JPH0683182B2 - Quasi-instantaneous compression pulse code code modulation signal demodulator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secreted quasi-instantaneous compressed voice pulse code modulation (PCM) signal demodulator.

2. Description of the Related Art A transmission signal for transmitting a quasi-instantaneously compressed audio PCM signal is
It is basically configured by data obtained by compressing sample data for each block at a predetermined time interval and a scale value indicating an amplitude range in which the maximum value of the amplitude of the sample data for each block is included.

Further, when the transmission data is encrypted, the identification code is added to the above in order to determine whether or not the demodulation device is encrypted. Confidentialization is realized by multiplying part or all of the transmission data by a pseudo-random code sequence (hereinafter referred to as PN code sequence).

FIG. 2 shows a block diagram of a conventional demodulator for quasi-instantaneous compression PCM signals. 1 is compressed data detecting means, 2 is scale value detecting means, 3 is decompressing means, 4 is D / A converting means, 5 is identification code detecting means, and 6 is decoding means.

It is composed of a quasi-instantaneously compressed audio PCM signal, a scale value for each block and an identification code. From the transmission signal, the compressed data detecting means 1 detects the compressed data, the scale value detecting means 2 detects the scale value, and the identification code detecting means 5 detects the identification code. The compressed data is expanded by the expansion / contraction means 3 according to the scale value. Stretched
The PCM signal is converted into an analog signal by the D / A converter 4.
The identification code detected by the identification signal detecting means 5 is given to the decoding means 6 as a control signal for declassifying the service-subscribing device. There is no decoding device 6 for the device that does not subscribe to the service, or because it does not operate, the digital signal sequence obtained by multiplying the original PCM signal by the PN code sequence is directly demodulated into a voice signal. become. (For example, Satellite Broadcasting Reception Technology Study Group Report No. 2
Part-Satellite Broadcasting Receiver Part 2 Desirable Performance Appendix-2) Problems to be Solved by the Invention However, in the above-mentioned configuration, a signal that has been encrypted is demodulated into a voice signal by a demodulator that does not subscribe to the service. In that case, the following problems occur.

Since the compressed data is multiplied by the PN code sequence, the decompressed data has bits rising randomly from the upper bits to the lower bits regardless of the original PCM data. This P
An analog signal obtained by D / A converting the CM data becomes a large amplitude impulse signal with certain probability. The larger the scale value, the larger the amplitude of the impulse signal. This large-amplitude impulse signal is supplied to audio equipment such as amplifiers and speakers, which causes problems such as overloading these equipment and causing local discomfort to non-subscribers.

The present invention provides a demodulation device that provides an appropriate confidential communication effect without overloading an external device even in the case of non-subscription of demodulation of a quasi-instantaneous compressed audio PCM signal that has been encrypted by PN code multiplication. The purpose is to do.

Means for Solving the Problems In order to solve the above problems, the present invention detects an identification signal indicating the presence or absence of anonymization, and when anonymization is performed, the upper limit of the scale value is set in the case of non-subscription. The compressed data is decompressed according to this limited scale value.

Effect According to the present invention, the amplitude of the audio signal is controlled at a level determined by the upper limit of the scale value because the scale value is limited by the predetermined upper limit even when the sent scale value is large. For this reason, there is no overload on the audio equipment, and an appropriate confidentialization effect can be obtained.

Embodiment FIG. 1 is a block diagram showing an embodiment of a quasi-instantaneous compression pulse code modulation signal demodulation device of the present invention.

1 is compressed data detecting means, 2 is scale value detecting means, 3
Is a data expansion means, 4 is a D / A conversion means, 5 is an identification code detection means, and 7 is a scale value limiting means. The input signal 11 includes PCM data obtained by quasi-instantaneously compressing an audio signal, a scale value for quasi-instantaneous compression, and an identification code indicating whether or not confidentiality is applied. When the confidentiality is applied, at least the PCM data is multiplied by the PN code sequence.

From this input signal, the compressed data detecting means 1 detects the compressed data, the scale value detecting means 2 detects the scale value, and the identification code detecting means 5 detects the identification code. The upper limit of the detected scale value is limited by the scale value limiting means 7. The upper limit of this scale value is determined by the identification code 51. The compressed data detected by the compressed data detecting means 1 is expanded according to the scale value whose upper limit is restricted by the data expanding means 3. The decompressed data is obtained as an analog audio signal D / A converted for each audio sample.

Here, the rule of quasi-instantaneous companding will be described by taking 14 bits → 8 bits and 8 bits → 14 bits as examples. FIG. 3 shows a decompression rule of 8 bits → 14 bits. Scale value is 7 from 1 to 7
In the case of the existence of 7 and the amplitude of the sample of the original PCM signal is the maximum range. The decompression process becomes a bit array of sample data as shown in FIG. 3 according to the scale width. When the scale value is 7, the compressed data is arranged in order from the 14-bit high-order bit, and it shifts toward the low-order bit as the scale value decreases, and the high-order bit has the same sign as the polarity bit (MSB) and is expanded sample. Is stretched to reduce the amplitude of.

In FIG. 1, when the identification code indicates the confidentiality of PCM data, when the scale value is limited to an upper limit of 1, for example, the D / A-converted voice signal is limited in amplitude and does not overload the audio equipment. The effect of moderate anonymization can be obtained. When the identification code indicates that confidentiality has not been applied, the original voice signal can be reproduced by setting the upper limit of the scale value to 7. Further, by fixing or limiting the scale value, the reproduced sound is made unnatural even when the ratio of multiplication of the PN code sequences is low, and as a result, the secret story effect can be enhanced.

In the above example, the case where the quasi-instantaneous companding of the linear PCM signal is described, but the same effect can be obtained even in another quantization method, for example, when the quasi-instantaneous companding of the differential PCM signal is performed.

EFFECTS OF THE INVENTION As described above, according to the present invention, by limiting the upper limit of the scale value, an appropriate confidentialization effect can be obtained without overloading the audio device for confidentialization, and the confidentialization is performed. It is possible to realize a demodulator for quasi-instantaneous compressed PCM audio.

[Brief description of drawings]

FIG. 1 is a block diagram of a demodulator of a quasi-instantaneous compressed signal which is an embodiment of the present invention, FIG. 2 is a block diagram of a demodulator of a conventional quasi-instantaneous compressed signal, and FIG. 3 is a rule of quasi-instantaneous companding. FIG. 1 ... Compressed data detection means, 2 ... scale value detection means, 3 ... expansion means, 4 ... D / A conversion means, 5 ... identification code detection means, 6 ... decoding means, 7 ... scale value Means of restriction.

Claims (1)

[Claims] 1. A quasi-instantaneous compression is performed by dividing a pulse code modulated audio signal into blocks of a predetermined number of sample data, and the compressed sample data obtained by this quasi-instantaneous compression and the degree of compression of each block. And a scale value shown, and an encryption code indicating the existence or non-existence of the anonymization, which is performed by multiplying a part or all of the compressed data and the scale value by a pseudo-random code sequence. When the transmission signal is formed,
Identification code detecting means for detecting the identification code, scale value detecting means for detecting the scale value, scale value limiting means for defining an upper limit of the scale value detected by the detected identification code, and limited scale value A quasi-instantaneous compression pulse code modulation signal demodulation device, characterized in that the transmission signal is demodulated by including a decompression means for decompressing the compressed data detected by.