Data processing: speech signal processing – linguistics – language – Speech signal processing – Application
Reexamination Certificate
1999-08-16
2002-03-19
Dorvil, Richemond (Department: 2641)
Data processing: speech signal processing, linguistics, language
Speech signal processing
Application
C704S226000, C704S225000, C704S228000, C386S349000, C379S392010
Reexamination Certificate
active
06360203
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to the field of speech signal processing, and, more particularly, to a dynamic voice operated filtering system for use in an aircraft voice intercom system and method thereof.
BACKGROUND
On board an aircraft, clear communications are essential for safe operation. For onboard voice communication between aircraft operators, an onboard electronic intercom system is the main communication system used. Typically, for pilots and other cockpit personnel, the onboard electronic intercom system includes headphones and microphones.
In operation, the microphone receives both voice signals and ambient background noise signals. Thus, the user(s) on the receiving end of the electronic intercom system will hear both voice and noise signals. As can be appreciated, the users generally dislike hearing the noise as being annoying. Further, the noise can inhibit clear, intelligible communication, causing miscommunication of information that could be extremely dangerous while the aircraft is in operation. Noise mixed with speech can make speech unintelligible and, further, noise that occurs between words and syllables of the voice signal may render the voice signal unintelligible and can increase operator fatigue.
Some conventional intercom systems try to reduce the effects of noise by using a compander system. Mixed noise and voice signals are compressed at the transmitting end and then expanded at the receiving end of the system. These systems are typically directed to reducing the effect of noise introduced electrically in the transmission channel, between the microphone and the headphone. Thus, acoustic ambient noise picked up by the microphone undesirably tends to pass through unchanged in these systems. Other conventional systems attempt to cancel noise by attempting to measure ambient noise without the voice signal and then subtract the “measured” noise from the combined voice and noise signal. These systems generally require two microphones, the first microphone being used to pick up the combined voice and noise signal while the second microphone attempts to pick up only the noise. The second microphone adds cost and complexity to the intercom system and may not provide good performance because the noise picked up by the second microphone may not accurately represent the noise picked up in the first microphone. Still other conventional systems use digital signal processing techniques to implement an adaptive noise filter. These systems typically require complex and costly digital signal processors. Accordingly, there is a need for an intercom system for aircraft applications that is low complexity and low-cost while providing good ambient noise suppression during operation.
SUMMARY
In accordance with the present invention, a dynamic voice operated filtering system for aircraft applications is provided. In one aspect of the present invention, the dynamic voice operated filtering system includes an input limiter, an expander, an output limiter and a user control. The input limiter receives an input signal representing a mixed voice and noise signal and filters the input signal. In one embodiment, the input limiter outputs an attenuated version of the input signal (IN
L
) to the expander, with the attenuation ranging from 0 dB to −50 dB. The input limiter attenuates the input signal so that the signal IN
L
received by the expander remains within the expander's dynamic range. The expander outputs a signal IN
X
, which represents an expanded version of signal IN
L
. In particular, the expander outputs signal IN
X
with amplitude as a function of the amplitude of signal IN
L
. In one embodiment, this function, in effect, ranges from relatively large amounts of attenuation to relatively moderate amounts of amplification. Thus, for example, the expander in effect attenuates signal IN
L
to serve as signal IN
X
when the signal IN
L
has a relatively low amplitude and amplifies signal IN
L
to serve as the signal IN
X
when the signal IN
L
has a relatively high amplitude. In one embodiment, the amplification and attenuation ranges from +20 dB to −60 dB. The output limiter then receives the signal IN
X
and, in response, limits the signal IN
X
. In one embodiment, the output limiter outputs an output signal representing an amplified version the signal IN
X
. This output signal would then be provided to one or more standard audio output devices of the aircraft intercom system.
In another aspect of the present invention, the attenuation of the input and output limiters can be adjusted by the user through the user control. This control in effect allows the user to adjust the offset of the combined voice and noise input signal. The user adjusts the limiter settings so that periods of silence (e.g., between spoken words) are relatively greatly attenuated while periods of speech are amplified without distortion. This scheme, in effect, filters out ambient background noise between spoken words so that the combined voice/background noise signals are amplified. As a result, this filtering scheme advantageously reduces irritating background noise between words and syllables, which in turn tends to make the speech transmitted by the aircraft intercom system more intelligible to listeners.
In yet another aspect of the present invention, the user control and the limiters are configured so that an adjustment of the user control that causes an increase (or decrease) of the attenuation in the input limiter causes a corresponding decrease (or increase) increase in the attenuation of the output limiter. In one embodiment, each limiter measures a signal level (e.g., a voltage proportional to rms power) of the signal received by the limiter and compares the signal level to a user-adjustable signal level provided by the user control. The difference between the two signal levels is used to control the attenuation provided by the limiter. In this way, the filtering system is dynamically adjusted by the combined voice and noise input signal to filter out ambient background noise between spoken words and amplify combined voice/background noise signals.
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dB Systems, Inc.
Dorvil Richemond
Nolan Daniel
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