RU2492579C2 - Device for embedding digital information into audio signal - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: device for embedding digital information into an audio signal includes, connected to its first input, a first input of a subtractor and a band-pass filter, the output of which is connected to the first input of an adder and the second input of the subtractor, the output of which is connected, through series-connected residual signal analyser and replacement signal former, to the second input of the adder, the output of which is connected to the first input of an additional adder and a signal divider, the output of which is connected, through series-connected amplitude spectrum computer, global masking threshold computer and subsidiary signal former, to the second input of the additional adder, wherein additional inputs of the replacement signal former and the subsidiary signal former are connected to the second input of the embedding device, and the output of the additional adder is connected to the output of the embedding device.

EFFECT: minimising duration of transmission with minimum possible coding redundancy of a separate information message.

6 dwg

Description

The proposed technical solutions relate to methods and devices for broadcasting, in particular to the technique of transmitting digital messages embedded in the audio program of analogue broadcasting stations.

Despite the fact that digital broadcasting has been developing recently (the corresponding standards, methods and devices for digital data transmission have appeared), analogue broadcasting systems based on amplitude (AM) and frequency modulation (FM) are still very popular due to a number of advantages, such as :

(1) simplicity, and consequently, the cheapness of the implementation of both transmitting and receiving equipment;

(2) the presence of a huge number of devices for receiving analog broadcasting signals (especially for FM standards);

(3) high quality sound programs (for FM stereo broadcasting).

It is worth noting that so far (2010) not a single country, even among the most advanced and technologically advanced, has completely abandoned analogue broadcasting. Given these circumstances, we can expect that analog broadcasting will continue to be one of the basic methods of sound broadcasting for decades.

However, analogue broadcasting systems still have drawbacks and limitations - this is, first of all, the lack of integrated digital services, such as multimedia content transfer (photos, formatted text, web services), already familiar and expected by the user of modern digital equipment.

Currently, there are options for expanding the functionality of analog broadcasting.

Known is the method proposed by Nokia for transmitting digital information together with the transmission of the main audio program in an analogue broadcasting system (Nokia Visual Radio - “Visual Radio”, [1]), which provides the transmission of multimedia content (web pages, graphics, etc.) simultaneously with audio transmission. In accordance with the concept of “Visual Radio”, additional multimedia information associated with the main audio program is pre-loaded onto the central server of the “visual radio” system, then this information is transmitted at certain points in time (synchronously with the sound program) via the mobile Internet via a mobile operator to a mobile phone to a user (FIG. 1). Thus, the user, together with the audio program transmitted over one communication channel, receives digital information associated with it through another communication channel. This method has several disadvantages:

(1) an active connection to the mobile Internet is mandatory, which is technically not always justified. Therefore, the scope of this technology is limited to mobile phones;

(2) consumption of mobile Internet graphics, which requires payment by the user (radio listener);

(3) the simultaneous download of the same data on the channels of the mobile Internet by each of the users, which leads to inefficient consumption of the mobile operator’s resource and even to network congestion with a large number of users (for example, during mass events, such as popular sports, etc.) .

The well-known "Method for transmitting digital information in sound broadcasting and telephone channels" (application for invention No. 2006144618, publ. 06/20/2008, Bull.17), in which the addition of the audio signal with a modulated signal obtained by wideband angular modulation of the subcarrier frequency by a digital signal information. This method has inherent disadvantages arising from the use of a separate subcarrier frequency, listed in the description of the closest analogue below.

Such an analogue is a digital broadcasting system (Radio Data System - RDS) [2] for FM radio stations operating in the range 87.5-108 MHz, including an audio program source connected to one input of an insert module connected to a radio transmitter for broadcasting, and the source of information messages connected to another input of the insertion module through the shaper (encoder) of information messages (figure 2). The system uses a method of transmitting digital information, in which, together with the main sound program, a digital data stream is transmitted. In this case, the digital information is pre-encoded, and in the insertion module, the encoded digital message is converted into an analog signal and the combination of the main program and the information message is arranged by means of their parallel transmission, using a separate subcarrier frequency that is not associated with the main sound program.

Such systems are used to transmit basic information about the radio station (for example, the name of the station), as well as other short current text information (for example, the name of the song being played), due to the fact that, as in traditional methods of digital broadcasting, they use a constant transmission speed, which is ineffective in this case, since this speed should be minimal, calculated for the worst case in order to avoid loss of information messages. In this regard, the use of this system for the transmission of multimedia data, such as, for example, web pages, is limited by the low speed of the digital stream, the high redundancy of the protocol, as well as the absence of a mechanism for error correction during transmission.

Besides:

- for RDS, a separate frequency resource is used, which could be more efficiently used to transfer other programs or data;

- data transmitted via RDS is not synchronized with the main program, which creates difficulties in relaying and organizing a channel for delivering a signal from a radio studio to a transmitter;

- To transmit RDS signals, radio equipment is required, which requires economic costs for calibration, certification and maintenance. In addition, the radio must support RDS decoding at the hardware level, and if this is not provided by the manufacturer (for example, to minimize the cost of the receiver), then there is no way to decode RDS data programmatically;

- the impossibility of using AM broadcasting where additional subcarriers cannot be used.

The aim of the proposed technical solutions is to create a device for inserting digital information into an audio signal and a method for transmitting digital information in a broadcasting channel, suitable for use in both FM and AM systems, allowing large amounts of information to be transmitted directly to the broadcasting channel without loss of subjective sound quality.

The goal is also to create a digital information transmission system in the broadcasting channel, which allows to minimize the duration with the minimum possible coding redundancy when transmitting a separate information message (up to the moment of confident reception by the user).

The purpose of the device for inserting digital information into an audio signal (hereinafter referred to as an insertion device) and a method for transmitting digital information in a broadcasting channel (hereinafter referred to as a transmission method) is achieved by the fact that the combined transmission of digital and audio signals is carried out by inserting (embedding) a digital information audio signal directly into a broadcast radio station associated or unassociated with the main audio program.

First option.

The first input of the insertion device receives the original audio signal, the second encoded digital information message, and the output - the total audio signal encoded with a digital information message. In this case, the first input of the subtractor and the bandpass filter are connected to the first input of the device, the first input of the adder and the second input of the subtractor are connected to the output of this device. The output of the subtractor through a series-connected analyzer of the residual signal and the generator (generator) of the replacement signal is connected to the second input of the adder, the output of which is the output of the device. An additional input of the driver of the replacement signal is the second input of the device.

Preferably, the output of the adder is connected to the output of the insertion device through an additional device for inserting digital information into the audio signal, with the first input of the additional insertion device connected to the output of the adder, the second input to the second input of the insertion device, and the output to the output of the insertion device.

The second option.

The original audio signal is supplied to the first input of the insertion device, the encoded digital information message is sent to the second, and the total audio signal with the encoded digital information message is output. At the same time, the first input of the adder and the signal divider are connected to the first input of the device, the output of which is through a series-connected amplitude spectrum calculator, a global masking threshold calculator, and an additional signal shaper connected to the second adder input, the output of which is the device output. The auxiliary input of the driver of the complementary signal is the second input of the device.

Preferably, the first input of the adder and the signal splitter are connected to the first input of the insertion device through an additional insertion device, the first input of the additional insertion device connected to the first input of the insertion device, the second input to the second input of the insertion device, and the output to the first input of the adder and signal divider.

A method for transmitting digital information in a broadcasting channel involves simultaneously transmitting an informational message and an audio signal, wherein a precoded informational message is converted into an audio signal using a psychoacoustic model, the original audio signal is converted by inserting an audio signal with an informational message into it, and the resulting total audio signal is transmitted to the broadcasting channel.

The insertion is expediently carried out by replacing part of the original audio signal with an audio signal with an information message.

It is also advisable to carry out the insertion by supplementing the original audio signal with an audio signal with an information message.

It is also advisable at the same time as the transmission to decode the total audio signal, and the transmission of the next information message should begin after the successful decoding of the previous one.

The described technical solution (the insertion of a digital transmission signal directly into the audio signal by partial replacement or addition when it is invisible) has a significant advantage. Built-in digital information does not impair subjective sound quality and is completely invisible to the listener, as It is well masked by the main sound signal. In this case, the communication signal is transmitted exclusively in the audible frequency range of 30 Hz to 15-16 kHz for FM radio stations and up to 5-10 kHz for AM radio stations, i.e. does not contain frequencies that could be inaudible to the human ear.

The goal is achieved in a digital information transmission system in a broadcasting channel (hereinafter referred to as a transmission system) containing an audio program source, an information message source, an information message shaper and an analog radio transmitter by introducing a device (module) for inserting an information message into the audio program and an information signal decoder. In this case, the source of the audio program is connected to the first input of the insertion device, the source of information messages is connected to the first input of the shaper of information messages, the output of which is connected to the second input of the insertion device, the output of which is connected to a radio transmitter, as well as a decoder connected to the second input of the shaper of information messages. In the case when the transmitted informational message is not restored in the decoder, the former sends it again to the insertion device for retransmission. Thus, the idea of this approach is that the shaper transmits an information message to the insertion device to continue embedding digital information in the audio signal of the radio program that is somehow related to the same information message (in the simplest case, it simply repeats the same message ) until it is highly likely to be delivered to potential recipients. The system allows you to apply minimal redundancy in message encoding and achieve the highest possible digital information transfer rate. In this case, the heterogeneity of the sound program of almost any radio station is used. As a rule, a sound program includes music of various styles, speech of DJs, advertisements, etc., therefore, due to objective reasons, the throughput of a data transmission channel when embedding a digital transmission signal in an audio program cannot be constant. At some points in time, the transmission speed can be very low, and at others it can significantly exceed the average throughput of the system.

It is advisable that the insertion device was made according to the first embodiment described above.

It is advisable that the insertion device was made according to the second embodiment described above.

It is possible to gradually increase coding redundancy in the information message generator with a low program throughput.

Additionally, between the output of the insertion device and the decoder, a radio channel simulator can be included to simulate interference and distortion of the output radio signal.

In practice, the proposed technical solutions, when a digital information signal is embedded in the audio program of analogue broadcasting radio stations, can be implemented both software and hardware. In the case of hardware implementation, the insertion device, the shaper of digital information messages, the decoder of the information message, the signal distortion simulator in the radio channel can be implemented as a separate software and hardware complex included in the gap of the audio signal coming from the source of the audio program to the radio transmitter. In the case of software implementation, the above modules can be implemented in the form of software (software) that is installed on the same computer as the software for broadcast automation. In this embodiment, the software for inserting an information signal can programmatically break the audio signal transmission circuit from the software source of the audio program to the software of the radio transmitter. For example, on a Windows system, this is possible using plug-ins for processing a DirectX signal or by implementing a driver for a virtual audio I / O device.

The implementation of the receiving device is possible by software on mobile phones and smartphones or on audio players and wearable computers, which include integrated devices for receiving sound broadcasting signals; or software on any mobile device that includes a microphone.

Next, the transmission method in the preferred embodiment will be described by the example of the operation of the device for inserting digital information into an audio signal and a digital information transmission system in a broadcasting channel in preferred embodiments.

Figure 1 - structural diagram of Nokia Visual Radio.

Figure 2 is a structural diagram of a Radio Data System.

Figure 3 is a structural diagram of a device for inserting digital information into an audio signal in a preferred embodiment (with an additional insertion device).

Figure 4 - options (a, b) selection band-pass filter of the main signal.

5 is a structural diagram of a system for transmitting digital information in a broadcasting channel in a preferred embodiment.

6 - options for receiving the transmitted digital information by the user (a - a mobile device with a built-in radio receiver, b - a mobile device through an autonomous radio receiver).

The bandpass filter 2 and the first input of the subtracter 3 are connected to the first input (Bx1) of the device for inserting digital information into the audio signal 1 (insertion device) shown in Fig. 3, and the second input of the subtractor 3 and the first input of the adder 4 are connected to the output of the filter ("+ "). The output of the subtractor through a series-connected residual signal analyzer 5 and the replacement signal generator (generator) 6 is connected to the second input of the adder 4. The additional input of the replacement signal generator is connected to the second input (Bx2) of the insertion device. The described part of the insertion device constitutes the main insertion device according to the first embodiment of the invention or the first insertion circuit of a digital information signal into an audio signal.

The output of the adder 4 is connected to the first input of the additional adder 7

("+"), As well as to its second input through a series-connected signal splitter 8, an amplitude spectrum calculator 9, a global masking threshold calculator 10, and a complementary signal shaper 11. The output of adder 7 is the output (s) of the insertion device. In this case, the additional input of the additional signal driver is connected to the second input (Bx2) of the insertion device. The described part of the insertion device constitutes an additional insertion device or a second (optional) insertion circuit.

The insertion device that implements the integrated embedding of information messages in the original audio signal operates as follows. Bx1 serves the original audio signal of the radio program. At the first stage, using a filter and a subtractor, the signal is divided into two components: the "main" component with the most audible signal content and the "residual" component with less noticeable content. In this case, both components can intersect in frequency, that is, for example, the filter can have a smooth decline at the border of the passband (Fig. 4a). In a preferred embodiment, the band-pass (dividing) filter forms one or more dips in the frequency domain, the least audible to the human ear [3] (Fig.4b). From the output of the subtractor, the “residual” signal enters the analyzer of the residual signal 5, where its spectral composition is analyzed (for example, using the Fourier transform or another method). The found spectral characteristics of the “residual” signal are transmitted to the shaper (generator) of the replacement signal 6, to the additional input (Bx2 of the insertion device) which also receives a coded digital message (including modulated, containing sync packets). In the shaper 6 form a "replacement" signal containing data of a digital message and having spectral characteristics similar to the "residual" signal. The “replacement” signal formed in this way takes into account the psychoacoustic features of sound perception by the human ear (insensitivity to phase distortion) and therefore is almost indistinguishable from the original “residual” signal. Next, in the adder 4, the "main" signal from the output of the filter is summed with a "replacement" signal that carries digital information. To facilitate the process of generating a "replacement" signal, it is possible to split the "residual" component of the signal into segments of a duration not exceeding the interval of quasistationarity of the original sound signal (approximately 10 ~ 40 ms). The “total" signal at the output of the adder 4 (the output of the device in the first embodiment) has the same spectral composition as the original signal, but a slightly changed structure of the phase spectrum (it contains the digital information component). With a careful choice of the shape of the band-pass filter, it is possible to achieve almost complete subjective acoustic invisibility of phase modifications introduced by the "residual" signal, converted into a "substitute".

At the second stage, a “complementary” signal is generated, which is additively added to the audio signal obtained at the first stage and which is the source for the additional insertion device. The formation of "complementary" acoustic signal is as follows. First, the audio signal (“total” - from the output of the first adder or “source” - from the Bx1 device in the second embodiment, when only the second circuit is used in the insertion unit) is split in the signal splitter 8 into short segments that do not exceed the interval of quasi-stationarity of the original audio signal. Then, in block 9, the amplitude spectrum of the audio segment is calculated using, for example, a fast Fourier transform (FFT), and then in block 10, the global masking threshold is calculated based on the psychoacoustic model. The global masking threshold determines the level and shape of the amplitude spectrum of the signal, which can be added to the total (original - in the second embodiment) audio segment, without compromising the subjective quality of the sound program. The procedure for calculating the global masking threshold based on the psychoacoustic model is known and used in almost all modern audio file compression schemes, such as, for example, MPEG Layer II / III [4], and therefore this procedure is not described in detail in this application.

Further, the global masking threshold is used in the shaper of the complementary signal 11 to form the amplitude spectrum of a modulated digital signal carrying an information message received from the device Bx2. The “complementary” signal thus formed in the additional adder is added to the audio signal generated at the first stage, with the resultant (“total” for the additional insertion device) being obtained. Since the “complementary” signal is always below the threshold of audibility (since it is the maximum possible signal not exceeding the masking threshold), its presence in the “total” signal at the output of the insertion device does not affect the subjective quality of this final sound signal.

Thus, one informational message is used to generate two types of signals (“replacing” and “complementing”) and their “coherent” summation. It turns out that as a result, one signal is added, consisting of two components. Due to this, a more confident reception (faster in the described insertion device) of the embedded message is achieved.

The described procedure for adding "substitute" and "complementary" signals allows you to achieve maximum data transfer speed through the information channel, with minimal acoustic noticeability of changes made to the original audio signal.

In the case of stereo broadcasting, to obtain better results, the specified insertion procedure is implemented separately for each audio channel.

The digital information transmission system in the broadcasting channel shown in FIG. 5 contains an audio program source 21 (IP) connected to the first input Bx1 of the information message insertion device 1 (HC) into the audio program, to the output (s) of which an analog radio transmitter 22 is connected. Source information messages 23 (IP) is connected to the first input Вх1 of the information message generator 24 (FIS), the output of which is connected to the second input Вх2 УВ 1, Output (Out) УВ 1 is also connected to the second input (Вх2) ФИС 24 through a serial connection a simulated radio channel 25 (RBI) and a decoder 26 information signal.

IP can be an internal archive on an electronic medium into which information messages are pre-recorded, or a local / global computer network from which information messages are dynamically loaded

The system operates as follows. IP 21 transmits the radio program to the first input (Vx1) of HC 1. At the required time from the IS 23, a digital information message is transmitted to the FIS 24. In this case, the messages can be either associated with the current sound stream or completely independent. A combination of these options is also possible. FIS at each time interval generates an information packet for transmission, which, one way or another, is associated with the current information message. In the simplest version, this can be a cyclic repetition of the same information, in a more complex version, they can use a gradual increase in coding redundancy and the transmission of additional redundant information bits associated with the original message. Such encoding methods are widely known (see, for example, [5]) and are not discussed in this application.

Then, in the FIS, modulation and insertion of clock packages into an encoded information message is carried out.

The received encoded message is transmitted to Vh2 HC 1, where it is inserted into the audio program, as described above, and the total audio signal is transmitted from the output of HC 1 through the analogue radio transmitter 22. From the output of HC 1, the total audio signal is also sent to decoder 26 (via RBI 25 ) In case of successful decoding of the message, the decoder gives a signal to FIS 24 to change the information message, by which the FIS stops transmitting to HC 1. Thus, it is assumed that the decoder on the user side should also have time to decode this message. RBI 25 is used to simulate typical or worst-case conditions for distortion of an audio signal when passing through a radio link. Typically, such an imitation consists in adding noise to the signal from HC 1 to reduce the signal-to-noise ratio, although other distortions can be simulated. Thus, more accurately predict the time interval necessary for reliable reception of the message at the receiving side. Only after decoding the total audio signal, the transition to the transmission of the next message is made (the FIS starts receiving and processing the message from the IC). Thus carry out the transmission of independent information messages.

The correct decoding in the decoder is determined in the usual way, using additional redundant information embedded in the transmitted FIS signal, for example, CRC (circular check), message hash, checksum, etc.

If necessary, synchronize the transmission of digital messages with the radio program also use known methods. For example, at the beginning of a new audio program (its fragment), an additional signal is sent to the input of the IC (not shown in FIG. 5) through an additional output of the IP, to send a new message to the FIS. The command submission time is determined by the playlist in the IP, which indicates when a new program starts, and it controls the transfer in this situation.

If there is a temporary absence of information messages (for example, when the message associated with this program has already been transmitted, and the next one has not yet arrived), the original audio signal (radio transmission from source 21) is received in the radio transmitter, i.e., the total audio signal is equal to the original one.

The described system allows you to use the heterogeneity of the sound program (fluctuating theoretical bandwidth of the radio channel) to match the duration of the transmission of a single embedded information message with the nature and properties of the outgoing material of the audio program.

Figure 6 (a, b) shows the options for the user to receive the radio program and the information messages transmitted therein. In the first embodiment (Fig. 6 (a)), on the receiving side, an information signal decoder can be integrated into a portable or mobile device with an integrated analogue broadcast radio. Moreover, the radio receiver receives the total signal and transmits to the audio output, from which the user perceives it through the loudspeaker as a normal radio broadcast, due to the above-described properties of this signal. From the audio output, the total signal is also input to the decoder, i.e. can be connected in parallel to a speaker or headphones. After receiving the decoding of the received digital message, it is transmitted through the decoder output to the information message display device for the user.

In an alternative embodiment (Fig. 6 (b)), digital messages embedded in the sound program can be received using two devices: a standard sound broadcasting radio receiver (with speaker) and a portable device with a built-in microphone and an information message decoder, through the output of which information messages are transmitted to the display device (Fig.6b). The latter option is possible, since all digital information is embedded directly in the audio signal, and accordingly it is transmitted (albeit with some losses) even when the sound is relayed through a loudspeaker-microphone chain.

Although the invention has been shown and described with reference to its specific embodiments, those skilled in the art should understand that various changes in form and content can be made without departing from the spirit and scope of the invention as defined by the appended claims.

Although the technical solution is described with a specific insertion device - as applied to AM-based systems, it should be clear to those skilled in the art that using an FIS and a decoder (possibly RBI) can achieve the claimed technical result in any analogue radio transmission systems - as with AM , and with FM, as well as in systems with the transmission of information messages at parallel frequencies.

The proposed technical solutions are universal, because do not require an additional frequency resource. When used in FM broadcasting, the free subcarrier (as opposed to the method in RDS systems) can be used to transmit additional data (for example, traffic information). In addition, the receiver does not require a mobile Internet channel, i.e. there is no need to pay for the service on the part of the user and the range of devices suitable for receiving multimedia content is expanding significantly.

Literature

[1] http://en.wikipedia.org/wiki/Visual_Radio (last accessed 2010.03.01).

[2] D. Kopitz, RDS: The Radio Data System, Artech House Publishers, 1998, 376 pp.

[3] I. Aldoshina, Fundamentals of Psychoacoustics, part 12: The volume of complex sounds,

// Sound engineer, No. 9, 2000 (http://rus.625-net.ru/audioproducer/2000/09/aldoshina.htm).

[4] Standard ISO-IEC 11172, part 3, Annex D

[5] A. Shokrollahi, Raptor Codes, IEEE Trans. Information theory, vol. 52, no. 6, pp. 2551-2567,2006.

Claims (1)

A device for inserting digital information into an audio signal containing the first input of the subtractor and a bandpass filter connected to its first input, the output of which is connected to the first input of the adder and the second input of the subtractor, the output of which is connected through a series-connected residual signal analyzer and a shaper of the replacement signal to the second input of the adder, the output of which is connected to the first input of an additional adder and a signal divider, the output of which is through series-connected amplitude calculator with ektra, calculator global masking threshold and the supplementary signal generator connected to the second input of the additional combiner, wherein the additional input of the substitute signal and the complementary signal generator connected to the second input inserter, and additional adder output is connected to the output of inserter.

Images