeral 161), the sound pressure level of the audio signal is limited or adjusted thereafter. Hence, after reaching the maximum value 151, though the audio signal continuously carries sounds of higher than or equal to the threshold value 101, the output sound pressure level (i.e., level when sound wave is outputted from the audio output unit a mobile terminal) is kept to a preset value less than or equal to the threshold value 101.
In
In
Next, a more detailed description is given of controlling an audio signal that may cause damage to hearing ability.
Referring to
The monitoring unit 210 determines the amplitude level of an input audio signal relative to the maximum amplitude level represented in a digital domain. For example, in the case of 16-bit representation, the maximum amplitude level is given by 32768, and 0 dBFS (decibels relative to full scale) may be assigned to the maximum possible level of 32768. The monitoring unit 210 may produce the amplitude level of the input audio signal relative to the maximum amplitude level of 32768 at every unit time. Time weighting or frequency weighting may be employed for producing the relative amplitude levels. For the purpose of description of the present invention, only A-weighting is utilized as an example of frequency weighting, but it should be noted that other weighting schemes known to artisians may be utilized. A-weighting attempts to match the response of the human ear to pure tones. A-weighting is known to those skilled in the art, and a description thereof is omitted. Briefly, A-weighting is the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level, (see http://en.wikipedia.org/wiki/A-weighting).
The actual output level producer 220 computes, for an audio signal with a relative amplitude level determined by the monitoring unit 210, the actual sound pressure level of the audio signal at the time when the audio signal is output through an actually installed amplifier (not shown) and a headset. To compute the actual sound pressure level at the time when the audio signal is output through the audio output unit 260, the actual output level producer 220 may utilize parameters such as the volume level set in the amplifier and the sensitivity of the headset at particular frequencies. For example, when the volume level is set by the user to a high value, the actual sound pressure level at the time of output will be higher than the sound pressure level at the time of input; and when the volume level is set to a low value, the actual sound pressure level at the time of output will be lower than the sound pressure level at the time of input. When the headset tends to raise the output level of a low-frequency audio signal, the actual sound pressure level of a low-frequency audio signal will be higher than the sound pressure level at the time of input. That is, parameters affecting the sound pressure level of an audio signal may be utilized for computing the actual sound pressure level. Here, the volume level set in the amplifier corresponds to the output level of an audio signal. The sensitivity of a headset at particular frequencies corresponds to the sensitivity of the headset to an audio signal according to output levels and frequencies, and may be specified at the manufacturing process or by settings and pre-stored as a conversion table in the storage unit 230 after realistic measurement through test signals of desired characteristics.
Parameters, other than the volume level set in the amplifier or the sensitivity of a headset at particular frequencies, affecting the sound pressure level of an audio signal may also be utilized.
The signal control unit 240 performs audio signal control so that an audio signal with a computed actual sound pressure level higher than or equal to a preset level is not output for longer than or equal to a given time duration. To control the sound pressure level of an output audio signal, the signal control unit 240 may include a stimulus obtainer 242, a stimulus accumulator 244, and a hearing conservation determiner 246. Specifically, the stimulus obtainer 242 computes a stimulus estimate Hp for an audio signal through dividing a preset unit exposure time by the permissible time corresponding to an actual sound pressure level computed by the actual output level producer 220. The stimulus accumulator 244 computes a cumulative stimulus value Ha by accumulating multiple stimulus estimates Hp obtained for a given time duration. In the description, stimulus estimates obtained during 24 hours are accumulated. However, the duration for accumulating stimulus estimates may be altered according to the regulation or settings. The hearing conservation determiner 246 determines the stage of hearing conservation on the basis of the cumulative stimulus value from the stimulus accumulator 244, and may control the audio output unit 260 and status display unit 250 to perform an operation according to the determined stage. In the present invention, three stages including “hearing conservation off (safe mode)”, “hearing conservation warning (warning mode)”, and “hearing conservation on (limit mode)” are defined. This is described later in connection with
The audio output unit 260 and the status display unit 250 operate according to the output of the hearing conservation determiner 246. That is, the audio output unit 260 outputs an audio signal of a sound level indicated by the output of the hearing conservation determiner 246, and the status display unit 250 provides the user with information on associations between the sound level of the output audio signal and the threshold value.
For example, the signal control unit 240 computes stimulus estimates Hp for the output sound pressure level (dBA) of an audio signal, accumulates the stimulus estimates Hp obtained during past 24 hours corresponding to sound pressure levels higher than or equal to the threshold value into a cumulative stimulus value Ha, obtains a value Hrs through normalizing the cumulative stimulus value Ha by the maximum permissible time Hmax not damaging hearing ability, and performs hearing conservation according to the value Hrs. That is, Hrs of greater than or equal to 0.8 indicates the warning mode; and Hrs of greater than or equal to 1 (exceeding the maximum permissible time) indicates the limit mode, in which the output level of the audio signal is limited for hearing conservation. In the limit mode, the stimulus estimate Hp for the output sound pressure level is set to zero, and the cumulative stimulus value Ha for 24 hours gradually decreases over time. Thereby, hearing stress is reduced. Accumulation of stimulus estimates may be effectively carried out through a moving window scheme described later in connection with
Referring to
Referring to
The stimulus obtainer 242 checks whether the average value is greater than or equal to the threshold value for triggering a hearing conservation program (730). If the average value is greater than or equal to the threshold value, the stimulus obtainer 242 computes the stimulus estimate Hp for the unit time on the basis of the average value (740). Here, the average value greater than or equal to the threshold value indicates that the input audio signal carries a sound pressure level that may damage hearing ability, and may correspond to a noise level given in Table 1. The stimulus estimate (0<=Hp<=1) is computed, using Equation 1, by dividing the unit time (unit exposure time) by the permissible time corresponding to the average value (noise level).
stimulus estimate (Hp)=unit time/permissible time (0≦Hp≦1) [Equation 1]
Table 1 indicates that exposure to an audio signal carrying a sound pressure level of 90 dBA for 8 hours or more may damage hearing ability; exposure to an audio signal carrying a sound pressure level of 95 dBA for 4 hours or more may damage hearing ability; exposure to an audio signal carrying a sound pressure level of 100 dBA for 2 hours or more may damage hearing ability; exposure to an audio signal carrying a sound pressure level of 105 dBA for 1 hour or more may damage hearing ability; exposure to an audio signal carrying a sound pressure level of 110 dBA for 30 minutes or more may damage hearing ability; and exposure to an audio signal carrying a sound pressure level of 115 dBA for 15 minutes or more may damage hearing ability. For example, when an average value of 90 dBA is obtained for a unit time of 6 seconds, the permissible time for 90 dBA is 8 hours and hence the stimulus estimate Hp is 6/28800. If the average value is less than the threshold value, the stimulus obtainer 242 sets the stimulus estimate Hp for the unit time to zero (750). A stimulus estimate of zero does not contribute to the cumulative exposure time controlling the sound level of an audio signal.
Referring back to
Referring to
Referring back to
Referring to
Referring back to
Referring to
In the warning mode 422, the stimulus accumulator 244 of the signal control unit 240 updates the cumulative stimulus value Ha using a new stimulus estimate Hp (422). The hearing conservation determiner 246 checks whether the cumulative stimulus value Ha is greater than the warning reference value Tw (424). If the cumulative stimulus value Ha is not greater than the warning reference value Tw, the hearing conservation returns to step 422. If the cumulative stimulus value Ha is greater than the warning reference value Tw, the hearing conservation determiner 246 checks whether the cumulative stimulus value Ha is greater than the limit reference value TI (426). If the cumulative stimulus value Ha is less than the limit reference value TI, the hearing conservation determiner 246 notifies the user of the warning mode (428), and returns to step 422. If the cumulative stimulus value Ha is greater than the limit reference value TI, the hearing conservation determiner 246 transitions to the limit mode 430. As described before in connection with
In the limit mode 430, the stimulus accumulator 244 of the signal control unit 240 updates the cumulative stimulus value Ha using a new stimulus estimate Hp (432). The hearing conservation determiner 246 checks whether the cumulative stimulus value Ha is greater than the limit reference value TI (434). If the cumulative stimulus value Ha is greater than the limit reference value TI, the hearing conservation determiner 246 outputs an audio control signal for limiting the sound pressure level of the output audio signal (438), and returns to step 432. If the cumulative stimulus value Ha is not greater than the limit reference value TI, the hearing conservation determiner 246 checks whether the cumulative stimulus value Ha is less than or equal to the safe reference value Ts (436). If the cumulative stimulus value Ha is less than or equal to the safe reference value Ts, the hearing conservation determiner 246 transitions to the safe mode 410. If the cumulative stimulus value Ha is not less than or equal to the safe reference value Ts, the hearing conservation determiner 246 proceeds to step 438. Here, the safe reference value Ts may be set to 0.5, and may cause the cumulative stimulus value Ha to be decreased by a sufficient amount to suppress undesired circular transitions from the limit mode 430 to the safe mode 410 and back from the safe mode 410 to the warning mode 422 or limit mode 430.
As apparent from the above description, the present invention provides an audio signal control method and apparatus that controls the sound output level of an audio signal so that the user is not exposed to excessive noise that may damage hearing ability. The method enables real time computation of the level of exposure to sounds, and can be effectively applied to a hearing conservation device. The method and apparatus may be employed in portable devices such as a portable media player and mobile terminal for compliance to occupational safety regulations related to hearing protection. To protect hearing ability of the user, a fatigue index (=“exposure time”/“permissible time”) is accumulated for a preset time duration and a warning message is produced when the cumulative fatigue index exceeds a preset permissible value.
Although exemplary embodiments of the present invention have been described in detail hereinabove, it should be understood that many variations and modifications of the basic inventive concept herein described, which may appear to those skilled in the art, will still fall within the spirit and scope of the exemplary embodiments of the present invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2008-0128239 | Dec 2008 | KR | national |
