Sound signals are recorded in music according to the level accepted by the standard - from 90 to 92 decibels, and if the sound pressure is different when listening, you need to start the process of changing the frequency characteristics in order to adjust this sound loudness. What it is will be described in this article.
Frequency and pressure
The human ear is tuned to sounds of different frequencies having the same sound pressure, which are perceived (of course, subjectively) by sounds of different volumes. Hearing best perceives a frequency of about three kilohertz, and this sensitivity decreases if the frequencies become more than three or less than three kilohertz, when the sound pressure drops. This effect can be compensated, and any connoisseur of sound amplifying equipment knows that this is loudness.
At a sound pressure level of 90-92 decibels, the desired tonal balance is set when recording music. Further, even when listening in any other conditions, with less pressure, the ear will feel a lack of frequencies - high and low, and therefore loudness will be needed. That this, of course, is a subjective sensation, everyone knows, but the body still needs to eliminate this drawback. And this effect is compensated by changing the frequency characteristics, as a rule, according to equal volume curves (Fletcher-Manson). And this is exactly how loudness should be implemented, so that it would pacify the auditory sensations, and the listening was comfortable.
Execution
High-class sound amplification equipment has a regulator with loudness compensation, that is, it can be implemented quite simply. The regulator changes the volume level and simultaneously affects the amplitude and frequency characteristics of the amplifier path according to the Fletcher-Manson curves. At the request of the user, you can both turn loudness on and off, for which a special button is provided. The simplest sound amplifying devices allow you to adjust the loudness with an equalizer, a timbral block, or even manually, changing the amplitude-frequency characteristic of the sound path.
You can use the volume control with loudness. Many audio enthusiasts do just that, listening to a variety of myths, legends and misconceptions. The main goal is to set the high and low frequencies to the maximum in order to achieve the sound you like, even if it is completely different on the medium, even if it is a brand. These people know how to enable loudness and what it is for. It’s good that the equalizer lends itself to settings, and you can bring the sound to a state that will bring comfort to the sound sensations.
Loudness
This is the function of loudness compensation on sound amplifying equipment. What kind of function is it and what is it intended for, many music lovers answer the same way: for the brightness of the sound (some even openly define this brightness as a sound similar to the letter V, that is, with high extreme frequencies - high and low). But this is not at all true. High fidelity - High Fidelity, or just Hi-Fi - is just the sound close to the original, which meets one of certain standards.
There is even a special science called psychoacoustics, which studies the perception of sound by human hearing. The processes that occur in the brain from exposure to sound waves on it are very complex. But he does not need loudness adjustment at all. Initially, the human ear was not intended to listen to music, it was necessary for survival, to communicate with oneself and was not equipped at all with the functions of a spectrum analyzer for measuring loudness parameters. Best of all, a person perceives the mid-frequency range, and all the sensations of changes in pitch due to its intensity (volume) exist only in his head. And even such changes are called phantom frequencies, and they are formed only in certain conditions.
Curve Graph
This effect is best demonstrated using a graph of curves at equal volume, which is present among the illustrations for this article, and how it works will be described right now. The curves shown on the graph characterize how we perceive the same sound volume at different frequencies. The lower the volume (sound intensity), the more the lines “curve”.
It was precisely to correct their curvature that loudness was invented, that is, in order to adjust the volume to those values that we perceive as smooth sound. If you listen to music at low volume, unevenness becomes most critical to perception. And if the signal volume becomes higher, the ear begins to perceive different frequencies linearly, and in this case any meaning of such correction is lost.
Yamaha
One of the most competent implementations found in Yamaha amplifiers. However, the owners of this equipment not only do not always know why to turn on loudness. How to turn it on, they sometimes do not know either. A little has already been said about the destination. Now about where the loudness is located in the Yamaha amplifier. It is made not as a separate button, but as an adjustment knob, with the rotation of which the depth of correction changes along with the volume, which is relative to the previously selected main knob. This correction exactly matches the curves on the graph.
The sound becomes quieter than previously selected and “curves” on the graph, however, it is perceived much more evenly by ear. It turns out that at high volumes any correction is absent, but at low it is maximum. Only here the average consumer with an ill-educated hearing needs something completely different. He is used to listening only to a “crooked” sound, and therefore he needs a button for constant correction. The saddest thing is that the customer is always right, and many manufacturers indulge their consumers. The result is deplorable - most of the equipment "at zero" does not sound.
"Natural" sound
Among professional musicians with absolute hearing, there are many opponents of such an “improvement" in sound. The equipment is good only when it sounds clean "at zero", that is, without adjustments. A question will surely arise regarding the perception of sound by ordinary hearing, which hears it differently from what it is. Most of these people, and is it not fair to resort to correction? Fair, but only if the volume is low. On the big one, no correction is needed.
Man is also forced to perceive the sound of natural instruments with distortion, and you can only compare the sound of audio systems with them. Sound fidelity can only be assessed by a well-trained ear. And it is necessary to clarify that the studio equipment does not have loudness. This is by and large a snag. Hearing sensitivity is different to different frequencies, and this dependence varies with changes in sound pressure.
Volume control
If the volume level is small, and the amplification equipment does not have a high class, you can not expect high-quality sound reproduction. High-quality amplifiers have a variety of schemes to compensate for the frequency response (amplitude-frequency characteristic), when low and high frequencies are amplified at a low volume, equalizing sound quality. The volume control with loudness helps a lot here. The schemes for performing such a regulator are quite simple, they do not require scarce parts, even some adjustment is not needed.
Here problems may arise of a different plan. Even an ideally designed controller with loudness will match the compensation curves and the curves of equal sound intensity at a precisely defined coefficient of transmission of the signal path - from its source to the final output. The volume level of the timbre balance is achieved at the same knob position with loudness for any source. The tonal balance is violated along with the deviation of this coefficient from the calculated one.
Loudness Resistor
Most of these resistor circuits are built on the basis of variable resistances (resistance is a resistor), for which additional taps were provided. Their disadvantage is that only special variable resistors with loudness of small depth are used.
They also have a certain non-linearity and gradation when reproducing the upper and even lower frequencies. However, these schemes are used quite often both in the manufacture of new equipment, and for the refinement of ready-made amplifiers, receivers and radio tape recorders.
For confident work
If a normal volume control is used in the device, that is, a normal variable resistor, it is necessary to work separately with loudness. A special circuit is included instead of it, if this resistance was not included in the circuit of amplification feedback nodes.
However, this necessarily takes into account the output resistance to the volume control in the previous stage, it should be much less than the resistance of the resistor. The input resistance of the next stage is also taken into account, which must be greater than the resistance of the resistor. And the greater the difference in resistances, the better the coordination of loads, which is why the equipment as a whole works more confidently.
For guitarists
Many guitarists notice a proportional loss in the sound of high frequencies when the volume of their instrument is reduced. This effect is especially noticeable when singles are on the guitar. In fact, this, experts say, is not a problem at all. Just in this way you get a less overloaded and darker sound, quite suitable for a rhythm part. For solos, the volume increases, the sound cuts better in the mix and generally becomes brighter. You just need to listen to your tool and leave the circuit as is, without any changes.
The reasons for the loss of high frequencies can be very many. Cables and all electronics work together as a filter, as a loudness resistor. This is especially evident at low frequencies, since the low-pass filter only works up to the threshold, having crossed which, it cuts off all frequencies altogether. Therefore, the maximum volume takes the blocked frequencies out of the audible range, and if you rotate the potentiometer (i.e. lower the volume), the resistance of the circuit rises, shifting the cutoff frequency of the low-pass filter to the range that we hear.
Troubleshooting
Cables should be high quality, low capacitance, which much less affect the disappearance of high frequencies. Of course, there are some inconveniences here. Firstly, such a cable is expensive, and secondly, it is tough and heavy. A long cable has a larger capacity than a short one. The inconvenience here is that movement around the stage will be limited.
You can compensate for the loss in the high frequencies, if you solder the capacitor to the input and output to the ungrounded legs of the resistor, then there will be a filter in the circuit that adds the output signal to more high frequencies. The capacitance of the capacitor sets the frequency that passes the signal above the threshold. And the larger the capacity, the lower the frequency threshold.
Loudness in the computer
Personal computers, mobile devices, media players, and other similar equipment, and the same under Linux or Windows, control the volume controls linearly. You can twist the slider almost to the very bottom and not change the volume, but then each pixel changes it noticeably. But it should be regulated in decibels. There is practically no loudness anywhere. Everything is done only by adjusting the sound. Frequency response is always adjusted depending on the sound card.
An API provides an interface, but specific functions may not be available. Somewhere there is a good graphic equalizer, somewhere at least the sliders - to tighten the tones of low and high frequencies, but somewhere there is nothing at all available. And even where there is, concrete advice can neither be received nor given: each operating system dictates its own. The "seven" - like that, the "dozens" - that way, and Linux is generally a special article.