BACKGROUND OF THE INVENTION

The present invention relates to ambient noise-reduction systems for communications apparatus such as cellular phone handsets, walkie-talkies or the like, and it relates more especially to systems for handsets that are capable of being used both with and without listening devices such as earphones, headphones or headsets. That is, the user of the apparatus may choose, at any given time, to listen directly to the internal loudspeaker provided in the apparatus, or to listen using a wired or wireless listening device connected temporarily to the handset.

It has been proposed to provide ambient noise reduction in a cellular phone handset, by providing a signal processing device that receives a signal derived from detected ambient noise, and generates a sound that tends to cancel the effect of the ambient noise at the ear of the user.

It has now been recognized that, if ambient noise reduction is to be provided in a communications apparatus that can be listed to either directly by means of an internal loudspeaker or by means of a separate listening device, the ambient noise reduction must take account of the fact that the use of the separate listening device changes the sound environment, in terms both of the degree of exposure to ambient noise and of the noise-sensing and signal-processing approaches needed to reduce the ambient noise as perceived by the user.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided noise reduction circuitry, comprising:a first input, for receiving signals from at least one first microphone;a second input, for receiving signals from at least one second microphone; andmeans for determining whether a second microphone is connected to the second input;wherein the noise reduction circuitry is adapted to generate a noise cancellation signal by applying a first transfer function to the signals received from the first microphone when it is determined that no second microphone is connected to the second input;and is adapted to generate a noise cancellation signal by applying a second transfer function to the signals received from the second microphone when it is determined that a second microphone is connected to the second input, wherein the second transfer function is different from the first transfer function.

According to a second aspect of the present invention, there is provided a communications apparatus, comprising:at least one internal microphone, for detecting ambient noise around the apparatus;an internal speaker, for generating a sound signal to be heard by a user of the apparatus;means for receiving a listening device, the listening device comprising a listening device speaker and a listening device microphone, for detecting ambient noise around the listening device;means for determining whether a listening device is connected to the apparatus; andnoise reduction circuitry, wherein the noise reduction circuitry comprises:a first input, for receiving signals from the or each internal microphone;a second input, for receiving signals from the listening device microphone; andmeans for receiving a signal from the means for determining whether listening device is connected to the apparatus;wherein the noise reduction circuitry is adapted to generate a noise cancellation signal by applying a first transfer function to the signals received from the internal microphone, and to apply the noise cancellation signal to the internal speaker, when it is determined that no listening device is connected to the apparatus;and is adapted to generate a noise cancellation signal by applying a second transfer function to the signals received from the listening device microphone and to apply the noise cancellation signal to the listening device speaker, when it is determined that a listening device is connected to the apparatus, wherein the second transfer function is different from the first transfer function.

According to a third aspect of the present invention, there is provided a listening device, comprising means for identifying the listening device to a distinguishing device provided on a communications apparatus.

Thus, one embodiment of the invention can provide a cellular telephone handset provided with a loudspeaker means mounted internally thereof and further comprising an ambient noise-reduction system; wherein the said system comprises at least one local sound sensor means for sensing ambient noise received at said handset and for developing first electrical signals indicative of the sensed ambient noise, and signal processing means for operating upon said first electrical signals in accordance with a first processing mode to develop processed first signals for application to said internal loudspeaker means in a sense tending to reduce said ambient noise as perceived by a user of the handset; and wherein the handset further comprises receptor means adapted to removably receive a connector device for temporarily connecting said handset to at least one earphone or headphone having loudspeaker means directly associated therewith, connection sensor means for detecting the connection of said connector device to said receptor means and at least one further sound sensor means for sensing ambient noise received at said at least one earphone or headphone and for developing second electrical signals indicative of the ambient noise sensed by said further sound sensor means; the handset comprising means responsive to said detection by the connection sensor means for causing said processing means to operate upon said second electrical signals in accordance with a second processing mode, different from the first, to develop processed second signals for application to the loudspeaker means associated with said at least one earphone or headphone in a sense tending to reduce said ambient noise as perceived by a user of the handset with said at least one earphone or headphone.

In preferred embodiments of the invention, the signal processing means, whether operating in the first or the second mode, is provided by a processing unit within the handset.

In some preferred embodiments, the said processing unit comprises, or is incorporated within, a central processing unit (CPU) of the handset itself.

In other preferred embodiments, the said processing unit is separate from the handset CPU and comprises a dedicated integrated circuit (digital or analogue), or a discrete analogue circuit.

In still further preferred embodiments of the invention, the handset incorporates identifier means associated with the connection sensor means for distinguishing between at least two different types of earphone or headphone connectable to said handset, and further means for causing said processing means to operate upon second electrical signals provided to the handset in accordance with a processing mode dedicated to the type of earphone or headphone for the time being identified by said identifier means as being connected to said handset.

The identifier means preferably responds to a connector coding applied to earphones or headphones by their manufacturers.

Preferably, the connector coding comprises a digital numeric coding.

In some preferred embodiments, the handset comprises first and second relatively movable portions; the first portion presenting a keypad for use in operating the cellular telephone and a speech microphone into which the user may speak, and the second portion containing the internal loudspeaker means and the local sound sensor means.

In such embodiments it is preferred that the second portion further contains a screen to display operating information for said handset.

The second portion may be rendered movable in any convenient manner with respect to the first portion. In preferred embodiments, however, the first and second portions are hinged to one another (“clam-shell” style), to provide a “flip-up” configuration for the handset, or one portion is slidable with respect to the other to provide a “slider” configuration.

In any event, the local sound sensor means preferably comprises at least one ambient microphone disposed to receive ambient noise incident upon the handset. The ambient microphone is preferably mounted internally of said handset and provided with an inlet port through which said ambient noise can enter.

Further preferably, the siting and/or the configuration of said inlet port and/or of an acoustical conduit linking said port to said ambient microphone is adapted to render said ambient microphone preferentially sensitive to said ambient noise rather than the user's speech.

