Hands-free control system for a radiotelephone

An improved hands-free user-interactive control and dialing system is disclosed for use with a speech communications device. The control system (400) includes a dynamic noise suppressor (410), a speech recognizer (420) for implementing voice-control, a device controller (430) responsive to the speech recognizer for controlling operating parameters of the speech communications device (450) and for producing status information representing the operating status of the device, and a speech synthesizer (440) for providing reply information to the user as to the speech communications device operating status. In a mobile radiotelephone application, the spectral subtraction noise suppressor (414) is configured to improve the performance of the speech recognizer (424), the voice quality of the transmitted audio (417), and the audio switching operation of the vehicular speakerphone (460). The combination of noise processing, speech recognition, and speech synthesis provides a substantial improvement to prior art control systems.

BACKGROUND OF THE INVENITON 
The present invention relates generally to speech recognition control 
systems, and more particularly to a hands-free telephone control and 
dialing system especially suited for use in a noisy environment such as 
encountered in a vehicular radiotelephone application. 
In both radio and landline telephone systems, the user typically 
communicates by means of a handset that includes a speaker at one end 
which is placed close to the user's ear, and a microphone at the other end 
which is held close to the user's mouth. In operation, one hand of the 
user is occupied holding the telephone handset in its proper orientation, 
thereby leaving the user's only free hand to accomplish tasks such as 
driving a vehicle. In order to provide a greater degree of freedom for the 
user, speakerphones have commonly been used in landline telephone systems. 
Recently, vehicular speakerphones (VSP's) have been developed for use in 
automobiles. For example, U.S. Pat. No. 4,378,603 by Eastmond and U.S. 
Pat. No. 4,400,584 by Vilmur, both assigned to the same Assignee as the 
present invention, describe vehicular speakerphones with hands-free 
operation. 
Hands-free control systems which are responsive to human voice are 
disclosed in a number of U.S. patents. U.S. Pat. No. 4,520,576 by Vander 
Molen discloses a conversational voice command control system for a home 
appliance such as a clothes dryer. The control system recognizes voice 
commands and emits synthesized speech sounds, in an interaction with the 
user, to obtain the information necessary for setting the operating 
parameters. Speech recognition and speech synthesis have also been applied 
to radio transceiver control functions (on/off, transmit/receive, volume 
and squelch control, etc.) in U.S. Pat. No. 4,426,733 by Brenig. 
Additionally, U.S. Pat. No. 4,348,550 by Pirz et al. discloses a repertory 
dialing circuit for a telephone system which is controlled by the user's 
spoken word. 
However, the application of hands-free control to a vehicular speech 
communications system, such as a mobile radiotelephone, introduces several 
significant obstacles. When speech recognition is utilized in a vehicular 
environment, the high degree of ambient noise inherent in a vehicle 
presents a considerable problem to reliable voice control. Furthermore, a 
vehicular speakerphone typically has a microphone that is distant from the 
user's mouth, such as being mounted overhead on the automobile sun visor. 
Consequently, the required high microphone sensitivity causes a large 
increase in the amount of environmental background noise being applied to 
the speech recognizer, as well as being transmitted to the landline party. 
Numerous approaches to this noisy speech problem have been attempted, with 
only limited success. For example, it is well known that speech may be 
enhanced in an aircraft through the use of a separate microphone, located 
at a distance away from the user's first microphone, such that it picks up 
only background noise. The general characteristics of the background noise 
can then be removed by subtracting an estimate of the background noise 
from the desired signal. This technique has been shown to provide a 
limited improvement in signal-to-noise ratio (SNR). However, it is very 
difficult to achieve the required isolation of the second microphone from 
the speech source while at the same time attempting to pick up the same 
background noise environment as the first microphone. 
A simple high-pass filter is often used, perhaps in a microphone 
preamplifier, to reduce low frequency background noise. This may generally 
be perceived as an improvement in voice quality, but does little to 
improve the speech recognition process. Another approach, that of spectral 
subtraction noise suppression, has typically been used as a noise 
pre-processor to enhance the noise-degraded speech in preparation for 
further processing by a bandwidth compression system such as a vocoder. 
Although the aforementioned prior art techniques may perform adequately 
under nominal background noise conditions, the performance of these 
approaches become severely limited when used in specialized applications 
such as vehicular speakerphones. The more distant microphone delivers a 
much poorer signal-to-noise level to the land-end party due to road and 
wind noise conditions. In rapidly-changing high noise automobile 
environments, vehicular background noise may cause an automobile's speech 
recognition control system to malfunction. Furthermore, the performance of 
speakerphone audio switching circuitry may be significantly impaired in 
such environments. 
A need, therefore, exists for an improved hands-free control system for a 
mobile radio transceiver that provides sufficient background noise 
attenuation in high ambient noise environments. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to provide an 
improved method and apparatus for controlling a speech communications 
device in a noisy environment. 
A more particular object of the present invention is to provide an improved 
hands-free user-interactive control and dialing system for a mobile 
radiotelephone. 
A further object of the present invention is to improve the performance of 
the radiotelephone's speech recognition control system, the voice quality 
of the transmitted audio, and the audio switching operation of the 
vehicular speakerphone. 
In accordance with the present invention, an improved user-interactive 
control system for a speech communications device is provided such that 
the user's hands are free to accomplish other tasks. The control system of 
the present invention includes a means for dynamically suppressing 
background noise from an input speech signal; a means responsive to the 
noise suppression means for recognizing user-spoken command words; a means 
responsive to the speech recognition means for controlling operating 
parameters of the speech communications device and for producing status 
information representing the operating status of the device; and a means 
responsive to such status information for providing an indication to the 
user as to the speech communications device operating status. 
In the preferred embodiment, the hands-free user-interactive control system 
is used with a mobile radiotelephone employing a vehicular speakerphone. 
User-spoken input speech is first acoustically coupled to the control 
system, then noise-processed by a spectral subtraction noise suppressor. 
The noise-processed speech information is then applied to a speech 
recognizer which provides operating parameter control signals 
corresponding to predetermined user-spoken command words. A 
radio-interfacing control unit utilizes these control signals to dial 
telephone numbers spoken by the user or recalled from a stored telephone 
number directory in response to a corresponding command word, to store and 
recall telephone numbers from this directory, and to control radio 
functional operation. The control unit also provides status information to 
a speech synthesizer which provides audible feedback to the user as to the 
present operating status of the radiotelephone. Furthermore, 
noise-suppressed speech is used by the vehicular speakerphone to improve 
its switching performance, and used by the radio transmitter to improve 
the quality of the transmitted speech.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the accompanying drawings, FIG. 1 shows a general block 
diagram of user-interactive control system 100 of the present invention. 
Speech communications device 150 may include portions of any radio or 
landline voice communications system, such as, for example, 2-way radio 
systems, telephone systems, intercom systems, etc. User-spoken input 
speech is applied to microphone 105, which acts as an acoustic coupler 
providing an electrical input speech signal for the control system. Noise 
processor 110 performs dynamic noise suppression upon the input speech 
signal to provide noise suppression information to speech recognizer 120. 
Dynamic noise suppression, as used herein, refers to the process of 
adaptively filtering quasi-stationary background noise (i.e., noise 
exhibiting a relatively constant long-term power spectrum) from the 
desired signal. An example of dynamic noise suppression is the spectral 
subtraction or spectral gain modification technique known in the art. The 
noise suppression information may be comprised of either noise-suppressed 
speech itself, spectral subtraction noise suppression parameters to be 
used in the speech recognizer, or both. A further description of noise 
processor 110, as well as the spectral subtraction/spectral gain 
modification technique, may be found in the description of noise processor 
410 of FIG. 4. 
Speech recognizer 120 utilizes this noise suppression information by either 
directly performing speech recognition upon noise-suppressed speech, or by 
utilizing noise suppression parameters in the speech recognition process. 
Hence, much more accurate speech recognition performance is achieved with 
knowledge of the noise content of the speech signal. A further discussion 
of an appropriate speech recognition apparatus, and how the preferred 
embodiment incorporates noise suppression data into the speech recognizer, 
may be found in the description accompanying FIG. 4. 
Device controller 130 interfaces the control system to speech 
communications device 150. Device controller 130 translates device control 
data provided by speech recognizer 120 into control signals that can be 
recognized by the particular speech communications device. These control 
signals direct the device to perform specific operating functions as 
instructed by the user. A example of a device controller known in the art 
and suitable for use with the present invention is a microprocessor. 
Device controller 130 also provides device status data representing the 
operating status of speech communications device 150. This data is applied 
to speech synthesizer 140, and translated into user-recognizable speech 
when output via speaker 145. As will be apparent to those skilled in the 
art, other means to provide an indication to the user as to the speech 
communications device operating status may be utilized. Such indication 
may include a visible display (LED, LCD, CRT, etc.) or a sound transducer 
(tone generator or other audible signal). Thus, FIG. 1 illustrates how the 
present invention provides a user-interactive control system utilizing 
noise suppression, speech recognition, and speech synthesis to control the 
operating parameters of a speech communications device. 
FIG. 2 illustrates the application of the user-interactive control system 
to a speech communications terminal, such as, for example, a telephone 
terminal, a communications console, a 2-way radio, etc. Noise processor 
210, speech recognizer 220, terminal controller 230, and speech 
synthesizer 240, are the same in structure and operation as the 
corresponding blocks of FIG. 1. However, control system 200 further 
illustrates the internal structure of speech communications terminal 250. 
In this embodiment, microphone 205 and speaker 295 are incorporated into 
the speech communications terminal itself. A typical example of this 
microphone/speaker arrangement would be a telephone handset. Speech 
communications terminal 250 also has a transmitter block 260 coupled to a 
transmit path 265, a receive block 280 coupled to a receive path 285, and 
a terminal logic block 270 for controlling both the transmitter and 
receiver blocks. Terminal logic block 270 typically has access to the 
operating status information of speech communications terminal 250, and 
interfaces this information to terminal controller 230 via terminal 
interface path 235. 
The example of a "smart" telephone terminal employing voice-controlled 
dialing from a stored telephone number directory is now used to describe 
the operation of the control system of the present invention. Initially, 
the user speaks a verbal command into microphone 205, such as the command 
word "recall". The utterance is first noise-processed by noise processor 
210, then recognized as a valid user command by speech recognizer 220. In 
this example, terminal controller 230 then directs speech synthesizer 240 
to generate the verbal reply "name?" via speech synthesis output line 245 
through multiplexer 290 to speaker 295. (For details of multiplexer 290, 
refer to the description of multiplexer 470 of FIG. 4.) The user then 
responds by speaking a word such as "office"--a name in the directory 
index corresponding to a telephone number that he desires to dial. The 
word will be recognized as a valid command word if it corresponds to a 
predetermined name index stored in the terminal controller telephone 
number directory. If valid, controller 230 directs speech synthesizer 240 
to reply "office" thereby confirming the recognized command word. 
The user then says the command word "send", which when recognized by the 
control system, instructs terminal controller 230 to obtain the telephone 
number corresponding to the name "office" and send telephone number 
dialing information to terminal logic block 270 via terminal interface 
path 235. Terminal logic block 270 outputs this dialing information along 
transmit path 265 via transmitter 260. When the telephone connection is 
made, terminal receiver 280 provides audio from receive path 285 to 
speaker 295 via multiplexer 290. If a proper telephone connection cannot 
be made, terminal controller 230 reads the status of terminal logic block 
270 and generates status information, such as the reply word "busy", to be 
output to the user via speech synthesizer 240. In this manner, 
user-interactive voice-controlled directory dialing is achieved. 
In addition to noise-processing operational commands, the user's speech is 
also noise-processed before it is coupled to transmit path 265 via 
transmit audio line 215. Hence, noise processor 210 provides noise 
suppression information for the speech recognizer as well as a 
noise-suppressed speech signal for the transmitter audio. Accordingly, the 
performance of the control system's speech recognition process as well as 
the quality of the transmitted audio signal are substantially improved. 
Although speech recognition and speech synthesis allow a vehicle operator 
to keep both eyes on the road, a conventional handset or hand-held 
microphone prohibits him from keeping both hands on the steering wheel or 
from executing proper manual (or automatic) transmission shifting. For 
this reason, the control system of FIG. 3 incorporates a speakerphone to 
provide hands-free control of the speech communications terminal. The 
speakerphone performs the transmit/receive audio switching function, as 
well as the received/reply audio multiplexing function. 
Referring now to FIG. 3, control system 300 utilizes the same noise 
processor block 310, speech recognizer block 320, terminal controller 
block 330, speech synthesizer block 340 and speech communications terminal 
350 as the corresponding blocks of FIG. 2. However, microphone 305 and 
speaker 375 are not an integral part of the terminal 350. Instead, 
speakerphone 360 directs input speech signal from microphone 305 to noise 
processor 310 via input signal line 365. This input signal line may be 
switched in the case of a simplex speakerphone, or may be directly coupled 
in the case of a duplex speakerphone. Speakerphone 360 also controls the 
multiplexing of speech reply line 345 and receive audio line 355 to 
speaker 375. A more detailed description of the switching/multiplexing 
configuration of the speakerphone is described later in conjunction with 
FIG. 4. 
Hence, FIG. 3 illustrates the application of the present invention control 
system to a speech communications terminal employing a speakerphone to 
free the user's hands. In the preferred embodiment, spectral subtraction 
noise suppression is utilized to process the input speech for speech 
recognition as well as for the transmitted audio path. A further 
improvement to control system 300 may be realized by using 
noise-suppressed speech for the speakerphone audio switching. In a high 
noise environment, this technique provides a significant performance 
increase to simplex vehicular speakerphones. Thus, the noise processing 
block then performs three functions: improving speech recognition 
performance; improving transmitted voice quality; and improving 
speakerphone audio switching. 
FIG. 4 is a detailed block diagram of the hands-free control system of the 
present invention. In general, the control system arrangement is the same 
as that of FIG. 3, with the above-mentioned exception that the input 
speech signal from the microphone is first noise-processed before being 
applied to the speakerphone. Microphone 402, which is typically 
remotely-mounted at a distance from the user's mouth (i.e., on the 
automobile sun visor), acoustically couples the user's voice to control 
system 400. This speech signal is generally amplified by preamplifier 404 
to provide input speech signal 405. 
Noise processor block 410 first converts the analog input speech signal to 
digital form at analog-to-digital converter 412. This digital data is then 
applied to spectral subtraction noise suppressor 414, which performs the 
actual dynamic noise suppression function. Any dynamic noise suppression 
implementation may be utilized in block 414, however, the present 
embodiment utilizes a particular form of spectral subtraction noise 
suppression--the channel filter-bank technique. Under this approach, the 
audio input signal spectrum is divided into individual spectral bands by a 
bank of bandpass filters, and particular spectral bands are attenuated 
according to their noise energy content. 
The value of the attenuation is dependent upon the signal-to-noise ratio 
(SNR) of the detected signal. The SNR is calculated from a background 
noise estimate for that channel and a channel energy estimate. When voice 
is present in an individual channel, the channel signal-to-noise ratio 
will be high. Thus, the noise suppressor increases the gain for that 
particular channel. The amount of the gain rise is a function of the 
estimated SNR--the greater the SNR, the more the individual channel gain 
will be raised from the base gain (all noise). If only noise is present in 
the individual channel, the SNR will be low, and the gain for that channel 
will be reduced to the base gain. Since voice energy does not appear in 
all of the channels at the same time, the channels containing a low voice 
energy level (mostly background noise) will be suppressed (subtracted) 
from the voice energy spectrum. A spectral subtraction noise suppression 
prefilter of this type is described in R. J. McAulay and M. L. Malpass, 
"Speech Enhancement Using a Soft-Decision Noise Suppression Filter," IEEE 
Trans. Acoust., Speech, Signal Processing, vol. ASSP-28, no. 2, (April 
1980), pp. 137-145. 
Noise suppressor 414 provides noise suppression data 418 for use by speech 
recognition block 420. This noise suppression data may consist of actual 
noise-suppressed speech, or alternatively may represent spectral 
subtraction noise suppression parameters to be incorporated into the 
speech recognition algorithm. In the first case, speech recognizer 424 
would be performing speech recognition upon noise-suppressed speech 
itself. In the latter case, speech recognizer 424 would simply utilize the 
noise suppression data to compensate for the background noise in the 
speech recognition process. In the present embodiment, this noise 
suppression data includes channel filter-bank data (signal information), a 
per-channel background noise estimate of the input speech signal (noise 
information), and noise-processed signal energy with the current 
background noise energy level (word boundary information). This signal, 
noise, and word boundary information is utilized during speech recognition 
to adjust the word-matching process to compensate for high background 
noise levels. Other background noise compensation algorithms for speech 
recognition may also be used, such as those described in the article by J. 
Peckham, J. Green, J. Canning, and P. Stevens, entitled "A Real-Time 
Hardware Continuous Speech Recognition System," IEEE International 
Conference on Acoustics, Speech, and Signal Processing, May 3-5 1982, vol. 
2, pp. 863-866, and the references contained therein. In either case, 
noise processing results in a considerable improvement in speech 
recognition performance. 
In the present embodiment, an 8-bit microcomputer performs the function of 
speech recognizer 424, and an EEPROM functions as template memory 422. 
Moreover, several other control system blocks of FIG. 4 are implemented in 
part by the same microcomputer with the aid of a CODEC/FILTER and a DSP 
(digital signal processor). The above referenced article describes still 
another microprocessor architecture. Hence, the present invention is not 
limited to any specific hardware or any specific type of speech 
recognition. More particularly, the present invention contemplates the use 
of: speaker dependent or speaker independent speech recognition; isolated 
or continuous word recognition; and a software-based or hardware-based 
implementation. 
Template memory 422 stores word templates to be matched to the incoming 
speech in speech recognizer 424. During training, speech recognizer 424 is 
instructed by the control unit to send word templates to template memory 
422 via memory bus 426. During recognition, speech recognizer 424 compares 
the previously stored templates from memory 422 against noise-processed 
speech information. The recognition algorithm of the present embodiment 
incorporates near-continuous speech recognition, dynamic time warping, 
energy normalization, and a Chebyshev distance metric to determine a 
template match. Prior art recognition algorithms, such as described in J. 
S. Bridle, M. D. Brown, and R. M. Chamberlain, "An Algorithm for Connected 
Word Recognition," IEEE International Conference on Acoustics, Speech, and 
Signal Processing, May 3-5 1982, vol. 2, pp. 899-902, may also be used. On 
the whole, speech recognition block 420 utilizes background noise 
information from noise processor block 410 to increase speech recognizer 
performance in a high background noise environment. 
Controller block 430, consisting of control unit 434 and directory memory 
432, serves to interface speech recognition block 420 and speech synthesis 
block 440 to radiotelephone 450 via interface busses 428, 438 and 458 
respectively. Control unit 434 is typically a controlling microprocessor 
which is capable of interfacing data from radio logic 452 to the other 
blocks. Control unit 434 also performs operational control of 
radiotelephone 450, such as: unlocking the control head; placing a 
telephone call; ending a telephone call; etc. Depending on the particular 
hardware interface structure to the radio, control unit 434 may 
incorporate other sub-blocks to perform specific control functions as DTMF 
dialing, interface bus multiplexing, and control-function decision-making. 
Directory memory 432, an EEPROM, stores the plurality of telephone numbers 
and names, thereby permitting directory dialing. Memory bus 436 sends 
information to directory memory 432 during the process of entering 
telephone names and numbers, and provides this stored directory 
information to control unit 434 in response to the recognition of a valid 
directory dialing command. Depending on the particular telephone device 
used, it may be more economical to incorporate directory memory 432 into 
the telephone device itself. In general, however, controller block 430 
performs the telephone directory storage function, the telephone number 
dialing function, and the radio operational control function. 
Controller block 430 also provides status information representing the 
operating status of the radiotelephone. This status information may 
include information as to the names and telephone numbers stored in 
directory memory 432 ("Office", "555-1234", etc.), directory status 
information ("Directory Full", "Name?", etc.), speech recognition status 
information ("Ready", "User Number?", etc.), or radiotelephone status 
information ("Call Dropped", "System Busy", etc.). Hence, controller block 
430 is the heart of the user-interactive speech recognition/speech reply 
control system of the radio. 
Speech synthesis block 440 performs the voice reply function. Voice reply 
data is fed to channel bank speech synthesizer 444 via interface bus 438. 
Using this information, speech synthesizer 444 recalls reply words from 
reply memory 442, synthesizes these reply words, and outputs them to 
digital-to-analog converter 446. The voice reply is then routed to the 
user. In the present embodiment, channel bank speech synthesizer 444 is 
the speech synthesis portion of a 19-channel vocoder. An example of such a 
vocoder may be found in J. N. Holmes, "The JSRU Channel Vocoder", IEE 
PROC., vol. 127, pt. F, no. 1, (February, 1980), pp. 53-60. The 
information provided by supply memory 442 may also include whether the 
input speech frame should be voiced or unvoiced, the pitch rate if any, 
and the gain of each of the 19 filters. However, as will be obvious to 
those skilled in the art, any speech synthesis apparatus may be utilized. 
Furthermore, the present invention contemplates that any means of 
providing a reply to the user would perform the basic reply function of 
speech synthesizer block 440. For example, a visual indication (such as a 
display light) or an audible indication (such as a reply tone) may be 
substituted. 
As we have seen, the present invention teaches the implementation of noise 
suppression with speech recognition and speech synthesis to provide a 
user-interactive control system for a speech communications device. In the 
present embodiment, the speech communications device is a radio 
transceiver, such as a cellular mobile radiotelephone. However, any speech 
communications device warranting hands-free user-interactive operation in 
a noisy environment may be used. For example, any simplex radio 
transceiver requiring hands-free control may also take advantage of the 
improved control system of the present invention. 
Referring now to radiotelephone block 450 of FIG. 4, radio logic 452 
performs the actual radio operational control function. Specifically, it 
directs frequency synthesizer 456 to provide channel information to 
transmitter 453 and receiver 457. The function of frequency synthesizer 
456 may also be performed by crystal-controlled channel oscillators. 
Duplexer 454 interfaces transmitter 453 and receiver 457 to a radio 
frequency (RF) channel via antenna 459. In the case of a simplex radio 
transceiver, the function of duplexer 454 may be performed by an RF 
switch. For a more detailed explanation of representative radio 
transceiver circuitry, refer to Motorola Instruction Manual 68P81066E40 
entitled "DYNA T.A.C. Cellular Mobile Telephone." 
Speakerphone 460, also termed a VSP (vehicular speakerphone) in the present 
application, provides: hands-free acoustic coupling of the user-spoken 
audio to the control system; the synthesized speech reply signal to the 
user; and the received audio from the radiotelephone to the user. As 
previously mentioned, noise processor block 410 performs spectral 
subtraction noise suppression upon the input speech signal 405, to produce 
noise suppression information for speech recognition. This information is 
also used by digital-to-analog converter 416 which produces 
noise-suppressed microphone audio 415. The noise-suppressed speech signal 
is applied to VSP transmit audio switch 462, which routes noise-suppressed 
microphone audio 415 to radio transmitter 453 via transmit audio 417. VSP 
transmit switch 462 is controlled by VSP signal detector 464. Signal 
detecter 464 compares microphone audio 415 against receive audio 455 to 
perform the VSP switching function. 
When the mobile radio user is talking, signal detector 464 provides a 
positive control signal via detector output 461 to close transmit audio 
switch 462, and a negative control signal via detector output 463 to open 
receive audio switch 468. Conversely, when the landline party is talking, 
signal detector 464 provides the opposite polarity signals to close 
receive audio switch 468, while opening transmit audio switch 462. When 
the receive audio switch is closed, receiver audio 455 from radiotelephone 
receiver 457 is routed through receive audio switch 468 to multiplexer 470 
via switched receive audio output 467. In some communications systems, it 
may prove advantageous to replace audio switches 462 and 468 with variable 
gain devices that provide equal but opposite attenuations in response to 
the control signals from the signal detector. In either case, the use of 
noise-suppressed microphone audio 415, as opposed to input speech signal 
405, assists signal detector 464 in making accurate audio path control 
decisions. Hence, the noise suppression/speakerphone configuration of FIG. 
4 significantly improves the noise falsing and desensitization performance 
of a vehicular speakerphone. 
Multiplexer 470 switches between voice reply audio 445 and switched receive 
audio 467 in response to multiplex signal 435 from control unit 434. 
Whenever the control unit sends status information to the speech 
synthesizer, multiplexer signal 435 directs multiplexer 470 to route the 
voice reply audio to the speaker. VSP audio 465 is usually amplified by 
audio amplifier 472 before being applied to speaker 475. The vehicle 
speakerphone embodiment described herein is only one of numerous possible 
configurations. It should be emphasized, however, that the present 
invention teaches the technique of utilizing noise-suppressed microphone 
audio for the VSP audio switching. This technique provides a notable 
improvement in speakerphone performance. 
In summary, FIG. 4 illustrates a radiotelephone having a hands-free 
user-interactive speech-recognizing control system for controlling 
radiotelephone operating parameters upon a user-spoken command. The 
control system provides audible feedback to the user via speech synthesis 
as to the radiotelephone operating status. The vehicle speakerphone 
provides hands-free acoustic coupling of the user-spoken input speech to 
the control system, the speech reply signal from the control system to the 
user, and the receiver audio to the user. The implementation of noise 
processing to the control system improves the performance of the 
radiotelephone's speech recognition, the voice quality of the transmitted 
audio, and the audio switching operation of the vehicular speakerphone. 
The combination of noise suppression, speech recognition, and speech 
synthesis provides a substantial improvement to prior art control systems. 
While specific embodiments of the present invention have been shown and 
described herein, further modifications and improvements may be made by 
those skilled in the art. All such modifications which retain the basic 
underlying principles disclosed and claimed herein are within the scope of 
this invention.