JPS6336683B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a loudness correction circuit that performs correction according to the loudness characteristics of an amplifier whose amplification degree is made variable based on the amount of change in the amplification degree and the sound pressure level of an input signal. When playing back musical sound signals through various transmission media (records, tape recordings), it is well known that when listening to a signal (original sound) that was collected at a high volume during recording at a low volume, a lack of bass can be felt. ing. This is because the loudness characteristics, which indicate the equal sensitivity characteristics of sound loudness, are different when listening to the original sound and when listening at a low volume. The difference in loudness characteristics caused by attenuating the sound pressure level with respect to the original sound during listening is particularly noticeable at low frequencies, and the difference is due to the difference between the sound pressure level during listening and the sound pressure level of the original sound. It depends and changes. For this reason, various loudness correction circuits have been proposed in the past, but since the correction characteristics are fixed uniformly depending on the amount of attenuation, it is not always possible to perform the optimal correction for each level of the input signal. I couldn't say yes. Therefore, attempts have recently been made to determine the correction characteristics by considering the level of the input signal as well as the amount of attenuation. In other words, in Figure 1, SSSTevens is “PerceivedLevel of
Noise by Mark Vlland Decibels(E)”, J.
Acoust.Soc.Am., vol.575−601 (1972). This is a part of the low frequency characteristics of the isosensitive characteristics announced in . In the figure, P100, P80 and P60 are 100dB, 80dB and 60dB indicated by solid lines A, B and C, respectively.
The value at 40Hz of the isosensitive characteristic of
They are 115.8dB, 97.9dB and 83.9dB. If you are currently listening by amplifying the input signal using an amplifier with variable amplification and driving the speaker, setting the amplification to the specified amplification will reduce the sound pressure level from the speaker, that is, the input signal. The sound pressure level shall be equal to the sound pressure level of the original sound. in this state
If you listen to a sound that has an 80 dB equal-sensitivity characteristic B with a 20 dB level attenuation, it will shift in parallel as shown by the dotted line C', and the 40 Hz sound will become 77.9 dB. However, since the value at 40Hz in the original isosensitive characteristic C at 60dB, which has been attenuated by 20dB, is 83.9dB, simply moving the 80dB isosensitive characteristic by 20dB in parallel as described above will over-attenuate it by 6.0dB. . Therefore, if you make a large correction by this 6.0dB, the difference in hearing will disappear,
This allows for balanced playback.
Conversely, if you listen to an 80 dB sound (97.9 dB) with 20 dB louder, it will similarly shift in parallel and become 117.9 dB at 40 Hz.
The value for 40Hz of the equal sensitivity characteristic of 100dB
This results in a difference of 2.1dB compared to 115.8dB. Therefore 40
At Hz, if you correct it by 2.1dB, the difference in hearing will disappear.

[Table] If this relationship is displayed, it will look like Table 1. Table 1 is necessary when listening with attenuation of 5 dB, 10 dB, and 15 dB for various values of the sound pressure level of the original sound, that is, the sound pressure level of the input signal obtained by reproducing the input signal with a specified amplification degree. This shows the amount of correction for each frequency. From the 5 dB attenuation term in Table 1, the sound pressure level of the input signal is 85 dB or higher at a frequency of 20 Hz.
If a sound of 80 dB is attenuated by 5 dB, each will be 1.6 dB.
Or it can be seen that a correction of 1.8dB is required. Furthermore, from this, the sound pressure level of the input signal is 85 dB.
It can be seen that when attenuating by 10 dR, a correction of 3.4 dB, which is the sum of the above-mentioned 1.6 dB and 1.8 dB, is required. In this way, from the table when the attenuation amount is 5 dB, the attenuation amount is
Although it is possible to calculate the correction amount for attenuation amounts of 10 dB, 15 dB, or more, the above table also shows the correction amounts for attenuation amounts of 10 dB and 15 dB for reference. However, there is a drawback in that an extremely complicated control circuit is required to perform such correction. The present invention determines the amount of loudness correction as described above using a simple circuit based on both the attenuation amount and the sound pressure level of the input signal, and will be described in detail below with reference to embodiments. FIG. 2 shows an embodiment of the present invention. In the figure, the input terminal 1 of the left channel is connected to an adder 5, and also to a correction circuit 21 and an adder 11 via a variable attenuator 3. The input terminal 2 of the right channel is connected to an adder 5 and also to a correction circuit 24 and an adder 11 via a variable attenuator 4. The outputs of the correction circuits 21 and 24 are amplified by amplifiers 22 and 25 and connected to left and right speakers 23 and 26. Adder 5
and 11 are applied to detectors 7 and 13 via filters 6 and 12, respectively, and their detection outputs are connected to comparators 8 and 14, respectively. Comparators 8 and 14 include differential amplifiers 8-1 to 8-9 and 14-1 to 14-8 whose non-inverting input terminals are commonly connected to a signal terminal, and reference power supply terminals 8-21 and 14-21, respectively. Series resistors 8-11 to 8-19 and 14- for voltage division connected to
11 to 14 to 18, and the connection points between the reference power supply terminal and each series resistor are connected sequentially to the inverting input terminal of each differential amplifier, respectively, and are well known, so a detailed explanation will be omitted. Comparators 8 and 1
The reference power supply terminal 4 has a reference power supply 29 and a resistor 30.
The output terminals of the detectors 7 are connected to each other via the respective detectors. The outputs of the differential amplifiers 8-1 to 8-7 are outputted to the AND circuits 9-1 to 9-7 of the AND circuit group 9, respectively.
is connected to one input terminal of the differential amplifier 8-8.
and 8-9 are connected to adding resistors 10-8 and 10-9 of adder 10, respectively. The output of each AND circuit 9-1 to 9-7 is sent to an adder 10
are added to the addition resistors 10-1 to 10-7. The outputs of the differential amplifiers 14-1 to 14-8 are applied to the adding resistors 15-1 to 15-8 of the adder 15, and each adding resistor is commonly connected to the inverting input terminal of the differential amplifier 15-12 of the adder 15. It is also connected to a negative power supply 15-11 via a resistor 15-9. The non-inverting input terminal of the differential amplifier 15-12 is grounded, and the output is negatively fed back to the inverting input terminal via the resistor 15-10. Differential amplifier 14-1~1
The outputs of 4-7 are connected to inverters 16-7 to 1, respectively.
6-1 to the other input terminals of AND circuits 9-7 to 9-1. The outputs of the adders 10 and 15 are added to the adding resistors 19 and 20 of the adder 18, and are added as a control output signal 17, which is applied to the control terminals of the correction circuits 21 and 24. The operation of the above configuration will be explained. The input signal added by the adder 5 is band-limited by a bandpass filter having a center frequency of 1 KHz and a bandwidth of 1 KHz at the next stage, and then detected by a detector 7. This detection output is level-compared by a comparator 8, and converted into the total level of sound pressure obtained from the left and right speakers 23 and 26 when the attenuation degrees of the attenuators 3 and 4 are zero. When the total sound pressure exceeds 115 dB, all of the differential amplifiers 8-1 to 8-9 are turned on, and therefore one input terminal of the AND circuits 9-1 to 9-7 becomes a high level. From this state, every time the sound pressure decreases by 5 dB, the differential amplifier 8-1 is sequentially turned off, and when the sound pressure is 75 dB or less, all the differential amplifiers are turned off.
Further, as the number of AND circuits 9-1 to 9-9 that are turned on increases, the output voltage of the adder 10 gradually increases from zero to negative values, and when all of them are turned on, the output voltage becomes -2.7V. It has been adjusted. Next, the outputs of attenuators 3 and 4 are added together, band-limited, and detected in the same manner as described above, and the outputs of attenuators 3 and 4 are detected by comparator 14.
is added to the left and right input signals, and the level is compared with the left and right input signals to measure the average attenuation of attenuators 3 and 4. If the attenuation is 5 dB or less, the differential amplifiers 14-1 to 1
4-8 are all turned on. From this state, every time the degree of attenuation increases by 5 dB, the differential amplifiers 14-1 and 14-1 are sequentially turned off, and when the degree of attenuation exceeds 40 dB, all of the differential amplifiers 14-1 to 14-8 are turned off. Here, the differential amplifiers 14-1 to 14-8 are assumed to have a ground level in the off state and a positive voltage in the on state, and the adder 15 is connected to the differential amplifier 14-1.
As more and more of ~14-8 are turned on, the output voltage decreases by 0.3V from 5.7V, and when all of them are turned on, it becomes 3.6V.
5-1 to 15-10 have been adjusted. Here, if the attenuation amounts of the attenuators 3 and 4 are 35 dB or more, the differential amplifiers 14-1 to 14-7 are off. Therefore, the outputs of the inverters 16-1 to 16-7 are at a high level, so the AND circuits 9-1 to 9-
The other input terminals of 7 all go high. When the attenuation is 30dB to 35dB, the differential amplifier 14-7
is turned on, and therefore only the other input terminal of AND circuit 9-1 becomes low level. From this state, each time the attenuation decreases by 5 dB, the differential amplifier 14-
The differential amplifiers are turned on in sequence from 6 to 14-1, and all the differential amplifiers are turned on when the attenuation amount is 5 dB or less. Therefore, the AND circuit is 9-2~
The other input terminals become low level one after another in the order of 9-7. In this way, the level of the other input terminal of AND circuits 9-1 to 9-7 is determined according to the amount of attenuation. Next, when the sound pressure level of the left and right input signals is 75 dB or less, the differential amplifiers 8-1 to 8-9 are at a low level, so the AND circuit output does not become a high level, and therefore the output of the adder 10 is zero. be. As the sound pressure level increases, the output level of the differential amplifiers 8-9 becomes higher sequentially, and at 80 to 85 dB, the output of the adder 10 increases.
The output will be −0.6V. Here, for example, if the attenuation amount is 35 dB or more, the other input terminal of each AND circuit will be at a high level, so if the sound pressure level becomes 85 dB or more and further increases by 5 dB, the The output becomes high level one by one, and the output of the adder 10 is also added by -0.3V, and when the sound pressure level is 115 dB or more, it becomes -2.7V. In addition, each time the attenuation becomes 35 dB or less and further decreases by 5 dB, the other input terminals of the AND circuit 9-1 become low level, and the attenuation decreases by 5 dB.
Below 5dB, the other input terminal of all AND circuits becomes low level. Therefore, the maximum value of the output voltage of the adder 10 in the negative direction is limited depending on the amount of attenuation. The negative output of adder 10 and the positive output of adder 15 thus obtained are added by adder 18 to obtain control voltages as shown in Table 2. This control voltage is applied to the correction circuit 21 to control the frequency characteristics of the audio signal obtained from the speaker 23. To further explain Table 1 above,

【table】

Claims (1)

[Claims] 1. An amplifier with a variable amplification level, a plurality of level detection means having mutually different detection levels that detect the level of the input signal of the amplifier and generate an output, and a level detecting means that detects the level of the input signal of the amplifier and generates an output, and a level detecting means that detects the level of the input signal of the amplifier and generates an output according to the degree of decrease in the amplification level with respect to the reference amplification level. means for obtaining an output corresponding to the amplification degree, and means for turning on and off the output of the level detection means whose detection level is higher than a predetermined value among the plurality of level detection means according to the output corresponding to the amplification degree; A loudness correction circuit comprising means for obtaining a control output by adding the output of the level detection means and the output corresponding to the amplification degree, and controlling the low frequency characteristic of the amplifier by the control output.