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Mobile Phone Patent Abstract
The invention relates to equalization in a digital phone, advantageously
a mobile phone. According to the invention, the equalization (4)
of a reproduced sound is changed according to the operating conditions
of the phone. Information about the conditions is obtained by monitoring
the sound volume (19) set by the user, measuring the background
noise (17) in the operating environment of the phone through the
phone's microphone (9) and/or monitoring the quality (16) of the
connection between the phone and the communication network. The
low frequency emphasis is reduced in a very noisy environment and
increased in a quiet environment. The telephone according to the
invention is advantageously a mobile phone in a digital cellular
network.
Mobile Phone Patent Claims
What is claimed is:
1. A method for improving the quality and intelligibility of sound
reproduced by a telephone apparatus in which the reproduced sound
is handled in a digital form and equalized according to a certain
frequency response, wherein there is generated control information
describing operating conditions of said telephone apparatus and
the frequency response of said equalization is changed on the basis
of said control information to optimize the quality and intelligibility
of the sound reproduced in a given situation, wherein the telephone
apparatus comprises an outgoing channel with a microphone for transmitting
an outgoing signal to a distant location and an incoming channel
for receiving an incoming signal, the method further comprising
steps of:
generating the control information by sensing sound by said microphone
at an input to the outgoing channel;
applying said equalization to said incoming signal;
adjusting said equalization in response to the control information
obtained by the sensing of the sound at the input to the outgoing
channel;
by said microphone, recording the sound to be transmitted via said
outgoing channel, measuring noise recorded through said microphone,
and employing data representing noise measured by said measuring
step for generation of said control information by said generating
step; and
by use of voice activity detection means, determining whether or
not a user is speaking on the telephone during a call, and conducting
said noise measuring step only during those moments when the user
is not speaking according to information from said voice activity
detection means.
2. The method of claim 1, characterized in that the proportional
intensity of a certain frequency area is changed in said equalization,
and said changing of the frequency response includes at least one
of the following measures: changing of the gain of said frequency
area, changing of the width of said frequency area, changing of
the center frequency of said frequency area.
3. The method of claim 1, characterized in that said control information
includes a first information element which is formed on the basis
of the phone sound volume (19) set by the user.
4. The method of claim 3, characterized in that said first information
element describes the gain of the low-frequency part of the sound
reproduced, whereby the gain is increased when the user turns the
phone sound volume (19) down and the gain is decreased when the
user turns the phone sound volume (19) up.
5. The method of claim 1, characterized in that said control information
includes a second information element which is formed on the basis
of the noise (17) measured in the operating environment of said
telephone apparatus.
6. The method of claim 5, characterized in that said second information
element describes the gain of the low-frequency part of the sound
reproduced, whereby the gain is increased when the measurement shows
that the noise (17) in the operating environment is low, and the
gain is decreased when the measurement shows that there is a lot
of noise (17) in the operating environment.
7. The method of claim 1, characterized in that said control information
includes a third information element which is formed on the basis
of the quality (16) of the communication connection between said
telephone apparatus and the communication network.
8. The method of claim 7, characterized in that said equalization
is changed on the basis of said third information element to compensate
for the low quality of the communication connection.
9. The method of claim 8, characterized in that said third information
element describes the gain of the low-frequency part of the sound
reproduced, whereby the gain is increased when the quality (16)
of said communication connection is bad, and the gain is decreased
when the quality (16) of said communication connection is good.
10. A method for improving the quality and intelligibility of sound
reproduced by a telephone apparatus in which the reproduced sound
is handled in a digital form and equalized according to a certain
frequency response, wherein there is generated control information
describing the operating conditions of said telephone apparatus
and the frequency response of said equalization is changed on the
basis of said control information to optimize the quality and intelligibility
of the sound reproduced in a given situation, the method further
comprising recurrently the following steps:
a) without any special temporal order
the first information element is generated according to how the
user adjusts the phone sound volume,
it is monitored when the user is not speaking during a call, and
the noise in the operating environment of the phone is measured
during such moments and the second information element is formed
on the basis of the noise measurement,
the quality of the connection between the telephone and the communication
networked used via it is monitored and the third information element
is formed accordingly, and
b) according to the information elements formed
the gain of the low-frequency part of the sound reproduced is changed
inversely proportionally to the sound volume set by the user, whereby
value pairs representing a certain sound volume and the corresponding
gain form a monotonically falling curve (A;B;C;) in a system of
coordinates where the gain is represented as a function of the sound
volume setting,
said gain is scaled inversely proportionally to measured noise,
whereby said curve shifts downwards (A->B; B->C) in said system
of coordinates when the noise increases and upwards (C->B; B->A)
when the noise decreases, and
if the connection between the communication network and the phone
is bad, said gain of the low-frequency part is set constant, whereby
it does not depend on the sound volume setting.
11. The method of claim 1, characterized in that said control information
includes a fourth information element which is formed on the basis
of auxiliaries (18) connected to said phone.
12. A telephone apparatus including a loudspeaker for the reproduction
of sound and a digital signal processing means for the digital processing
of the sound reproduced, which signal processing means includes
an equalizer which has a certain frequency response, wherein said
telephone apparatus includes means for the generation of control
information describing its operating conditions and a means for
changing the frequency response of said equalizer on the basis of
said control information, wherein the telephone apparatus comprises:
an outgoing channel for transmitting an outgoing signal to a distant
location and an incoming channel for receiving an incoming signal;
means for generating the control information by sensing sound at
an input to the outgoing channel, the reproduced sound appearing
at an output of the incoming channel, said equalization being applied
to said incoming signal;
means for adjusting said equalization in response to the control
information obtained by the sensing of the sound at the input to
the outgoing channel;
a control block for collecting the data describing said operating
conditions and for generating said control information;
a microphone for recording the sound to be transmitted via a telephone
connection, noise measuring means for measuring noise recorded through
said microphone, and means for conveying data representing noise
measured by said measuring means to said control block for the generation
of said control information; and
voice activity detection means for determining whether or not a
user is speaking on the phone during a call, and said noise measuring
means is operative to measure noise only during those moments when
the user is not speaking according to the information from said
voice activity detection means.
13. The telephone apparatus of claim 12, characterized in that
it includes a sound volume adjusting device (19) which can be used
by the user and a means for conveying information about the sound
volume set with said adjusting device to said control block (15)
for the generation of said control information.
14. The telephone apparatus of claim 12, characterized in that
said noise measuring means (13; 13a, 13b, 13c) include a weighting
filter (13b) which weights noise measurement at certain frequencies.
15. The telephone apparatus of claim 12, characterized in that
it includes a means for monitoring the quality (16) of the communication
connection between it and the communication network and a means
for conveying the information describing the quality of the connection
to said control block (15) for the generation of said control information.
16. The telephone apparatus of claim 12, characterized in that
it includes a digital signal processor (1) which includes said equalizer
(4).
17. The telephone apparatus of claim 16, characterized in that
said digital signal processor (1) also includes said control block
(15).
18. The telephone apparatus of claim 16, characterized in that
said digital signal processor (1) also includes said noise measuring
means (13, 13a, 13b, 13c).
19. The telephone apparatus of claim 12, characterized in that
it is a mobile phone in a digital cellular network.
20. The telephone apparatus of claim 12, characterized in that
it includes a connecting means for the connection of auxiliaries
and a means for conveying the information (18) describing the connected
auxiliaries to said control block (15) for the generation of said
control information.
21. The telephone apparatus of claim 20, characterized in that
said auxiliaries include hands-free equipment.
22. A telephone apparatus including a loudspeaker for the reproduction
of sound and a digital signal processing means for the digital processing
of the sound reproduced, which signal processing means includes
an equalizer which has a certain frequency response, wherein said
telephone apparatus includes means for the generation of control
information describing its operating conditions and a means for
changing the frequency response of said equalizer on the basis of
said control information;
wherein said equalizer realizes the transfer function ##EQU2##
wherein the Zs represent delays of a time unit and said control
information comprises variable parameters K, a1 and a2, of which
K represents the gain and a1 and a2 represent the center frequency
and the bandwidth.
23. A method for improving the quality of sound reproduced by a
receiver of a communications system which comprises also a transmitter,
the method comprising steps of:
constructing the receiver with a filter having a passband extending
across the spectrum of the incoming signal;
measuring ambient sonic noise level at the transmitter by use of
a microphone of the transmitter to provide a measurement thereof,
and employing the microphone for a transmission of speech from the
system;
establishing a plurality of spectral shapes for said passband wherein
an individual one of said spectral shapes defines a relationship
between amplitude and frequency of a signal transmission characteristic
of the filter;
providing a relationship between said spectral shapes and said
ambient noise level for signal equalization;
selecting a spectral shape for said passband corresponding to the
measurement of the ambient noise level;
generating control information from said measurement of the ambient
noise level; and
by use of voice activity detection means, determining whether or
not a user is speaking on the telephone during a call, and conducting
said noise measuring step only during those moments when the user
is not speaking according to information from said voice activity
detection means.
24. A method according to claim 23, further comprising steps of:
outputting a sonic signal from said receiver;
providing a relationship between said spectral shapes and a loudness
of said sonic signal; and
wherein said selecting step is based both on said relationship
between said spectral shapes and said ambient noise level and said
relationship between said spectral shapes and said loudness of said
sonic signal.
25. A method according to claim 24 wherein the receiver is part
of a mobile phone of the communication system.
26. A receiver circuit of a communications system having an incoming
signal channel and a transmission signal channel, the receiving
circuit serving to improve the quality of sound of an incoming signal
reproduced by the receiver circuit in response to a measurement
of an ambient noise signal at the transmission channel of the system,
the circuit comprising:
a filter with a passband extending across the spectrum of the incoming
signal, and being located in the incoming signal channel;
means for measuring ambient sonic noise level at an input to the
transmission channel by a microphone of the transmission channel
to provide a measurement of the ambient noise level;
means for establishing a plurality of spectral shapes for the passband
wherein an individual one of the spectral shapes defines a relationship
between amplitude and frequency of a signal transmission characteristic
of the filter;
means for providing a relationship between spectral shapes of the
passband and said ambient noise level, wherein the passband may
have any one of a plurality of said spectral shapes, an individual
one of the spectral shapes defining a relationship between amplitude
and frequency of a signal transmission characteristic of the filter;
means responsive to the measurement of the ambient noise level
for selecting one of said spectral shapes for said passband corresponding
to the measurement of the ambient noise level to accomplish signal
equalization of said incoming signal; and
voice activity detection means for determining whether or not a
user is speaking into the microphone during a call, and said noise
measuring means is operative to measure noise only during those
moments when the user is not speaking according to the information
from said voice activity detection means.
27. A receiver circuit according to claim 26, further comprising:
means for outputting a sonic signal from said receiver;
means for providing a relationship between said spectral shapes
and a loudness of said sonic signal; and
wherein said selecting means is responsive both to said relationship
between said spectral shapes and said ambient noise level and to
said relationship between said spectral shapes and said loudness
of said sonic signal.
28. A receiver circuit according to claim 27 wherein the receiver
is part of a mobile phone of a communication system.
Mobile Phone Patent Description
textBACKGROUND OF THE INVENTION
The invention relates in general to speech signal processing and
in particular to equalization of a speech signal in a mobile phone
in order to improve the intelligibility of transmitted speech.
It is a widely known and used method to improve the auditory effect
of sound, and of speech, which is a special case of sound, with
an equalizer. The frequency spectrum of a sound can be equalized,
whereby the frequency response peaks or pits corresponding to certain
frequencies are equalized closer to the average level, or certain
frequencies or frequency areas can purposely be amplified or attenuated
so that they deviate from the mean level. In addition to improving
the auditory effect, equalization can also help people suffering
from certain types of hearing defects discern sounds better.
Equalization can be performed electrically or mechanically. Electrical
equalization requires the use of various filter circuits in the
device that processes sound. Known solutions in the field of analog
signal processing include passive RC filters, active filters based
on operational amplifiers and special equalizer chips, and in the
digital field, digital signal processors which can be programmed
to realize very complex filter arrangements. Mechanical equalization
is performed by selecting the mechanical properties of the loudspeaker
reproducing sound and of its immediate vicinity such that a desired
frequency response is achieved.
In mobile phones, equalization is needed to improve the quality
and intelligibility of the sound that travels from the loudspeaker
to the user's ear. The sound from the loudspeaker seems distorted
because usually the loudspeaker does not reproduce all frequencies
in the same way and because there occurs an acoustic leakage between
the loudspeaker and the user's ear which affects different frequencies
in different ways. FIG. 1 is a graph illustrating two frequency
response measurements: in the measurement arrangement corresponding
to the upper curve the loudspeaker and the instrument corresponding
to an ear are protected against acoustic leakage (strong acoustic
coupling) and in the arrangement corresponding to the lower curve
the acoustic leakage corresponds to normal usage of a mobile phone.
The figure shows clearly that as the acoustic coupling gets weaker
because of the leakage, especially the reproduction of low frequencies
(<1 kHz) gets worse.
A known method which has been used in attempting to equalize the
distortion of sound is the use of special loudspeakers applying
acoustic feedback. The method is of a mechanical nature, because
in it an attempt is made to build the loudspeaker such that its
mechanical properties compensate for the attenuation of low frequencies.
An air gap is left between the loudspeaker and its mounting body,
whereby the width of the air gap is a significant factor as regards
acoustic feedback. To achieve correct dimensioning and operation,
strict mechanical tolerances must be followed in the assembly of
the loudspeaker, which increases manufacturing costs. The frequency
response of the mechanical arrangement cannot be changed later,
which makes the arrangement inflexible. Furthermore, the method
cannot be applied in the implementation of a hands-free loudspeaker
which is a widely used option in mobile phones.
By suitable design of the electromechanical properties, a loudspeaker
can be realized which by nature amplifies low-frequency signals.
Also this arrangement is inflexible, since the frequency response
is determined in the manufacturing process of the loudspeaker and
it cannot be changed e.g. with an electrical control signal.
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