FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION (See Section 10 and Rule 13)
Title of invention:
METHOD AND SYSTEM FOR SECURE SPEECH TRANSMISSION
WITH LOW BIT RATE
Applicant
Tata Consultancy Services Limited A company Incorporated in India under the Companies Act, 1956
Having address:
Nirmal Building, 9th floor,
Nariman point, Mumbai 400021,
Maharashtra, India
Preamble to the description
The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD [001] The disclosure herein generally relates to speech transmission, and, more particularly, to method and system for secure speech transmission with low bit rate.
BACKGROUND [002] Transmission of secure speech signal is a challenging task since encrypting the digitized speech signal adds overheads and randomizes the bit stream to a level where recovery of original signal becomes difficult. In past few years, speech related applications such as voice search, and voice authentication have unprecedented surge in use. In such applications, the speech of the user is recorded and sent to a web server that hosts the application. This creates potential privacy concerns where the data that identifies the user can be subject to theft. Moreover, such data can be intercepted while transmitting the speech in its raw form. Such data can be easily intercepted and obtained by malicious agents for privacy and security of the user. In addition, data transmission for various speech applications in raw form requires high bit-rate transmission. For any speech application that sends data to a web-server (such as speech recognition using Google®, Alexa®, Siri® voice search), the voice of the speaker/identified user is transmitted in raw form over a communication channel. Such raw transmission is vulnerable for exploitation by any harmful agent and compromises the user privacy.
SUMMARY [003] Embodiments of the present disclosure present technological improvements as solutions to one or more of the above-mentioned technical problems recognized by the inventors in conventional systems. For example, in one embodiment, a system for secure speech transmission with low bit rate is provided. The system includes receiving, a speech signal comprising a plurality of successive frames and encoding by a speech encoder, the speech signal at transmitter, by generating a secure speech code for the encoded speech signal comprising a compression ratio for each frame of the speech signal with each filter of the Mel Filter bank, wherein the compression ratio is computed based on (i) a speech signal energy, and (ii) a basis function energy, wherein the generated secure speech code

for the encoded speech signal is transmitted over a communication channel to a corresponding receiver. Here, the secure speech code is computed by, generating, a basis function nb with same duration length of the speech signal in time domain,
wherein the basis function is band limited to white noise signal filtered based on a center frequency and a cutoff frequency using a Mel Filter bank comprising one or more filters. Further, one or more overlapping frames Wo and a window length are obtained from each frame of the speech signal and the basis function, wherein the one or more overlapping frames are determined based on a current frame overlapping with the plurality of successive frames. Further, a total number of bits required for the encoded speech signal are determined using the duration length of the speech signal and a sampling frequency fs and then a total number of frames for the speech signal and the basis function are determined based on a frame length and the one or more overlapping frames. Further, for each frame of the speech signal, the method computes a speech signal energy of frequency bands corresponding to a filter associated with the Mel Filter bank based on (i) the duration length of the speech signal, (ii) the sampling frequency fs, and (iii) a bit resolution. Then, a basis function energy is computed corresponding to the frame of the filter associated with the Mel Filter bank. Further, the secure speech code comprising the compression ratio for the encoded signal is computed based on (i) the speech signal energy, and (ii) the basis function energy.
[004] In one embodiment the receiver decodes the secure speech code for the encoded speech signal to reconstruct the original speech signal by converting, each basis function into frames having the same window length and the one or more overlapping frames as obtained at the transmitter. Then, a transmitted ratio with the same basis function as obtained is multiplied at the transmitter to obtain Mel frequency band energies of the speech signal and using an overlap add technique the Mel frequency band energies are converted to obtain the original reconstructed signal.
[005] In another aspect, a method for secure speech transmission with low bit rate is provided. The method includes receiving, a speech signal comprising a plurality of successive frames and encoding by a speech encoder, the speech signal

at transmitter, by generating a secure speech code for the encoded speech signal comprising a compression ratio for each frame of the speech signal with each filter of the Mel Filter bank, wherein the compression ratio is computed based on (i) a speech signal energy, and (ii) a basis function energy, wherein the generated secure speech code for the encoded speech signal is transmitted over a communication channel to a corresponding receiver. Here, the secure speech code is computed by, generating, a basis function nb with same duration length of the speech signal
in time domain, wherein the basis function is band limited to white noise signal filtered based on a center frequency and a cutoff frequency using a Mel Filter bank comprising one or more filters. Further, one or more overlapping frames Wo and a window length are obtained from each frame of the speech signal and the basis
function, wherein the one or more overlapping frames are determined based on a current frame overlapping with the plurality of successive frames. Further, a total number of bits required for the encoded speech signal are determined using the duration length of the speech signal and a sampling frequency fs and then a total number of frames for the speech signal and the basis function are determined based on a frame length and the one or more overlapping frames. Further, for each frame of the speech signal, the method computes a speech signal energy of frequency bands corresponding to a filter associated with the Mel Filter bank based on (i) the duration length of the speech signal, (ii) the sampling frequency fs, and (iii) a bit resolution. Then, a basis function energy is computed corresponding to the frame of the filter associated with the Mel Filter bank. Further, the secure speech code comprising the compression ratio for the encoded signal is computed based on (i) the speech signal energy, and (ii) the basis function energy.
[006] In one embodiment the receiver decodes the secure speech code for the encoded speech signal to reconstruct the original speech signal by converting, each basis function into frames having the same window length and the one or more overlapping frames as obtained at the transmitter. Then, a transmitted ratio with the same basis function as obtained is multiplied at the transmitter to obtain Mel frequency band energies of the speech signal and using an overlap add technique

the Mel frequency band energies are converted to obtain the original reconstructed signal.
[007] In yet another aspect, a non-transitory computer readable medium provides one or more non-transitory machine-readable information storage mediums comprising one or more instructions, which when executed by one or more hardware processors perform actions includes an I/O interface and a memory coupled to the processor is capable of executing programmed instructions stored in the processor in the memory to receiving, a speech signal comprising a plurality of successive frames and encoding by a speech encoder, the speech signal at transmitter, by generating a secure speech code for the encoded speech signal comprising a compression ratio for each frame of the speech signal with each filter of the Mel Filter bank, wherein the compression ratio is computed based on (i) a speech signal energy, and (ii) a basis function energy, wherein the generated secure speech code for the encoded speech signal is transmitted over a communication channel to a corresponding receiver. Here, the secure speech code is computed by, generating, a basis function n b with same duration length of the speech signal in time domain, wherein the
basis function is band limited to white noise signal filtered based on a center frequency and a cutoff frequency using a Mel Filter bank comprising one or more filters. Further, one or more overlapping frames Wo and a window length are
obtained from each frame of the speech signal and the basis function, wherein the one or more overlapping frames are determined based on a current frame overlapping with the plurality of successive frames. Further, a total number of bits required for the encoded speech signal are determined using the duration length of the speech signal and a sampling frequency fs and then a total number of frames for the speech signal and the basis function are determined based on a frame length and the one or more overlapping frames. Further, for each frame of the speech signal, the method computes a speech signal energy of frequency bands corresponding to a filter associated with the Mel Filter bank based on (i) the duration length of the speech signal, (ii) the sampling frequency fs, and (iii) a bit resolution. Then, a basis function energy is computed corresponding to the frame of the filter associated with the Mel Filter bank. Further, the secure speech code comprising the compression

ratio for the encoded signal is computed based on (i) the speech signal energy, and (ii) the basis function energy.
[008] In one embodiment the receiver decodes the secure speech code for the encoded speech signal to reconstruct the original speech signal by converting, each basis function into frames having the same window length and the one or more overlapping frames as obtained at the transmitter. Then, a transmitted ratio with the same basis function as obtained is multiplied at the transmitter to obtain Mel frequency band energies of the speech signal and using an overlap add technique the Mel frequency band energies are converted to obtain the original reconstructed signal.
[009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[010] The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles:
[011] FIG. 1 illustrates an exemplary block diagram of a secure speech transmission system according to some embodiments of the present disclosure.
[012] FIG. 2A and FIG.2B illustrates a high level architectural overview of a speech signal transmitted securely with low bit rate using the system of FIG.1, in accordance with some embodiments of the present disclosure.
[013] FIG. 3 is a flow diagram illustrating a method of processing the speech signal for secure speech transmission with low bit rate using the system of FIG.1, in accordance with some embodiments of the present disclosure.
[014] FIG.4 illustrates experimental results of Mel filter bank energies of the speech signal for Libri speech clean subset using the system of FIG.1, in accordance with some embodiments of the present disclosure.
[015] FIG.5 illustrates experimental results of Mel filter bank energies of the speech signal for ESC 50 speech clean subset using the system of FIG.1, in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS [016] Exemplary embodiments are described with reference to the accompanying drawings. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. Wherever convenient, the same reference numbers are used throughout the drawings to refer to the same or like parts. While examples and features of disclosed principles are described herein, modifications, adaptations, and other implementations are possible without departing from the scope of the disclosed embodiments.
[017] Referring now to the drawings, and more particularly to FIG. 1 through FIG.5, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments and these embodiments are described in the context of the following exemplary system and/or method.
[018] Embodiments herein provides a method and system for secure speech transmission system with low bit rate. The method disclosed, enables secured transmission of speech signal with low bit rate. The method disclosed is an efficient, accurate and scalable technique for secure speech encoding and decoding for transmission of speech signal over a communication channel to preserve the privacy of user data. Also, the encoding of the speech signal enables transmission with lower bit rate than uncompressed speech. Moreover, recognition models can be trained directly on encoded data for additional security. Also, for the secure transmission of the user speech signal is encoded using a generative model and the encoded coefficients are transmitted to receiver. Such encoded information is not interpretable without the knowledge of basis function(s) used while encoding. Such encoding also reduces the effective amount of data sent to the web-server for recognition purpose. Moreover, using the raw speech it is possible to extract various information about user such as speaker identity, spoken content using open source models that work on standard feature set. If the recognition models are trained to recognize the encoded representation rather than standard feature set used in speech processing, then the transmission of raw speech is not required.

[019] Referring now to the drawings, and more particularly to FIG. 1 through FIG.5, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments and these embodiments are described in the context of the following exemplary system and/or method.
[020] FIG. 1 illustrates an exemplary block diagram of a secure speech transmission system, in accordance with some embodiments of the present disclosure. In an embodiment, the system 100 includes processor (s) 104, communication interface (s), alternatively referred as or input/output (I/O) interface(s) 106, and one or more data storage devices or memory 102 operatively coupled to the processor (s) 104. The system 100, with the processor(s) is configured to execute functions of one or more functional blocks of the system 100. Referring to the components of the system 100, in an embodiment, the processor (s) 104 can be one or more hardware processors 104. In an embodiment, the one or more hardware processors 104 can be implemented as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and/or any devices that manipulate signals based on operational instructions. Among other capabilities, the processor(s) 104 is configured to fetch and execute computer-readable instructions stored in the memory. In an embodiment, the system 100 can be implemented in a variety of computing systems, such as laptop computers, notebooks, 10 hand-held devices, workstations, mainframe computers, servers, a network cloud, and the like.
[021] The I/O interface(s) 106 can include a variety of software and hardware interfaces, for example, a web interface, a graphical user interface, and the like and can facilitate multiple communications within a wide variety of networks N/W and protocol types, including wired networks, for example, LAN, cable, etc., and wireless networks, such as WLAN, cellular, or satellite. In an embodiment, the I/O interface (s) 106 can include one or more ports for connecting a number of devices (nodes) of the system 100 to one another or to another server.
[022] The memory 102 may include any computer-readable medium known in the art including, for example, volatile memory, such as static random

access memory (SRAM) and dynamic random access memory (DRAM), and/or non-volatile memory, such as read only memory (ROM), erasable programmable ROM, flash memories, hard disks, optical disks, and magnetic tapes. The modules 108 can be an Integrated Circuit (IC) (not shown), external to the memory 102, implemented using a Field-Programmable Gate Array (FPGA) or an Application-Specific Integrated Circuit (ASIC). The names (or expressions or terms) of the modules of functional block within the modules 108 referred herein, are used for explanation and are not construed to be limitation(s). The modules 108 includes the time series time predictor module 110 for processing of a plurality of human body inputs received from one or more external sources. Further, the memory 102 may comprises information pertaining to input(s)/output(s) of each step performed by the processor(s) 104 of the system 100 and methods of the present disclosure.
[023] FIG. 2A and FIG.2B illustrates a high level architectural overview of a speech signal transmitted securely with low bit rate using the system of FIG.1, in accordance with some embodiments of the present disclosure. FIG.2A includes a speech encoder, and a speech decoder. The speech encoder includes a generative model comprising a short time Fourier transform (STFT), a Mel filter bank with one or more filters. The speech decoder includes an overlap add technique. The speech encoder of the system 100 obtains a speech signal comprising a plurality of successive frames as input from one or more external sources, wherein the input speech signal is processed at transmitter end. For example, the external sources may include user speech, or voice data received from any sources. The speech decoder of the system 100 reconstructs the original speech signal by processing the encoded speech signal at receiver. FIG.2B depicts the generative model of the speech encoder of the system 100 having Mel Filter bank with one or more filters. Functions of the components of the system 100, for processing speech signal, are explained in conjunction with FIG.2 through FIG.5 providing flow diagram, architectural overviews, and performance analysis of the system 100.
[024] FIG. 3 is a flow diagram illustrating a method of processing the speech signal for secure speech transmission with low bit rate using the system of FIG.1, in accordance with some embodiments of the present disclosure. In an

embodiment, the system 100 comprises one or more data storage devices or the memory 102 operatively coupled to the processor(s) 104 and is configured to store instructions for execution of steps of the method 300 by the processor(s) or one or more hardware processors 104. The steps of the method 300 of the present disclosure will now be explained with reference to the components or blocks of the system 100 as depicted in FIG.1, FIG.2A, and FIG.2B and the steps of flow diagram as depicted in FIG.3. Although process steps, method steps, techniques or the like may be described in a sequential order, such processes, methods and techniques may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps to be performed in that order. The steps of processes described herein may be performed in any order practical. Further, some steps may be performed simultaneously.
[025] Referring now to the steps of the method 300, at step 302, the one or more hardware processors 104 receiving a speech signal comprising a plurality of successive frames. Considering an example, referring now to FIG.2A the input received as speech signal received as inputs are processed to generate a secure speech code. The speech signal includes the plurality of successive frames. In one use case scenario of voice assistant the input speech signal of the user is stored in the web based server. Further, the user’s input speech signal is converted to text wherein the speech signal sent to the server can be intercepted and used maliciously. The system encodes the speech signal before sending to the web server that cannot be recovered as basis signals are not known to the interceptor. Moreover, the system compresses the amount of data sent to the server making the communication faster. At the receiver, user’s speech signal is decoded and used for recognition purpose.
[026] Referring now to the steps of the method 300, at step 304, the one or more hardware processors 104 encode, by using a speech encoder, the speech signal at transmitter, by generating a secure speech code for the encoded speech signal comprising a compression ratio for each frame of the speech signal with each filter of the Mel Filter bank, wherein the compression ratio is computed based on (i) a speech signal energy, and (ii) a basis function energy, wherein the generated secure

speech code for the encoded speech signal is transmitted over a communication channel to a corresponding receiver.
[027] In one embodiment, generating the secure speech code comprises the following steps where, initially a basis function nb is generated with same
duration length of the speech signal in time domain, wherein the basis function is band limited to white noise signal filtered based on a center frequency and a cutoff frequency sing a Mel Filter bank comprising one or more filters. Here, the basis function nb is generated with the following properties,
Where,
a) B is the orthogonal basis functions
b) Each basis function nb is strictly band-limited.
c) The bands of any basis do not overlap with each other.
d) Basis functions cover entire frequency spectrum defined by the sampling frequency fs of the signal.
e) One realization of the basis signals is band-limiting white noise signal filtered as per above properties
Further, one or more overlapping frames Wo and a window duration length are
obtained from each frame of the speech signal and the basis function nb ,
wherein the one or more overlapping frames are determined based on a current frame overlapping with the plurality of successive frames. Then, a total number of bits required for the encoded speech signal are determined using the duration length of the speech signal and a sampling frequency fs. Here, for Ts long speech signal is sampled at the sampling frequency fs and 16-bit resolution which is represented in equation 1,
Further, a total number of frames for the speech signal and the basis function nb are determined based on a frame length and the one or more overlapping frames. The transmission using the present disclosure with B number of orthogonal basis functions nb , and Wo samples frame overlap, and n bit floating point resolution,
the number of bits to transmit is represented below in equation 2,


For each frame of the speech signal, a speech signal energy of frequency bands corresponding to a filter associated with the Mel Filter bank is computed based on (i) the duration length of the speech signal, (ii) the sampling frequency fs, and (iii) a bit resolution. Further, a basis function energy is computed corresponding to the frame of the filter associated with the Mel Filter bank. The basis function energy is computed based on (i) the duration length of the speech signal multiplied with the sampling frequency fs, (ii) a total number of overlapping frames, (iii) a total number of basis function nb and (iv) the total number of bits to be transmitted. The secure speech code comprising the compression ratio is computed for the encoded signal based on (i) the speech signal energy, and (ii) the basis function energy as represented in equation 3,

The basis function energy is computed based on (i) the duration length of the speech signal multiplied with the sampling frequency fs, (ii) a total number of overlapping frames, (iii) a total number of basis function, and (iv) the total number of bits to be transmitted.
[028] In one embodiment, the receiver decodes the secure speech code from the encoded speech signal to reconstruct the original speech signal by, converting each basis function nb into frames nb(t) having the same window length and the one or more overlapping frames (Wo) as obtained at the
transmitter. Further, for the received a(b,t) a transmitted ratio is multiplied with the same basis function nb(t) as obtained at the transmitter to obtain Mel frequency band energies of the speech signal. Further, using an overlap add technique, the Mel frequency band energies are converted to obtain the original reconstructed signal.
[029] In one embodiment, the raw speech signal or features extracted from speech using traditional feature-extraction algorithms contain speech and speaker information that can be easily extracted, even using general purpose, openly available algorithms. The present disclosure provides ensures secure transmission for encoding the speech features using a linear-algebraic generative model. These

speech features can be represented in terms of weighted sum of pre-defined basis functions. The orthogonal basis functions has entire feature space, representing any speech signal using the basis function and the coefficients corresponding to each basis function. The set of coefficients corresponding to a set if basis tend to be unique due to orthogonality property of the basis functions. Using this property, a secure set of coefficients can be computed using the set of the basis functions. To ensure the reconstruction of the speech signal, the receiver must have access to the same set of basis functions.
[030] FIG.4 illustrates experimental results of Mel filter bank energies of the speech signal for Libri speech clean subset, in accordance with some embodiments of the present disclosure Left column in FIG. 4 depicts Mel-filter bank energies of utterances from Libri speech test-clean subset and the right column depict Mel-filter bank energies of same utterances after encoding-decoding process 40 band-limited white noise signals were used to encode-decode the signals.
[031] FIG.5 illustrates experimental results of Mel filter bank energies of the speech signal for ESC 50 speech clean subset, in accordance with some embodiments of the present disclosure Left column in FIG. 5 depicts Mel-filter bank energies of noise signals from ESC-50 test-clean subset and the right column depicts Mel-filter bank energies of the same noise signals after encoding-decoding process 40 band-limited white noise signals were used to encode-decode the signals.
[032] The embodiments of present disclosure herein address unresolved problem of speech transmission. The embodiments thus provide method and system for secure speech transmission with low bit rate. Moreover, the embodiments herein further provide the speech encoder and the speech decoder for encoding and decoding resulting in secure speech code transmission. The present disclosure preserves the crucial parts of speech as well as non-speech signals during encoding-decoding process, while providing compression ratio upto a predefined unit having a value four.
[033] The written description describes the subject matter herein to enable any person skilled in the art to make and use the embodiments. The scope of the

subject matter embodiments is defined by the claims and may include other modifications that occur to those skilled in the art. Such other modifications are intended to be within the scope of the claims if they have similar elements that do not differ from the literal language of the claims or if they include equivalent elements with insubstantial differences from the literal language of the claims.
[034] It is to be understood that the scope of the protection is extended to such a program and in addition to a computer-readable means having a message therein; such computer-readable storage means contain program-code means for implementation of one or more steps of the method, when the program runs on a server or mobile device or any suitable programmable device. The hardware device can be any kind of device which can be programmed including e.g., any kind of computer like a server or a personal computer, or the like, or any combination thereof. The device may also include means which could be e.g., hardware means like e.g., an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination of hardware and software means, e.g., an ASIC and an FPGA, or at least one microprocessor and at least one memory with software processing components located therein. Thus, the means can include both hardware means, and software means. The method embodiments described herein could be implemented in hardware and software. The device may also include software means. Alternatively, the embodiments may be implemented on different hardware devices, e.g., using a plurality of CPUs.
[035] The embodiments herein can comprise hardware and software elements. The embodiments that are implemented in software include but are not limited to, firmware, resident software, microcode, etc. The functions performed by various components described herein may be implemented in other components or combinations of other components. For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can comprise, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.
[036] The illustrated steps are set out to explain the exemplary embodiments shown, and it should be anticipated that ongoing technological

development will change the manner in which particular functions are performed. These examples are presented herein for purposes of illustration, and not limitation. Further, the boundaries of the functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternative boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Alternatives (including equivalents, extensions, variations, deviations, etc., of those described herein) will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Such alternatives fall within the scope of the disclosed embodiments. Also, the words “comprising,” “having,” “containing,” and “including,” and other similar forms are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.
[037] Furthermore, one or more computer-readable storage media may be utilized in implementing embodiments consistent with the present disclosure. A computer-readable storage medium refers to any type of physical memory on which information or data readable by a processor may be stored. Thus, a computer-readable storage medium may store instructions for execution by one or more processors, including instructions for causing the processor(s) to perform steps or stages consistent with the embodiments described herein. The term “computer-readable medium” should be understood to include tangible items and exclude carrier waves and transient signals, i.e., be non-transitory. Examples include random access memory (RAM), read-only memory (ROM), volatile memory, nonvolatile memory, hard drives, CD ROMs, DVDs, flash drives, disks, and any other known physical storage media.
[038] It is intended that the disclosure and examples be considered as exemplary only, with a true scope of disclosed embodiments being indicated by the following claims.

We Claim:
1. A processor implemented method (300) for secure speech transmission with
low bit rate, the method comprising:
receiving (302), via one or more hardware processors, a speech signal comprising a plurality of successive frames; and
encoding (304), by a speech encoder via the one or more hardware processors, the speech signal at transmitter, by generating a secure speech code for the encoded speech signal comprising a compression ratio for each frame of the speech signal with each filter of the Mel Filter bank, wherein the compression ratio is computed based on (i) a speech signal energy, and (ii) a basis function energy, wherein the generated secure speech code for the encoded speech signal is transmitted over a communication channel to a corresponding receiver.
2. The method as claimed in claim 1, wherein the secure speech code is
computed by,
generating, a basis function nb with same duration length
of the speech signal in time domain, wherein the basis function is band limited to white noise signal filtered based on a center frequency and a cutoff frequency using a Mel Filter bank comprising one or more filters;
obtaining, one or more overlapping frames Wo and a window length from each frame of the speech signal and the basis
function, wherein the one or more overlapping frames Wo are determined based on a current frame overlapping with the plurality of successive frames;
determining, a total number of bits required for the encoded speech signal using the duration length of the speech signal and a sampling frequency fs;

determining, a total number of frames for the speech signal and the basis function based on a frame length and the one or more overlapping frames Wo;
computing, for each frame of the speech signal, a speech signal energy of frequency bands corresponding to a filter associated with the Mel Filter bank based on (i) the duration length of the speech signal, (ii) the sampling frequency fs, and (iii) a bit resolution;
computing, a basis function energy corresponding to the frame of the filter associated with the Mel Filter bank; and
computing, the secure speech code comprising the compression ratio for the encoded signal based on (i) the speech signal energy, and (ii) the basis function energy.
3. The method as claimed in claim 2, wherein the basis function energy is computed based on (i) the duration length of the speech signal multiplied with the sampling frequency fs, (ii) a total number of overlapping frames, (iii) a total number of basis function, and (iv) the total number of bits to be transmitted.
4. The method as claimed in claim 1, wherein the receiver decodes the secure speech code for the encoded speech signal to reconstruct the original speech signal by,
converting, each basis function into frames having the same window length and the one or more overlapping frames Wo as obtained at the transmitter;
multiplying, a transmitted ratio with the same basis function as obtained at the transmitter to obtain Mel frequency band energies of the speech signal; and
converting, using an overlap add technique, the Mel frequency band energies to obtain the original reconstructed signal.

5. A system (100), for secure speech transmission with low bit rate
comprising:
a memory (102) storing instructions;
one or more communication interfaces (106); and
a one or more hardware processors (104) coupled to the memory (102) via the one or more communication interfaces (106), wherein the one or more hardware processors (104) are configured by the instructions to:
receive, a speech signal comprising a plurality of successive frames; and
encode, by a speech encoder via the one or more hardware processors, the speech signal at transmitter, by generating a secure speech code for the encoded speech signal comprising a compression ratio for each frame of the speech signal with each filter of the Mel Filter bank, wherein the compression ratio is computed based on (i) a speech signal energy, and (ii) a basis function energy, wherein the generated secure speech code for the encoded speech signal is transmitted over a communication channel to a corresponding receiver.
6. The system (100) as claimed in claim 5, wherein the secure speech code is
computed by,
generating, a basis function nb with same duration length of the
speech signal in time domain, wherein the basis function is band limited to white noise signal filtered based on a center frequency and a cutoff frequency using a Mel Filter bank comprising one or more filters;
obtaining, one or more overlapping frames Wo and a window length from each frame of the speech signal and the basis function, wherein the one or more overlapping frames are determined based on a current frame overlapping with the plurality of successive frames;

determining, a total number of bits required for the encoded speech signal using the duration length of the speech signal and a sampling frequency fs;
determining, a total number of frames for the speech signal and the basis function based on a frame length and the one or more overlapping frames;
computing, for each frame of the speech signal, a speech signal energy of frequency bands corresponding to a filter associated with the Mel Filter bank based on (i) the duration length of the speech signal, (ii) the sampling frequency fs, and (iii) a bit resolution;
computing, a basis function energy corresponding to the frame of the filter associated with the Mel Filter bank; and
computing, the secure speech code comprising the compression ratio for the encoded signal based on (i) the speech signal energy, and (ii) the basis function energy.
7. The system (100) as claimed in claim 6, wherein the basis function energy is computed based on (i) the duration length of the speech signal multiplied with the sampling frequency fs, (ii) a total number of overlapping frames, (iii) a total number of basis function, and (iv) the total number of bits to be transmitted.
8. The system (100) as claimed in claim 5, wherein the receiver decodes the secure speech code for the encoded speech signal to reconstruct the original speech signal by,
converting, each basis function into frames having the same window length and the one or more overlapping frames as obtained at the transmitter;
multiplying, a transmitted ratio with the same basis function as obtained at the transmitter to obtain Mel frequency band energies of the speech signal; and

converting, using an overlap add technique, the Mel frequency band energies to obtain the original reconstructed signal.