JPS5914960B2 - Distortion measurement method for multi-channel record system - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for measuring distortion in a multi-channel record system, which can comprehensively measure various distortions caused by all causes in a multi-channel record system at once, and can also be used to evaluate the auditory sense of music. The purpose of this invention is to provide a distortion measurement method that can evaluate matching systems.

Generally, each multi-channel audio signal is a direct wave signal in an audible frequency band and an angle-modulated signal in a predetermined frequency band, and a multiplexed signal of these two signals is used as a single channel signal on the left and right walls of a single sound groove. It is known that multi-channel records, which are cut and recorded individually, generate various distortions during the recording and playback process.

This distortion mainly includes 1 modulation distortion (distortion caused by incorrect modulation), 2 phase distortion (0 distortion caused by sidebands not being in phase), and 3 amplitude distortion (caused by a breakdown in the amplitude relationship of sidebands). 4 interference distortion (distortion caused by interference of angle modulated wave signals of other channels due to crosstalk), 5 detection distortion (distortion due to incorrect detection), etc. Although there are other distortions, the above distortions are thought to account for most of the 5. In the case of multi-channel records, among the above distortions, interference distortion is particularly large, accounting for more than 50% of the total. Therefore, the present applicant previously proposed a method for measuring the above-mentioned interference distortion in Japanese Patent Application No. 48-61108.

This method is a method in which a carrier wave of a predetermined frequency is angularly modulated with a predetermined degree of modulation using a single signal with a low frequency of about 100H2, and the harmonic distortion rate of the demodulated signal is measured. The reason for using a single signal is that it is easy to measure and is sufficient considering that interference distortion accounts for most of the distortion in a multi-channel record playback system. The reason for using a low frequency signal of about 100H2 is as follows. That is, in a multi-channel record system, in order to make full use of the frequency band, a frequency modulation method with a frequency shift of 800H2 is used, for example, for frequencies below about 800H2. Therefore, the modulation index is 8, especially in the low frequency band below about 10OH2.
At this time, the amplitude of the seventh and higher harmonics becomes particularly large. On the other hand, in a multi-channel reflex 5 code reproducing system, harmonics from the 1st to the 9th order are measured most frequently in the detection output. Therefore, using a low frequency signal of about 100H2 makes it easier to measure distortion.

However, the measurement method proposed above has a problem in that the evaluation of quality by the measurement method and the evaluation of the auditory sensation of music often do not match.

The present invention solves the above-mentioned problems, and one embodiment thereof will be described below with reference to the drawings.

The present invention is based on the following results, and is based on the following results:
z~3kHz) and low frequency (approximately 50~200H)
A carrier wave of a predetermined frequency is angularly modulated with at least two or more single frequency signals each corresponding to z), and this angularly modulated signal is used to measure distortion in a multichannel record system. Here, as described later,
When cross-modulation occurs with the above-mentioned low frequency signal, the frequency at which the cross-modulation distortion is most easily felt is the above-mentioned frequency (approximately 200
Hz to 3kHz). In the multi-channel record system, the following description will be made on the premise that the phases of the unmodulated carrier waves of the channels to be transmitted are synchronized with each other. That is, firstly, in the measurement method proposed above, for music that is close to a single note, the measurement results match the aural evaluation. Secondly, with this proposed method, the measurement results and auditory evaluations often do not match for complex music. Third, we added a mid-range frequency signal of, for example, about 2 kHz to the above-mentioned low-frequency signal of about 100 Hz, modulated the carrier wave with these two signals, and measured the demodulated signal. The results showed an extremely good agreement with the evaluation of music audibility. did.
Fourth, when the signal modulated by the above two signals is demodulated, the first
In addition to harmonic components indicated by 1 in the figure, a large amount of cross-modulation components indicated by 2 were generated. Here, in the same figure, f1 is approximately 100
Hz. f2 indicates the frequency spectrum of the demodulated signal with a single frequency of about 2 kHz. Fifth, even if signals modulated by the same two signals are used, depending on the multi-channel record system, as shown in FIGS. 2A and B, respectively,
The ratio of the harmonic components 1'', f and the cross-modulation components 2', 7 was not constant. From the above five results, the angle-modulated frequency signal (hereinafter, for convenience of explanation,
By analyzing the harmonics and cross-modulation distortion of the measured signal (called the signal under test), it is possible to obtain agreement with the evaluation of the auditory sensation of music. It is concluded that sufficient agreement is not obtained with the auditory evaluation by the authors. Therefore, in this embodiment, the mid-range frequency is, for example, about 2 kHz, and the low-range frequency is, for example, about 1 kHz.
The third signal is an angle-modulated carrier wave of, for example, 30 kHz of the channel to be measured (left or right) using two signals of 00 Hz.
An angle-modulated wave signal having a frequency spectrum as shown by 3 in FIG. A is used as a signal to be measured. By transmitting this signal under test through a multi-channel record system, demodulating the transmitted signal, and measuring the distortion of the obtained demodulated signal, the total distortion of the entire multi-channel record system can be measured. , it is possible to perform measurements that correspond well to the auditory sense of music. For example, the modulation quality of a modulator can be measured by using the measurement method of the present invention after checking the quality of the demodulator and other multichannel record transmission systems. Application measurements can be made in exactly the same way in other transmission parts of a multi-channel recording system. In addition, in order to approximate the same condition as when playing music from a multi-channel record, the measurement channel and reaction channel (non-measurement channel) are also set to 30kHz as shown in Figure 3B.
The modulated wave signal 4 obtained by angle-modulating the carrier wave of z with a single frequency signal of 5 kHz may be transmitted in a state that does not interfere with measurement.

Here, in the present invention, all signal frequencies to be transmitted are:
In order to allow states with all phase relationships to appear at once, they are selected so that there are no multiple relationships. Note that the non-measurement channel transmits at least only an unmodulated carrier wave that is phase-synchronized with the unmodulated carrier wave of the measurement channel.

Furthermore, in order to bring the measurement results even closer to the evaluation of the auditory sense of music, the number of modulation signals may be increased to three or more. However, in this case, the measurement becomes complicated, and the effects commensurate with the complexity cannot be expected. As described above, the method for measuring distortion of a multi-channel record system according to the present invention uses at least one or more single frequency signals at low frequencies and one single frequency signal at mid-range frequencies that have no multiple relationship with each other. Alternatively, an angle-modulated wave signal obtained by angle-modulating a carrier wave of a predetermined frequency with a superimposed signal consisting of two or more single frequency signals is used as the measurement channel signal, and the signal of the non-measurement channel is an unmodulated wave signal that is phase-synchronized with the carrier wave. A carrier wave or an angle-modulated wave signal in which this carrier wave is modulated with another signal that does not have a specific phase relationship with the signal of the measurement channel, and both channel signals are transmitted by a multi-channel record system, and this transmission is performed. Since the distortion of the bitonic signal of the measurement channel is measured among the measured signals, the total amount of distortion of the entire multi-channel record system can be comprehensively measured at once, and this measurement result can be used when playing music in the multi-channel record system. It has the advantage of being able to match the auditory perception extremely well and being relatively easy to measure.

[Brief explanation of the drawing]

Figure 1 shows the frequency spectrum of an example of distortion distribution when reproducing a two-signal modulated wave to be evaluated and measured by the method of the present invention, and Figures A and B show reproduction using different multi-channel record systems. Figures 3A and 3B are frequency spectrum diagrams showing the difference in distortion distribution of the two signal modulated waves obtained by the method of the present invention, respectively. FIG. 3 is a diagram showing a frequency spectrum of an example of an angle-modulated signal. 1,1″,1ku...harmonic component, 2,2゛,2″
-... Cross-modulation component, f1... Frequency spectrum of low frequency signal, F2... Frequency spectrum of middle frequency signal.

Claims (1)

[Claims] 1 A superimposed signal consisting of at least one or two or more single frequency signals of a low frequency range and one or two or more single frequency signals of a midrange frequency that have no multiple relationship with each other, and has a predetermined frequency. An angle-modulated wave signal obtained by angle-modulating a carrier wave is used as a measurement channel signal, and a non-measurement channel signal is an unmodulated carrier wave that is phase-synchronized with the carrier wave, or the carrier wave has a specific phase relationship with the measurement channel signal. The angle-modulated wave signal is modulated with another signal that has no A method for measuring distortion in a multi-channel record system.