TELEPHONE APPARATUS WITH VOLUME CONTROL

Abstract: The volume of a loudspeaker in a telephone is automatically adjusted according to the ambient noise at the telephone location. During a predetermined time window which exists during the initial period of a telephone call, the ambient noise is measured, and the volume of the loudspeaker adjusted accordingly. For example, the time period may exist between the time when the telephone goes off-hook, until the time when the handset is placed near the ear. Adjusting the ambient noise during this period has the advantage of not having to filter out the user's speech, as would be the case when measuring the ambient noise while the user is speaking. Furthermore, there is no requirement for circuitry which detects gaps in speech.

Description: TELEPHONE APPARATUS WITH VOLUME CONTROL FIELD OF THE INVENTION The invention relates to a method and a circuit arrangement for automatically adjusting the volume of a loudspeaker in a telephone in response to ambient noise levels, and in particular to the ambient noise measured during the initial dead time of a telephone call. BACKGROUND OF THE INVENTION When making or answering a telephone call, the background noise at the subscriber' s location is often intrusive and does not permit the subscriber to hear what the other subscriber is saying. Additionally, the volume of speech from the handset can be intrusive in quiet environments . This problem is particularly relevant to mobile phones which, by their very nature, may be used in a diverse range of locations. Consider the case of a phone call being made from a church to a building site. When the call is made from the phone (in the church for instance) , very little background noise exists, and the volume of the phone should ideally be turned down accordingly, so that the voice of the other subscriber does not echo around the church. When the call is received at the building site, a large amount of background noise exists, and the volume of the phone should ideally be turned up to compensate, avoiding the problem of having to find a quiet area to hear a received call. Various systems have been designed to overcome this problem by adjusting the volume of a loudspeaker in a telephone in response to ambient noise detected in the vicinity of the telephone. The simplest of these have manual buttons for adjusting the volume according to the background noise. These have the disadvantage of requiring the caller to manually adjust the volume during a call. This can be cumbersome, particularly on a mobile phone. In addition, until such time as the volume is adjusted, there will be a period during which the volume will be at an undesirable level . Another known method is to automatically measure the ambient noise, and automatically adjust the loudspeaker volume accordingly. With such methods, it is important that the ambient noise is not detected at times when the user is speaking, so that the speaker's voice does not corrupt the measured ambient noise level. To overcome this problem, these systems must measure the ambient noise during gaps in speech, and then adjust the volume of the telephone's loudspeaker in relation to the ambient noise measured in these gaps. Figure 1 shows the steps involved in adjusting the loudspeaker volume in this type of system. A speech detector continually monitors the speech for any gaps, as shown in steps SI and S2. When a gap is detected, the ambient noise level is measured in step S3. The volume of the loudspeaker is then adjusted automatically in step S4 in response to the measured ambient noise . This type of system has the disadvantage of requiring complex speech detectors, implemented either in hardware or software, to determine when the gaps in speech exist . Other known systems adjust the volume continuously throughout the duration of a telephone call, by continuously measuring the ambient noise, regardless of whether the user is speaking. Such systems have the disadvantage of requiring complex algorithms to compensate or cancel the user' s voice signal from the measured ambient noise. The aim of the present invention is to overcome these disadvantages of automatically adjusting the volume of a loudspeaker in response to ambient noise, by measuring the ambient noise at a predetermined time when it is known that there will be no speech. SUMMARY OF THE INVENTION According to the first aspect of the invention, there is provided a method of automatically adjusting the volume of a loudspeaker in a telephone according to the ambient noise at the telephone location, wherein the method comprises the steps of defining a predetermined time window which exists during the initial period of a telephone call, measuring the ambient noise during the predetermined time window, and adjusting the volume of the loudspeaker in relation to the measured ambient noise. According to a second aspect of the invention, there is provided a circuit arrangement for automatically adjusting the volume of a loudspeaker in a telephone in relation to the ambient noise at the telephone location, wherein the circuit arrangement comprises means for defining a predetermined time window which is triggered by a predetermined signal at the beginning of a telephone call, means for measuring the ambient noise during the predetermined time window, and means for adjusting the volume of the loudspeaker in relation to the measured ambient noise. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a method of adjusting loudspeaker volume according to the prior art, Figures 2a to 2d show the signals present during the initial stages of a telephone call at a called telephone set, Figures 3a to 3e show the signals present during the initial stages of a telephone call at a calling telephone set, Figure 4 shows a method of adjusting the loudspeaker volume according to the present invention. DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION Figures 2a-2d show the various signals which are present during the initial stages of receiving and answering a telephone call at a called telephone set. In response to a ringing signal shown in 2a, the called party answers the call at time t-_. This can be accomplished by either lifting the handset in a conventional telephone, or by accepting the call in a mobile phone, for example by pressing the "receive" key. From the time when the handset of a conventional telephone is first taken off-hook, or the mobile phone is first turned on to accept an incoming call, there will inevitably be at least a few milliseconds during which the phone is operational, but the person answering the call has not spoken. This corresponds to the time it takes the called person to raise the telephone handset to the proximity of the ear. The called person does not speak until time t 2 shown in figure 2b. Thus, there is a period of dead-time Y which exists between times tl and t2, as shown in figure 2c. Typically, there will be a minimum delay of approximately 500 milliseconds before the user speaks. This delay of typically 500 milliseconds is due to the speed of reaction of a human being in speaking after picking up the handset. With mobile phones, they have to be held in front of the user to be turned on, then moved up to the side of the user' s head before the user can hear. The operation of mobile phones in this manner is such that there will always be this period of initial dead-time Y during which the ambient noise can be measured. Although the ambient noise may be measured at any time during this dead-time Y, it is preferably measured during at least a part of a time window X shown in figure 2d, whereby X is typically 200 milliseconds, ie. less than the known dead-time Y. In this way, an element of safety margin is built into the system. Figures 3a to 3e show the signals which are present during the initial stages of a telephone call at a calling telephone set . The user turns on the mobile telephone, or lifts the receiver of a conventional telephone at time t as shown in figure 3a. After the user has dialled the telephone number, the ringing signal will begin at time t 2 , and end at time t 3 corresponding to the time at which the called party answers the telephone, figure 3b. Figure 3c shows that the called party will not speak until time t 4 , which again is typically 500 milliseconds after t 3 . As mentioned above, this corresponds to the time taken by the called party to answer the call and raise the handset to the ear. Since the calling telephone becomes operational at point t x , it is possible to measure the ambient noise during the period Z (shown in figure 3d) . This corresponds to the initial dead-time between the telephone being made operational and the called party speaking. Preferably, the ambient noise is measured at the calling telephone during at least a part of the time window W shown in figure 3e. This corresponds to the time from which the called party answers the call, until the called party speaks. This avoids the possibility of the ambient noise measurement being corrupted between times t x and t 3 , which may occur if the calling party speaks while dialling or waiting for the called party to answer. However, the ambient noise could be measured at the calling telephone during any window between times t 2 and t 4 . The dialling operation ends at time t 2 , which means that the "bleeps" that are generated when dialling, will not corrupt the ambient noise measurements . Any ringing tone measured during this period can be easily removed, since this is also generated in the calling phone. Figure 4 shows the steps involved in adjusting the volume of the telephone. A time window in defined in step SI at a predetermined time described above in relation to figures 2a-2d and 3a-3e. The ambient noise is then measured during this time window, S2, and the volume of the loudspeaker adjusted accordingly, S3. If little or no background noise is detected, then the volume of the phone is turned down. If background noise over a certain threshold is detected, then the volume is turned up. Preferably, the volume is adjusted in proportion to the background noise. Some digital telephones have circuitry for generating "comfort noise" during silent intervals. This comfort noise is intended to reassure the listener than the telephone line has not gone dead. In telephones having this feature, the comfort noise signal may be used to adjust the loudspeaker volume at subsequent intervals during the call . This is made possible by the fact that the comfort noise signal is only present when there is no speech. The volume adjustment function could therefore be initiated during these gaps if there is sufficient time for the ambient noise measurements to be carried out. Preferably, the background noise should still be filtered out as much as possible using existing filtering techniques so as not to pass on much of the building site noise to the subscriber in the church for example. The invention described above allows speech to be transmitted at a constant volume level, thus enabling the handset to remove the need for shouting in a church to make the voice be heard at a building site, and removing the need for whispering at a building site in order to not disturb a church environmen . The invention is not limited to the details described in the preferred embodiment, but may be realised using alternatives readily apparent to a person skilled in the art, within the scope of the invention as defined in the claims. For example, the solution may be implemented using either hardware or software. Also, although the invention has been described in relation to measuring noise level and adjusting the speaker volume, the invention may also measure, for example, the dynamic range of ambient noise, or adjust particular frequencies of the loudspeaker output. Also, when measuring the ambient noise during a time window, this may be an instantaneous measurement, or an average measurement taken over the period.

Claims: Claims 1. A method of automatically adjusting the volume of a loudspeaker in a telephone according to the ambient noise at the telephone location, the method comprising the steps of : defining a predetermined time window which exists during the initial period of a telephone call; measuring the ambient noise during the predetermined time window; and adjusting the volume of the loudspeaker in relation to the measured ambient noise. 2. A method according to claim 1 wherein the time window is triggered by the off-hook signal of a called telephone . 3. A method according to claim 1 wherein the time window is triggered by the receive button of a called mobile telephone. 4. A method according to claim 1 wherein the time window is triggered by the off-hook signal of a calling telephone . 5. A method according to claim 1 wherein the time window is triggered by the send button of the calling mobile telephone . 6. A method according to any preceding claim wherein the time window has a fixed length. 7. A method according to claim 6 wherein the time window is less than 500 milliseconds. 8. A method according to claim 6 wherein the length of the time window is set in relation to a period during which no speech is expected. 9. A method according to any preceding claim wherein the volume may be further adjusted by defining a further time window, the further time window being triggered by a signal normally used to create comfort noise. 10. A method according to any preceding claim wherein the dynamic range of the ambient noise is measured. 11. A method according to any preceding claim wherein particular frequencies of the loudspeaker output are adjusted in accordance with the measured ambient noise. 12. A circuit arrangement for automatically adjusting the volume of a loudspeaker in a telephone in relation to the ambient noise at the telephone location, the circuit arrangement comprising: means for defining a predetermined time window which is triggered by a predetermined signal at the beginning of a telephone call; means for measuring the ambient noise during the predetermined time window; and means for adjusting the volume of the loudspeaker in relation to the measured ambient noise . 13. A circuit arrangement according to claim 12, wherein the predetermined signal is the off-hook signal of the called telephone . 14. A circuit arrangement according to claim 12 wherein the predetermined signal is the depressing of -lithe receive button on a called mobile telephone . 15. A circuit arrangement according to claim 12 wherein the predetermined signal is the off-hook signal of a calling telephone. 16. A circuit arrangement according to claim 12 wherein the predetermined single is the depressing of the "send" button on the telephone. 17. A circuit arrangement according to any of claims 12 to 16 wherein the time window has a fixed length. 18. A circuit arrangement according to claim 17, wherein the time window is less than 500 milliseconds. 19. A circuit arrangement according to claim 17, wherein the length of the time window is set in relation to a period during which no speech is expected. 20. A circuit arrangement according to any of claims 12 to 19, wherein the means for generating a predetermined time window can generate a further time window in which the ambient noise may be measure, the further time window being triggered by a signal normally used to generate comfort noise. 21. A circuit arrangement according to any of claims 12 to 20 wherein the means for measuring ambient noise measures the dynamic range of the ambient noise. 22. A circuit arrangement according to any of claims 12 to 21 wherein particular frequencies of the loudspeaker output are adjusted in accordance with the measured ambient noise. 23. A method of automatically adjusting the volume of a loudspeaker in a telephone substantially as herein described with reference to, and as shown in, figures 2 to 4 of the accompanying drawings . 24. A circuit arrangement for automatically adjusting the volume of a loudspeaker in a telephone substantially as herein described with reference to, and as shown in, figures 2 to 4 of the accompanying drawings .

Inventors: HURST JEFFREY, HURST, JEFFREY
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 1999
Main classification: H04M1
IPC codes: H04M1