JPH02299332A - Additional signal multiplexing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a method for adding identification signals, control signals, and various other information signals (additional signals) to sampled and quantized signals (main signals) such as digital audio signals and digital video signals. ) is concerned with a method of multiplexing additional signals.

Conventional technology One of the conventional methods of transmitting not only the main signal but also additional signals on the main signal transmission path (transmission path in a broad sense that includes recording and reproduction).
Frequency multiplexing is widely used as one method. This adds a carrier additional signal modulated by the additional signal to an empty area in the frequency band of the transmission path. The frequency of the carrier wave is set so that the occupied band of the carrier additional signal falls within the transmittable band of the transmission path, so that the frequency is set within the transmittable band beyond the band of the additional signal from the boundary of the transmittable band. If the band of the carrier additional signal and the band of the main signal overlap, one will interfere with the other, so it is necessary to limit the band using a filter.

Problems to be Solved by the Invention This frequency multiplexing method can also be used in digital transmission paths for sampled and quantized signals.

However, in order to perform modulation and demodulation using digital signal processing, a large-scale digital filter, a ROM (read-only memory) to generate a sine wave, and a multiplier are required, resulting in a large circuit scale. Ta.

Another problem is that when working with a receiving device (or reproducing device) that is not designed to transmit additional signals, the additional carrier signal inevitably interferes with the output of the main signal to some extent.

Means for Solving the Problems The present invention multiplexes an additional signal onto a main signal sampled and quantized at a sampling frequency Fs, the additional signal being obtained by modulating a carrier wave with a frequency Fs/2. A method for multiplexing additional signals, characterized in that a carrier additional signal is added to the main signal.

Effect: Due to the above configuration, the method for multiplexing additional signals of the present invention has the carrier frequency at the Nyquist frequency, so there is almost no deterioration in the frequency band of the main signal, and multiplexing and separation of additional signals can be realized with a simple circuit. , and the Nyquist frequency is sufficiently attenuated by a low-pass filter during DA (digital-to-analog) conversion of the main signal, so the multiplexed additional signal can be removed without providing a special filter. In other words, even in a receiving device (or reproducing device) that does not assume multiplexing of additional signals, no deterioration (interference) occurs in the main signal obtained.

In a time-based discrete system in which analog signals are sampled, frequencies from frequency O to the Nyquist frequency can be used, but the empty space around the Nyquist frequency caused by band limitation before AD conversion has not been used in the past. The present invention utilizes this. Furthermore, if the carrier frequency is the Nyquist frequency, the upper sideband generated by AM modulation is folded back to match the lower sideband, so the folded spectrum does not interfere with demodulation.

An embodiment diagram shows a recording device (transmission bag rIL) and a reproducing device (receiving device) that transmit a main signal (audio signal) and an additional signal to which an additional signal multiplexing method in an embodiment of the present invention is applied.
FIG.

However, the frequency band of the additional signal is sufficiently narrower than that of the audio signal.In the same figure, 101 is the input terminal for the audio signal;
02 is an input terminal for additional signals, 103 is a recording device, 104
105 is a reproduction device, 108 is an audio signal output terminal, and 107 is an additional signal output terminal.

In the recording device 103, 108 is an LPF (low pass filter), 109 is an AD converter, 110 is an additional signal multiplexing circuit, 111 is a recording means, 112 is a carrier wave generator, 113 is a multiplier, and 114 is an adder. It is.

In the reproducing device 105, 115 is a reproducing means, 116 is an additional signal separation circuit, 117 is a DA converter, and 118 is an L
PF, 119 is a carrier wave generator, 120 is a multiplier, 121
is a digital filter.

The operation of the above configuration will be explained below.

In the recording device 103, the audio signal input from the terminal 101 is band-limited by the LPF 108 to 1/2 of the sampling frequency Fs (=48 kHz), that is, below the Nyquist frequency, and then sampled and quantized by the AD converter 109 and converted into digital data. This becomes the audio signal (main signal). The additional signal inputted from the terminal 102 is multiplied by the carrier wave from the carrier wave generator 112 in the multiplier 113, and becomes the carrier additional signal which is a digital AM (amplitude modulation) signal. The additional signal is added to the digital audio signal by the adder 114 and recorded on the magnetic tape 104 by the recording means 111.

Since the audio signal, which is the main signal, is band-limited below the Nyquist frequency by the LPF 108, there is no need to provide a new filter to band-limit the main signal in order to add the carrier additional signal whose carrier frequency is the Nyquist frequency. do not have. That is, there is no need to narrow the frequency band of the main signal in order to transmit the additional signal.

In the reproducing device 105 , a signal obtained by adding the digital audio signal and the additional signal is reproduced from the magnetic tape 104 by the reproducing means 115 and inputted to the DA converter 117 and the separation circuit 118 . The output signal of the DA converter 117 is band-limited by the LPF 118 to a frequency lower than the Nyquist frequency Fs/2 (for example, 22 to 23 kHz), so the additional signal is removed, and the audio signal is sent to the terminal 10.
It is output from θ. That is, there is no need to newly provide a filter for removing the additional signal in order to obtain the main signal. In the separation circuit 116, the signal from the reproducing means 115 is multiplied by the carrier wave from the carrier generation circuit 119 in the multiplier 120, and unnecessary components are removed by the digital filter 121 to obtain only the additional signal, which is output from the terminal 107.

Since the band of the additional signal is narrow, the digital filter 121 may be realized by a simple circuit whose transfer function H(Z) can be expressed by the following equation (where K is an integer).

To generate a carrier wave at the Nyquist frequency, it is only necessary to alternately generate "1" and "-1" in the time axis discrete system of the sample frequency Fs, so the carrier wave generator 112.11
9, no ROM is required and the sampling frequency Fs is set to 1/
Only a frequency divider with a frequency of 2 is required.

Multipliers 113 and 120 can be configured with only adders and subtracters because the value of the carrier wave as one input is "1" or "-1".

These additional signals include messages (lyrics, musical scores, etc.),
Possible examples include a control signal (control of a slide projector, etc. corresponding to an audio signal), an identification signal, and the simplest example is the presence or absence of an unmodulated carrier wave, which can be used as an identification signal to prohibit digital dubbing.

As described above, according to this embodiment, by setting the carrier frequency of the additional signal to the Nyquist frequency, the additional signal can be multiplexed with a simple circuit, there is no need to narrow the band of the main signal, and Even in a playback device that does not assume multiplexing of additional signals, it is possible to reproduce audio signals without interference caused by additional signals.

As described in detail, according to the present invention, multiplexing of additional signals can be realized with a simple circuit without limiting the band of the main signal, and a receiving device ( Since the multiplexed additional signal does not interfere with the main signal even in playback devices), its practical value is great.

[Brief explanation of drawings]

The figure is a block configuration diagram showing a recording device and a reproducing device to which an additional signal multiplexing method according to an embodiment of the present invention is applied. 103--Recording device, 105.0-Reproducing device, 110
...multiplexing circuit, tte--separation circuit.

Claims (1)

[Claims] An additional signal is multiplexed on a main signal sampled and quantized at a sampling frequency Fs, and a carrier additional signal obtained by modulating a carrier wave with a frequency Fs/2 by the additional signal is added to the main signal. Characteristic method for multiplexing additional signals.