WO2023130018A1 - Method and detector for providing an alert message for left/right phase inversion - Google Patents

Abstract

Embodiments of a method and detector for providing an alert message at a unit of a digital radio broadcast system is provided. The method comprises providing a multichannel audio stream comprising a first audio channel and a second audio channel, analyzing the first audio channel and the second audio channel regarding phase inversion of the channels, and creating the alert message if the first audio channel is phase inverted with respect to the second audio channel.

Description

METHOD AND DETECTOR FOR PROVIDING AN ALERT MESSAGE FOR LEFT/RIGHT PHASE INVERSION

CLAIM OF PRIORITY

[0001] This application is related to and claims priority to U.S. Provisional Application No. 63/295,452 filed on December 30, 2021 , and entitled “LEFT/RIGHT PHASE INVERSION DETECTION TO MINIMIZE PARAMETRIC STEREO NULLING IN HD RADIO,” which is hereby incorporated by reference in its entirety.

BACKGROUND

[0002] Digital radio broadcasting technology delivers digital audio and data services to mobile, portable, and fixed receivers. One type of digital radio broadcasting, referred to as in-band on-channel (IBOC) digital audio broadcasting (DAB), uses terrestrial transmitters in the existing Medium Frequency (MF) and Very High Frequency (VHF) radio bands. HD RadioTM technology, developed by iBiquity Digital Corporation, is one example of an IBOC implementation for digital radio broadcasting and reception. IBOC DAB signals can be transmitted in a hybrid format including an analog modulated carrier in combination with a plurality of digitally modulated carriers. Using the hybrid mode, broadcasters may continue to transmit analog AM and FM simultaneously with higher-quality and more robust digital signals, allowing themselves and their listeners to convert from analog-to-digital radio while maintaining their current frequency allocations.

[0003] The HD Radio system allows multiple services to share the broadcast capacity of a single station. One feature of digital transmission systems is the inherent ability to simultaneously transmit both digitized audio and data. Thus the technology also allows for wireless data services from AM and FM radio stations. First generation (core) services include a Main Program Service (MPS) and the Station Information Service (SIS). Second generation services, referred to as Advanced Application Services (AAS), include information services providing, for example, multicast programming, electronic program guides, navigation maps, traffic information, multimedia programming and other content. The AAS Framework provides a common infrastructure to support the developers of these services. The AAS Framework provides a platform for a large number of service providers and services for terrestrial radio. It has opened up numerous opportunities for a wide range of services (both audio and data) to be deployed through the system. Thus, the broadcast signals can include metadata, such as the artist, song title, or station call letters. Special messages about events, traffic, and weather can also be included. For example, traffic information, weather forecasts, news, and sports scores can all be scrolled across a radio receiver's display while the user listens to a radio station.

[0004] Other types of digital radio broadcasting systems include satellite systems such as Satellite Digital Audio Radio Service (SDARS , e.g., XM Radio™, Sirius®), Digital Audio Radio Service (DARS, e.g., WorldSpace®), and terrestrial systems such as Digital Radio Mondiale (DRM), Eureka 147 (branded as DAB Digital Audio Broadcasting®), DAB Version 2, and FMeXtra®. As used herein, the phrase "digital radio broadcasting" encompasses digital audio and data broadcasting including in- band on-channel broadcasting, as well as other digital terrestrial broadcasting and satellite broadcasting.

[0005] Both AM and FM In-Band On-Channel (IBOC) broadcasting systems utilize a composite signal including an analog modulated carrier and a plurality of digitally modulated subcarriers. Program content (e.g., audio) can be redundantly transmitted on the analog modulated carrier and the digitally modulated subcarriers. The analog audio is delayed at the transmitter by a diversity delay.

[0006] Multiple codecs are known to reduce the bandwidth of a transmission. One known codec is the parametric stereo codec. The parametric stereo codec mode of the HD Radio codec provides for a mono channel signal by adding together the left audio channel and the right audio channel of a stereo signal. It further produces parameters that are sent along in the bit stream to a decoder so that the stereo signal can be recuperated from the single mono channel signal and the parameters sent. This way, bits are saved over the course of coding two separate channels (left and right).

[0007] However, parametric encoding fails when the left audio channel is inverted with respect to the right audio channel (L/R phase inversion), the reason being that internally an encoder first renders a monoaural audio stream which results in a nearly null audio stream used in the remaining encoder processing. L/R phase inversion may also occur in other situations.

[0008] There is a need to improve the handling of situations in which phase inversion of left and right channels of a multichannel audio stream occurs.

SUMMARY

[0009] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0010] Aspects of the present invention provide for a left/right phase inversion detection system and method that is embedded into the audio streams of a digital audio signal. The system and method serve to alert an operator of a digital radio broadcast system that there are potential wiring or inversion issues with their equipment.

[0011] Embodiments of the system and method disclosed herein thus use novel techniques to give an operator of a hybrid digital radio broadcast system the information that there could be a phase inversion of the left audio channel or right audio channel.

[0012] In an embodiment, a method for providing an alert message at a unit of a digital radio broadcast system is provided. The method comprises providing a multichannel audio stream comprising a first audio channel and a second audio channel, analyzing the first audio channel and the second audio channel regarding phase inversion of the channels, and creating the alert message if the first audio channel is phase inverted with respect to the second audio channel.

[0013] In a further embodiment, a detector in or connected to a digital radio broadcast system is provided. The detector comprises: an input configured to receive a multichannel audio stream comprising a first audio channel and a second audio channel, an analyzing module configured to analyze the first audio channel with respect to the second audio channel regarding phase inversion, and an alert module configured to create an alert message if the first audio channel is phase inverted with respect to the second audio channel.

[0014] Accordingly, alert messages are created based on the phase relation between the first audio channel and the second audio channel which may be provided to an operator of the hybrid digital radio broadcast system.

[0015] Alert messages in the context of the present invention may be any kind of messages that serve to provide an operator with specific information of urgency.

[0016] In an embodiment, the multichannel audio stream is a stereo audio stream. The first audio channel is a left audio channel and the second audio channel is a right audio channel.

[0017] In a further embodiment, the analyzing step comprises determining pulse coded modulated audio frames from the multichannel audio stream, applying left-right cross correlators to the audio frames resulting in correlation results, applying power estimators with a threshold factor to the audio frames resulting in power estimation results, and analyzing the first audio channel with respect to the second audio channel regarding phase inversion on the basis of the correlation results and the power estimation results.

[0018] In an embodiment, the analyzing step comprises determining ratios between the correlation results and the power estimation results, and analyzing the first audio channel with respect to the second audio channel regarding phase inversion on the basis of the ratios.

[0019] In a more specific embodiment, the analyzing step comprises queuing the ratios, integrating the ratios over time resulting in time integrated ratios, and analyzing the first audio channel with respect to the second audio channel regarding phase inversion on the basis of the time integrated ratios.

[0020] In a further embodiment, analyzing the first audio channel and the second audio channel regarding phase inversion of the channels includes one of: deciding that there is a phase invasion; deciding that there is no phase inversion; and declare an indeterminant error. Accordingly, a 3-way decision scheme is provided for (in-phase, out-of-phase, and indeterminant) with respect to the creation of an alert message. Accordingly, if the data is not good enough, for whatever reason, to allow for a clear decision if there is phase inversion or not, the detector may then declare an indeterminant error, thereby avoiding a false detection.

[0021] According to an embodiment, the analyzing step comprises analyzing the first audio channel with respect to the second audio channel in an audio client remote to or within a digital radio broadcast system.

[0022] Alternatively or additionally, the analyzing step comprises analyzing the first audio channel with respect to the second audio channel in an exporter of a digital radio broadcast system.

[0023] The providing step may comprise providing a main program stereo audio stream and/or providing a secondary program stereo audio stream.

[0024] In a further embodiment, the method further comprises encoding the multichannel audio stream with a parametric stereo codec. A parametric stereo codec is known to the skilled person and provides for a mono audio channel by adding the first audio channel and the second audio channel and by further providing parameters that are sent along in the bit stream so that the stereo signal can be fabricated from the single mono channel and the parameters sent. In case of a phase inversion, parametric stereo coding does not work properly as discussed before. Therefore, in an embodiment, the multichannel audio stream is not encoded with a parametric stereo codec if an alert message has been created. However, this represents one possible consequence only when detecting a phase inversion.

[0025] The encoded multichannel audio may be transmitted over a network which may be the Internet. In particular, when the detector is located at an audio client located remote from a digital radio broadcasting system, the encoded multichannel audio stream may be transmitted through a network to an importer of the digital radio broadcasting system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements. The drawings are provided to illustrate embodiments of the inventions described herein and not to limit the scope thereof. [0027] FIG. 1 illustrates a block diagram of a transmitter for use in an in-band on- channel (IBOC) digital radio broadcasting system.

[0028] FIG. 2 illustrates a block diagram of a typical broadcast configuration where left/right phase inversion may occur.

[0029] FIG. 3 illustrates a schematic representation of a left/right phase inversion detector for audio.

[0030] FIG. 4 shows the dependence of integration time on the probability of a false alarm.

[0031] FIG. 5 shows the dependence of the average time to detection on integration time.

DETAILED DESCRIPTION

[0032] The following description describes various embodiments of methods and systems that provide improved broadcasting of IBOC radio signals. FIG. 1 is a functional block diagram of a portion of the components of a studio site 10, an FM transmitter site 12, and a studio transmitter link (STL) 14 that can be used to broadcast an FM IBOC DAB signal. The studio site includes, among other things, studio automation equipment 34, an Ensemble Operations Center (EOC) 16 that includes an importer 18, an exporter 20, an exciter auxiliary service unit (EASU) 22, and an STL transmitter 48. The transmitter site includes an STL receiver 54, a digital exciter 56 that includes an exciter engine (exgine) subsystem 58, and an analog exciter 60. While in FIG. 1 the exporter is resident at a radio station's studio site and the exciter is located at the transmission site, these elements may be co-located at the transmission site.

[0033] At the studio site, the studio automation equipment supplies main program service (MPS) audio 42 to the EASU, MPS data 40 to the exporter, supplemental program service (SPS) audio 38 to the importer, and SPS data 36 to the importer. MPS audio serves as the main audio programming source. In hybrid modes, it preserves the existing analog radio programming formats in both the analog and digital transmissions. MPS data, also known as program service data (PSD), includes information such as music title, artist, album name, etc. Supplemental program service can include supplementary audio content as well as program associated data. [0034] The importer contains hardware and software for supplying advanced application services (AAS). A “service” is content that is delivered to users via an IBOC DAB broadcast, and AAS can include any type of data that is not classified as MPS, SPS, or Station Information Service (SIS). SIS provides station information, such as call sign, absolute time, position correlated to GPS, etc. Examples of AAS data include real-time traffic and weather information, navigation map updates or other images, electronic program guides, multimedia programming, other audio services, and other content. The content for AAS can be supplied by service providers 44, which provide service data 46 to the importer via an application program interface (API). The service providers may be a broadcaster located at the studio site or externally sourced third- party providers of services and content. The importer can establish session connections between multiple service providers. The importer encodes and multiplexes service data 46, SPS audio 38, and SPS data 36 to produce exporter link data 24, which is output to the exporter via a data link.

[0035] The exporter 20 contains the hardware and software necessary to supply the main program service and SIS for broadcasting. The exporter accepts digital MPS audio 26 over an audio interface and compresses the audio. The exporter also multiplexes MPS data 40, exporter link data 24, and the compressed digital MPS audio to produce exciter link data 52. In addition, the exporter accepts analog MPS audio 28 over its audio interface and applies a pre-programmed delay to it to produce a delayed analog MPS audio signal 30. This analog audio can be broadcast as a backup channel for hybrid IBOC DAB broadcasts. The delay compensates for the system delay of the digital MPS audio, allowing receivers to blend between the digital and analog program without a shift in time. In an AM transmission system, the delayed MPS audio signal 30 is converted by the exporter to a mono channel signal and sent directly to the STL as part of the exciter link data 52.

[0036] The EASU 22 accepts MPS audio 42 from the studio automation equipment, rate converts it to the proper system clock, and outputs two copies of the signal, one digital 26 and one analog 28. The EASU includes a GPS receiver that is connected to an antenna 25. The GPS receiver allows the EASU to derive a master clock signal, which is synchronized to the exciter's clock by use of GPS units. The EASU provides the master system clock used by the exporter. The EASU is also used to bypass (or redirect) the analog MPS audio from being passed through the exporter in the event the exporter has a catastrophic fault and is no longer operational. The bypassed audio 32 can be fed directly into the STL transmitter, eliminating a dead-air event.

[0037] STL transmitter 48 receives delayed analog MPS audio 50 and exciter link data 52. It outputs exciter link data and delayed analog MPS audio over STL link 14, which may be either unidirectional or bidirectional. The STL link may be a digital microwave or Ethernet link, for example, and may use the standard User Datagram Protocol or the standard TCP/IP.

[0038] The transmitter site includes an STL receiver 54, an exciter 56 and an analog exciter 60. The STL receiver 54 receives exciter link data, including audio and data signals as well as command and control messages, over the STL link 14. The exciter link data is passed to the exciter 56 , which produces the IBOC DAB waveform. The exciter includes a host processor, digital up-converter, RF up-converter, and exgine subsystem 58. The exgine accepts exciter link data and modulates the digital portion of the IBOC DAB waveform. The digital up-converter of exciter 56 converts from digital-to-analog the baseband portion of the exgine output. The digital-to-analog conversion is based on a GPS clock, common to that of the exporter's GPS- based clock derived from the EASU. Thus, the exciter 56 can include a GPS unit and antenna 57. The RF up-converter of the exciter up-converts the analog signal to the proper in- band channel frequency. The up-converted signal is then passed to the high power amplifier 62 and antenna 64 for broadcast. In an AM transmission system, the exgine subsystem coherently adds the backup analog MPS audio to the digital waveform in the hybrid mode; thus, the AM transmission system does not include the analog exciter 60. In addition, the exciter 56 produces phase and magnitude information and the analog signal is output directly to the high power amplifier.

[0039] IBOC DAB signals can be transmitted in both AM and FM radio bands, using a variety of waveforms. The waveforms include an FM hybrid IBOC DAB waveform, an FM all-digital IBOC DAB waveform, an AM hybrid IBOC DAB waveform, and an AM all-digital IBOC DAB waveform.

[0040] FIG. 2 illustrates a block diagram of a typical broadcast configuration where left/right phase inversion may occur. The block diagram shows an audio client 201 , an importer 202, an exporter 203 and an exgine 204. The importer 202, the exporter 203 and the exgine 204 are arranged in a digital radio broadcasting system. They may correspond to importer 18, exporter 20 and exciter 58 of the broadcast system of FIG. 1 . While the importer 202 and the exporter 203 may be arranged in a studio site of a digital radio broadcasting system, the exgine 204 may be arranged in the transmitter site of the digital radio broadcasting system.

[0041] In FIG. 2, the importer 202, the exporter 203 and the exgine 204 are connected to a first network which may be a local area network (LAN) 205. However, this represents an embodiment only. In alternative embodiments, the importer 202 and the exporter 203 are provided by the same hardware/software and the exgine 204 may be connected through studio transmitter link (STL) as discussed with respect to FIG. 1.

[0042] LAN 205 respectively the digital radio broadcasting system is connected to a second network, which may be the Internet 206 or any other packet-switched network. Over networks 206, 205 audio sources may be connected to the digital radio broadcasting system. The audio sources are remotely located from the digital radio broadcasting system. FIG. 2 depicts an audio client 201 which represents or is connected to an audio source. The audio client 201 is connected via the Internet 206 to the digital radio broadcasting system. In particular, the audio client 201 is connected to the importer 202 of the digital radio broadcasting system.

[0043] Secondary program audio streams 207 (such as HD2, HD3, or HD4 of HD Radio) may be transmitted to the digital radio broadcasting system via the audio client 201. However, the connection between the audio client 201 and the digital radio broadcasting system may be restricted to a limited available bandwidth. In order to cope with a limited bandwidth, the secondary program audio stream 207 is encoded by encoder 5 in the audio client 201 . [0044] The secondary program audio stream 207 may be a stereo audio stream which comprises a left audio channel and a right audio channel. In an embodiment, encoder 5 encodes such audio stream with parametric encoding. In such case, the resulting audio stream is a mono channel audio stream. Parametric encoding of the secondary program audio stream 207 also produces parameters of the encoding which are sent along with the mono channel audio stream. A respectice decoder may be arranged in the digital radio broadcasting system, e.g., in importer 202.

[0045] However, parametric encoding is only sensible if the mono channel audio stream does not result in a nearly null audio stream. This would be the case if the left audio channel is phase inverted with respect to the right audio channel. In this case there will be little sound out of the codec. In order to avoid a vanishing mono channel audio stream, a left/right phase inversion detector 3 is embedded in the audio client 201 into the audio stream of the secondary program audio. The left/right phase inversion detector monitors the audio and detects if the left audio channel is phase inverted with respect to the right audio channel or vice versa, as explained by example in FIG. 3.

[0046] In the case a phase inversion is detected between the left audio channel and the right audio channel of the secondary program audio stream 207, an alert message is brought out an operator such as an operator of the digital radio broadcasting system to inform that there is potentially a wired or inversion issue with the equipment of the digital radio broadcasting system.

[0047] A main program audio stream 208 (such as HD1 of HD Radio) is transmitted to the digital radio broadcasting system via exporter 203, as discussed with respect to Fig. 1. In exporter 203, the main program audio stream 208 may be encoded for broadcast by an encoder 51. Parametric or other encoding may be used. A left/right phase inversion detector 31 may be included in exporter 203 as well to detect a potential phase inversion in the main program audio stream 208. The left/right phase inversion detector monitors the audio and detects if the left audio channel is phase inverted with respect to the right audio channel or vice versa, as explained by example in FIG. 3. In such case, an alert message is produced which can be considered and evaluated by an operator.

[0048] FIG. 3 is a schematic representation of an embodiment of a left/right phase inversion detector 3 for audio. A 2-channel audio stream 301 is shown. The 2-channel audio stream 301 is a stereo audio stream 301 and comprises a left audio channel and a right audio channel. The stereo audio stream 301 is in FIG. 3 pulse code modulated. The pulse code modulated audio frame 302 comprises K=2048 samples of stereo audio interlaced in left/right order. The left channels samples are Lj(k), for 0<k<K-1 and the right channel samples are Ri(k), for 0<k<K-1 , for the i-th pulse code modulated audio frame 302.

[0049] To the i-th pulse code modulated audio frame 302 a left/right cross correlator

303 is applied. The left/right cross correlator 303 measures a similarity between left and right channels. If the channels are not phase inverted, then the cross correlation is a large positive number (correlated). If the channels are phase inverted, then the cross correlation is a large negative number (anti-correlated). The magnitude of the output varies the audio power in addition to the degree in L/R similarity. For the i-th pulse code modulated audio frame 302 the cross correlation

Cl = ^iLiWR_l(k')

[0050] In addition, to the i-th pulse code modulated audio frame 302 a power estimator

304 is applied. For the i-th pulse code modulated audio frame 302 the power estimation

[0051] The cross correlation Ci and the power estimation pi are used in a power conditioned normalizer 305 for estimating the normalized cross correlation. The power conditioned normalizer 305 removes the variance of the cross correlation on the audio power. If pi is larger than a threshold value P, then di = Ci/pi, otherwise di = 0, where di is the normalized cross correlation. The parameter P is set to filter out low power audio for follow on processing. The normalizing of the cross correlation is done such that di = 1 means the left and right channels are identical and di = -1 means the left channel is exactly the negative of the right channel.

[0052] To the normalized cross correlation di of the i-th pulse code modulated audio frame 302 a moving averager 306 is applied. The moving averager 306 filters out outlying normalized cross correlations over an integration time N. Other integration means than a moving averager may be used. The successive normalized cross correlations di are queued and averaged. In FIG. 3 the successive normalized cross correlations would be queued over 2048 samples and averaged with

[0053] On the averaged normalized cross correlation ai of the i-th pulse code modulated audio frame 302 an out-of-phase thresholder 307 is applied. The out-ofphase thresholder 307 compares the averaged normalized cross correlation ai against an out-of-phase threshold T. If ai < -T then the detector declares phase inversion. If ai > +T then the detector declares in-phase. If -T < ai < +T the detector declares an indeterminant result.

[0054] In FIG. 4 a diagram of the dependence of the ..integration time" on the ..probability of false alarm" is shown. The diagram shows a hyperbola. Thus, a false alarm decreases with increasing integration time with a hyperbolic dependence.

[0055] In FIG. 5 a diagram of he dependence of the ..average time to detection" on the ..integration time" is shown. The graph in the diagram increases linear. Thus, the average time to detection increases with integration time with linear dependence.

Alternate Embodiments and Exemplary Operating Environment

[0056] Many other variations than those described herein will be apparent from this document. For example, depending on the embodiment, certain acts, events, or functions of any of the methods and algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (such that not all described acts or events are necessary for the practice of the methods and algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, such as through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and computing systems that can function together.

[0057] The various illustrative logical blocks, modules, methods, and algorithm processes and sequences described in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and process actions have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of this document.

[0058] The various illustrative logical blocks and modules described in connection with the embodiments disclosed herein can be implemented or performed by a machine, such as a general purpose processor, a processing device, a computing device having one or more processing devices, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor and processing device can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0059] Embodiments of the system and method described herein are operational within numerous types of general purpose or special purpose computing system environments or configurations. In general, a computing environment can include any type of computer system, including, but not limited to, a computer system based on one or more microprocessors, a mainframe computer, a digital signal processor, a portable computing device, a personal organizer, a device controller, a computational engine within an appliance, a mobile phone, a desktop computer, a mobile computer, a tablet computer, a smartphone, and appliances with an embedded computer, to name a few.

[0060] Such computing devices can typically be found in devices having at least some minimum computational capability, including, but not limited to, personal computers, server computers, hand-held computing devices, laptop or mobile computers, communications devices such as cell phones and PDA’s, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, audio or video media players, and so forth. In some embodiments the computing devices will include one or more processors. Each processor may be a specialized microprocessor, such as a digital signal processor (DSP), a very long instruction word (VLIW), or other micro-controller, or can be conventional central processing units (CPUs) having one or more processing cores, including specialized graphics processing unit (GPU)-based cores in a multicore CPU.

[0061] The process actions or operations of a method, process, or algorithm described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module executed by a processor, or in any combination of the two. The software module can be contained in computer-readable media that can be accessed by a computing device. The computer-readable media includes both volatile and nonvolatile media that is either removable, non-removable, or some combination thereof. The computer-readable media is used to store information such as computer- readable or computer-executable instructions, data structures, program modules, or other data. By way of example, and not limitation, computer readable media may comprise computer storage media and communication media.

[0062] Computer storage media includes, but is not limited to, computer or machine readable media or storage devices such as Bluray discs (BD), digital versatile discs (DVDs), compact discs (CDs), floppy disks, tape drives, hard drives, optical drives, solid state memory devices, RAM memory, ROM memory, EPROM memory, EEPROM memory, flash memory or other memory technology, magnetic cassettes, magnetic tapes, magnetic disk storage, or other magnetic storage devices, or any other device which can be used to store the desired information and which can be accessed by one or more computing devices.

[0063] A software module can reside in the RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of non-transitory computer-readable storage medium, media, or physical computer storage known in the art. An exemplary storage medium can be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The processor and the storage medium can reside in an application specific integrated circuit (ASIC). The ASIC can reside in a user terminal. Alternatively, the processor and the storage medium can reside as discrete components in a user terminal.

[0064] The phrase “non-transitory” as used in this document means “enduring or long- lived”. The phrase “non-transitory computer-readable media” includes any and all computer-readable media, with the sole exception of a transitory, propagating signal. This includes, by way of example and not limitation, non-transitory computer-readable media such as register memory, processor cache and random-access memory (RAM).

[0065] The phrase “audio signal” is a signal that is representative of a physical sound. [0066] Retention of information such as computer-readable or computer-executable instructions, data structures, program modules, and so forth, can also be accomplished by using a variety of the communication media to encode one or more modulated data signals, electromagnetic waves (such as carrier waves), or other transport mechanisms or communications protocols, and includes any wired or wireless information delivery mechanism. In general, these communication media refer to a signal that has one or more of its characteristics set or changed in such a manner as to encode information or instructions in the signal. For example, communication media includes wired media such as a wired network or direct-wired connection carrying one or more modulated data signals, and wireless media such as acoustic, radio frequency (RF), infrared, laser, and other wireless media for transmitting, receiving, or both, one or more modulated data signals or electromagnetic waves. Combinations of the any of the above should also be included within the scope of communication media.

[0067] Further, one or any combination of software, programs, computer program products that embody some or all of the various embodiments of the system and method described herein, or portions thereof, may be stored, received, transmitted, or read from any desired combination of computer or machine readable media or storage devices and communication media in the form of computer executable instructions or other data structures.

[0068] Embodiments of the system and method described herein may be further described in the general context of computer-executable instructions, such as program modules, being executed by a computing device. Generally, program modules include routines, programs, objects, components, data structures, and so forth, which perform particular tasks or implement particular abstract data types. The embodiments described herein may also be practiced in distributed computing environments where tasks are performed by one or more remote processing devices, or within a cloud of one or more devices, that are linked through one or more communications networks. In a distributed computing environment, program modules may be located in both local and remote computer storage media including media storage devices. Still further, the aforementioned instructions may be implemented, in part or in whole, as hardware logic circuits, which may or may not include a processor. [0069] Conditional language used herein, such as, among others, "can," "might," "may," “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list.

[0070] While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made without departing from the scope of the disclosure. As will be recognized, certain embodiments of the inventions described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A method for providing an alert message at a unit of a digital radio broadcast system, the method comprising: providing a multichannel audio stream comprising a first audio channel and a second audio channel; analyzing the first audio channel and the second audio channel regarding phase inversion of the channels; and creating the alert message if the first audio channel is phase inverted with respect to the second audio channel.

2. The method of claim 1 , wherein the multichannel audio stream is a stereo audio stream, wherein the first audio channel is a left audio channel and the second audio channel is a right audio channel.

3. The method of claim 1 or 2, wherein the analyzing step comprises determining pulse coded modulated audio frames from the multichannel audio stream; applying left-right cross correlators to the audio frames resulting in correlation results; applying power estimators with a threshold factor to the audio frames resulting in power estimation results; and analyzing the first audio channel with respect to the second audio channel regarding phase inversion on the basis of the correlation results and the power estimation results.

4. The method of claim 3, wherein the analyzing step comprises determining ratios between the correlation results and the power estimation results; and analyzing the first audio channel with respect to the second audio channel regarding phase inversion on the basis of the ratios.

5. The method of claim 4, wherein the analyzing step comprises queuing the ratios; integrating the ratios over time resulting in time integrated ratios; and analyzing the first audio channel with respect to the second audio channel regarding phase inversion on the basis of the time integrated ratios.

6. The method of any of the preceding claims, wherein analyzing the first audio channel and the second audio channel regarding phase inversion of the channels includes one of deciding that there is a phase invasion; deciding that there is no phase inversion; declare an indeterminant error.

7. The method of any of the preceding claims, wherein the providing step comprises providing a main program audio stream.

8. The method of any of the claims 1 to 6, wherein the providing step comprises providing a secondary program audio stream.

9. The method of any of the preceding claims, further comprising encoding the multichannel audio stream with a parametric stereo codec.

10. The method of claims 9, wherein the multichannel audio stream is not encoded with a parametric stereo codec if an alert message has been created.

11. A detector in or connected to a digital radio broadcast system, the detector comprising: an input configured to receive a multichannel audio stream comprising a first audio channel and a second audio channel; an analyzing module configured to analyze the first audio channel with respect to the second audio channel regarding phase inversion; and an alert module configured to create an alert message if the first audio channel is phase inverted with respect to the second audio channel.

12. The detector of claim 11 , wherein the multichannel audio stream is a stereo audio stream, the first audio channel is a left audio channel and the second audio channel is a right audio channel.

13. The detector of claim 11 or 12, wherein the analyzing module is configured to determine pulse coded modulated audio frames from the multichannel audio stream; apply left-right cross correlators to the audio frames resulting in correlation results; apply power estimators with a threshold factor to the audio frames resulting in power estimation results; and analyze the first audio channel with respect to the second audio channel regarding phase inversion on the basis of the correlation results and the power estimation results.

14. The detector of claim 13, wherein the analyzing module is configured to determine ratios between the correlation results and the power estimation results; and analyze the first audio channel with respect to the second audio channel regarding phase inversion on the basis of the ratios.

15. The detector of claim 14, wherein the analyzing module is configured to queue the ratios; integrate the ratios over time resulting in time integrated ratios; and analyze the first audio channel with respect to the second audio channel regarding phase inversion on the basis of the time integrated ratios.

16. The detector of any of claims 11 to 15, wherein the analyzing module is configured to decide that there is a phase invasion; decide that there is no phase inversion; declare an indeterminant error. 21

17. The detector of any of claims 11 to 16, wherein the analyzing module is arranged in an audio client.

18. The detector of any of claims 11 to 16, wherein the analyzing module is arranged in an exporter of a digital radio broadcast system.

19. The detector of any of claims 11 to 18, further comprising an encoder configured to encode the multichannel audio stream with a parametric stereo codec.

20. The detector of claim 19, wherein the encoder is configured to refrain form encoding the multichannel audio stream with a parametric stereo codec if an alert message has been created by the alert module.