JPS639318A - Muting system - Google Patents

Abstract

PURPOSE:To reduce the generation of click noise by providing a most significant bit detection circuit, a bit change detection circuit, a timing circuit and a muting circuit and applying the relase of mute at least in the vicinity of the so-called zero cross point of an analog signal waveform. CONSTITUTION:The bit change detection circuit 5 receives an output of the most significant bit detection circuit 4 to compare the content of the most significant bit detected in the preceding time with that detected this time, detects the presence of the change, and when the bit content has a change, it is outputted to a timing circuit 6, which generates a control signal to release the mute at least in a proper range surrounded at the forming point of time of a digital signal near a digital signal having a change in the bit content and outputs the result to a muting circuit 7. Since a steep leading edge or trailing edge appearing at an analog signal is very less at the point of time of mute release, the generated quantity of click noise is reduced remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a muting method, and particularly to a muting technique in a digitized state of an analog signal.

(Prior art) For example, in systems where analog signals such as TV audio signals and musical tone signals are digitized and transmitted, and then converted back to analog at the receiving end to produce the desired audible sound, transmission abnormalities such as code errors and fading occur. In this case, on the receiving end side, a muting method is adopted in which the transmission signal, which is in the state of a digital signal before being converted to an analog signal, is muted for a period of time until it is restored to a normal state.

FIG. 4 shows an example of a conventional muting method.

In FIG. 4, this muting system includes a data input terminal 1, a data output terminal 2, a mute signal input terminal 3, and a muting circuit 7 interposed between the data input terminal 1 and the data output terminal 2.

A timing circuit 8 is provided between the mute signal input terminal 3 and the muting circuit 7.

A predetermined mute signal is supplied from the outside to the timing circuit 8 via the mute signal input terminal 3. As described above, this mute signal is a signal that specifies the muting period, and rises when muting is started and falls when muting is canceled, for example, as shown in FIG. 5(b).

The timing circuit 8 generates control signals for starting and canceling muting in response to the rise and fall of the mute signal, and outputs them to the muting circuit 7.

The transmitted digital signal is supplied to the muting circuit 7 via the data input terminal 1 as a data input. As described above, this digital signal is obtained by sampling and encoding an analog signal such as a voice signal or a musical tone signal.

The muting circuit 7 mutes the digital signal during the period from the generation of the mute start control signal output by the timing circuit 8 to the generation of the mute release control signal when sending the data input to the data output terminal 2. do.

Then, the digital signal sent to the data output terminal 2 is converted into an analog signal by a D/A converter (not shown) and becomes an audible sound. For example, in FIG. The solid line in the figure shows the output signal of the D/A converter, and during the mute period T shown in (b) of the same figure, there is no output signal and there is no sound, and code errors etc. become harsh noise. It prevents it from happening.

(Problem to be Solved by the Invention) However, in such a conventional muting method, the timing of muting is at an arbitrary point in the analog signal waveform, so at the start of muting, for example, the fourth
There may be a sudden fall as shown by the symbol (a) in FIG. 2(a), and a sudden rise as shown by the symbol (b) in FIG.

These have a problem in that they generate impulsive noise, resulting in harsh or lick noise.

The present invention has been made in view of such conventional problems, and its purpose is to associate the timing of muting with the analog signal waveform, thereby reducing at least the amount of click noise generated at the time of canceling mute. The object of the present invention is to provide a muting method that can significantly reduce the amount of noise.

(Means for resolving intermixing points) In order to achieve the above object, the muting method of the present invention has the following configuration.

That is, the muting method of the present invention includes a most significant bit detection means for sampling an analog signal and detecting the most significant bit of an encoded digital signal; Bit change detection means that compares the contents of the bit and the most significant bit detected this time and detects whether there is a change; A means that generates control signals for starting mute and canceling mute in response to a mute signal input from the outside. and a timing means in which at least the unmute control signal is generated within an appropriate range including the formation point of the digital signal at which the bit content has changed and surrounded by the formation point of the digital signal in the vicinity of the digital signal. and; muting means for muting the digital signal during a period from when the mute start control signal is generated to when the mute release control signal is generated.

(Operation) Next, the operation of the muting system of the present invention configured as described above will be explained.

A digital signal obtained by sampling and encoding an analog signal is supplied to the most significant bit detection means and the muting means, respectively.

The most significant bit detection means detects the most significant bit of the digital signal, that is, detects the polarity of the analog signal.

The bit change detection means receives the output of the most significant bit detection means, compares the contents of the most significant bit of the previous detection and the most significant bit of the golden detection, detects the presence or absence of a change, and detects a change in the bit contents. When there is a change in the polarity of the analog signal, that fact is output to the timing means.

When the timing means generates the mute start and mute release control signals in response to the externally inputted mute signal, at least the mute release control signal is configured to detect the formation point of the digital signal at which the bit contents have changed. The control signal is generated within an appropriate range surrounded by the formation point of the digital signal in the vicinity of the digital signal, and each control signal thus generated is output to the muting means.

The muting means mutes the digital signal during a period from when the mute start control signal is generated to when the mute release control signal is generated.

As a result, when a digital signal that has been muted by the muting means is converted into an analog signal by a D/A converter, at least the point at which muting is canceled is the point at which the polarity of the analog signal changes, that is, near the so-called zero cross point. The sharp rising and falling parts that appear in the analog signal at the time of unmuting are very small, so
The amount of impulsive noise, ie, click noise, generated by that portion can be significantly reduced or eliminated.

As explained above, according to the muting method of the present invention, muting can be canceled at least within the range of digital signals that include a digital signal whose most significant bit has changed and are in the vicinity of the digital signal, that is, analog Since this is done near the so-called zero-crossing point of the signal waveform, when the digital signal after muting is converted to analog, the abrupt rising and falling parts that appear in the analog signal can be minimized by canceling mute. This has the effect of significantly reducing or eliminating the amount of impulse noise, ie, click noise, generated by that part.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1st
The figure is a configuration block diagram of a muting method according to an embodiment of the present invention. This muting method consists of a data input terminal 1, a data output terminal 2, a mute signal input terminal 3, a most significant bit detection circuit 4, a bit change detection circuit 5, a timing circuit 6, and a muting circuit 7.
Equipped with.

As before, the transmitted digital signal is supplied to the data input terminal 1 as a data input.
This digital signal is input to the most significant bit detection circuit 4.

The most significant bit detection circuit 4 detects the most significant bit of each digital signal while passing the series of input digital signals as they are to the subsequent muting circuit 7, and outputs the detected contents to the bit change detection circuit 5. 0As is well known, when digitizing an analog signal, the sample values obtained by sampling the analog signal at fixed time intervals are encoded with a predetermined number of bits. If so, the most significant bit in each digital signal is used to indicate whether the sample value is positive or negative. In other words, the content of the most significant bit changes at the midpoint of the dynamic range when it is converted into a signal.

The bit change detection circuit 5 is the most significant bit detection circuit 4.
After receiving the output of
When the change is detected, a notification to that effect is output to the timing circuit 6.

For example, in FIG. 2, the sample values of the analog signal are plotted, but between sample value A and the next sample value B, sample value A is on the positive value side,
Sample value B is on the negative value side. Furthermore, between the sample value C and the next sample value, the sample value C is on the negative value side, and the sample value is on the positive value side. This bit change detection circuit 5 detects that there is a change in the content of the most significant bit at the time when the detection content of the most significant bit for sample value D is accepted, and also detects that there is a change in the content of the most significant bit for sample value D. When the bit detection contents are accepted, it is detected that there has been a change in the contents of the most significant bit. In other words, assuming that the analog signal is oscillating above and below the zero level as shown in FIG. 2, the zero cross point of the oscillating waveform is detected.

The mute signal is supplied to the timing circuit 6 via the mute signal input terminal 3 as in the conventional case (see FIG. 3(b)).
)).

The timing circuit 6 generates a mute start control signal in response to the output of the bit change detection circuit 5 that is input after the mute start point of the mute signal shown in FIG. 3(b), and outputs it to the muting circuit 7. do. Further, in response to the output of the bit change detection circuit 5 inputted after the mute signal is released, a mute release control signal is generated and outputted to the muting circuit 7.

The muting circuit 7 mutes the digital signal during the period from the generation of the mute start control signal to the generation of the mute release control signal, and outputs the muted digital signal to the data output terminal 2. .

The digital signal sent to the data output terminal 2 is converted into an analog signal by an A/D converter (not shown) and becomes an audible sound.

FIG. 3(a) shows the output signal of the D/A converter that converts the digital signal after mute processing into an analog signal, and the symbol T in the figure shows
1 is a silent period according to the present invention.

That is, the timing of the silent period T is different from the timing of the mute period T shown in (b), and the start and end points of the silent period T are approximately zero cross points of the analog signal waveform. Become. There is no sharp rising or falling portion at the start and end of the silent period T1, unlike in the prior art. This is because the output time of the bit change detection circuit 5 is set as the start time or end time of the silent period T, but bit change detection is performed at the start time and end time of the silent period T1 within a range where click noise can be ignored. It can be set at an appropriate time before or after the output time of the circuit 5.

In addition, in the above embodiment, click noise is prevented from occurring even at the start of muting, but since noise due to transmission abnormality etc. is generated even before muting is started, click noise at the start of muting is prevented. It is not so important to suppress the click noise, and at least the click noise may be prevented from occurring only at the end of the silent period due to muting.In other words, in combination with the conventional method, when muting starts, click noise may be prevented from occurring at any point in the analog signal waveform. It is also possible to forcibly mute and use the method of the present invention only when canceling the mute.

Furthermore, the method of the present invention can also be applied to mute processing for each channel or some channels of a system that time-division multiplexes and transmits a plurality of channels in which audible sound signals are digitized.

In addition, you can prevent click noise from occurring at the start and end of mute, so if you pay attention to this point,
It is also possible to use it as an on/off switch to switch the audible sound signal in a digitized state.

(Effects of the Invention) As explained above, according to the muting method of the present invention, muting can be canceled at least in the range of digital signals in the vicinity of the digital signal, including the digital signal whose most significant bit has changed. Since the process is performed within the range of 100%, that is, near the so-called zero-crossing point of the analog signal waveform, when the digital signal after muting is converted to analog, the sharp rising and falling parts that appear in the analog signal when muting is canceled are eliminated. It can be made very small, and has the effect of greatly reducing or eliminating the amount of impulsive noise, that is, click noise, generated by that part.

[Brief explanation of the drawing]

FIG. 1 is a configuration block diagram of a muting method according to an embodiment of the present invention, FIG. 2 is a diagram showing sampled analog signals, and FIG. 3 is an output characteristic diagram according to the method of the present invention.
Figure 4 is a block diagram of the configuration of the conventional muting method.
FIG. 5 is an output characteristic diagram according to the conventional method. 1...Data input terminal, 2...Data output terminal, 3...Mute signal input terminal,
4...Most significant bit detection circuit, 5...
... Bit change detection circuit, 6 ... Timing circuit, 7 ... Muting circuit. Agent Patent Attorney Yoshi Yahata Hiromoto Okari 0 Minnie Nishi Ngj Dai n Usu 2 Example No. 2 / Zujo Nbuson 7 ゛ Method of using obsolete analog signals 2 Figure T - Mute 0 Part 2藺T+-----The present invention during the period of a martyr.
Figure T-1111 Mute 0 Sho Agony
figure

Claims (1)

[Claims] Most significant bit detection means for detecting the most significant bit of a digital signal obtained by sampling and encoding an analog signal;
Bit change detection means receives the output of the most significant bit detection means and compares the contents of the most significant bit of the previous detection with the most significant bit of the current detection to detect the presence or absence of a change; In response, mute start and mute release control signals are generated, and at least the mute release control signal is generated from a digital signal in the vicinity of the digital signal including the point in time when the digital signal was formed at which the bit content changed. a timing means for generating the signal within a suitable range surrounded by the signal formation time; a muting means for muting the digital signal during a period from the time when the mute start control signal is generated to the time when the mute release control signal is generated; A muting method characterized by having and;