Patent Publication Number: US-2022224791-A1

Title: Systems and methods for detecting inmate to inmate conference calls

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 16/989,399, filed on Aug. 10, 2020, which is a continuation application of U.S. patent application Ser. No. 16/189,524, filed on Nov. 13, 2018 (now U.S. Pat. No. 10,742,801), which is a continuation application of U.S. patent application Ser. No. 15/686,938, filed on Aug. 25, 2017 (now U.S. Pat. No. 10,129,392), which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Field 
     The disclosure relates to systems and methods for detecting conference calls occurring between inmates in a plurality of correctional facilities based on frequency analysis. 
     Background 
     In a controlled environment, such as a correctional facility, inmates have limited opportunities to interact with the outside world. Inmates are allowed to communicate with friends, families, and/or loved ones through telephone calls as it improves recidivism and provides incentives for inmates to follow rules and policies of the correctional facility. 
     However, inmates often utilize telephone calls to communicate with restricted calling parties in order to engage in illicit activity outside of the prison, threaten parties of interest such as judges and attorneys, and witnesses, and/or communicate with inmates in other prison facilities regarding potential illegal activities. In order to maintain security, correctional facilities may prevent inmates from calling certain contacts by blacklisting or blocking telephone numbers of restricted calling parties. Nevertheless, inmates may circumvent such procedures set by the correctional facility and utilize three-way calling or conference calling schemes to communicate with restricted calling parties without having to dial telephone numbers that have been blocked. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate embodiments of the present disclosure and, together with the description, further serve to explain the principles of the disclosure and to enable a person skilled in the pertinent art to make and use the embodiments. 
         FIG. 1  illustrates a block diagram of an inmate conference call detection system, according to embodiments of the present disclosure. 
         FIG. 2  illustrates a block diagram of an inmate conference call detection server in the inmate conference call detection system, according to embodiments of the present disclosure. 
         FIG. 3  illustrates an example power spectrum graph of frequencies detected during an inmate communication, according to embodiments of the present disclosure. 
         FIG. 4  illustrates a flowchart diagram of a method for generating frequency data from inmate communications for conference call detection, according to embodiments of the present disclosure. 
         FIG. 5  illustrates a flowchart diagram of a method for detecting inmate to inmate conference calls based on frequency data from inmate communications, according to embodiments of the present disclosure. 
         FIG. 6  illustrates a block diagram of a general purpose computer that may be used to perform various aspects of the present disclosure. 
     
    
    
     The present disclosure will be described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
     DETAILED DESCRIPTION 
     The following Detailed Description refers to accompanying drawings to illustrate exemplary embodiments consistent with the disclosure. References in the Detailed Description to “one exemplary embodiment,” “an exemplary embodiment,” “an example exemplary embodiment,” etc., indicate that the exemplary embodiment described may include a particular feature, structure, or characteristic, but every exemplary embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same exemplary embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an exemplary embodiment, it is within the knowledge of those skilled in the relevant art(s) to affect such feature, structure, or characteristic in connection with other exemplary embodiments whether or not explicitly described. 
     The exemplary embodiments described herein are provided for illustrative purposes, and are not limiting. Other exemplary embodiments are possible, and modifications may be made to the exemplary embodiments within the spirit and scope of the disclosure. Therefore, the Detailed Description is not meant to limit the invention. Rather, the scope of the invention is defined only in accordance with the following claims and their equivalents. 
     Embodiments may be implemented in hardware (e.g., circuits), firmware, software, or any combination thereof. Embodiments may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. Further, any of the implementation variations may be carried out by a general purpose computer, as described below. 
     For purposes of this discussion, any reference to the term “module” shall be understood to include at least one of software, firmware, or hardware (such as one or more circuit, microchip, or device, or any combination thereof), and any combination thereof. In addition, it will be understood that each module may include one, or more than one, component within an actual device, and each component that forms a part of the described module may function either cooperatively or independently of any other component forming a part of the module. Conversely, multiple modules described herein may represent a single component within an actual device. Further, components within a module may be in a single device or distributed among multiple devices in a wired or wireless manner. 
     The following Detailed Description of the exemplary embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge of those skilled in relevant art(s), readily modify and/or adapt for various applications such exemplary embodiments, without undue experimentation, without departing from the spirit and scope of the disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and plurality of equivalents of the exemplary embodiments based upon the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein. 
     Inmate Conference Call Detection System 
     There is a need for new technologies, systems, and methods to enhance the detection of inmates communicating with restricted calling parties such that correctional facilities may intervene quickly and efficiently during calls where illegal activities may be occurring. Accordingly,  FIG. 1  illustrates a block diagram of an inmate conference call detection system  100 , according to embodiments of the present disclosure. Inmate conference call detection system  100  includes an inmate conference call detection server  120  configured to receive communication data from a communication center  110 . In this disclosure, communication data refers to data collected during real-time audio communications between parties, such as voice calls between an inmate in a controlled environment (e.g., correctional facility) using inmate communication system  130  and an outsider using outsider communication system  140 . In some embodiments, communication data includes the communication itself, such as audio of a voice calls, as well as data related to the voice call, as will be described in further detail below. In some embodiments, inmate conference call detection server  120  may be referred to as inmate-to-inmate conference call detection server  120  or conference call detection server  120  as described herein. The inmate conference call detection server  120  connects to the communication center  110  via a network  101 . The network  101  includes at least one of a local area network (LAN), wireless area network (WAN), or the Internet. 
     In some embodiments, outsider communication system  140  may refer to a second inmate communication system of a second correctional facility that differs from the correctional facility of inmate communication system  130 . The communication center  110  connects the inmate communication system  130  to the outsider communication system  140 . For example, the communication center  110  facilitates call routing for parties within a correctional facility and outside parties, such as via devices within the inmate communication system  130  and outsider communication system  140 . Inmate communication system  130  includes one or more communication devices available to inmates to perform voice calls within a correctional facility and includes any or all devices such as a plurality of telephones  132  (e.g., telephones  132   a - 132   n ) and a plurality of wireless communication devices  134  (e.g., wireless communication devices  134   a - 134   n ). In an embodiment, the telephones  132  comprise payphones and/or landline phones that are located locally within the correctional facility, such as in a designated area or room of the controlled environment. For example, the telephones  132  utilize analog “plain old telephony service” (POTS) lines or integrated services digital network (ISDN) lines. In another embodiment, the telephones  132  comprise Voice over Internet (VoIP) phones and communicate using digital packet-based communication schemes. 
     Wireless communication devices  134 , such as smart phones and other mobile communication devices, are also available to inmates to perform voice calls. These voice calls are routed through a wireless access point  138  (e.g., a router), in which the wireless access point  138  provides connectivity to the wireless communication devices  134 . In some embodiments, the telephones  132  and/or the wireless communication devices  134  are located in an area of the correctional facility that is different from the location of the communication center  110  and/or inmate conference call detection server  120 . The communication center  110  connects to the telephones  132  and wireless communication devices  134  in the inmate communication system  130  via a network  103 . The network  103  comprises at least one of a LAN, WAN, or the Internet. The communication center  110  also connects to the outsider communication system  140 . Outsider communication system  140  includes one or more communication devices available to outsiders or individuals external to the correctional facility and/or outside of the inmate communication system  130 . For example, outsiders include individuals outside of the correctional facility or inmates located in another correctional facility that is different from the correctional facility of inmate communication system  130 . In some embodiments, outsiders may include at least one of approved calling parties (e.g., individuals with whom inmates are permitted to contact and communicate), and restricted calling parties (e.g., individuals with whom inmates are restricted from contacting and communicating). Outsider communication system  140  includes communication devices, such as a plurality of telephones  142  (e.g., telephones  142   a - 142   n ) and a plurality of wireless communication devices  144  (e.g., wireless communication devices  144   a - 144   n ). 
     In an embodiment, the telephones  142  comprise payphones and/or landline phones that are located locally within a second correctional facility, such as in a designated area or room of the controlled environment. For example, the telephones  142  utilize analog “plain old telephony service” (POTS) lines or integrated services digital network (ISDN) lines. In another embodiment, the telephones  142  comprise Voice over Internet (VoIP) phones. The communication center  110  connects to the outsider communication system  140  via a network  105 , in which the network  105  comprises at least one of a WAN, the Internet, and the Public Switched Telephone Network (PSTN). In an embodiment, the WAN facilitates communications with an outsider communication system  140  in other nearby prisons, such as correctional facilities within the same county, state, jurisdiction, or the like. For example, telephones  142  and/or wireless communication devices  144  located at other correctional facilities provide cross-facility visitations between inmates. In another embodiment, the PSTN is used to provide connectivity to the telephones  142  and wireless communication devices  144  over traditional data networks. 
     In some embodiments, inmates may utilize communication devices (e.g., telephone  132  or wireless communication device  134 ) in the inmate communication system  130  to communicate with a restricted calling party by using a conference bridge  115 . For example, each inmate is restricted from contacting certain individuals, such as other inmates, judges, prosecuting attorneys, victims associated with legal proceedings against each inmate, witnesses associated with legal proceedings against each inmate, and other restricted calling parties. In order to evade such restrictions, inmates use their respective communication devices in the inmate communication system  130  to dial a phone number corresponding to conference bridge  115  in order to communicate with restricted calling parties in the outsider communication system  140 . 
     The conference bridge  115  allows two or more inmates to communicate together by connecting communication devices together in a conference call. The conference bridge  115  and corresponding conference call can be set up by a third party who provides the conference call phone number and/or one or more access codes to the inmates who wish to communicate with each other. For example, a first inmate and a second inmate both dial the conference call phone number on their respective devices in inmate communication system  130  and outsider communication system  140 , respectively, and the conference bridge  115  connects the first inmate and the second inmate together on a conference call. Thus, inmates are able to communicate with restricted contacts by using the conference bridge  115  and without having to dial the phone number of a restricted contact. 
     In other embodiments, inmates are solely able to dial phone numbers of approved calling parties that have been approved by the correctional facility. For example, inmates using inmate communication system  130  may be able to communicate with friends, family members, and/or loved ones and may solely be permitted to dial phone numbers corresponding to these approved calling parties. In order to circumvent the policies and regulations of the correctional facility and communicate with restricted calling parties, an inmate may use telephone  132  or wireless communication device  134  in inmate communication system  130  to dial a phone number that is listed on a whitelist of phone numbers for contacts with whom the inmate is allowed to communicate, and the phone call may be redirected or forwarded to another destination, such as the conference call phone number associated with the conference bridge  115 . A restricted calling party (such as another inmate in a second correctional facility) can also use telephone  142  or wireless communication device  144  in outsider communication system  140  to dial into the conference call phone number associated with the conference bridge  115  by using similar call forwarding schemes. Thus, by using conference calls through conference bridge  115 , inmates often circumvent security measures and regulations of correctional facilities in order to engage in illicit activity outside of the prison, threaten parties of interest such as judges and attorneys, and witnesses, and communicate with inmates in other prison facilities about possibly illegal activity. 
     In order to detect inmates communicating with restricted calling parties, inmate conference call detection server  120  is configured to analyze communication data obtained from voice calls occurring between inmates in inmate communication system  130  and outsiders (e.g., approved calling parties, restricted calling parties, and/or other inmates) in outsider communication system  140 . The inmate conference call detection server  120  detects conference calls that may be occurring between inmates and restricted calling parties (e.g., inmate to inmate conference calls) based on the analyzed communication data and further utilizes voice biometrics data to verify the identities of inmates and/or restricted calling parties in the detected conferences calls, as will be described in further detail below. 
     Inmate Conference Call Detection Server and Example Power Spectrum 
       FIG. 2  illustrates a block diagram of the inmate conference call detection server  200 , according to embodiments of the present disclosure. Inmate conference call detection server  200  represents an exemplary embodiment of inmate conference call detection server  120  in  FIG. 1 . Inmate conference call detection server  200  includes one or more servers or other types of computing devices that may be embodied in any number of ways. For instance, the modules, other functional components, and data may be implemented on a single server, a cluster of servers, a server farm or data center, a cloud-hosted computing service, and so forth, although other computer architectures may additionally or alternatively be used. 
     Further, while the figures illustrate the components and data of the inmate conference call detection server  200  as being present in a single location, these components and data may alternatively be distributed across different computing devices and different locations in any manner. Consequently, the functions may be implemented by one or more computing devices, with the various functionality described above distributed in various ways across the different computing devices. Multiple inmate conference call detection servers  200  may be located together or separately, and organized, for example, as virtual servers, server banks and/or server farms. The described functionality may be provided by the servers of a single entity or enterprise, or may be provided by the servers and/or services of multiple different entities or enterprises. 
     In the illustrated example, the inmate conference call detection server  200  includes one or more processors  202 , one or more computer-readable media  204 , and one or more communication interfaces  206 . Each processor  202  is a single processing unit or a number of processing units, and may include single or multiple computing units or multiple processing cores. The processor(s)  202  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. For instance, the processor(s)  202  may be one or more hardware processors and/or logic circuits of any suitable type specifically programmed or configured to execute the algorithms and processes described herein. The processor(s)  202  can be configured to fetch and execute computer-readable instructions stored in the computer-readable media  204 , which can program the processor(s)  202  to perform the functions described herein. 
     The computer-readable media  204  include volatile and nonvolatile memory and/or removable and non-removable media implemented in any type of technology for storage of information, such as computer-readable instructions, data structures, program modules, or other data. Such computer-readable media  204  include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, optical storage, solid state storage, magnetic tape, magnetic disk storage, network attached storage, storage area networks, cloud storage, or any other medium that can be used to store the desired information and that can be accessed by a computing device. Depending on the configuration of the inmate conference call detection server  200 , the computer-readable media  204  may be a type of computer-readable storage media and/or may be a tangible non-transitory media to the extent that when mentioned, non-transitory computer-readable media exclude media such as energy, carrier signals, electromagnetic waves, and signals per se. 
     The computer-readable media  204  is used to store any number of functional components that are executable by the processors  202 . In many implementations, these functional components comprise instructions or programs that are executable by the processors and that, when executed, specifically configure the one or more processors  202  to perform the actions attributed above to the inmate conference call detection server  200 . In addition, the computer-readable media  204  store data used for performing the operations described herein. 
     In the illustrated example, the computer-readable media  204  further includes communication module  208 , inmate profile module  210 , fast Fourier transform (FFT) module  212 , peak detection module  214 , inmate communication database  216 , conference call detection module  218 , and voice biometrics module  228 . Communication module  208  receives and manages communication data for inmate communications in correctional facilities. Communication module  208  facilitates monitoring, processing, and/or recording of audio collected during voice calls between an inmate in a controlled environment using inmate communication system  130  and an outsider using outsider communication system  140 . In some embodiments, communication module  208  receives inmate communication data, such as audio signals from inmate communications, from communication center  110 . For example, communication module  208  receives an audio signal for each inmate communication in a plurality of inmate communications from communication center  110 , and the audio signal of each inmate communication is represented as a time domain signal. In some cases, communication module  208  receives and stores inmate communication data (including time domain audio signals for each inmate communication) in the communication module  208  itself or in inmate communication database  216 . 
     In additional embodiments, communication module  208  is also configured to perform decryption and/or encryption of communication data received from the communication center  110 . In some cases, communication data includes audio signals collected during inmate communications and the metadata of each inmate communication. For example, communication module  208  decrypts communication data received from the communication center  110  to extract the audio signal for each inmate communication. The communication module  208  may also encrypt the communication data for security purposes and transmit the encrypted communication data to one or more computing devices associated with monitors, corrections officers, guards, or other employees of the correctional facility for additional review or investigation. In some embodiments, communication module  208  performs conversion of communication data received from the communication center  110  to different formats in order to extract and/or identify metadata from the communication data. 
     Metadata includes data associated with the communication data, which includes at least one of a date and time of the communication, a type of encoding (e.g., audio compression and decompression), a rate of encoding (e.g., bit rate), a location of devices utilized during the communication, which device(s) are being used for the communication (e.g., telephone  132  or wireless communication device  134 ), and other attributes or characteristics of the communication. In addition to obtaining and managing communication data, the communication module  208  communicates with inmate profile module  210 , fast Fourier transform (FFT) module  212 , peak detection module  214 , inmate communication database  216 , conference call detection module  218 , and/or voice biometrics module  228  to provide the stored inmate communication data for further analysis. 
     Inmate profile module  210  obtains and stores profile information and inmate calling information for each inmate in the correctional facility. In some embodiments, inmate profile module  210  obtains profile information related to the inmates from one or more of (a) a jail management system (JMS) or an offender management system (OMS) operated by the jurisdiction of the correctional facility, (b) public database containing information on the inmates, or (c) a questionnaire provided by a web page, a personal approved number (PAN) list, or booking information. In some embodiments, profile information obtained by inmate profile module  210  includes personal information for each inmate, such as names, previous residences or correctional facilities, authorized contacts (e.g., including a name, identity, phone number, and the like for each authorized contact), family members, and languages. In additional embodiments, the inmate profile module  210  also obtains booking information or case information for each inmate, such as names, addresses, and contact information (e.g., phone numbers) of one or more attorneys, judges, witnesses, or other individuals pertinent to an inmate&#39;s case. 
     By collecting this information, the inmate profile module  210  is configured to determine, for each inmate, a whitelist of contacts that the inmate is allowed to contact (e.g., approved calling parties) and/or a blacklist of contacts that the inmate is restricted from contacting (e.g., restricted calling parties). For example, the whitelist and/or blacklist include names, identities, and phone numbers for each listed contact. In some cases, conference call detection module  218  and/or voice biometrics module  228  communicates with inmate profile module  210  (as described below) to access the whitelist and/or blacklist data to identify whether or not an inmate is violating rules of the correctional facility by conference calling a restricted calling party (e.g., a blacklisted contact). 
     Fast Fourier Transform (FFT) module  212  manages the conversion of audio signals of inmate communications to frequency domain signals. In particular, FFT module  212  receives audio signals for inmate communications from the communication module  208  and computes a fast Fourier transform (FFT) of each audio signal in the time domain. The FFT is a computationally efficient mathematical technique that converts digital information from the time domain to the frequency domain for rapid spectral analysis. Furthermore, the FFT is an algorithmic optimization of the discrete Fourier transform (“DFT”), in that the FFT produces the same results at the DFT by using fewer computations than the DFT. In particular, the DFT breaks down a digital signal into its frequency components (e.g., a summation of harmonically-related cosine and sine waves). For a discrete (e.g., digital) signal, x[t], with N samples, the DFT is defined as: 
         X [ w   k ]=Σ n=0   N−1   x [ t   n ] e   −jw     k     t     n     ,k= 0,1,2, . . . , N− 1  (1)
 
     In equation (1), x[t n ] is the signal in the time domain, t n  is the n th  sampling instant, w k  is the k th  frequency sample (e.g., the k th  frequency component), and X[w k ] is the DFT of the signal. The DFT computes a complex coefficient for each frequency component that comprises the time domain signal, and e −jw     k     t     n    can be broken down into a cosine and sine component (e.g., e −jw     k     t     n   =cos(w k t n )+sin(w k t n )). Thus, the complex coefficient is a representation of a cosine and sine wave (each with a frequency w k ) that comprises the k th  frequency component of the signal. The real component of the complex coefficient is the magnitude of the cosine wave, and the imaginary component of the complex coefficient is the magnitude of the sine wave. 
     The complex coefficient can also be used to calculate the overall magnitude and phase of the corresponding component. Specifically, the magnitude (or amplitude) of the component is the square root of the sum of the squares of the real and imaginary components of the corresponding coefficient divided by N samples: 
     
       
         
           
             
               
                 
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     The phase is the cotangent of the imaginary component divided by the real component: 
     
       
         
           
             
               
                 
                   Phase 
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     Thus, the FFT module  212  uses the mathematical properties of the DFT (or the FFT) to compute magnitude and phase for each component that comprises a digital signal. By computing the FFT of an audio signal of each inmate communication, the FFT module  212  converts the audio signal in the time domain to a frequency domain signal in order to obtain spectral data from the audio signal. For example, spectral data includes magnitudes and phases for real and imaginary components of complex coefficients of each frequency component of an audio signal. In some embodiments, the FFT module  212  applies a Fourier transform to the time domain signal of each inmate communication over a predetermined window of time for the inmate communication. For example, the predetermined window of time includes a 512 sample width of the audio signal or a 1024 sample width of the audio signal. The predetermined window of time for converting an audio signal from the time domain to the frequency domain may be different or the same for each inmate communication received by the FFT module  212 . In some cases, FFT module  212  transmits the converted frequency domain signal and the resulting spectral data for each inmate communication to the peak detection module  214 , such that the peak detection module  214  may perform spectral analysis of the frequency domain signals. 
     Peak detection module  214  detects frequency peaks and corresponding frequency values in frequency domain signals of inmate communications. In some embodiments, peak detection module  214  receives spectral data from the FFT module  212 , including magnitudes and phases for real and imaginary components of complex coefficients of each frequency component of an audio signal. Using the spectral data, peak detection module  214  computes a power spectrum (e.g., a frequency spectrum graph) that plots the magnitude against frequency representation of the frequency domain signal obtained from each inmate communication. For example,  FIG. 3  illustrates an example power spectrum graph  300  of frequencies detected during an inmate communication, according to embodiments of the present disclosure. In particular, the power spectrum graph  300  illustrates an example of frequency spectrums detected at a point in time during an inmate communication. The power spectrum graph  300  shows a plurality of frequency peaks of various magnitudes. Peak detection module  214  identifies one or more frequency peaks in a frequency domain signal for each inmate communication using a power spectrum graph, such as power spectrum graph  300 . 
     In some cases, peak detection module  214  identifies frequency peaks in a frequency domain signal by applying a peak detection algorithm to identify the highest frequency peaks of the same amplitude. For example, peak detection module  214  identifies a first frequency peak in the frequency domain signal, a first frequency value corresponding to the first frequency peak, and a first amplitude value of the first frequency peak. The peak detection module  214  further identifies a second frequency peak in the frequency domain signal, a second frequency value corresponding to the second frequency peak, and a second amplitude value of the second frequency peak, wherein the first amplitude value and the second amplitude value are the same. In some cases, there may be several frequency peaks in the power spectrum, but peak detection module  214  may solely identify the frequency peaks of the highest amplitude (or magnitude) with respect to the other frequency peaks in the power spectrum. For example, with respect to the power spectrum graph  300  in  FIG. 3 , peak detection module  214  may identify two frequency peaks at 300 Hz and 420 Hz with the highest magnitude of 0.9 with respect to the magnitude values of the other frequency peaks in the power spectrum graph  300 . In other cases, peak detection module  214  may identify multiple frequency peaks (e.g., more than two peaks) that are of the same amplitude (e.g., and the highest amplitude). In some embodiments, peak detection module  214  may detect all frequency peaks with an amplitude over a predetermined threshold value. For example, with respect to the power spectrum graph  300  in  FIG. 3 , peak detection module  214  may identify all peaks with an amplitude above 0.7 or another predetermined threshold value by applying a peak detection algorithm to the power spectrum graph  300 . In some cases, peak detection module  214  may identify a frequency peak as a part of the frequency spectrum where a frequency value in the frequency domain signal is 3-4 dB higher (in amplitude) than the frequency values on either side of the peak. Additionally, peak detection module  214  communicates with inmate communication database  216  to store frequency data, including the one or more detected frequency peaks and frequency values for each inmate communication. 
     Inmate communication database  216  comprises any number of databases and/or servers, and stores and organizes data in one or more relational databases. Inmate communication database  216  runs a database management system, such as MYSQL′, to provide an example. In particular, inmate communication database  216  receives frequency data, including the one or more detected frequency peaks and frequency values for each inmate communication, from peak detection module  214  and generates records for each inmate communication. For example, inmate communication database  216  creates a record including frequency data regarding each detected frequency peak and the frequency value corresponding to each peak and stores each record. In some cases, inmate communication database  216  creates and manages a plurality of records for a plurality of inmate communications. The plurality of records in the inmate communication database  216  includes frequency information for calls received over a predetermined period of time, such as 30 days, one month, 6 months, one year, or any other time period. Additionally, the plurality of records may be updated by the inmate conference call detection server  200  periodically, such as every hour, day, week, or the like. The plurality of records managed and stored by inmate communication database  216  are accessible by conference call detection module  218  and/or voice biometrics module  228  in order to detect inmate to inmate conference calls and verify detected conference calls using voice biometrics. 
     Conference call detection module  218  detects inmate to inmate conference calls in correctional facilities. In particular, conference call detection module  218  detects inmate to inmate conference calls by determining whether portions of frequency domain signals for various inmate communications match each other. For example, conference call detection module performs frequency matching utilizing the frequency data identified by peak detection module  214  and stored in inmate communication database  216 . In some embodiments, frequency matching refers to matching a frequency peak, a frequency value, and time point(s) in a frequency domain signal of an inmate communication with a frequency peak, a frequency value, and time point(s) in a frequency domain signal of another inmate communication. In some embodiments, conference call detection module  218  performs queries to search for and retrieve frequency data from the inmate communication database  216  for frequency matching. For example, inmate conference call detection server  200  may receive communication data regarding an inmate communication, and conference call detection module  218  queries the inmate communication database  216  to search for a record in the inmate communication database  216  that matches a portion of the frequency domain signal corresponding to the received inmate communication. 
     In some embodiments, conference call detection module  218  determines whether an inmate communication matches frequency data in a record in the inmate communication database  216  by querying for records of inmate phone calls that overlap at or near real-time with the inmate communication and have the same dialed phone number as the inmate communication. For example, conference call detection module  218  first queries the inmate communication database  216  by providing a list of parameters corresponding to the received inmate communication. The parameters may be related to the metadata of the inmate communication data received from communication center. For example, conference call detection module  218  may query the inmate communication database  216  by providing values corresponding to parameters, such as at least one of a date of the inmate communication, a time of the inmate communication, a type of encoding of the communication, a rate of encoding of the communication, a location of the device utilized during the communication, a phone number dialed during the communication, and the like. The conference call detection module  218  transmits the query including the specified parameter values to the inmate communication database  216 , and the conference call detection module  218  receives a list of records from the inmate communication database  216  that match the specified parameter values. In some cases, by querying the inmate communication database  216 , the conference call detection module  218  narrows down the number of records in the inmate communication database  216  that may match the received inmate communication data. 
     After performing the query, the conference call detection module  218  may have multiple records to parse through in order to detect conference calls, and the conference call detection module  218  utilizes each record to find matches of the frequency data of the received inmate communication with frequency data stored in each record. For example, the conference call detection module  218  performs frequency matching to determine whether a portion of the frequency domain signal corresponding to the received inmate communication matches a first subset of frequency data stored in a first record. The first record stores data regarding each frequency peak, each frequency value, and time point(s) at which each frequency peak occurs for an inmate communication. The conference call detection module  218  determines whether frequency peaks and frequency values of a portion of the frequency domain signal corresponding to the received inmate communication matches the first subset of frequency data stored in a first record. 
     In particular, the conference call detection module  218  identifies how many frequency peaks and values stored in a first record match with the frequency peaks and frequency values of the portion of the frequency domain signal corresponding to the received inmate communication. In some embodiments, a frequency match refers to a frequency peak, a frequency value, and time point(s) in a frequency domain signal of a first inmate communication that are the same as or similar to a frequency peak, a frequency value, and time point(s) in a frequency domain signal of a second inmate communication. Conference call detection module  218  identifies the number of frequency matches between two inmate communications and determines whether the number of frequency matches is above or below a predetermined threshold value. In some embodiments, a predetermined threshold value comprises a value for a number of matches that indicates that a sufficient number of frequency data points have been matched to detect an inmate to inmate conference call. For example, the predetermined threshold value may comprise 5, 10, 25, 50, or another value indicating that the number of frequency matches meets a mandatory level for inmate to inmate conference call detection. 
     If the conference call detection module  218  determines that the number of frequency matches is below the predetermined threshold value, then conference call detection module  218  matches the one or more frequency peaks and frequency values of the portion of the new frequency domain signal with another subset of frequency data stored in another record in inmate communication database  216 . In particular, the conference call detection module  218  may continue to match the frequency peaks and frequency values of the portion of the new frequency domain signal with multiple subsets of frequency data (e.g., stored in multiple records in inmate communication database  216 ) until a sufficient number of frequency data points of the new frequency domain signal match with the frequency data in a particular subset. In other words, the conference call detection module  218  performs multiple iterations of frequency matching until the number of frequency matches is greater than or equal to the predetermined threshold value. 
     If the conference call detection module  218  determines that the number of frequency matches is above the predetermined threshold value, then conference call detection module  218  detects an inmate to inmate conference call between a first inmate and a second inmate. For example, the conference call detection module  218  detects that the first inmate (e.g., an inmate associated with the subset of frequency data stored in the first record) was conferenced in and/or communicating with a second inmate (e.g., an inmate associated with the received inmate communication). By identifying matching frequencies between frequency domain signals of various inmate communications, the conference call detection module  218  is configured to detect when inmates are circumventing policies of the correctional facility to communicate with others via conference calls. 
     In some embodiments, the conference call detection module  218  also communicates with inmate profile module  210  and/or voice biometrics module  228  to determine the identity of restricted calling parties with whom an inmate is communicating on a conference call. For example, the conference call detection module  218  accesses inmate profile module  210  to retrieve a blacklist of restricted calling parties and a white list of approved calling parties for an inmate to identify whether a called party is restricted or approved by the correctional facility. In some embodiments, the conference call detection module  218  communicates with voice biometrics module  228  to verify the identities of the inmate and the calling parties on a detected conference call, as will be described below. 
     Voice biometrics module  228  manages voice biometrics data and verifies the detection of inmate to inmate conference calls. For example, voice biometrics module  228  stores a voiceprint database comprising audio voiceprints of a plurality of inmates and a list of inmate identities corresponding to each audio voiceprint. In some embodiments, voice biometrics module  228  receives an alert or notification from conference call detection module  218  regarding a detected inmate conference call indicating matching frequencies between a received inmate communication and a record stored in the inmate communication database  216 . Voice biometrics module  228  accesses a portion of the audio corresponding to the received inmate communication (e.g., from communication module  208 ) and also audio corresponding to the record stored in the inmate communication database  216 . Voice biometrics module  228  then matches the two audio samples with audio voiceprints from the voiceprint database. For example, the voice biometrics module  228  matches the two audio samples with audio voiceprints corresponding to two inmates. In some embodiments, voice biometrics module  228  matches the audio samples with audio voiceprints by using combination of frequency estimation, hidden Markov models, Gaussian mixture models, pattern matching algorithms, neural networks, matrix representation methods, vector quantization, and/or decision tree methods. 
     Voice biometrics module  228  identifies a matching voiceprint from the database and a confidence value for each audio sample. The confidence value reflects the degree of match. A higher confidence value indicates a greater degree of matching than a lower confidence value. After the inmate identities have been determined using the voiceprints, the voice biometrics module  228  accesses inmate profiles corresponding to the two inmates from the inmate profile module  210  to identify restricted and approved calling parties in the detected inmate conference call. The voice biometrics module  228  may transmit notifications or alerts regarding the detected inmate to inmate conference call to one or more computing devices associated with monitors, corrections officers, guards, or other employees of the correctional facility for additional review or investigation. 
     Additional functional components stored in the computer-readable media  204  include an operating system  230  for controlling and managing various functions of the inmate conference call detection server  200 . The inmate conference call detection server  200  also includes or maintains other functional components and data, such as other modules and data, which include programs, drivers, and the like, and the data used or generated by the functional components. Further, the inmate conference call detection server  200  includes many other logical, programmatic and physical components, of which those described above are merely examples that are related to the discussion herein. 
     The communication interface(s)  206  include one or more interfaces and hardware components for enabling communication with various other devices, including communication devices operated by inmates and called parties, such as telephones  132  and/or  142 , wireless communication devices  134  and/or  144 , or other computing devices, over network  103  or network  105 . For example, communication interface(s)  206  facilitate communication through one or more of the Internet, cable networks, cellular networks, wireless networks (e.g., Wi-Fi, cellular) and wired networks. As several examples, the inmate conference call detection server  200  and communication devices communicate and interact with one another using any combination of suitable communication and networking protocols, such as Internet protocol (IP), transmission control protocol (TCP), hypertext transfer protocol (HTTP), cellular or radio communication protocols, and so forth. Examples of communication interface(s) include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, and the like. The inmate conference call detection server  200  may further be equipped with various input/output (I/O) devices  232 . Such I/O devices include a display, various user interface controls (e.g., buttons, joystick, keyboard, mouse, touch screen, and the like), audio speakers, connection ports and so forth. 
     System Operation 
     Operations of generating frequency data from inmate communications and detecting inmate to inmate conference calls based on the frequency data through inmate conference call detection system  100  will be described with respect to  FIGS. 4 and 5 . Although the physical devices and components that form the system have largely already been described, additional details regarding their more nuanced operation will be described below with respect to  FIGS. 1-3 . While  FIGS. 4 and 5  contain methods of operation of generating frequency data from inmate communications and detecting inmate to inmate conference calls based on the frequency data through inmate conference call detection server  200 , the operations are not limited to the order described below, and various operations can be performed in a different order. Further, two or more operations of each method can be performed simultaneously with each other. 
       FIG. 4  illustrates a flowchart diagram of a method  400  of generating frequency data from inmate communications for conference call detection, via a conference call detection server, such as inmate conference call detection server  200  of  FIG. 2 , according to embodiments of the present disclosure. The steps of method  400  are performed by modules of inmate conference call detection server  200 , such as communication module  208 , fast Fourier transform (FFT) module  212 , peak detection module  214 , and/or inmate communication database  216 . 
     Method  400  of  FIG. 4  begins with step  401  of monitoring a plurality of inmate communications. For example, communication module  208  of inmate conference call detection server  200  receives inmate communication data for a plurality of inmate communications from communication center  110 , wherein each inmate communication comprises an audio signal. Each inmate communication includes a participating inmate from among a plurality of inmates in the correctional facility. In some cases, communication module  208  of inmate conference call detection server  200  receives the inmate communication data from an inmate communication device, such as telephone  132  or wireless communication device  134 . 
     At step  402 , the inmate conference call detection server converts the audio signal of each inmate communication to a frequency domain signal. For example, the FFT module  212  converts the audio signal of each inmate communication from a time domain signal to a frequency domain signal by applying a Fourier transform to the time domain over a predetermined window of time. At step  403 , the inmate conference call detection server identifies one or more frequency peaks in the frequency domain signal for each inmate communication and frequency values corresponding to each frequency peak. For example, peak detection module  214  of inmate conference call detection server  200  identifies frequency peaks in a frequency domain signal by identifying the highest frequency peaks of the same amplitude in a power spectrum graph corresponding to the frequency domain signal of each inmate communication. The peak detection module  214  also identifies the frequency value of each of the frequency peaks of the same amplitude. 
     At step  404 , the inmate conference call detection server generates a record for each inmate communication comprising frequency data regarding the one or more frequency peaks and frequency values of each inmate communication. For example, inmate communication database  216  receives frequency data regarding the one or more detected frequency peaks and frequency values for each inmate communication from the peak detection module  214 . Using the frequency data, inmate communication database  216  creates a record including frequency data regarding each detected frequency peak and the frequency value corresponding to each peak, resulting in a plurality of records corresponding to a plurality of inmate communications. 
     At step  405 , the inmate conference call detection server stores the plurality of records in the inmate communication database. For example, inmate conference call detection server  200  stores the plurality of records in the inmate communication database  216 . The plurality of records stored in the inmate communication database  216  are accessible by conference call detection module  218  and/or voice biometrics module  228  in order to detect inmate to inmate conference calls and verify detected conference calls using voice biometrics. 
       FIG. 5  illustrates a flowchart diagram of a method  500  of detecting inmate to inmate conference calls based on frequency data from inmate communications, via a conference call detection server, such as inmate conference call detection server  200  of  FIG. 2 , according to embodiments of the present disclosure. The steps of method  500  are performed by modules of inmate conference call detection server  200 , such as communication module  208 , inmate profile module  210 , fast Fourier transform (FFT) module  212 , peak detection module  214 , inmate communication database  216 , and/or voice biometrics module  228 . In some embodiments, the steps of method  500  may be performed after the steps of method  400  of generating frequency data from inmate communications and storing the frequency data as a plurality of records in inmate communication database  216 . 
     Method  500  of  FIG. 5  begins with step  501  of monitoring a new inmate communication comprising a new audio signal. For example, communication module  208  of inmate conference call detection server  200  receives inmate communication data for a new inmate communication from communication center  110 , wherein the new inmate communication comprises a new audio signal. In some embodiments, communication module  208  of inmate conference call detection server  200  receives data for the new inmate communication from an inmate communication device, such as telephone  132  or wireless communication device  134 . In some cases, a new inmate communication refers to an inmate communication received at or near real-time from an inmate communication device subsequent to the steps of method  400  in  FIG. 4 . In particular, the new inmate communication refers to a subsequent inmate communication received and/or monitored by inmate conference call detection server  200  after inmate conference call detection server  200  generates and stores a plurality of records for frequency data of inmate communications in inmate communication database  216 . 
     At step  502 , the inmate conference call detection server converts the new audio signal of the new inmate communication to a new frequency domain signal. For example, the FFT module  212  converts the new audio signal of the new inmate communication from a time domain signal to a frequency domain signal by applying a Fourier transform to the time domain over a predetermined window of time. At step  503 , the inmate conference call detection server identifies one or more frequency peaks in the frequency domain signal for the new inmate communication and frequency values corresponding to each frequency peak. For example, peak detection module  214  of inmate conference call detection server  200  identifies frequency peaks in a frequency domain signal by identifying the highest frequency peaks of the same amplitude in a power spectrum graph corresponding to the frequency domain signal. The peak detection module  214  also identifies the frequency value of each of the frequency peaks of the same amplitude. 
     At step  504 , the inmate conference call detection server queries an inmate communication database to determine that a portion of the new frequency domain signal matches frequency data in a detected record in the inmate communication database. For example, conference call detection module  218  of the inmate conference call detection server  200  queries the inmate communication database  216  to search for a record in the inmate communication database  216  with frequency data that matches a portion of the new frequency domain signal for the new inmate communication. The conference call detection module  218  determines that a portion of the new frequency domain signal for the new inmate communication matches frequency data in a detected record in inmate communication database  216 , and the detected record includes a detected audio signal. The detected audio signal corresponds to an inmate communication associated with the detected record. At step  505 , the inmate conference call detection server matches one or more frequency peaks and frequency values of the portion of the new frequency domain signal with a first subset of frequency data. For example, conference call detection module  218  of the inmate conference call detection server  200  matches one or more frequency peaks and frequency values of the portion of the new frequency domain signal with a first subset of frequency data stored in a first detected record in inmate communication database  216 . 
     At step  506 , the inmate conference call detection server identifies a number of frequency matches based on the matching. For example, conference call detection module  218  of the inmate conference call detection server  200  identifies how many frequency matches have been made during the matching at step  505 . In particular, conference call detection module  218  identifies the number of matching frequency peaks between the frequency peaks and frequency values of the portion of the new frequency domain signal and the frequency peaks and frequency values of the first subset of frequency data stored in the first detected record in inmate communication database  216 . At step  507 , the inmate conference call detection server determines whether the number of frequency matches is above or below a predetermined threshold value. For example, conference call detection module  218  of the inmate conference call detection server  200  determines whether the number of frequency matches is above or below the predetermined threshold value in order to identify whether a sufficient number of frequency data points have been matched to detect an inmate to inmate conference call. 
     If the inmate conference call detection server determines that the number of frequency matches is below the predetermined threshold value, then method  500  in this example proceeds to step  508 . At step  508 , the inmate conference call detection server matches the one or more frequency peaks and frequency values of the portion of the new frequency domain signal with another subset of frequency data. For example, conference call detection module  218  of the inmate conference call detection server  200  matches one or more frequency peaks and frequency values of the portion of the new frequency domain signal with another subset of frequency data stored in another detected record (e.g., a second detected record) in inmate communication database  216 . In particular, the conference call detection module  218  may continue to match the frequency peaks and frequency values of the portion of the new frequency domain signal with multiple subsets of frequency data (e.g., stored in multiple records in inmate communication database  216 ) until a sufficient number of frequency data points of the new frequency domain signal match with the frequency data in a particular subset. In other words, the conference call detection module  218  performs multiple iterations of frequency matching at step  508  until the number of frequency matches is greater than or equal to the predetermined threshold value. 
     If the inmate conference call detection server determines that the number of frequency matches is greater than or equal to the predetermined threshold value, then method  500  in this example proceeds to step  509 . At step  509 , the inmate conference call detection server detects an inmate to inmate conference call between a first inmate associated with the first subset of frequency data and a second inmate associated with the new inmate communication. For example, conference call detection module  218  of the inmate conference call detection server  200  detects that the first inmate associated with the first subset of frequency data participated in a conference call with the second inmate associated with the new inmate communication in response to determining that the number of frequency matches is above the predetermined threshold value. 
     At step  510 , the inmate conference call detection server verifies the inmate to inmate conference call by matching the new audio signal corresponding to the portion of the new frequency domain signal and the detected audio signal (e.g., the audio signal corresponding to the first detected record) with voice biometric samples. For example, voice biometrics module  228  of the inmate conference call detection server  200  verifies the inmate to inmate conference call by matching a portion of the new audio signal corresponding to the portion of the new frequency domain signal and the detected audio signal with voice biometric samples. The voice biometrics module  228  stores audio voiceprints of a plurality of inmates and a list of inmate identities corresponding to the audio voiceprints. In particular, the voice biometrics module  228  verifies the inmate to inmate conference call by matching the new audio signal with an audio voiceprint corresponding to the second inmate associated with the new inmate communication and matching the detected audio with another audio voiceprint corresponding to the first inmate associated with the first subset of frequency data. 
     Exemplary Computer Implementation 
     It will be apparent to persons skilled in the relevant art(s) that various elements and features of the present disclosure, as described herein, can be implemented in hardware using analog and/or digital circuits, in software, through the execution of computer instructions by one or more general purpose or special-purpose processors, or as a combination of hardware and software. 
     The following description of a general purpose computer system is provided for the sake of completeness. Embodiments of the present disclosure can be implemented in hardware, or as a combination of software and hardware. Consequently, embodiments of the disclosure may be implemented in the environment of a computer system or other processing system. For example, the methods of  FIGS. 4-5  can be implemented in the environment of one or more computer systems or other processing systems. An example of such a computer system  600  is shown in  FIG. 6 . One or more of the modules depicted in the previous figures can be at least partially implemented on one or more distinct computer systems  600 . 
     Computer system  600  includes one or more processors, such as processor  604 . Processor  604  can be a special purpose or a general purpose digital signal processor. Processor  604  is connected to a communication infrastructure  602  (for example, a bus or network). Various software implementations are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the disclosure using other computer systems and/or computer architectures. 
     Computer system  600  also includes a main memory  606 , preferably random access memory (RAM), and may also include a secondary memory  608 . Secondary memory  608  may include, for example, a hard disk drive  610  and/or a removable storage drive  612 , representing a floppy disk drive, a magnetic tape drive, an optical disk drive, or the like. Removable storage drive  612  reads from and/or writes to a removable storage unit  616  in a well-known manner. Removable storage unit  616  represents a floppy disk, magnetic tape, optical disk, or the like, which is read by and written to by removable storage drive  612 . As will be appreciated by persons skilled in the relevant art(s), removable storage unit  616  includes a computer usable storage medium having stored therein computer software and/or data. 
     In alternative implementations, secondary memory  608  may include other similar means for allowing computer programs or other instructions to be loaded into computer system  600 . Such means may include, for example, a removable storage unit  618  and an interface  614 . Examples of such means may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, a thumb drive and USB port, and other removable storage units  618  and interfaces  614  which allow software and data to be transferred from removable storage unit  618  to computer system  600 . 
     Computer system  600  may also include a communications interface  620 . Communications interface  620  allows software and data to be transferred between computer system  600  and external devices. Examples of communications interface  620  may include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, etc. Software and data transferred via communications interface  620  are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface  620 . These signals are provided to communications interface  620  via a communications path  622 . Communications path  622  carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link and other communications channels. 
     As used herein, the terms “computer program medium” and “computer readable medium” are used to generally refer to tangible storage media such as removable storage units  616  and  618  or a hard disk installed in hard disk drive  610 . These computer program products are means for providing software to computer system  600 . 
     Computer programs (also called computer control logic) are stored in main memory  606  and/or secondary memory  608 . Computer programs may also be received via communications interface  620 . Such computer programs, when executed, enable the computer system  600  to implement the present disclosure as discussed herein. In particular, the computer programs, when executed, enable processor  604  to implement the processes of the present disclosure, such as any of the methods described herein. Accordingly, such computer programs represent controllers of the computer system  600 . Where the disclosure is implemented using software, the software may be stored in a computer program product and loaded into computer system  600  using removable storage drive  612 , interface  614 , or communications interface  620 . 
     In another embodiment, features of the disclosure are implemented primarily in hardware using, for example, hardware components such as application-specific integrated circuits (ASICs) and gate arrays. Implementation of a hardware state machine so as to perform the functions described herein will also be apparent to persons skilled in the relevant art(s). 
     CONCLUSION 
     It is to be appreciated that the Detailed Description section, and not the Abstract section, is intended to be used to interpret the claims. The Abstract section may set forth one or more, but not all exemplary embodiments, and thus, is not intended to limit the disclosure and the appended claims in any way. 
     The disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries may be defined so long as the specified functions and relationships thereof are appropriately performed. 
     It will be apparent to those skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the disclosure. Thus, the disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.