Noise reduction by mobile communication devices in non-call situations

In a preferred embodiment, the invention is a mobile communication device having a digital signal processor (DSP), a speaker output node, a local audio source, and an analog front-end (AFE), wherein: (1) the DSP receives a first audio signal corresponding to sound captured by a microphone near a user of the device, (2) if the device is operating in a call mode, the DSP derives a background noise signal from the first audio signal, for subtraction from the first audio signal before transmission to the AFE, and (3) if the device is operating in a non-call mode, then the DSP (i) generates a speaker output signal which substantially corresponds to the first audio signal subtracted from a local audio signal provided by the local audio source and (ii) provides the speaker output signal to a speaker via the speaker output node.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to mobile communication devices, and in particular to the reduction of noise heard by a user of a mobile communication device.

2. Description of the Related Art

An important function of a mobile communication device is to adequately transmit human voice over a wireless network. One method to improve the transmission of voice using a mobile communication device is to filter the signal to reduce the background noise that is transmitted by the mobile communication device along with a user's voice. Some techniques for reducing background noise rely on known differences in the characteristics, such as the frequency spectrum, between human voice and typical background noise. Some techniques rely on measured differences between audio samples at different locations, such as nearer to and farther from the user's mouth. Noise suppression techniques are used alongside other methods, such as echo canceling, to improve the transmission of voice using a mobile communication device.

Noise filtering, as well as other signal processing tasks, such as signal encoding and decoding, are typically performed by one or more digital signal processors (DSPs) in the mobile communication device. A DSP can be implemented in various ways, such as an application-specific integrated circuit (ASIC), a portion of an ASIC, a programmable circuit, software code, or a combination including any of the above.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is a mobile communication device comprising a digital signal processor (DSP), a microphone input node, a speaker output node, an analog front-end, and an antenna, wherein the mobile communication device is adapted to operate in a call mode and a non-call mode. The microphone input node is adapted to receive a first audio signal corresponding to sound captured by a microphone connected to the microphone input node and located near a user of the mobile communication device. If the mobile communication device is operating in the call mode, then (a) the DSP (i) derives a background noise signal from the first audio signal, wherein the background noise signal substantially characterizes background noise near the user, (ii) generates a second audio signal substantially equivalent to the sum of the first audio signal and an inverse of the background noise signal, and (iii) provides the second audio signal to the analog front-end; (b) the analog front-end receives the second audio signal and generates a corresponding first radio-frequency signal for transmission by the antenna to a wireless network; (c) the antenna receives from the wireless network a second radio-frequency signal for transmission to the analog front-end, which generates a corresponding received audio signal; and (d) the DSP provides to a speaker via the speaker output node a speaker output signal based on the received audio signal. If the mobile communication device is operating in the non-call mode, then the DSP (i) generates a speaker output signal based on at least the first audio signal, and (ii) provides the speaker output signal to a speaker via the speaker output node.

DETAILED DESCRIPTION

Mobile communication devices were developed to provide enhanced telephone call capabilities, and as such, one goal was the efficient transmittal of human voice from the talker to the listener, wherein part of the transmittal path is wireless. One category of techniques to better transmit the voices of the users includes the suppression in the transmitted signal of background noises that are not the talker's voice. One such technique involves sampling the background sounds around the phone using a microphone sufficiently isolated from the talker's sound, and using digital processing to reduce the background sounds relative to the talker's voice before transmittal to the listener. A simple version of this technique involves subtracting the background sound signal from (which is equivalent to adding an inverse of the background sound signal to) the captured combined signal, which contains the talker's voice with the background signal.

FIG. 1shows a simplified block diagram of a mobile communication device in accordance with one embodiment of the present invention. Mobile communication device101comprises DSP102, analog front-end105, internal audio source107, antenna106, microphone input node104, speaker output node109, and optional external audio source jack113. DSP102comprises noise characterizer110, noise suppressor111, received audio processor112, and possibly other circuitry (not shown) for encoding and decoding communication signals sent to and received from analog front-end105. Analog front-end105provides a communication and translation link between antenna106and DSP102. Optional external audio source jack113allows the connection of external local audio devices (e.g., MP3 players) to mobile communication device101. Microphone input node104connects microphone103to DSP102. Speaker output node109connects speaker108to DSP102. Microphone103and speaker108may be configured together in the form of an external stereo headphone and microphone set (not shown).

FIG. 2is a simplified block diagram illustrating the operation of mobile communication device101if mobile communication device101is connected on a call. The user's voice and any background noise are captured by microphone103, which converts the sound energy it picks up into electrical audio signal103a. Audio signal103amay be analog or digital. Audio signal103ais provided via microphone input node104to DSP102, which optionally includes an A/D converter (not shown) to convert audio signal103ainto a digital signal if it has not already been converted to the digital domain. The digital version of audio signal103ais provided to both noise characterizer110and noise suppressor111.

Noise characterizer110derives the background noise from audio signal103apicked up by microphone103and generates background noise signal110a, which substantially characterizes the background noise. Noise characterizer110generates background noise signal110aby one or more methods, such as sampling the sounds picked up by microphone103during periods the user is not talking, derivation based on known characteristics of human voice and/or background noise, or using a second microphone (not shown), which is sufficiently isolated from the user's voice, to provide a background noise signal.

Noise suppressor111receives background noise signal110a, subtracts background noise signal110afrom audio signal103a(e.g., by inverting background noise signal110aand adding the inverted signal to audio signal103a), and generates noise-suppressed audio signal111a. Noise-suppressed audio signal111ais provided to analog front-end105.

Analog front-end105acts as an intermediary between DSP102and antenna106, which transmits a signal corresponding to noise-suppressed audio signal111ato the wireless network (not shown) that connects the user to the listener (not shown). Analog front-end105comprises an analog audio block (not shown) for converting audio signals between the digital and analog domains. Analog front-end105also comprises an analog radio block (not shown) for transforming an audio signal to and from a corresponding radio frequency signal that is transmitted via antenna106. The term radio frequency as used herein refers generally to any frequency suitable for wireless transmission from the mobile communication device to a wireless network. Analog front-end105is connected to antenna106via path106a. If analog front-end105receives an incoming radio frequency signal from antenna106that corresponds to an audio signal, analog front-end105transforms the incoming radio frequency signal into digital received audio signal105a, which it provides to received audio processor112, which is located in DSP102.

Received audio processor112processes signal105ato enhance or control the signal through means known in the art, such as volume control. Received audio processor112may also rely on known spectral characteristics of voices and/or noise to suppress noise in signal105a. Received audio processor112provides speaker output signal108avia speaker output node109to speaker108, which converts the audio signal into an audible sound signal. Speaker output signal108amay be converted from digital to analog by DSP102or by a D/A converter (not shown) external to DSP102.

Noise characterizer110, noise suppressor111, received audio processor112, and one or more optional A/D and D/A converters (not shown) can share one or more physical components of DSP102if DSP102is implemented as hardware. These blocks are labeled and described separately here to facilitate description of their functions and not necessarily to define their physical structure. Speaker108can be in the form of headphones, an earpiece, an external speaker, or any suitable conveyor of audio information to a user.

Increasingly, mobile communication devices are providing audio features in addition to their person-to-person vocal communication service. Examples of such audio features, usually utilized when the user is not engaged in a telephone conversation, include the ability to listen to the audio signals of videos, music, and spoken recordings (e.g., podcasts). These audio signals can be received from a source local to the mobile communication device. The local audio source can be an internal audio source, or the local audio source can be an external audio source, connected to the mobile communication device by wire, or even wirelessly (e.g., by using Bluetooth® technology). If the local audio source is an external device, then local audio source107can function as simple pass-through, or can process the signal from the external device to adjust volume, balance, equalization, etc. If a user is listening to audio from a local audio source, as opposed to being on a call, then the mobile communication device, and particularly the DSP, are not likely to be as engaged in processing a communication signal to or from a wireless communication network. Therefore, in non-call situations, components and processing power may be more readily available for noise filtering, including for the reduction of perceived background noise in the vicinity of the user.

FIG. 3is a simplified block diagram illustrating operation of mobile communication device101if the device is not connected on a call and is providing an audio signal from internal audio source107, wherein mobile communication device101is used to reduce the background noise heard by the user.

In a non-call situation, as depicted inFIG. 3, mobile communication device101is not engaged in a telephone call, but is ready to make and receive calls, and to send and receive standby maintenance information (e.g., time, network status, telephone status, etc.), or relatively brief messages (e.g., text messages, instant messages, etc.). The DSP may be used to periodically process a communication signal via analog front-end105as the mobile communication device monitors a paging channel to see if there are any calls coming in for it, and periodically monitors the serving and neighboring cells. Thus, in a non-call situation, analog front-end105can communicate with a wireless network via antenna106, wherein analog front-end105and antenna106operate in an intermittent mode.

Optionally, mobile communication device101can be disconnected from any wireless network, wherein antenna106is not sending or receiving an information signal. Thus, in a disconnected situation, antenna106and analog front-end105are in an incommunicado mode, which can help reduce battery power consumption, and also allows use of non-call features of the mobile communication device without transmitting information via antenna106if transmittals from the device would be undesirable (e.g., when transmission would interfere with the normal operation of other devices nearby). Thus, in non-call situations, DSP102is not engaged in processing large amounts of data to and/or from analog front-end105, and is more readily available for other uses, such as noise suppression when the user is listening to local audio signal107a, which is received from internal audio source107.

Internal audio source107can be non-volatile semiconductor memory, such as flash ROM, magnetic memory such as a hard disc drive, optical memory such as a miniature digital video disc, or any suitable audio source, which may, for example, be connected to internal audio source107via signal113aby plugging an external audio source (not shown) into external audio source jack113. The content provided by internal audio source107can be pre-recorded audio (e.g. mini-DVD, removable flash ROM device), downloaded and saved audio, recorded and saved audio (e.g., sound recorded using microphone103), composed audio (e.g., tunes composed on communication device101using a keypad), or any other suitable audio. Internal audio source107provides audio signal107ato noise suppressor111, which is part of DSP102. Processing parameters which may be preset or set by the user, such as volume control or equalization, may be applied to audio signal107abefore provision to noise suppressor111.

Noise characterizer110receives audio signal103a, which contains the background noise, from microphone103via microphone input node104. Noise characterizer110may process audio signal103abased on the signal's characteristics or optional user input (e.g. desired level of noise reduction). Noise characterizer110provides background noise signal110ato noise suppressor111. Noise suppressor111subtracts background noise signal110afrom local audio signal107a, to generate noise-inverted audio signal111b, which is provided to received audio processor112.

Received audio processor112may process noise-inverted audio111bin accordance with the signal's characteristics or optional user input (e.g., volume control). Received audio processor112provides to speaker108, via speaker output node109, speaker output signal108a, which corresponds to noise-inverted audio signal111b. Speaker108in turn converts electronic audio signal108ainto a sound signal that can be heard by the user. The user hears speaker output signal108a, which substantially corresponds to the sum of local audio signal107aand the inverse of audio signal103a, as well as the background noise, which substantially corresponds to audio signal103a. Thus the overall effect is that the background noise and its inverse substantially cancel each other out, and the user hears sound substantially equivalent to local audio signal107a.

Speaker output signal108amay be converted from digital form to analog form by a D/A converter (not shown) within DSP102, or by a D/A converter (not shown) external to DSP102. In a preferred embodiment, speaker108is in the form of stereo headphones worn by the user. In a preferred embodiment, microphone103is located on or proximate to headphones108, such as on the side of the headset, where it can sample the background noise as close as possible to the user's ear (not illustrated). If two microphones are used, such as if each headphone has a microphone, then the signals from the microphones can be combined to provide average noise reduction to both ears, or each signal can be separately processed to provide separate noise reduction to each ear (not illustrated). In addition, if, for example, internal audio signal107ais a stereo audio signal, then DSP102can process the left side audio and noise signals and the right side audio and noise signals separately, wherein each side's signals are processed as generally described elsewhere herein.

Noise suppressor111can also operate to provide quiet to the user without receiving local audio signal107afrom internal audio source107, if, for example, internal audio source107is powered off or disconnected, or if it is not included in mobile communication device101, or is otherwise unavailable. Noise suppressor111can generate noise-inverted audio signal111bbased on background noise signal110a, which is in turn based on audio signal103a, wherein noise-inverted audio signal111bis used to reduce the amount of background noise heard by the user, thereby providing the user with relative quiet.

In an alternative embodiment (not shown), speaker output signal108ais converted into a wireless signal (e.g., using Bluetooth® technology) for transmission to headphones108from speaker output node109, which transmits speaker output signal108afrom received audio processor112. Similarly, in an alternative embodiment (not shown), audio signal103ais converted into a wireless signal (e.g., using Bluetooth® technology) for transmission from microphone103to microphone input node104for further transmission to noise characterizer110.

In an alternative embodiment (not shown), speaker108and microphone103are together in the form of a mono-aural earpiece wherein microphone103is located along the wire that connects earpiece108to mobile communication device101. In an alternative embodiment (not shown), microphone103is an integrated microphone of mobile communication device101. In an alternative embodiment (not shown), speaker108is an integrated speaker of mobile communication device101. In an alternative embodiment (not shown), mobile communication device101comprises more than one microphone, any of which can be used as microphone103. In an alternative embodiment (not shown), mobile communication device comprises more than one speaker, any one or more of which can be used as speaker108.

In an alternative implementation of the embodiment illustrated inFIG. 2, noise characterizer110inverts the background noise signal, and provides inverted background noise signal110ato noise suppressor111. Noise suppressor111adds inverted background noise signal110ato audio signal103ato generate noise-suppressed audio signal111a. In an alternative implementation of the embodiment illustrated inFIG. 3, noise characterizer110inverts the background noise signal, and provides inverted background noise signal110ato noise suppressor111. Noise suppressor111adds inverted background noise signal110ato local audio signal107ato generate noise-inverted audio signal111b.

In an alternative implementation, illustrated inFIG. 4, audio signal103ais provided directly to noise suppressor111, bypassing noise characterizer110. Noise suppressor111then subtracts audio signal103afrom local audio signal107ato generate noise-inverted audio signal111b. In an alternative implementation, illustrated inFIG. 5, noise suppressor111generates speaker output signal108aand provides signal108ato speaker108, bypassing received audio processor112. Speaker108converts speaker output signal108ainto a sound signal that can be heard by the user, wherein hearing includes hearing silence if, for example, local audio signal107ais not provided to noise suppressor111. In an alternative implementation, noise characterizer110inverts the background noise signal, and provides inverted background noise signal110ato noise suppressor111. Noise suppressor111adds inverted background noise signal110ato local audio signal107ato generate speaker output signal108a. In an alternative implementation, illustrated inFIG. 6, audio signal103ais provided to noise suppressor111, bypassing noise characterizer110, and noise suppressor111generates speaker output signal108afor provision to speaker108, bypassing received audio processor112.

In an alternative embodiment, DSP102converts noise-suppressed audio signal111afrom digital to analog before transmission to analog front-end105, which does not then perform a digital-to-analog conversion. In an alternative embodiment, DSP102converts received audio signal105afrom analog to digital, thus analog front-end105does not then perform an analog-to-digital conversion.

The present invention may be implemented as circuit-based processes, including possible implementation as a single integrated circuit (such as an ASIC or an FPGA), a multi-chip module, a single card, or a multi-card circuit pack. As would be apparent to one skilled in the art, various functions of circuit elements may also be implemented as processing steps in a software program. Such software may be employed in, for example, a digital signal processor, micro-controller, or general-purpose computer.

Although the steps in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those steps, those steps are not necessarily intended to be limited to being implemented in that particular sequence.

The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures. Furthermore, the use of particular terms and phrases herein is for the purpose of facilitating the description of the embodiments presented and should not be regarded as limiting.

References in descriptions of alternative embodiments to particular figures or previously-described embodiments do not limit the alternatives to those particular shown or previously-described embodiments. Alternative embodiments described can generally be combined with any one or more of the other alternative embodiments shown or described.