JP5526305B2 - Audio compressor - Google Patents

Description

  The present invention relates to an improvement in an audio compressor that compresses an audio signal.

  Conventionally, various proposals relating to an audio compressor for compressing an audio signal have been made. For example, the multiplier adjusts (compresses or expands) the amplitude level of the input audio signal according to the gain adjustment data (GR) corresponding to the amplitude level of the input audio signal, and performs filter control according to the gain adjustment data (GR). There is one that generates data and controls a filter that controls the frequency component of the input audio signal based on the filter control data (see, for example, Patent Document 1). Then, the high frequency component is attenuated in association with the amplitude compression, and the low frequency component is relatively emphasized to enable the production of “sound thickness”.

JP 2004-112414 A (page 3-5, FIG. 1)

  However, the conventional apparatus has a problem that the compression effect depends on the level of the input source. In other words, the compression effect obtained when the input source level is low or high is different. Therefore, in order to obtain a certain compression effect, fine parameter adjustments (threshold adjustment, etc.) are required for each input source level.

  The present invention has been made to solve such a conventional problem, and an object thereof is to provide an apparatus in which the compression effect is constant regardless of the input level.

In order to achieve the above object, the present invention provides an ALC unit (10) for inputting a music signal and generating and outputting a signal of a predetermined level regardless of the input level.
A full-wave rectification unit (20) that inputs the signal output from the ALC unit (10) and generates and outputs the full-wave rectification signal;
An envelope detector (30) for generating and outputting an envelope waveform for the full-wave rectified signal output by the full-wave rectifier (20);
A gain converter (40) for outputting a compression gain obtained by dividing a preset threshold value (t) by the envelope signal output by the envelope detector (30);
A multiplication unit (50) for multiplying and outputting the musical sound signal and the compression gain obtained by the gain converter (40).

  In this invention, the envelope detector (30) generates and outputs an envelope waveform for the full-wave rectified signal output by the full-wave rectifier (20), and the gain converter (40) sets a preset threshold value (t). The compression gain divided by the envelope signal output from the envelope detection unit (30) is output, and the multiplication unit (50) multiplies the musical sound signal by the compression gain obtained by the gain converter (40) and outputs the result. However, since the ALC unit (10) for inputting a music signal and generating and outputting a signal of a predetermined level regardless of the input level is provided in the preceding stage of the full wave rectification unit (20), the full wave rectification unit (20 ) Is the same regardless of the input level. As a result, the compression effect can be made constant regardless of the input level.

Further, in this audio compressor, the preset threshold value can be changed in a range larger than 0 and smaller than 1, and the gain converter applies the compression gain to the envelope waveform not exceeding the threshold value. The gain converter may be configured not to be obtained, and further, the gain converter may be configured to clip the compression gain obtained by the division by a predetermined value (for example, 1.0). In order to avoid dividing by 0 when calculating the compression gain, the envelope detector may be configured to output a predetermined non-zero constant as the envelope signal when it determines that it outputs 0. preferable.

  According to the present invention, it is possible to realize an apparatus in which the compression effect is constant regardless of the input level.

It is a lineblock diagram of audio compressor 1 of an embodiment of the present invention. It is explanatory drawing of operation | movement. It is explanatory drawing of operation | movement.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Constitution)
FIG. 1 is a configuration diagram of an audio compressor 1 according to an embodiment of the present invention. The audio compressor 1 is an ALC unit (Auto level controller) 10 for inputting a music signal such as a musical sound signal and a voice signal, and an output signal of the ALC unit 10 is input to generate and output a full-wave rectified signal. A threshold value (t) is set in advance, and a wave rectifier 20, an envelope detector 30 that inputs the full-wave rectified signal generated and output by the full-wave rectifier 20, and generates and outputs an envelope signal corresponding thereto. A gain converter 40 that obtains a compression gain by dividing the threshold (t) by the envelope signal, and an output signal is generated by multiplying the compression gain obtained by the gain converter 40 and the input signal input to the audio compressor 1. And a multiplication unit 50.

  The threshold value (t) “t” of the gain converter 40 can be changed and set within a range of “0.0 <t <1.0”, for example, and when the compression gain is obtained, the value is set to “1.0”, for example. ", It is configured to clip. Further, the gain converter 40 is configured not to newly calculate a compression gain for an envelope signal that does not exceed the threshold t. As the threshold value t is decreased, compression is gradually applied, and as the threshold value t is increased, compression is gradually less likely to be applied.

  As a configuration having a relatively large time constant, the ALC unit 10 measures the average level of the input signal itself over a long period of time, and can correct the level difference when obtaining the compression gain. The envelope detection unit 30 has a function of attenuating the peak component of the input signal with a constant attenuation time. Further, since the output of the envelope detection unit 30 is used as a divisor in the next stage gain converter 40, it is controlled so as not to output "0". As a specific example, when the envelope detection unit 30 determines that it outputs “0”, it outputs a predetermined 8-bit non-zero signal (“00000001”. This example is merely an example, and “0” is output. When it is determined that “” is output, a small value other than “0” may be output instead.

(Operation)
As shown in FIG. 2A, it is assumed that input signals having three levels of large, medium, and small are input to a location indicated by reference numeral a in FIG. Then, since the ALC unit 10 outputs a signal of a predetermined level regardless of the input level, the signal of the same level is output as shown in FIG. The signal at the location indicated by symbol b in FIG. Specifically, when the input signal is positive, the ALC unit 10 raises the maximum value that the ALC unit 10 can output, and when the input signal is negative, the ALC unit 10 reduces the output value to the minimum value that can be output.

Next, a full-wave rectification signal shown in FIG. 2C is output by the full-wave rectification unit 20 (a signal at a point c in FIG. 1). Further, the full-wave rectified signal generated and output by the full-wave rectification unit 20 is generated and output by the envelope detection unit 30 to generate a signal having a waveform as shown in FIG. The signal at the location indicated by the symbol d in FIG. 1). In FIG. 3A, “t” indicates a threshold value set by the gain converter 40, and compression is applied only to a portion exceeding the threshold value t (conversely, the threshold value t is lower than the threshold value t). You ca n’t apply compression to small parts).

The gain converter 40 obtains a compression gain by dividing the threshold value t by the envelope signal from the envelope detection unit 30 (see FIG. 3B: a signal at a position indicated by symbol e in FIG. 1). This division result is clipped by “1.0”, for example. In FIG. 3B, this clipping position “1.0” is indicated by a horizontal dotted line. Then, the multiplication unit 50 multiplies the compression gain obtained sequentially and the input signal input to the audio compressor 1 and outputs the result as an output signal (a signal at a location indicated by reference sign f in FIG. 1). As a result, a waveform as shown in FIG. 3C can be obtained. As can be seen from FIG. 3C, the shape of the output signal is the same regardless of the difference in amplitude for input signals of three levels, large, medium, and small. The compression effect is constant.

  As described above, according to the embodiment of the present invention, the envelope detector 30 generates and outputs an envelope signal for the full-wave rectified signal output by the full-wave rectifier 20, and the gain converter 40 sets in advance. The compression gain obtained by dividing the threshold value t by the envelope signal output from the envelope detection unit 30 is output, and the multiplication unit 50 multiplies the input signal and the compression gain obtained by the gain converter 40 and outputs the result. Since the ALC unit 10 that inputs an input signal and generates and outputs a signal of a predetermined level regardless of the input level is provided in the previous stage of the full-wave rectifying unit 20, the signal level input to the full-wave rectifying unit 20 Are the same regardless of the input level. As a result, the compression effect can be made constant regardless of the input level.

  The audio compressor 1 may be realized in whole or in part by hardware, or may be realized in whole or in part by a CPU or DSP executing a predetermined program.

  As described above, the audio compressor of the present invention can be used in the audio field and the like.

DESCRIPTION OF SYMBOLS 1 Audio compressor 10 ALC part 20 Full wave rectification part 30 Envelope detection part 40 Gain converter 50 Multiplication part

Claims (5)

An ALC unit for inputting a music signal and generating and outputting a signal of a predetermined level regardless of the input level;
A full-wave rectifier that inputs the signal output from the ALC unit and generates and outputs the full-wave rectified signal;
An envelope detector that generates and outputs an envelope signal for the full-wave rectified signal output by the full-wave rectifier;
A gain converter that outputs a compression gain by dividing a preset threshold by the envelope signal output by the envelope detector;
An audio compressor comprising: a multiplication unit that multiplies the musical sound signal and a compression gain obtained by the gain converter and outputs the multiplication signal. The audio compressor according to claim 1.
The audio compressor according to claim 1, wherein the preset threshold value can be changed in a range larger than 0 and smaller than 1. The audio compressor according to any one of claims 1 and 2,
The gain converter is
An audio compressor characterized in that the compression gain is not obtained for the envelope signal not exceeding the threshold value. The audio compressor according to any one of claims 1, 2, and 3,
The gain converter is
An audio compressor, wherein the compression gain obtained by the division is clipped by a predetermined value. The audio compressor according to any one of claims 1, 2, 3 and 4.
The envelope detector is
An audio compressor characterized by outputting a predetermined non-zero constant as an envelope signal when it determines that it outputs zero.

Images