Abstract:
A noise reduction headset including a negative feedback active noise reduction signal processing path for providing active noise reduction, an electronic communication signal processing path, a talk-through signal processing path for providing talk-through capability, comprising at least one talk-through microphone separate from the electronic communication signal processing path, and a switching element for disabling one or both of the noise reduction signal path and the talk-through signal path.

Description:
BACKGROUND 
     The invention pertains to noise reduction headsets, and more particularly to noise reduction headsets having active noise reduction circuitry and talk-through circuitry. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a noise reduction headset includes active noise reduction circuitry for providing active noise reduction; talk-through circuitry for providing talk-through capability; and switching element for disabling one or both of the noise reduction circuitry and the talk-through circuitry. 
     In another aspect of the invention, a noise reduction headset includes a first signal path, including active noise reduction and talk-through; a second signal path, including talk-through and not including active noise reduction; a selection circuit constructed and arranged to select either the first signal path or the second signal path. 
     In another aspect of the invention, a noise reduction headset includes an active noise reduction signal path; and a talk through signal path, comprising a microphone and a frequency selective filter for filtering input from the microphone, the filter constructed and arranged to significantly attenuate frequencies not in the speech band. 
     In still another aspect of the invention, a method for operating a noise reduction headset containing an active noise reduction signal path and a talk-through signal path includes providing electrical power to the active noise reduction control signal path and to the talk-through signal path; in the event that the electrical power to the active noise reduction control signal path is below a first threshold level disabling the noise reduction control signal path. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS. 1 ,  2 , and  3  are block diagrams of an active noise reduction headset including “talk-through capability. 
         FIGS. 4A ,  4 B,  4 C,  4 D, and  4 E are parts of a schematic circuit diagram implementing the active noise reduction headset of  FIGS. 1-3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown a block diagram of an active noise reduction headset with “talk through” capability. Active noise, reduction (ANR) headsets are discussed in U.S. Pat. No. 4,455,675. ANR headsets typically include an earcup that fits in the ear (intra aural), on the ear (supra aural), or around the ear (circumaural). The earcup provides passive attenuation of ambient noise. In addition, ANR headsets include electronic circuitry that significantly attenuates undesired noise, for example by radiating acoustic energy that opposes ambient noise. ANR headsets typically include electronic circuitry to allow electronic communication with the user of the ANR headset. 
     In  FIG. 1 , elements above line  2  are elements that are external to the earcup of the headset. Elements below line  2  are internal to the earcup of the headset. Electronic communications terminal  4  is coupled to audio EQ circuitry  6  and to summer  8 . Audio EQ circuitry  6  is coupled to summer  10 . Summer  10  is coupled to active noise reduction compensation and gain circuitry  12  which is in turn coupled to “HV” (or ON) switch terminal  14 HV of switch  14 . The ambient sound represented by summer  16  includes acoustic communication and ambient acoustic noise. Ambient sound enters the earcup through two paths; one path includes talk-through microphone  18  and another path is acoustic energy transmitted through the earcup. The earcup passively attenuates that acoustic energy transmitted through it, as represented passive attenuation block  20 . Talk through microphone  18  is coupled to talk through band limiting filter  21  and EQ and gain circuitry  22 , through optional switch  24 , if present. Talk through EQ and gain circuitry  22  is coupled to summers  8  and  10 . Summer  8  is coupled to “LV” (or OFF) switch terminal  14 LV switch terminal of switch  14 . The “HV” and “LV” terminology will be explained below. The acoustic characteristics of the earcup and of the driver (not shown separately in this diagram) are represented by driver and earcup acoustics block  26 , which couples switch  14  and summer  28 . Passive attenuation block  20  is coupled to summer  28 , which is acoustically coupled to active noise reduction microphone  30 , which is coupled to summer  10 . The block diagram of  FIG. 1  shows an exemplary arrangement of elements. Summers  8  and  10  refer to a summation of signals in an element of the circuitry of  FIG. 1 . Summers  16  and  28  represent a summation of acoustic energy that occurs in the environment and in the volume enclosed by the headset, respectively, and not in a circuit element. 
     The operation of the ANR headset of  FIG. 1  will be described in the discussion of  FIGS. 2 and 3 . 
       FIG. 2  shows the elements of the ANR headset of  FIG. 1  that are active with switch  14  in the “HV” (ON) position. The combined acoustic communication and ambient acoustic noise present in the environment is attenuated by the earcup, as represented by passive attenuation block  20 , and at summer  28 , becomes a part of a feedback loop as will be described below. Electronic communication from element  4  is equalized at EQ circuitry  6 . The signal from the talk-through microphone is band limited at filter  21  and processed by talk-though EQ and gain circuitry  22 . The equalized electronic communication signal from EQ circuitry  6  and the equalized, amplified, and band-limited talk-through microphone signal from element  22  are summed at summer  10 . Summer  10 , ANR compensation and gain circuitry  12 , driver and acoustics block  26 , summer  28 , and ANR microphone  30  form a feedback loop which acts to significantly attenuate sound that does not correspond to the electronic communication signal or the amplified and equalized talk through signal. If switch  24  is in the OFF position, the talk-through feature is substantially disabled and the headset operates as a conventional feedback type ANR headset. In some embodiments, element  22  may include noise removal elements for reducing the content of the signal representing ambient acoustic noise while not reducing the content of the signal representing acoustic communication. Methods and devices for discriminating between acoustic noise and acoustic communication are disclosed in U.S. Pat. Nos. 5,768,473, 5,699,436, 5,481,615, and 5,105,377, U.S. Pat. App. 2001/0046304 and U.S. Pat. App. 2002/0141599. 
     Other ANR headsets may use ANR circuitry that is feed forward circuitry instead of feedback circuitry. 
     The band limiting filter  21  may be either a high pass filter or a bandpass filter. A high pass filter would have a break frequency at about the bottom end of the speech band, for example 300 Hz. A band pass filter would have a passband approximating the speech band, for example 300 Hz to 4.5 kHz. Band limiting the signal from the talk through microphone at about the speech band results in the ANR attenuating noise that is outside the speech band while enabling a signal representative of acoustic communication at frequencies within the speech band to be communicated to the user. A high pass filter may also be used, because generally most noise that is desired to be canceled is at low frequencies, and because generally ANR is more effective at low frequencies than at high frequencies. 
       FIG. 3  shows the elements of the ANR headset of  FIG. 1  that are active with switch  14  in the OFF or “LV” position. The active noise reduction feedback loop of  FIGS. 1 and 2  is substantially disabled, and the headset is operated as a “talk through” headset. Sound corresponding to the band limited equalized and amplified signal from the talk through microphone is radiated to the user&#39;s ear. The band limiting by filter  21  facilitates the user hearing acoustic communication, while still retaining the passive attenuation represented by passive attenuation block  20 . With switch  24  in the OFF position, the talk through feature is disabled and the headset operates as a passive headset. With the circuit of  FIG. 1  and the switch  14  is in the LV or OFF position, the electronic communications terminal  4  may be active. In some embodiments, as will be described below, the LV switch position may be associated with a condition in which there is no signal at the electronic communications terminal  4 , so the electronic communications terminal and the coupling to the summer  8  is shown in broken line. In other implementations, the circuitry could be configured so that the electronic communications circuitry functions if the ANR circuitry is not operating. 
     Switches  14  and  24  may be manual or automated switches. In one implementation, switch  24  is omitted so that, with switch  14  in either the HV position (as in  FIG. 2 ) or in the LV position (as in  FIG. 3 ), the headset has talk-through capability. In one implementation, switch  14  is an automatic switch. If electrical power sufficient to operate the ANR circuitry is supplied to the headset, the headset operates in the manner shown in  FIG. 2 . If electrical power not sufficient to operate the ANR circuitry but sufficient to operate the talk through circuitry is supplied to the headset, the headset operates in the manner shown in  FIG. 3 . If the electrical power is not sufficient to operate the ANR circuitry or the talk-through circuitry, then the headset can operate as a passive noise reduction headset, similar to the headset of  FIG. 3  with switch  24  in the OFF position. Measuring the electrical power is most conveniently done by measuring the voltage supplied to the headset, so “HV” refers to high voltage and “LV” refers to low voltage. The headset may be configured so that it is connectable to a communications device such as a console, intercom, or a jack in a vehicle, which provides both electrical power to operate the ANR circuitry and the communication signal to the headset; therefore if the headset is not connected to the communications device, the headset receives no electronics communications signal. If the headset is not connected to the communications device, the headset operates as a talk through headset if it is supplied with a source of power (such as a battery) sufficient to operate the talk through circuitry, or as a passive headset if it is not supplied with a source of power sufficient to operate the talk through circuitry. 
     A headset according to  FIGS. 1-3  is advantageous over conventional ANR headsets with talk through capability. A user can be provided with ANR with or without talk through capability; or talk-through capability with or without ANR; or passive attenuation without either ANR or talk-through capability. The switching can be manual, allowing the user to select a desired combination of features, or may be implemented in an automated manner so that, for example, the user selects features by connecting the headset to, or disconnecting from, a communications device or power source. 
     Referring to  FIGS. 4A-4E , there is shown a schematic diagram of a circuit implementing the active noise reduction headset of  FIGS. 1-3 .  FIGS. 4A-4D  are the upper left portion, the upper right portion, the lower right portion, and the lower left portion, respectively, of a circuit. The circuit of  FIG. 4E  connects to the circuit portion of  FIG. 4A  at points “A′ and “K” as shown. Points “L” and “M” connect to elements not germane to this specification. The circuit elements that implement the blocks of  FIGS. 1-3  are surrounded by broken lines. 
     Numerous uses of and departures from the specific apparatus and techniques disclosed herein may be made, including arranging the elements in a different order, without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features disclosed herein and limited only by the spirit and scope of the appended claims.