JPH0329531A - Muting circuit - Google Patents

Abstract

PURPOSE:To reduce the generation of noisy sound by masking forcibly a digital voice data after a prescribed time elapses when a zero cross point of an input digital voice data is not easily detected after the input of a mute signal. CONSTITUTION:A gate switching section 11 sends a signal turning on a gate from the point of time when a zero cross point is detected within a count time T of a timer 15 just after the input of a mute signal and at the point of time of the end of count of the timer 15 when no zero cross point is detected, a gate section 12 masks a digital voice data to make all bits of an output data zero. Thus, till the muting period is finished, the voice is in no voice state whose level is zero. Thus, an event of outputting an erroneous data or a data with bad quality is avoided and generation of noisy sound is reduced.

Description

[Detailed description of the invention] [! Field of Application of Kurigami] This invention relates to a muting circuit for audio signals. [Prior Art] FIG. 3 is a block circuit diagram showing a conventional muting circuit. In the figure, (10) is a zero-crossing detection unit that always detects zero-crossing points in digital audio data, and (11) is a gate opening/closing unit that detects zero-crossing points immediately after the start or end of the user signal. hand,
Sends out a gate signal to turn ON/OFF the gate of input digital audio data. (12) is a gate section, which gates the digital audio data in response to the gate signal from the gate opening/closing section (It). (13) stores input digital audio data <RAM, (14) data R A
M is a multiplier that multiplies the digital audio data output from (13) by a certain constant coefficient, and (13).
(14) constitutes a digital filter (20). FIG. 4 is a signal waveform and timing diagram of this conventional example, in which (a) shows the output audio signal and (b) shows the mute signal. Next, we will explain the operation. For example, when digital audio data encoded in two's complement format is input, the point where the most significant bit data changes from "1" to "0" or from "0" to "1" is This is the zero crossing point. The zero-crossing detection unit <lO> constantly detects this zero-crossing point. Once the digital audio data is RA
M (13), then multiplied by a certain coefficient in a multiplier (l4) and output. Gate opening/closing part (
When the main ute signal is input, l1) sends out a signal to turn on the gate from the zero cross point immediately after that, and the gate part (l2) masks the digital audio data,
Set all bits of the output audio data to ``O''. By doing this, from then on until the muting period ends,
The output audio will be silent with level zero. Next, when the mute signal ends, the gate opening/closing section (11)
sends out a signal to turn off the gate at the zero cross point immediately after that, and the gate section (l2) outputs digital audio data. As a result, the waveform of the output audio signal is ′! The waveform will be as shown by the solid line in Figure J4 (a). [Problem to be Solved by the Invention] Since the conventional muting circuit is configured as described above, human voice data has a waveform as shown by the broken line in FIG. After the signal is input,
If the zero-crossing point is not detected easily, erroneous data or poor-quality data as shown by the solid line in Figure 4(a) may be output as is until the zero-crossing point is detected, resulting in abnormal noise. There was a problem with this. This invention was made in order to solve the above-mentioned problems, and it is possible to create a main utility circuit in which abnormal noise is less likely to be transmitted even if the zero-crossing point is not easily detected after the main utility signal is input. The purpose is to obtain. [! Means for Solving the Problem 1 If a zero-crossing point is not detected within a certain period of time after a mute signal is input, the muting circuit of the present invention forcibly masks the input digital audio data after the certain period of time has elapsed. It is characterized by having a means. [Operation] The masking means of the present invention forcibly masks input digital audio data if a zero-crossing point is not detected within a certain period of time after a mute signal is input. Therefore, it does not continue to output incorrect data or data of poor quality, and the generation of abnormal noises is reduced. [Embodiment of the Invention] An embodiment of the invention will be described below with reference to the drawings. ′! Figure J1 is a block circuit diagram of this embodiment, (15)
is a timer that counts the time (T) equivalent to the capacity of RAM (13). Fig. 2 is a signal waveform and timing diagram of this embodiment, Fig. 2 (a) is the audio signal, Fig. 2 (b) is the output signal, and T in the figure is the counting time of the timer (15). Next, we will explain the operation. Digital audio data is temporarily stored in the RAM (13), then multiplied by a certain coefficient in the multiplier (14) and output. This R A M (13) The timer (15), which counts the time T corresponding to the capacity of Immediately after the mute signal is input, the gate opening/closing unit (11) outputs the output if a zero-crossing point is detected within the time period T measured by the timer (l5), and from that point on, and if no zero-crossing point is detected, When the timer (!5) finishes counting, it sends out a signal to turn on the gate, and the gate section (l2) masks the digital audio data and sets all bits of the output data to ``0''. The audio remains silent at level 0 until the muting period ends.Next, when the input of the mute signal is finished, the gate opening/closing section (1
1) sends out a signal to turn off the gate from the zero cross point immediately after that, and the gate section (12) outputs digital audio data. As a result, the output audio signal has a waveform as shown by the solid line in Figure 2 (a), and incorrect data or poor quality data is output to the timer (l6) beyond the measured time T. As a result, a muting circuit that generates less abnormal noise can be obtained. Note that in the above embodiment, digital audio data encoded in two's complement format was used, and inversion of the most significant bit data of the data was used for zero-cross detection, but no matter how encoded digital audio data is Zero-crossing detection may be any means that can detect zero-crossing points. Further, the timer (l5) may be one that measures time, or one that counts data or clocks. [Effects of the Invention] As described above, according to the present invention, even if the zero-crossing point of the input digital audio data is not easily detected after the mute signal is input, the digital audio data is forcibly output after a certain period of time has elapsed. Since it is configured to mask, it does not continue to output erroneous data or data of poor quality, and has the effect of providing a muting circuit that reduces the occurrence of abnormal noise.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram of an embodiment of the present invention, Fig. 2 is a signal waveform and timing diagram of this embodiment, Fig. 3 is a block circuit diagram of a conventional muting circuit, and Fig. 4 is this conventional example. Figure 2 shows the signal waveform and tying diagram of . (10) - Zero cross detection section, (1l)... Gate opening/closing section, (l2)... Gate section, (l3)... Data RAM, (l4)... Multiplier, (15) ...Timer. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] (1) A digital filter that temporarily stores digital audio data in RAM, multiplies it by a certain coefficient, and outputs it, a means for detecting the zero-crossing point of the output data of this digital filter, and a means for detecting the zero-crossing point of the output data of this digital filter, and a timer that counts a time T corresponding to the capacity of the RAM;
If the zero-crossing detection means detects a zero-crossing point before the time T has elapsed after the mute signal is input, then from that time, or after the time T has elapsed if it has not detected a zero-crossing point. A muting circuit comprising a gate opening/closing means for gating digital audio data input from the input terminal and releasing the gate from the zero-crossing point of the digital audio signal immediately after the input of the muting signal and outputting the gated digital audio data.