JPS6336684B2 - - 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 musical sound signals through various transmission media (records, tape recordings), when listening at a volume lower than the original sound volume at the time of recording, there is a feeling of insufficient bass, and when listening at a high volume, there is an overabundance of bass. It is well known that it feels like This is because the loudness characteristics, which indicate the equal sensitivity characteristics of sound loudness, differ depending on the sound pressure level, so the frequency characteristics can be heard differently when listening to the original sound and when listening at a volume lower or louder than the original sound. The difference in loudness characteristics caused by attenuating or increasing the sound pressure level relative to the original sound during listening is particularly noticeable at low frequencies, and the difference is the difference between the sound pressure level during listening and the sound of the original sound. It changes depending on the difference in pressure level, and at the same time changes depending on the sound pressure level when listening. On the other hand, various loudness correction circuits have been proposed in the past, but since these uniformly determine the correction characteristics according to the amount of attenuation of the volume adjustment volume of the playback device, they cannot be used for input signals that vary in various ways. It could not be said that optimal correction was performed for each level. 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, Figure 1 shows SS Stevens' “Perceived Level of
Noise by Mark Vlland Decibels(E)”, J.
Acoust.Soc., 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 the values at 40Hz of the 100dB, 80dB and 60dB isosensitive characteristics shown by solid lines A, B and C, respectively.
They are 115.8dB, 97.9dB and 83.9dB. Now, if we consider the case where an input signal is amplified by an amplifier with variable amplification level and the speaker is driven for listening, if the amplification level is set to the specified amplification level, the sound pressure level from the speaker will be In other words, the sound pressure level of the input signal is assumed to be equal to the sound pressure level of the original sound. For example, if you listen to a sound at a level above the 80 dB equal-sensory characteristic B and attenuate the level by 20 dB in such a state, the 40 Hz sound will shift in parallel as shown by the dotted line C'.
It becomes 77.9dB. However, the value at 40Hz at 60dB, which is attenuated by 20dB, is 83.9dB.
Therefore, as mentioned above, simply calculate the equal sensitivity characteristic of 80dB.
A parallel shift of only 20 dB would result in over-attenuation by 6.0 dB. Therefore, at 40Hz, this
By making a large correction of 6.0 dB, the difference in hearing disappears, and balanced playback becomes possible. Conversely, if you listen to the 80dB sound louder (97.9dB), it will similarly shift in parallel and at 40Hz.
This results in a difference of 2.1 dB from the value of 115.8 dB for 40 Hz of the 100 dB isosensitive characteristic. Therefore, at 40Hz, if the signal is corrected by 2.1dB, the difference in hearing will disappear. 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 section in Table 1, if the sound pressure level of the input signal is 85 dB or 80 dB at a frequency of 20 Hz and is attenuated by 5 dB, respectively.
It can be seen that a correction of 1.6dB or 1.8dB is required.

[Table] From this, the sound pressure level of the input signal is 85 dB.
If the sound is attenuated by 10dB, it will be 1.6dB as mentioned above.
It can be seen that a correction of 3.4dB, which is an addition of 1.8dB, is required. In this way, it is possible to calculate the amount of correction for attenuation of 10 dB, 15 dB, or more from the table for attenuation of 5 dB, but for reference, the amount of correction for attenuation of 10 dB and 15 dB is also calculated. Shown in the table above. Therefore, it is sufficient to perform corrections as shown in Table 1, but such corrections have the drawback of requiring an extremely complicated control circuit.
The present invention has been made to improve such drawbacks, and it determines the amount of loudness correction as described above based on both the amount of attenuation and the sound pressure level of the input signal using a simple circuit. This will be explained in detail according to examples. 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 are differential amplifiers 8-1 to 8- whose non-inverting input terminals are commonly connected to comparison signal input terminals 8-20 and 14-20, respectively.
9 and 14-1 to 14-7, and the reference power terminal 8-
Series resistors 8-11 to 8-19 and 14-11 to 14-1 for voltage division connected to 21 and 14-21
7, 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, and are well-known, so a detailed explanation will be omitted. The output terminals of the detector 7 are connected to the reference power terminals of the comparators 8 and 14 via a reference power source 29 and a resistor 30, respectively. The outputs of the differential amplifiers 8-1 to 8-6 are respectively connected to one input terminal of the AND circuits 9-1 to 9-6 of the AND circuit group 9, and the outputs of the differential amplifiers 8-7 to 8
-9 outputs are summing resistors 10-7 to 10-9 and 15-7 to 15-9 of adders 10 and 15, respectively.
connected to. The output of each AND circuit 9-1 to 9-6 is the addition resistor 10 of adder 10 and 15, respectively.
-1 to 10-6 and 15-1 to 15-6. Differential amplifiers 14-1 to 14-7
The output of is the addition resistor 10-10 to 10 of the adder 10.
-16, and the outputs of 14-1 to 14-6 are connected to the other input terminals of AND circuits 9-6 to 9-1 via inverters 16-6 to 16-1, respectively. Each summing resistor is a differential amplifier 10
-19 and 15-11, and the addition resistor 10 is connected to the inverting input terminal of the differential amplifier 10-19.
-17 to the negative power supply 17. The non-inverting input terminal of the differential amplifier is grounded and the output is connected to a resistor of 10
Negative feedback is provided to the inverting input terminal via -18 and 15-10. The output of the adder 10 is sent to the polarity inversion circuit 1
8, the polarity is inverted. Control voltages 19 and 20 appearing at the outputs of polarity inversion circuit 18 and adder 15 are applied to control terminals of correction circuits 21 and 24.
Here, the correction circuit 21 is the correction circuit 2 at the front stage and the rear stage.
1-1 and 21-2, and the control voltage 19
and 20 are correction circuits 21-1 and 21-, respectively.
Control 2. Similarly, the control voltages 19 and 20 control the correction circuits 24-1 and 24-2 in the preceding and subsequent stages of the correction circuit 24, respectively. The operation of the above configuration will be explained. The left and right total input signals added by the adder 5 are band-limited by the next stage bandpass filter with a center frequency of 1 KHz and a bandwidth of 1 KHz, and then detected by the detector 7. This detection output is output from comparator 8
The levels are compared and converted into the total level of sound pressure obtained from the left and right speakers 23 and 26 when the degree of attenuation of the attenuators 3 and 4 is zero. If the total sound pressure of the input signal is 115dB or more, use a differential amplifier 8-1~
8-9 are all turned on, and therefore one input terminal of AND circuits 9-1 to 9-6 becomes 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. In addition, the outputs of attenuators 3 and 4 are added, band-limited, and detected in the same manner as described above, and the outputs of attenuators 3 and 4 are detected by comparator 14.
The average attenuation of attenuators 3 and 4 is measured by comparing the level with the total left and right input signals, and if the attenuation is 5 dB or less, differential amplifier 14-
1 to 14-7 are all turned on. Also, from this state, each time the attenuation increases by 5 dB, the differential amplifier increases by 14 dB.
The differential amplifiers 14-1 to 14-7 are turned off sequentially from -1, and when the degree of attenuation is 35 dB or more, all of the differential amplifiers 14-1 to 14-7 are turned off. Here, the differential amplifiers 14-1 to 14-7
shall be at ground level in the off state and a positive voltage in the on state. Here, if the attenuation of attenuators 3 and 4 is 30 dB or more, differential amplifiers 14-1 to
14-6 is off. Therefore, the inverter 16-
Since the outputs of circuits 1 to 16-6 are at high level, the other input terminals of AND circuits 9-1 to 9-6 are all at high level. When the amount of attenuation reaches 25 dB to 30 dB, the differential amplifier 14-6 is turned on, so that only the other input terminal of the AND circuit 9-1 becomes low level.
From this state, each time the attenuation decreases by 5 dB, the differential amplifiers are turned on in the order of differential amplifiers 14-5 to 14-1, and when the attenuation is 5 dB or less, all the differential amplifiers are turned on. becomes. Therefore, the other input terminals of the AND circuit sequentially become low level in the order of 9-2 to 9-6. Like this, AND circuit 9
The level of the other input terminal -1 to 9-6 is determined according to the amount of attenuation. The adder 10 includes the differential amplifiers 14-1 to 14-
7 are all off, and as more of the differential amplifiers 8-9 to 8-7 and AND circuits 9-6 to 9-1 are turned on, the output voltage decreases by 0.3V from 5.7V until all of them are turned on. Each resistor 10-1 to 10-9 is adjusted so that the voltage becomes 3.3V when turned on. Also,
Each resistor 10-16 to 10-10 is a differential amplifier 14
The output voltage is adjusted to decrease by 0.3V as more of -7 to 14-1 are turned on. Additionally, the adder 15 is connected to the differential amplifier 14-
1 to 14-7 are all off and differential amplifiers 8-9 to 8
As more of -7 and AND circuits 9-6 to 9-1 turn on, the output voltage increases by -0.6V from -3.0V, and when all are turned on, the output voltage increases to -7.8V.
Each of the resistors 15-1 to 15-9 is adjusted so that. Therefore, the output voltage of the adder 10 is determined when the sound pressure level of the left and right input signals is, for example, 80 to 85 dB and the attenuation amount is
If it is 35dB or more, differential amplifiers 8-8 and 8-9
only turns on and becomes 5.4V. In this case, the other input terminal of each AND circuit becomes a high level, so as the sound pressure level increases by 5 dB, the output of the AND circuit 9-6 becomes a high level one after another, and the output of the adder 10 also becomes 0.3. V is added,
When the sound pressure level is 115dB or higher, it becomes 3.3V. Furthermore, 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 when the attenuation becomes 5 dB or less, the other input terminals of all AND circuits become low level. Becomes a low level. Therefore, the maximum value of the output voltage of the adder 10 is limited depending on the amount of attenuation. The positive output of the adder 10 thus obtained is turned into a negative output by the polarity inversion circuit 18, and a control voltage 19 as shown in Table 2-1 is obtained. Next, the output voltage of this adder 15 is determined when the sound pressure level of the left and right input signals is, for example, 80 to 85 dB as described above.
If the attenuation is 35dB or more, differential amplifier 8-8
And 8-9 turns on and becomes -3.6V. In this case, the other input terminal of each AND circuit has a high level, so if the sound pressure level increases by 5 dB, the

【table】

Claims (1)

[Claims] 1. An amplifier having a variable amplification means, a plurality of level detection means having mutually different detection levels that detect the level of an input signal of the amplifier and generate an output, and means for obtaining an output corresponding to the amplification degree; means for controlling on/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; means for adding the outputs of the plurality of controlled level detection means and outputs corresponding to amplification degrees to obtain first and second control outputs; and controlling low frequency characteristics of the amplifier by the first control outputs. The loudness correction circuit is characterized in that the second control output controls the ultra-low frequency characteristics of the amplifier.