HK1018373B - Method and apparatus for adaptive volume control for a radiotelephone - Google Patents

Description

Method and apparatus for adaptive volume control

Technical Field

The present invention relates to the field of audio systems, and more particularly to audio systems such as cellular radiotelephones for use in environments having high ambient noise levels such as car noise.

Background

Cellular radiotelephones often provide a hands-free function for safety and convenience. By using a speaker and an external microphone, the driver of the car can participate in a telephone conversation without having to take his hands off the steering wheel. Fig. 1 shows a conventional hands-free system. As shown, the radiotelephone 130 is connected to a far-end speaker 110 and a microphone 120 located in a vehicle (represented by block 100). Typically, the volume of the speaker 110 must be adjusted to be quite large in order to be able to exceed the ambient noise (e.g., engine noise, wind noise, and road noise) in order for the driver to hear the caller's voice. The radiotelephone 130 typically still uses the moving coil speaker 110. In fact, radiotelephones often incorporate a speaker in the handset of the radiotelephone, thereby limiting the size of the speaker 110 to the space available in the handset.

Fig. 2 shows a schematic cross-sectional view of a moving coil loudspeaker. The pliable edge suspension 220 and the pliable center suspension 230 freely suspend the diaphragm element 270 in the open frame housing 290. The diaphragm member 270 is nominally conical in shape. The diaphragm member 270 is mechanically connected to the voice coil 240, which is disposed around the permanent magnet 280. An electrical audio signal (i.e., an alternating current of varying frequency and amplitude) is coupled to the coil 240 through a pair of wire pairs 250.

The alternating current of the electrical audio signal coupled to the coil 240 generates a magnetic field with a direction that is parallel or non-parallel to the magnetic field of the permanent magnet 280. The direction of the magnetic field depends on the direction of the current through the coil 240. An attractive or repulsive force is established by the alternating current in the coil 240 relative to the magnetic field of the permanent magnet 280. Due to the mechanical coupling between the coil 240 and the diaphragm 270 and the free movement of the diaphragm in a plane parallel to the forces generated by the parallel or non-parallel magnetic fields (i.e., perpendicular to plane 215), changes in direction and magnitude of the current generated by the audio electrical signal are converted into axial displacement of the diaphragm 270.

The pressure wave generated by the axial displacement of the diaphragm 270 propagates in air as an acoustic wave. For a given frequency, a larger displacement is associated with a larger volume. The magnitude of the sound pressure level or volume is directly related to the amount of displacement of the diaphragm member 270 relative to the plane 215. To increase the volume (i.e., sound pressure level) of the sound emanating from a moving coil speaker as shown in fig. 2, the amplitude of the drive signal applied to electrical contacts 250 may simply be increased, which results in an increased excursion 210 of diaphragm 270.

In order to reproduce sound truly, the speaker 200 should have a fairly flat frequency response. In other words, electrical signals of the same amplitude should produce the same sound pressure level regardless of the frequency of the signal in the operational frequency range of the loudspeaker. Fig. 3 shows the frequency response of a plurality of loudspeakers. Solid line 310 of fig. 3 represents the ideal flat frequency response of a loudspeaker.

Unfortunately, the frequency response that can be provided to the speaker 200 is actually worse than ideal. Due to factors such as size and materials, most loudspeakers (particularly inexpensive types) have a fairly significant dependence between sound reproduction characteristics and frequency. An example of the characteristics of a conventional speaker is shown by the dotted line of fig. 3. Fig. 3 also shows the resonant frequency 330 of the speaker. As shown in fig. 3, the resonant frequency 330 is the frequency at which the speaker produces the maximum sound pressure level at a given input signal level.

As seen in fig. 2, the diaphragm 270 is effectively limited by the absolute magnitude 210 of the deflection. Overload or clipping of the speaker occurs when the magnitude of the drive signal applied to the electrical terminals 250 requires the diaphragm 270 to move beyond the physical limits of the suspension 220, 230 or beyond the open frame cover 290 of the speaker. Fig. 4 shows that applying a fixed gain to a loudspeaker 410 having the loudspeaker characteristics shown in dotted lines results in a response shown as 420. As can be seen from fig. 4, loudspeaker overload will generally first occur at the resonant frequency 330 of the loudspeaker. Overload of the speaker occurs in response to the clip level 400 (shown in fig. 4) being exceeded. Although shown as a linear function in fig. 4 for illustrative purposes, the clip level 400 is highly non-linear in nature and frequency dependent. Overload of the loudspeaker causes distortion of the signal near the resonant frequency and produces harmonic overtones that interfere with the audio signal at higher frequencies.

The use of a speaker in a radiotelephone device amplifies the overload phenomenon because the speaker reproduces primarily human speech. As shown in fig. 5, the power density spectrum of human speech is somewhat shifted for lower frequencies. The main energy of human speech is at or below 500Hz, however, the higher frequencies associated with the lower amplitude levels (i.e., 1000-3000Hz) provide most of the intelligibility. As can be seen from fig. 5, the power density of human speech often closely coincides with the resonant frequency of conventional speakers used in wireless telephone handsets. For example, conventional types of speakers used in wireless telephone handsets typically have a resonant frequency near 600 Hz. Therefore, a volume level that does not produce an overload when reproducing music or other audio signals may cause an overload when reproducing human speech.

Loudspeaker overload produces harmonic overtones at higher frequencies where intelligibility information of human speech is present. At high volumes combined with the informative higher frequencies of the audio signal, overload causes wideband distortion, thereby making it difficult to understand the language. When overload occurs, increasing the amplitude of the audio signal does not increase the intelligibility of the speech conveyed in the audio signal. Thus, for example, a car driver will be faced with the situation: relying on increasing the volume to overcome the ambient noise of a car would result in an unsharp, though loud, distorted sound.

U.S. patent No.5,467,393 entitled "Apparatus and method for speaker Volume and Intelligibility Control" assigned to the assignee of the present invention by Rasmusson discusses selectively compressing the signal provided to the speaker according to the Volume setting for the sound level produced by the speaker. The inventive solution improves the intelligibility of human speech produced by a loudspeaker at high volume levels. Compression of the signal applied to the speaker prevents overloading of the speaker and the level of compression can be adjusted according to the volume setting.

However, if the background noise level in the vicinity of the phone is variable, the language reproduced by the speaker of such a wireless phone may still be difficult to understand. For example, when a speakerphone is used in a car, the background noise level varies with speed and wind, with upward or downward scrolling of the wind, or other vehicle passing, etc. As background noise increases, speech produced by the speakers may be overwhelmed. On the other hand, when the background noise subsides, the speaker may become too loud. While the near-end user may compensate by manually adjusting the speaker volume, doing so while driving may be difficult or even unsafe.

European patent No. 0682437 a2 entitled "Device and Method For automatic Volume In a Communication Apparatus" by Yamashita discusses performing Sound Volume control when no voice signal is present In the transmitted audio signal.

European patent No. 0500356A2 entitled "loud speaker Telephone device including Noise compression Circuit" by Tomiyori et al discusses a Noise compression Circuit for use in a speakerphone device.

Accordingly, there remains a need in the art for a speakerphone that compensates for background noise level variations in the vicinity of the telephone.

Summary of The Invention

It is an object of the present invention to provide an improved speakerphone.

It is another object of the present invention to provide improved hands-free functionality of a speakerphone under variable ambient noise conditions.

These and other objects are achieved in accordance with the present invention by providing a loudspeaker radiotelephone system and method in which the amplitude of sound produced by the loudspeaker is adaptively controlled based on the amplitude of sound received in the microphone such that the amplitude of sound produced by the loudspeaker increases or decreases as the amplitude of sound received in the microphone increases or decreases. Thus, a speakerphone used in a noisy environment (such as in an automobile) may adapt to varying noise levels without causing unsafe actions by the driver. That is, when the noise level in the car changes due to various factors (e.g., wind, engine, and heavy traffic), the volume of the speakers will automatically adjust so that the distant speech of the call is not overwhelmed or does not have to be broadcast at a volume that is too high relative to the noise in the car.

In addition, the radiotelephone system and method of the present invention preferably reduces the echo portion of the signal produced by the microphone so that the sound produced by the speaker does not significantly affect the selection of the amplitude of the sound produced thereby. In other words, the reduction in echo reduces feedback from the speaker that would otherwise be perceived by the wireless telephone system as noise in the car. The volume of the speaker does not increase according to the reproduction of voice by the speaker.

The present invention includes an adaptive volume control radiotelephone system, comprising: a microphone generating an audio electric signal corresponding to an output of sound; a speaker for producing sound corresponding to an incoming audio electrical signal, and a transceiver for transmitting radiotelephone communications to and receiving radiotelephone communications from a remote party in response to the microphone to produce the incoming audio electrical signal, the adaptive volume control radiotelephone system further comprising:

an adaptive volume controller responsive to the output electrical audio signal and selecting the amplitude of the sound produced by the loudspeaker in accordance with the noise level monitored by the microphone such that the amplitude of the sound produced by the loudspeaker increases with increasing amplitude of the sound received at the microphone and decreases with decreasing amplitude of the sound received at the microphone; and

an echo reducer responsive to an input audio electrical signal and reducing an echo portion of an output audio electrical signal such that sound produced by the speaker does not significantly affect operation of the adaptive volume control.

The present invention also includes a method for adaptively controlling the volume of a telephone, the telephone including a microphone for producing an output audio electrical signal corresponding to sound, a speaker for producing sound corresponding to an input audio electrical signal, and a transceiver responsive to the microphone for transmitting and receiving radiotelephone communications to and from a remote party, the method comprising the steps of: generating an audio electrical signal corresponding to an input of a wireless telephone communication received from a remote party, generating sound at the speaker corresponding to the input audio electrical signal, generating an output audio electrical signal corresponding to the sound at the microphone, and transmitting the telephone communication to the remote party in response to the output audio electrical signal, the method characterized by:

selecting the amplitude of sound produced by the loudspeaker such that the amplitude of sound produced by the loudspeaker increases with increasing amplitude of sound received at the microphone and the amplitude of sound produced by the loudspeaker decreases with decreasing amplitude of sound received at the microphone; and

reducing the echo portion of the output audio electrical signal so that the sound produced by the loudspeaker does not significantly affect the performance of the amplitude selection step.

In accordance with an embodiment of the present invention, an adaptive volume control radiotelephone system includes a microphone, a speaker, a transceiver, and an adaptive volume control. The microphone produces an output electrical audio signal corresponding to the sound, and the speaker produces the sound corresponding to the input electrical audio signal. The transceiver transmits radiotelephone communications to the remote party in response to the microphone and receives radiotelephone communications from the remote party over the radio frequency channel to generate the input audio electrical signal. The adaptive volume controller is responsive to the output audio electrical signal and selects the magnitude of the sound produced by the speaker such that the magnitude of the sound produced by the speaker increases with increasing magnitude of the sound received at the microphone and decreases with decreasing magnitude of the sound received at the microphone. Thus, the volume of the speaker is automatically adjusted corresponding to the volume of the noise received at the microphone.

Such a wireless telephone system also preferably includes an echo reducer. The echo reducer is responsive to an input electrical audio signal and reduces an echo portion of an output electrical audio signal so that sound produced by the speaker does not significantly affect the operation of the adaptive volume control. Thereby, the influence of the acoustic feedback on the adaptive volume control is reduced.

The wireless telephone system may also include a near-end user voice detector that detects when the near-end user is speaking. An adaptive volume controller is responsive to the near-end user voice detector so that the amplitude of the sound produced by the speaker is not increased when the near-end user speaks. Alternatively, the adaptive volume control can continue to select the magnitude of the sound produced by the speaker as the near-end user speaks, such that the magnitude of the sound produced by the speaker increases as the near-end user speaks. Thus, the far-end party can more easily insert a conversation as the near-end user speaks.

The radiotelephone system may also include a volume estimator that estimates the amplitude of received radiotelephone communications. The adaptive volume controller is also responsive to the volume estimator such that changes in the amplitude of sound produced by the speaker due to changes in the amplitude of received radiotelephone communications are reduced. The radiotelephone system may also include a speaker overload reducer. The speaker overload reducer controls the amplitude in response to the selected volume and selectively increases the amplitude of the high frequency portion of the input audio electrical signal to reduce overload of the speaker and thereby improve intelligibility of human speech reproduced by the speaker. A noise compressor may also be included for reducing the noise portion of the output audio electrical signal. Thus, the near-end user's voice is more accurately transmitted to the far-end party.

The radiotelephone of the present invention provides an adaptive volume control such that the volume of the speaker is proportionally adjusted to the volume of the sound received at the microphone. Thus, as noise increases near the radiotelephone (e.g., as the car window rolls down), the volume of the speaker increases. Conversely, when the noise near the radiotelephone is reduced (e.g., when the car window is rolled up), the volume of the speaker is reduced. Furthermore, the echo reducer can reduce the acoustic feedback effect that would otherwise cause the speaker volume to increase in response to its own operation.

Brief description of the drawings

Fig. 1 is a simplified block diagram showing a conventional hands-free device for a radiotelephone for use in automotive applications.

Fig. 2 is a simplified cross-sectional view of a conventional moving coil speaker.

Fig. 3 illustrates frequency characteristics of a conventional moving coil speaker.

Fig. 4 illustrates the frequency characteristics of a conventional moving coil speaker at low and high sound levels.

Fig. 5 illustrates a power density spectrum for a long period of continuous human voice.

Fig. 6 is a block diagram of a cellular radiotelephone in accordance with the present invention.

Fig. 7 is a flow chart showing operations for adaptively controlling the volume of the radiotelephone of fig. 6.

Description of the preferred embodiments

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; this embodiment is provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art

The scope of the invention.

Fig. 6 shows a block diagram of a cellular radiotelephone 21 according to the invention. This wireless telephone 21 includes a microphone 23 for generating an audio electrical signal corresponding to the sound output, and a speaker 25 for generating sound corresponding to the input audio electrical signal.

The transceiver 27 transmits radiotelephone communications to the remote party in response to using the microphone 23 of another radiotelephone or a conventional landline telephone. The transceiver 27 also receives radiotelephone communications from a remote party. For example, the transceiver 27 may transmit radiotelephone communications to or receive radiotelephone communications from a base station of a cellular telephone system over a radio frequency channel, thereby facilitating communications with another cellular radiotelephone or landline telephone.

In a preferred embodiment, transceiver 27 transmits and receives digital communications. Thus, received communications may be processed by a Digital Signal Processor (DSP)33 to produce a digital input audio electrical signal, which may be converted from a digital signal to an analog signal by the speaker's digital-to-analog converter 29. In addition, the output audio electrical signal may be converted from an analog signal to a digital signal by the analog-to-digital converter 31 of the microphone and then processed by the digital signal processor 33 to produce the transmitted communication.

Alternatively, the transceiver 27 may send and receive analog communications, and these communications may be processed by an analog processor, thereby eliminating the need for a digital-to-analog converter for the speaker and an analog-to-digital converter for the microphone. In yet another alternative, the transceiver may send and receive analog communications, and these communications may be processed by a digital signal processor. Thus, the radiotelephone may include a D-a converter for the speaker and an a-D converter for the microphone as well as D-a and a-D converters between the transceiver and the digital signal processor.

The radiotelephone of the present invention also includes an adaptive volume control 35 that is responsive to the output audio electrical signal produced by the microphone 23. The adaptive volume control 35 selects the magnitude of the sound produced by the speaker 25 such that the magnitude of the sound produced by the speaker 25 increases with increasing magnitude of the sound received at the microphone 23 and decreases with decreasing magnitude of the sound received at the microphone 23. In particular, the output of the adaptive volume control 35 may be applied to a variable gain amplifier 34 which adjusts the gain applied to the input audio electrical signal in response to the selected amplitude. The volume of the speaker is automatically adjusted corresponding to the volume of the noise received at the microphone.

In other words, the output audio electrical signal produced by the microphone 23 may be used to represent a background noise level that changes as the conditions surrounding the radiotelephone change. To better understand the sound reproduced by the speaker 25, the volume of the speaker should increase as the background noise increases and decrease as the background noise decreases. Adaptive volume control 35 selects the volume of speaker 25 based on the background noise level, which is monitored by microphone 23.

As shown in fig. 6, the outgoing electrical audio signal produced by the microphone 23 is processed through a noise compressor 36 before being transmitted by the transceiver to the remote party. In particular, the noise estimator 38 monitors the output electrical audio signal and determines the noise portion of the signal. (in the case of a speakerphone used in an automobile, the noise may be caused by wind, road, engine, heavy traffic, etc..) this estimate of the noise portion of the signal may be provided to a noise compressor 36 where the noise portion of the output audio electrical signal is reduced. In addition, a signal representing the magnitude of the noise is supplied by the noise estimator 38 to the adaptive volume controller 35. This signal is used by the adaptive volume control to select the amplitude of the sound to be produced by the loudspeaker 25.

Thus, the radiotelephone of the present invention can automatically adapt to changing background noise levels without requiring action by the near-end user. This feature is particularly advantageous when used in a speaker radiotelephone in an automobile because the background noise level can be highly variable, there is a distance between the near-end user and the speaker, and manual adjustment of the volume while driving is therefore dangerous. Thus, this wireless telephone 21 can automatically adjust to changing background noise levels (which may be caused, for example, by rolling up or down a window, changing speed, changing wind, passing other vehicles, or being passed by other vehicles, etc.).

Also, because the adaptive volume control 35 may be implemented through digital signal processing, its functionality may be provided by programming a digital signal processor as used in conventional digital cellular radiotelephones. In other words, adaptive volume control may be provided by programming existing hardware. Thus, this functionality can be provided without adding significant manufacturing cost or bulk to the radiotelephone.

The radiotelephone 21 may also include an echo reducer 37 that is responsive to the incoming audio electrical signal. The echo reducer 37 reduces the echo portion of the audio electrical signal corresponding to the output of sound produced by the microphone. By reducing the echoic portion of the output audio electrical signal, the sound produced by speaker 25 does not significantly affect the operation of adaptive volume control 35. In addition, the quality of the output audio electrical signal is improved for transmission by the transceiver to the remote party.

This aspect of the invention is particularly advantageous when used in a hands-free speaker radiotelephone in an automobile. This is because there may be an acoustic feedback path from the speaker 25 to the microphone 23. Without the echo reducer 37, the far-end speech reproduced by the loudspeaker 25 may be received by the microphone 23 (acoustic feedback), which indicates a higher background noise level, causing the adaptive volume control 35 to increase the volume. This feedback will increase the volume as long as the far-end party continues to speak. The echo reducer 37 reduces this problem by reducing the feedback.

The echo reducer 37 may be implemented by using an echo reducing filter, such as a Finite Impulse Response (FIR) filter 39, the output of which is subtracted from the output audio electrical signal in a subtractor 41. The coefficients of FIR filter 39 may be continuously improved by using a Least Mean Square (LMS) algorithm. As shown, the output of the subtractor 41 may be provided to a coefficient modifier 43, which modifies the coefficients of the FIR filter 39 using an LMS algorithm.

Various implementations of echo reduction filters are discussed in, for example, the following patents: U.S. Pat. No.5,237,562 entitled "Echo Path Transition Detection" to Fujii et al; esaki et al, U.S. Pat. No.5,131,032 entitled "Echo cancellation Communication Apparatus Employing the Same"; koike's U.S. Pat. No.5,084,865 entitled "Echo Canceller with FIR and IIR Filters for canceling Long Tail Echoes". More echo reduction filters are discussed in the following patents: U.S. Pat. No.5,475,731, 1996, 2, 24 to Rasmusson entitled "Echo cancellation System and Method Using Echo Estimate to modified Error Signal" (Echo cancellation System and Method for correcting Error signals Using Echo estimation); U.S. patent application Ser. No.08/393,711, 1995, 2, 24, entitled "Apparatus and method for Canceling Acoustic echo Including nonlinear distortion of a speakerphone," Apparatus and method for Canceling Acoustic echo; U.S. patent application Ser. No.08/393,726 entitled "Apparatus and method for adaptive precompensation for Loudspiaker simulations" to Dent et al, all of which are assigned to the assignee of the present invention. All six of the above references are incorporated herein by reference.

As discussed above with respect to adaptive volume control 35, its functionality may be provided through digital signal processing. No additional hardware may be required by programming an existing digital signal processor. Thus, the echo reducer 37 can be realized without adding significant manufacturing cost or volume. In addition, the echo reducer 37 has an advantage of reducing the return of the echo of the far-end side to the far-end side.

The wireless telephone 21 may also include a near-end user voice detector 45 for detecting when the near-end user 45 of the wireless telephone 21 is speaking. In accordance with this aspect of the invention, adaptive volume control 35 is also responsive to near-end user voice detector 45 such that the amplitude of the sound produced by speaker 25 is not increased when the near-end user speaks. In particular, the noise estimate produced by the noise estimator 38 is not updated while the near-end user of the radiotelephone 21 is speaking, so that the volume of the sound produced by the speaker 25 is not increased while the near-end user is speaking. This feature also has the advantage of not including the near-end user's voice in the noise estimate, which is removed from the output audio electrical signal by the noise compressor 36.

The near-end user voice detector 45 preferably detects human speech by recognizing harmonic structures, such as vowel sounds that are relatively unique to human speech. Alternatively, the near-end user voice detector 45 may operate by determining a minimum threshold for a predetermined frequency, typically associated with human speech, or by determining a minimum threshold for amplitude (assuming that human voice is above it). The voice detector is also adapted to learn and recognize specific voice patterns of the near-end user. By not adjusting the volume of the speaker 25 when the near-end user is speaking, the voice volume of the far-end party is not increased when the parties are talking. As with the adaptive volume controller 35, the near-end user voice detector 45, the noise estimator 38, and the noise compressor 36 may be implemented in the DSP 33.

Alternatively, adaptive volume control 35 can continue to select the magnitude of the sound produced by speaker 25 while the near-end user is speaking. Thus, the amplitude of the sound produced by speaker 25 increases as the near-end user speaks. This feature may have the advantage that: the far-end party may more easily insert the conversation as the near-end user speaks. Also, the radiotelephone 21 may include a near-end user input for selecting whether the adaptive volume control 35 is updated to the speaker-selected amplitude when the near-end user speaks. This near end user input may be a double throw switch that sets and clears a flag in the digital signal processor. In this case, adaptive volume control 35 preferably has a relatively short time constant (fast response) so that the volume of speaker 25 is quickly adjusted when the near-end user starts or stops speaking.

The radiotelephone 21 may also include a volume estimator 47 that estimates the amplitude of radiotelephone communications received by the transceiver 27. Adaptive volume controller 35 is responsive to volume estimator 47 such that changes in the amplitude of sound produced by speaker 25 due to changes in the amplitude of radiotelephone communications received by transceiver 27 are reduced. Therefore, the change in the volume of the voice reproduced by the speaker 25 due to the change in the volume of the voice of the far-end side can be reduced. The volume of the far-end party's voice may vary from call to call due to differences in gain along different communication channels. For example, different gains may be due to differences in remote telephones, differences in landline connections, and differences in cellular radio frequency channels, among others. In addition, the volume of the far-end party's speech may change within a call due to movement of the far-end party relative to the far-end telephone, changes in the far-end party's voice, etc

As shown in fig. 6, the volume estimator 47 receives radiotelephone communications as input from the transceiver 47. The volume estimator 47 generates an output representing the average volume of the far-end party's speech. Preferably, the volume estimator produces an output based on the average volume taken over a sufficiently long time interval to account for pauses and other anomalies in speech. Volume estimator 47 also preferably identifies time intervals when the far-end party is not speaking so that background noise from the far-end phone is not significantly amplified during periods of silence. The output of the volume estimator 47 is applied to the adaptive volume controller 35. Thus, adaptive volume control 35 may select the amplitude of the sound produced by speaker 25 as a function of the noise received by microphone 23 and the changes in the radiotelephone communications received from transceiver 27.

The radiotelephone 21 may also include a speaker overload reducer 51 responsive to the magnitude of the selected adaptive volume control 35. The speaker overload reducer 51 selectively increases the amplitude of the high frequency portion of the input audio electrical signal to reduce overload of the speaker. Therefore, the intelligibility of human voice reproduced by the speaker can be improved at high volume. Specifically, the variable gain amplifier 34 uniformly adjusts the amplitude of the input audio electrical signal of all frequencies in a range in which speaker overload is unlikely to occur. If the adaptive volume control 35 selects an amplitude outside this range, a further increase in gain may be provided by the overload reducer 51. The overload reducer 51 selectively increases the amplitude of the high frequency portion of the input audio electrical signal to further increase the volume of the speaker 25 without causing overload.

Thus, if adaptive volume control 35 selects an amplitude that is likely to cause overload or clipping of speaker 25, overload reducer 51 selectively increases the amplitude of the high frequency portion of the input audio electrical signal, thereby reducing overload and enhancing intelligibility. Reducing overload of a speaker is discussed in U.S. patent No.5,467,393 entitled "Apparatus and Method for Volume and intelligibility Control for Loudspeaker," assigned to Rasmusson and the assignee of the present invention. This patent is incorporated herein by reference.

The functions of the radiotelephone 21, including the adaptive volume controller 35, the overload reducer 51, the noise estimator 38, the noise compressor 36, the near-end user voice detector 45, the volume estimator 47, and the variable gain amplifier 34 discussed above, may be implemented through digital signal processing calculations. Thus, each of these features can be implemented in the DSP 33. Since many cellular radiotelephones include a DSP, these functions can be implemented by programming the DSP without adding additional hardware. Thus, each of these functions can be added without significantly increasing the manufacturing cost or bulk of the radiotelephone. Furthermore, a transceiver may be defined to include one or more of such functions, as will be appreciated by those skilled in the art.

The functionality and other functionality of the adaptive volume control 35 of the present invention is particularly advantageous when used in hands-free speaker radiotelephones in automobiles, as this application involves an acoustic feedback path through a potentially noisy environment. Thus, the adaptive volume control 35 matches the speaker volume to the noise level received by the microphone. However, these functions may also be used for a hand-held cellular radiotelephone, a satellite radiotelephone, a cordless landline telephone, a hands-free speakerphone, or a conventional landline telephone. In addition to providing voice communications, the telephones discussed above may also include components for data, video, and/or multimedia communications. In either of these applications, the near-end user may wish to have the phone automatically adjust its volume based on the noise received at the microphone.

The operation for adaptively controlling the volume of the radiotelephone of fig. 6 is shown in fig. 7. Transceiver 27 receives radiotelephone communications from a remote party, block 61. At block 63, the received radiotelephone communications are processed by the DSP33 and the speaker 25 generates sounds corresponding to the incoming electrical audio signals. At block 65, the microphone 23 generates an output electrical audio signal, and at block 67, the echo portion of the output electrical audio signal is reduced. At block 69, the outgoing electrical audio signals are processed by the DSP33 to generate radiotelephone communications signals for transmission by the transceiver 27.

At block 71, the magnitude of the sound produced at the speaker 25 is selected. In particular, this amplitude is chosen such that it increases with increasing amplitude of the sound received in the microphone 23 and decreases with decreasing amplitude of the sound received in the microphone 23. Thus, the volume of speech reproduced by speaker 25 may approximately match the volume of noise in the vicinity of the radiotelephone.

The operation of selecting the amplitude may include detecting when the near-end user is speaking and maintaining a constant sound amplitude produced by speaker 25 while the near-end user is speaking. Thus, the amplitude of the sound produced by speaker 25 does not increase significantly when the near-end user speaks. Alternatively, the amplitude may be selected such that the amplitude of the sound produced by speaker 25 increases when the near-end user speaks. In this way, the far-end party can more easily plug in the conversation while the near-end user is speaking.

In addition, the amplitude of the received radiotelephone communications can be estimated and the variation in the amplitude of the sound produced by the speaker due to the variation in the amplitude of the received radiotelephone communications is reduced. Thus, the variation of the voice of the far-end side reproduced by the speaker can be reduced.

The amplitude of the high frequency portion of the input audio electrical signal can be selectively increased to reduce overloading of the speaker and to improve intelligibility of human speech reproduced by the speaker. Thus, at high volume, overload of the speaker may be reduced and clarity may be improved as the volume of the speaker increases. The noise portion of the output audio electrical signal may also be reduced, thereby allowing the near-end user's speech to be more accurately transmitted to the far-end party.

In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims (14)

1. An adaptive volume control radiotelephone system (21), comprising: a microphone (23) for generating an audio electrical signal corresponding to the output of sound; a speaker (25) for producing sound corresponding to an incoming audio electrical signal, and a transceiver (27) for transmitting radiotelephone communications to and receiving radiotelephone communications from a remote party in response to the microphone (23) to produce the incoming audio electrical signal, said adaptive volume control radiotelephone system (21) comprising:

an adaptive volume controller (35) responsive to the output audio electrical signal and selecting the magnitude of sound produced by said speaker (25) in dependence on the noise level monitored by the microphone (23) such that the magnitude of sound produced by said speaker (25) increases with increasing magnitude of sound received at said microphone (23) and decreases with decreasing magnitude of sound received at said microphone (23); and

an echo reducer (37) responsive to an input audio electrical signal and reducing an echo portion of an output audio electrical signal so that sound produced by the speaker (25) does not significantly affect the operation of the adaptive volume control (35).

2. An adaptive volume control radiotelephone system (21) according to claim 1 further comprising a near-end user voice detector (45) that detects when a near-end user is speaking, wherein said adaptive volume control (35) is further responsive to said near-end user voice detector such that the amplitude of sound produced by said speaker (25) is not increased when the near-end user is speaking.

3. The adaptive volume control radiotelephone system (21) according to claim 1 wherein said adaptive volume control (35) is capable of continuing to select the magnitude of the sound produced by said speaker (25) while the near-end user is speaking such that the magnitude of the sound produced by said speaker (25) increases while the near-end user is speaking.

4. An adaptive volume control radiotelephone system (21) according to claim 1 further comprising a volume estimator (47) that estimates the amplitude of radiotelephone communications received from a remote party, wherein said adaptive volume controller is further responsive to said volume estimator (47) such that changes in the amplitude of sound produced by said speaker (25) due to changes in the amplitude of received radiotelephone communications are reduced.

5. An adaptive volume control radiotelephone system (21) according to claim 1 further comprising a speaker overload reducer (51) responsive to a selected magnitude of said volume control and having means for selectively increasing the magnitude of the high frequency portion of the input audio electrical signal to reduce overload of said speaker (25) and thereby increase intelligibility of human speech reproduced by said speaker (25).

6. An adaptive volume control radiotelephone system (21) in accordance with claim 1 further comprising a noise compressor (36) that reduces the noise portion of the output audio electrical signal so that the near-end user's speech is more accurately transmitted to the far-end party.

7. An adaptive volume control radiotelephone system (21) according to claim 1 wherein said telephone system (21) comprises a radiotelephone system (21), wherein said telephonic communications comprise radiotelephone communications, and wherein said radiotelephone communications are received from a remote party over a radio frequency channel to produce an incoming audio electrical signal.

8. A method for adaptively controlling the volume of a telephone (21), the telephone including a microphone (23) for producing an output audio electrical signal corresponding to sound, a speaker (25) for producing sound corresponding to an input audio electrical signal, and a transceiver (27) responsive to the microphone (23) for transmitting and receiving wireless telephone communications to and from a remote party, the method comprising the steps of: generating an audio electrical signal corresponding to an input of a radiotelephone communication received from a remote party, generating sound corresponding to the input audio electrical signal at the speaker (25), generating an output audio electrical signal corresponding to the sound at the microphone (23), and transmitting a telephone communication to the remote party in response to the output audio electrical signal, the method characterized by:

selecting the amplitude of the sound produced by the loudspeaker (25) such that the amplitude of the sound produced by the loudspeaker (25) increases with increasing amplitude of the sound received at the microphone (23) and the amplitude of the sound produced by the loudspeaker (25) decreases with decreasing amplitude of the sound received at the microphone (23); and

reducing the echo portion of the output audio electrical signal so that the sound produced by the loudspeaker does not significantly affect the performance of the amplitude selection step.

9. The method according to claim 8, wherein said amplitude selecting step comprises detecting when the near-end user is speaking and maintaining a constant amplitude of the sound amplitude produced by said speaker (25) while the near-end user is speaking, such that the sound amplitude produced by said speaker (25) is not increased while the near-end user is speaking.

10. The method according to claim 8, wherein said amplitude selecting step comprises selecting the amplitude of the sound produced by said speaker (25) when the near-end user is speaking such that the amplitude of the sound produced by said speaker (25) increases when the near-end user is speaking.

11. The method of claim 8, further comprising the steps of:

estimating the amplitude of a radiotelephone communication received from a remote party; and

variations in the amplitude of sound produced by the speaker (25) due to variations in the amplitude of radiotelephone communications received from a remote party are reduced.

12. The method of claim 8, further comprising the steps of:

the amplitude of the high frequency portion of the input electrical audio signal is selectively increased to reduce overloading of the speaker (25) and thereby improve intelligibility of human speech reproduced by the speaker (25).

13. The method of claim 8, further comprising the steps of:

the noise portion of the output audio electrical signal is reduced, thereby allowing the near-end user's speech to be more accurately transmitted to the far-end party.

14. The method according to claim 8, wherein said telephone (21) comprises a wireless telephone (21), and wherein said telephone communication comprises a wireless telephone communication.