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An overhead microphone assembly has a plurality of unidirectional microphone elements. The
microphone assembly is overhead and generally located above the desired sound source and
below the undesired sound source. The signals from the plurality of microphone elements are
provided to a microphone steering processor that can mix and gate the signals to ensure the best
signal to noise ratio. The microphone steering processor is also capable of dynamically tracking
the source if tracking (source localization) is desired. The resulting acoustic signal from the
microphone steering processor can be further subjected to processing such as echo cancellation,
noise cancellation and acoustic gain control. [Selected figure] Figure 2
Ceiling microphone assembly
The present invention generally relates to a microphone assembly in a system required to
convert an audio signal into an electrical signal.
A microphone is a basic and essential element in any acoustic system.
There are many types of microphones currently used. In general, those microphones fall into four
categories as listed in FIG. The first category is omnidirectional microphone 102. It has uniform
polar response, ie it can accept sound waves from any direction, and an electrical signal is
generated with the same gain. The second type of microphone is a dipole microphone 104, which
can respond to sound waves from mainly two opposite directions. Sound waves coming from
other directions have very little gain. Sound waves coming from directions that are 90 ° to the
axis of the microphone element are not accepted, ie the gain is zero. The third type of
microphone is a cardioid microphone 106, which can receive sound waves from one primary
direction. The response gain decreases as the incident angle of the sound wave deviates from the
primary direction. The response gain drop becomes larger when the incident angle is larger than
the threshold. The gain is zero at 180 ° from the primary direction. The fourth type of
microphone is a hypercardioid microphone 108. The high parkar geoid microphone 108 is like a
hybrid of a dipole microphone and a cardioid microphone. It has a primary direction and a
secondary direction, the secondary direction being the opposite direction of the primary
direction. It can respond to sound waves that are in both the primary and secondary directions,
but the gain for the secondary direction is less than the gain for the primary direction.
It is possible to assemble an array of microphones to compete for the above four microphone
characteristics in an application. For example, non-directional microphones can be grouped
together. The controller can process the signal in such a way as to generate a signal that is very
directional, and thus the array of such microphones functions as if it were a directional
microphone Do. Another example is described in US Pat. No. 5,715,319, in which several
directional microphones are arranged in a circular array. The resulting microphone array
functions like an omnidirectional or omnidirectional microphone. In this application, the
microphone elements are referred to as general single element microphones or multi-element
arrays that behave like a single element microphone. For example, a unidirectional microphone is
a single cardioid microphone or microphone array that receives sound waves from the primary
direction and does not receive sound waves from most other directions. The microphone
elements in the microphone array can be non-directional, bipolar or hypercardioid or a
Any one of the four types of microphones identified above is an audio system and has various
disadvantages, particularly in video conferencing and audio conferencing applications. For
example, omnidirectional microphones that collect speech equally from all directions have lower
noise and echo levels because they can not accept echoes and noise under typical unprocessed
room conditions Are of poor quality in audio or video conferencing applications. A cardioid
microphone only accepts sound waves directed towards it and does not accept most sound waves
coming from other directions. This type of microphone can provide greater signal-to-noise ratio
(SNR) and higher voice quality, but covers only a very small area in a conference room.
Participants in a voice or video conference need to speak to the microphone in turn. In some
conference room settings, several such microphones are connected to the system at the same
time, so most participants in the conference use nearby microphones available to speak Can.
It is generally accepted that a person must have a microphone during a lecture in a large hall, but
it is still unnatural and inconvenient. Under the circumstances of the meeting, it is not preferable.
In an actual meeting, the conference participants prefer to look at the facial expressions and
other body language of the participants while they are speaking.
Prior art devices exist to avoid the many limitations of microphone elements. For example, the
Polycom SoundStation VTX-1000 speakerphone by the applicant of the present invention uses
three microphone elements to provide good room coverage, SNR and frequency response. Such
speakerphones can meet many requirements in setting up a conference room as seen on most
conference room tables.
There is a great demand to eliminate inconvenient microphones, or at least to get out of view
during a meeting and to minimize their interference. It is desirable to have a microphone system
that can cover the entire conference room while at the same time maintaining high voice quality
and minimizing signal to noise ratio. There is a need to have a microphone system that can
provide other high quality speech processing.
In the present invention, multiple unidirectional microphone elements are used in the
microphone assembly. As a microphone assembly, in general, the preferred sound source is
placed overhead. The signals from the plurality of microphone elements are provided to a
microphone steering processor that mixes and gates the signals to ensure the best signal to noise
ratio. The stealing processor also performs dynamic tracking of the audio source when such
tracking (audio source positioning) is desired. The acoustic signal obtained from the steering
processor can be further processed such as echo cancellation, noise reduction and automatic gain
control. The microphone of the present invention can cover a large conference room. The
microphones can also be scaled, i.e., as the conference room gets larger, the capabilities of the
microphones can be appropriately enhanced by adding more microphones.
BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention,
reference will now be made in detail to the preferred embodiments with reference to the
accompanying drawings.
FIG. 2 shows a typical meeting room arrangement 244.
The meeting participants 210 are seated at the meeting room table 222 and are facing the video
monitor 252 on the wall 242. A microphone 202 (or several microphone elements in a speaker
book such as a Polycom SoundStation VTX-1000 speakerphone) can be placed on the conference
room table 222. Utterances 232 propagate through the conference room and are reflected by
walls, eg 242 and ceiling 240. Reflected sound waves, also referred to as room echoes, are
generally undesirable and, if necessary, not acceptable to the microphone. It can be done when a
cardioid microphone is used. The cardioid microphone only receives sound waves in one
direction. Reflected sound waves in the opposite direction are not accepted. Thus, the cardioid
microphone does not accept the first stage echoes from the unwanted room, leading to an
improved echo ratio over the direct case.
According to embodiments of the present invention, the single-cardioid microphone element can
only accept sound waves in a small area along the primary direction, so that the microphone can
accept speech from many directions as required As can be done, several microphone elements
are provided at the microphone. FIGS. 3 (a) to 3 (c) illustrate the audio response coverage of a
microphone having three cardioid microphone elements. The cardioid microphone element is
connected to a microphone steering controller (eg, shown in FIG. 9) that controls and processes
signals generated by the cardioid microphone element. In this embodiment, there are three
elements 302, 304 and 306, each spaced 120 degrees apart. The corresponding response
coverage is shown in FIGS. 3 (a) to 3 (c). The microphone steering controller selects the best
microphone element by detecting the best speech quality among those three elements. In FIG. 3
(a), when the participant 310 speaks, the microphone element 302 with the response 312 is
activated. The other microphone elements 304 and 306 are disabled and ignored by the
microphone steering controller. Similarly, when participant 320 speaks, only microphone
element 304 is activated to respond 314. When participant 330 speaks, only microphone
element 306 is activated to respond 314. In FIGS. 3 (a) to 3 (c), while speakers 310, 320 and 330
are shown as three different people, they can only move one of three different locations within
the conference room. It can be a person, or some combination of them.
When more than one person speaks, more than one microphone element can be selected. The
microphone steering controller is designed to intelligently distinguish between human speech
and other noise, such as air conditioner noise, so that the controller is "not fooled" by the noise.
This ensures that the best acoustic quality is always maintained as the speaker (or the instructor
in the long distance education application) roams the room where the air conditioner is installed.
The tracking speed of the controller is virtually instantaneous, since it has no mechanical moving
parts. The microphone steering controller readily determines which microphone element has
been selected, and the signal is further processed by the controller or other downstream
processor, as required. The microphone steering controller can also perform gating and mixing to
combine signals from two or more microphone elements to generate an output microphone
The microphones according to the above embodiment are shown to be much better than existing
commercially available microphones. FIG. 4 shows contours of speech quality. A commercially
available omnidirectional microphone is used as a reference. The distance for omnidirectionality
to produce a very good sound is about 8 feet, as shown by contour line 414. Contour lines 412
for the above embodiment of the present invention are also shown. Contour line 4112 is
approximately 14 feet from the microphone and covers an area of approximately 600 square
5 to 7 show further characteristics of the microphone of the above embodiment. FIG. 5 shows a
frequency response curve 510 in the direction of the microphone element. FIG. 6 further
illustrates the frequency response for different angles of incidence. The microphone has three
identical cardioid microphone elements located at 120 ° apart, which are symmetrical so that
only one cardioid microphone element at 0 ° to + 60 ° It is sufficient to check the performance
only. The performance curve at -60 ° to 0 ° is symmetrical to the performance curve at 0 ° to
+ 60 °. As shown in FIG. 6, the frequency responses for all incident angles in the range of 0 °
to 60 ° almost overlap each other and show a very uniform angular response. This means that
where the speaker walks in the room around the microphone, the tonality remains the same.
Because of the uniform response across different angles of incidence, single frequency equalizers
can flatten their frequency response, even though the frequency response is not flat.
FIG. 7 shows very detailed polar responses for various frequencies in the range of 250 Hz to
3500 Hz. While their plots (702-714) show wide-angle sound collection, the average before and
after rejection is very good, keeping at 20 dB at 1000 Hz and 15 dB at 3500 Hz.
In the above embodiment, one microphone has three cardioid microphone elements. The number
of cardioid microphone elements may be more or less based on the characteristics of those
cardioid microphone elements and the needs of a particular application. In particular, when the
conference room or the lecture hall is larger than 600 square feet provided by a single
microphone as described above, install additional microphones in cooperation with each other
under the control of the microphone steering controller be able to. In one embodiment, three
microphones are installed in the lecture hall. The total coverage is 1800 square feet, which is a
huge conference room that can seat about 150 people comfortably.
Figures 8 (a) and 8 (b) show a typical conference room according to an embodiment of the
invention, using two microphones as described above. FIG. 8 (a) is a plan view, and FIG. 8 (b) is a
side view. The conference room is equipped with a video monitor 8101 and a video camera 8105
at one end of the conference room. The conference table 8119 is located at the center of the
conference room. Microphones 8110 and 8120 are overhead microphones. The microphones are
maintained above the conference participants. In this conference room, there are no other objects
between the overhead microphone and the conference participants. The microphone elements in
the overhead microphone can receive sound waves directly from the conference participants. In
one embodiment, the overhead microphone is suspended from the ceiling above the conference
participants. In this way, there are no microphones, associated wires or other components placed
around the conference table that would interfere with the conference participants. Further details
regarding the assembly are described below with reference to FIG. 10A. In this embodiment, each
microphone 8110 or 8120 has three cardioid microphone elements 8111-8116. Conference
participants such as reference numerals 8121, 8122 and 8123 can be seated anywhere in the
conference room. Their voice is picked up by any one of the six cardioid microphone elements
8111 to 8116. Because they are placed overhead, ie above all participants, only direct speech
8132 and 8134 are accepted by the microphones 8110 and 8120. The first stage reflected voice
or room echoes 8142 or 8144 are not accepted by the microphones 8110 and 8120.
Loudspeakers 8102 and 8104 are provided to play speech from the end of the conference.
Echoes or howlings between the microphone and the speaker are eliminated by acoustic signal
processing. There are many effective methods for acoustic echo cancellation and howling
cancellation. Any of them can be used in this embodiment of the invention.
The installation of the overhead microphone array removes the microphones from the
conference table in the conference room configuration. In contrast to typical tabletop
microphones or speakers incorporating a microphone, the overhead microphone array does not
interfere with the conference participants "out of sight". At the same time, the overhead
microphones will acoustically "go into view" as compared to any desktop microphones. When
there are several or more people in a conference, most people behind the first row do not have a
direct view direction towards the table top microphone. Speech from those persons behind the
first row is not well received by the microphone due to the obstruction of an object or person in
between. On the other hand, overhead microphones are provided above all of the conference
participants, regardless of how many people are in between. As long as the microphone is kept
overhead, only its height is a design choice and almost an aesthetic choice. The microphones can
be ceilings, below the ceiling and close to the ceiling, or slightly above them when people are
sitting. Typically, the upper half of the room, ie, the space between the floor and the room ceiling
to the room ceiling, is considered the room overhead space. In most conference rooms, there is
nothing between the lower speaker in the room and the overhead microphone. The overhead
microphone can always receive sound waves from any speaker in the room directly, so that the
generated microphone signal has the best acoustic quality.
In the embodiment shown in FIGS. 8 (a) and 8 (b), two microphones 8110 and 8120 can be used
for the two acoustic channels. Those two independent acoustic channels can form a stereo sound
field. They can be sent independently to other places in the conference. Similarly, at other
locations, if multiple acoustic channels are set up and received by the local location, they will
form a stereo sound field that distinguishes space. Spatial discriminatory stereo sound fields can
be coupled with the video display to simulate a more life-like conferencing experience.
FIG. 9 is a block diagram for signal processing for the embodiment shown in FIGS. 8 (a) and 8 (b).
Microphone elements 8111 to 8116 are grouped into two sets of microphones. Microphone
elements 8112, 8114 and 8116 are for microphone 8110 as shown in FIG. 8 (a) and microphone
elements 8111, 8113 and 8115 are for microphone 8120. The signals from the microphone
elements are provided to two steering controllers 942 and 941 respectively. The steering
controllers 942 and 941 operate independently to form two separate acoustic channels. The
operation of the steering controller 942 or 941 is the same to detect, select and mix the best
signal quality from the microphone elements at the connected microphones. If one microphone
element is identified as the best signal source, that signal passes as a signal 954 to downstream
processing components. Signals from other elements are discarded. When more than one factor
is selected, mixing occurs in the steering controller to generate signal 954. A similar process
occurs to generate signal 953 from steering controller 941. The acoustic signal 954 or 953 is
typically provided to a signal processor such as an acoustic echo canceller 962 or 961 to remove
echo signals from the speakers in the conference room. The substantially echo-free signals 952
and 951 are then provided to the processor 971 for further processing, as required. For example,
the acoustic signal can be frequency equalized to correct for non-flat frequency response, as
shown in FIGS. Noise in the acoustic signal can be reduced to improve intelligibility, and white
noise can be added to compensate for echo cancellation or noise reduction. The signal strength
can also be adjusted to compensate for the different gains in the microphones. Acoustic signals
can also be encoded for transmission in network systems such as, for example, the Internet,
Integrated Services Digital Network (ISDN) or Plain Old Telephone Service (POTS). The
conditioned signal 957 is sent to the other part of the conference. For clarity, steering, echo
cancellation and other processing are shown to be performed by different processing.
In actual embodiments, those functions tend to be performed by a single processor. The
functions may also be separated and performed by two or more processes with different
distributions of tasks.
10A-10B illustrate in more detail the overhead microphones used in the conferencing system
shown in FIG. FIG. 10A (a) is a side view, and FIG. 10A (b) is a plan view. In this embodiment
shown in FIG. 10A (a), it has a support structure 8223 with poles 8222 and the like. The support
structure 8223 secures the microphone 8110 to the ceiling of the conference room. The lower
end of the pole 8222 holds the main body of the microphone 8110. The microphone 8110 has
three microphone elements 8112, 8114 and 8116. Each element is a cardioid microphone
element. Each is spaced 120 ° apart from one another. In this way, the microphone 8110 can
accept audio from the 360 ° range. If the microphone elements used in the microphones have
different angular response ranges, the number of microphone elements used will be different.
Each microphone element in the microphone is coupled to a microphone steering controller (not
shown). The connection between the microphone element and the microphone steering
controller can have many different ways. The processors can be located at different locations and
connected to the microphone elements by simple wire connections. The wiring from the
microphone element passes through the center of the support pole 8222 which penetrates the
space above the ceiling to a controller located in the rest of the conference room.
It is highly preferable in some situations to provide a processor mounted on the microphone so
that only the processed microphone signal is transmitted to the acoustic system. FIG. 10A (c)
shows a processor 8225 in the microphone 8110. In this way, less information may be required
to be communicated between the microphone element and the controller. The processor may
also perform other signal processing tasks, such as tasks related only to the microphone itself,
such as acoustic gain control, frequency response equalization and noise reduction. Because the
microphone element and the onboard signal processor are low power components, they can be
powered by a small battery for an extended period of time. Also, with the additional wireless
transceiver, which can be a low power consumption component, the microphone can be a
wireless microphone that does not require a wired connection with an external system. Thus, the
microphones are very flexible and can be easily added or removed from any position. The
transceiver at the microphone can transmit its signal to an acoustic system that can communicate
with the wireless microphone.
In other embodiments, the microphone 8110 can also have a back shield 8220 positioned
directly above the microphone element. Thus, any sound from above the back shield is shielded
by the back shield 8220. For example, noise from above, such as noise from air conditioning
vents, fluorescent lights, etc., is shielded from reaching the microphone elements. Since most
ambient noise in the conference room is from overhead sources, placement of microphone
elements with such back shields can alleviate the need for noise reduction processing. Another
advantage of the back shield 8220 is that it can help to increase the microphone sensitivity gain
when the speaker is directly below the microphone 8110. Sound pressure is doubled due to back
shield boundary effects. This effect is used for superiority, as some of the acoustic energy is lost
if the speaker is seated directly under the microphone 8110, due to diffraction of the speaker's
head and due to the cardioid directivity. The doubled sound pressure compensates for the energy
loss and helps equalize the response of the microphone elements. Due to the reduction of
acoustic noise and the increase of acoustic signals, the need for signal processing, in particular
the need for noise reduction, is reduced.
The size of the back shield is variable. It is preferable to make the back shield as large as
possible, i.e. very large in comparison to each microphone element, in order to receive the most
benefit of shielding. When the microphone elements are arranged in a circle, the radius of the
back shield 8220 is typically at least twice the radius of that circle 8121 as shown in FIG. 10A
(b). The back shield can be made of any sound reflecting or sound absorbing material. Typical
shield diameters are about 12 inches to 30 inches.
A back shield can also be provided at each individual microphone element rather than one shield
for all microphone elements. The back shield for each individual microphone element is smaller.
For example, the individual shields 8132, 8134 and 8136 for the microphone elements 8112,
8114 and 8116, respectively, are smaller than the shield 8220. The individual shields can also be
better directed to give better blocking of unwanted noise.
Each microphone element can be placed separately or can be housed together in the same
housing as shown in FIGS. 10B (f) and 10B (g). The lower portion of the housing 8224 is a sound
wave from below and is, for example, sound transmissive (shown in dashed lines) to allow speech
from a conference participant to reach the microphone element. The upper part (and the side of
the housing, if necessary) is solid so as to be sound-permeable (indicated by a solid line). Sound
waves from directions other than below can not reach the microphone element inside the
housing. The housing 8224 itself can provide some shielding and reflective effects. A back shield
8220 is mounted directly above the microphone housing 8224 to provide good shielding.
The overhead microphone assembly may be installed in a conference room and used in a
conferencing system. The overhead microphone assembly can also be used in many other
applications, such as, for example, video conferencing or conferencing in the room only. The
sound system can amplify the participant's speech so that everyone in the room can hear the
speech. Once the speech is captured by the overhead microphone assembly, the speech signal is,
for example, amplified and reproduced at the same position, transmitted to the far end position,
wirelessly broadcast, or recorded on permanent media for further reproduction. It can be used by
any method such as
The overhead microphone assembly as shown in FIGS. 10A (a) and 10A (b) is fixed in place by a
hollow rod attached to the ceiling of the conference room. It can also be mounted in an
appropriate position overhead by any other method. For example, the microphone can be
attached to the bottom of the hanging luminaire or accessory. It can also be attached to a support
arm extending from the wall. A vibration absorbing insulator can also be inserted between the
microphone and its support structure or ceiling in order to reduce vibration noise from
equipment in the building.
Ceiling mounted microphones have been used in many prior art applications. Most of them are
used for safety and surveillance purposes. In those applications it is not the fidelity of the sound,
but the non-visibility of the microphone, for example the interest in the visual size of the
microphone. Although some prior art ceiling mounted microphones are used in conference
rooms, voice quality is less desirable. In particular, as noted above, omnidirectional microphone
elements typically do not provide good quality acoustic signals in a conference room setting,
especially when there are several people participating in the conference.
In the present invention, an overhead microphone having a plurality of microphone elements is
used. Microphones according to embodiments of the present invention can significantly improve
voice quality, increase coverage, reduce acoustic noise levels received by the microphone, and
reduce microphone interference by conference participants. It can greatly improve the liveliness
of the conference call.
Although the above example uses overhead microphones in a conference room, overhead
microphones can be used in many other places where high quality microphones are desired. Such
locations include, but are not limited to, classrooms, large halls, live art theaters, and the like.
Although exemplary embodiments of the present invention have been described in detail with
reference to the drawings, it will be understood that various modifications can be made without
departing from the scope and spirit of the present invention.
It is a figure shown about four kinds of microphone elements and those characteristics.
It is a figure shown about the setting of a meeting room. Figures 3 (a) to 3 (c) illustrate an
embodiment of the present invention in which three unidirectional microphone elements are
used and oriented in the microphone. FIG. 5 compares the response of a microphone according
to an embodiment of the present invention with the response of a representative omnidirectional
microphone that is commercially available. FIG. 6 shows the frequency response of a microphone
according to an embodiment of the present invention. FIG. 5 shows the angular response and
frequency response of a microphone according to an embodiment of the present invention. FIG. 5
shows the angular response and frequency response of a microphone according to an
embodiment of the present invention. FIGS. 8 (a) and 8 (b) are plan and side views, respectively,
illustrating settings in a conference according to an embodiment of the present invention. FIG. 5
is a block diagram illustrating signal processing for a microphone. 10A (a) to 10A (c) are
diagrams showing the physical arrangement of a portion of the ceiling module according to an
embodiment of the present invention. 10B (d) to 10B (g) are diagrams illustrating the physical
arrangement of a portion of the ceiling module according to an embodiment of the present
Explanation of sign
102 omnidirectional microphone 104 dipole microphone 106 cardioid microphone 108 high
parker geoid microphone 202 microphone 210 conference participant 222 conference room
table 232 speech 240 ceiling 242 wall 244 conference room arrangement 252 picture monitor
302 microphone element 304 microphone element 306 microphone element 310 Participants
312 Responses 314 Microphone Elements 320 Participants 330 Participants 412 Contours 414
Contours 510 Frequency Response Curves 610 Frequency Response Curves 702 High Angle
Sound Collection Plot 704 High Angle Sound Collection Plot 706 High Angle Sound Collection
Plot 708 High Angle Sound Collection Plot 712 High Angle Sound Collection Plot 714 High Angle
Sound Collection Plot 8101 Video Monitor 8102 Speaker 8104 Speaker 8 05 Video Camera
8110 Overhead Microphone 8111 to 8116 Cardioid Microphone Element 8119 Conference
Table 8120 Overhead Microphone 8121 to 8123 Conference Participant 8132 Back Shield 8134
Back Shield 8136 Back Shield 8220 Back Shield 8220 Pole 8222 Support Structure 8224
Housing 8225 Processor 941-942 Steering controller 953-954 Acoustic signal 957 Adjusted
signal 961-962 Acoustic echo canceller 971 Processor