JPH0448014Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an automatic volume adjustment device, and more particularly to a device that automatically adjusts the volume based on the respective signal levels of a noise signal and an audio signal.

BACKGROUND ART Conventionally, there has been a device of this type as shown in FIG. In the figure, ambient noise is picked up by a noise sensor 1, converted into an electrical signal, and supplied to a noise detection circuit 2 as a noise signal. The noise detection circuit 2 outputs the logarithmic value of the signal level of the input noise signal with respect to the reference level. Noise detection circuit 2
The output passes through an amplifier 3 and becomes one input of a subtracter 4. The audio signal input via the input terminal 4 is supplied to a variable gain circuit 6 and a signal detection circuit 7. The signal detection circuit 7 outputs the logarithmic value of the signal level of the audio signal with respect to the reference level. The output of this signal detection circuit 7 passes through an amplifier 8 to a subtracter 4.
Use other inputs. The subtracter 4 subtracts the output of the amplifier 8 from the output of the amplifier 3, and controls the gain of the variable gain circuit 6 by the subtracted output. The output of the audio signal 6 is power amplified by a power amplifier 9, and outputted from a speaker 10 as reproduced sound.

Note that as the noise detection circuit 2 and the signal detection circuit 7, a logarithmic amplifier or the like having a well-known configuration is used.

In this configuration, the noise signal level is n, the reference noise signal level is nr, the audio signal level is s, the reference audio signal level is sr, the amplifier 3,
If the gains of 8 are β and α (β, α<0), the output of amplifier 3 is β×20log(n/nr) = β(20logn−20lognr) =β(N−Nr) =βΔN, and The output of the amplifier 8 is α×20log(s/sr)=β(20logs−20logsr)=β(S−Sr)=βΔS. Then, the subtraction output of the subtractor 4 becomes βΔN−αΔS. Assuming that the coefficient of the gain control signal versus gain of the variable gain circuit 6 is 1, the gain G of the variable gain circuit 6 is as follows: G=βΔN−αΔS. That is, as the signal level of the noise signal increases, the gain G increases, and as the audio signal level increases, the gain G decreases. As a result, when listening to music, when the ambient noise increases, the gain G increases and the output level increases, preventing so-called masking due to noise. Also, when the music input level increases, the gain G decreases and the output level increases. This means that noise caused by excessive output can be prevented.

Here, if the input is S[≠V] and the output is So[≠V], then the relational expression So=S+(βΔN−αΔS) is expressed, and the input/output characteristics are as shown in FIG.

In Fig. 4, Ss on the S axis is the signal detection circuit 7.
This is the detectable lower limit level of the signal level, and also the starting point of gain reduction due to the signal level. Normally, the signal detection circuit 7 is designed so that the detectable lower limit level Ss and the reference level Sr match, and the graph of the input/output characteristics moves upward in parallel as the parameter ΔN increases. Further, Sc is the detectable upper limit level, and signal compression is not performed above this level. .

In the conventional device configured in this way, volume compression starts when the input level S reaches the reference level Sr, but the output level is not constant, and the volume compression start point at the output depends on the noise level at that point. changes. However, from an auditory perspective, it is preferable for the starting point of volume compression to be constant regardless of the noise level.

Summary of the invention This invention was created in view of the points mentioned above.
An object of the present invention is to provide an automatic volume adjustment device that enables a more audible volume adjustment operation by starting volume compression at a certain output level.

The automatic volume adjustment device according to the present invention has two variable gain circuits connected in series with each other that receive an audio signal, and detects the logarithm of the signal level of a noise signal with respect to a reference level. Controls the gain of the variable gain circuit in the previous stage based on the output, detects the logarithm of the output level of the variable gain circuit in the previous stage with respect to the reference level, and controls the gain of the variable gain circuit in the subsequent stage based on the detected output. It is configured to do this.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, in which parts equivalent to those in FIG. 3 are designated by the same reference numerals. In the figure, two variable gain circuits 11 and 12 at the front stage and the rear stage are connected in series with each other.
are provided, and these variable gain circuits 11, 1
2 receives an audio signal supplied through an input terminal 5. The gain of the variable gain circuit 11 in the previous stage is controlled by the output of the amplifier 3 obtained by multiplying the logarithm value of the noise signal level with respect to the reference level by β. Further, the output level of the variable gain circuit 11 is converted into a logarithmic value with respect to a reference level by the signal detection circuit 7, and further multiplied by α by the amplifier 8. and,
The output of this amplifier 8 becomes a gain control signal for the variable gain circuit 12 at the subsequent stage.

In such a configuration, the output of the amplifier 3 is
As in the case of the conventional device shown in the figure, it is expressed as βΔN,
This becomes a gain control signal for the variable gain circuit 11 in the previous stage.
On the other hand, regarding the audio signal s, after passing through the variable gain circuit 11 in the previous stage, if s[V]=S[≠V]S, then S+βΔN[≠V] or s×10 ^BAN/20
[V]. The output level s' of the variable gain circuit 11 at the previous stage is logarithmically converted with respect to the reference level sr in the signal detection circuit 7 and output as ΔS'. This output ΔS' is expressed as ΔS'=20log(s'/sr)=20logs'-20log sr=S'-Sr. Then, this output ΔS′ is the amplifier 8
By passing through, it becomes αΔS', which becomes a gain control signal for the variable gain circuit 12 at the subsequent stage. The output of the variable gain circuit 11 at the front stage also passes through the variable gain circuit 12 at the rear stage, and these variable gain circuits 1
If the gains of 1 and 12 are Ga and Gb, then Ga=βΔN Gb=−αΔS′ =−α×20log(s×10 ^BAN/20 /sr) =−α{20log(s/sr)+20log10 ^BAN/20 } =-αΔS-αβΔN =-α(ΔS+βΔN), so the overall gain G is as follows:G=Ga+Gb=βΔN-αΔS-αβΔN=βΔN-α(ΔS+βΔN). Then, input is S[≠V] and output is So[≠
V], So=S+βΔN−α(ΔS+βΔN)=(S+βΔN)−α(S+βΔN)−αSr, resulting in the input/output characteristics as shown in FIG.

As is clear from FIG. 2, the volume compression by the audio signal does not depend on the noise ΔN and starts at a certain output level Sos rather than at the input level. Therefore, volume compression will be performed at this level regardless of noise.

Effects of the invention As explained above, according to the automatic volume adjustment device according to the invention, the compression of the output volume by the audio signal starts from a certain output level regardless of the noise, so that better volume adjustment operation can be achieved. It becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
2 is a graph showing the input/output characteristics of the variable gain section in FIG. 1, FIG. 3 is a block diagram showing a conventional example, and FIG. 4 is a graph showing the input/output characteristics of the variable gain section in FIG. 3. . Explanation of symbols of main parts, 1... Noise sensor, 2
... Noise detection circuit, 6, 11, 12 ... Variable gain circuit, 7 ... Signal detection circuit, 9 ... Power amplifier.

Claims (1)

[Scope of utility model registration request] The automatic volume adjustment device includes a variable gain circuit that receives an audio signal as input, and adjusts the volume by controlling the gain of the variable gain circuit based on the signal level of a noise signal and the signal level of the audio signal. The variable gain circuit consists of two circuits, a front stage and a rear stage, connected in series with each other, and includes a noise detection circuit that outputs a logarithmic value of the signal level of the noise signal with respect to a reference level, and an output of the front stage variable gain circuit. a signal detection circuit that outputs a logarithmic value with respect to a reference level, the gain of the preceding variable gain circuit is determined based on the output of the noise detection circuit, and the gain of the subsequent variable gain circuit is determined based on the output of the signal detection circuit. An automatic volume adjustment device characterized in that the gain of each circuit is controlled.