Loudness. The art of audio

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Loudness

The art of audio

Among the many controls on the front panel of modern amplifiers is a button or less often a rotary knob called "LOUDNESS" ("loudness"). The theoretical basis for the need for a circuit that implements this adjustment is the so-called equal loudness curves, which are accepted as an international standard. These dependences were obtained on the basis of a study of the characteristics of human hearing and represent a certain average dependence, since people with normal hearing aged 18 to 25 years were involved as subjects. Minor differences exist both individually and according to age, gender and racial characteristics. The essence of this dependence boils down to the fact that human hearing has an unequal sensitivity to sounds of different frequencies, which, according to objective measurements, have the same sound pressure.

The human ear can pick up the quietest sounds at frequencies of about 3 kHz, and with an increase or decrease in frequency, the sensitivity decreases. And if the maximum sensitivity difference at low volume levels is more than 70 dB, then with increasing sound intensity it decreases and when the pain threshold level is reached (this is about 120 dB), the difference is only slightly more than 20 dB. (Curves of equal loudness). So what does loudness control in an amplifier do? One of the main tasks of the sound engineer during recording is to establish a tonal balance at a certain average listening volume level, which usually corresponds to a standard sound pressure level of 90-92 dB. In other words, the sound engineer modifies the frequency response in some way so that playback at a specified volume is perceived by the listener as natural. If you have a lower volume at home, and the amplifier characteristic is set to linear, then a lack of high and low frequencies will be subjectively felt.

It is to eliminate this shortcoming that the loudness compensation circuit is intended. In very ancient times, it was enough to regulate only low frequencies. This is how the low-frequency tone control appeared. Subsequently, with the expansion of the frequency range, a regulator for high frequencies was also added. However, the characteristics of standard tone control circuits do not quite meet the requirements for correcting the characteristics in terms of loudness and therefore another one was required specifically for carrying. Looking at the equal loudness curves, one would assume that the required boost at low and high could be up to 15-20 dB. But if we take into account what has been said about setting the tonal balance by the sound engineer, then we need to talk only about the difference in the frequency response, and in this case the rise should already be much less: 3-5 dB. In fact, if listening at home would always be carried out at the level for which the sound engineer did his job, then the need for loudness would disappear.

Some companies are guided by this and do not provide for any loudness compensation in their amplifiers. And in the direct path mode, which involves achieving minimal differences from the original intent of the sound engineer, in all amplifiers, as a rule, not only the tone and balance controls are turned off, but also loudness. But here there are problems with the unequal output signal level of various devices. For example, when listening to a CD player, you set the required level on the amplifier, and later, when playing a phonogram from a tape recorder, you have to set a different level.

Under such conditions, two options can be proposed. Or have two level controls, linear and thinly compensated, or the ability to adjust the sensitivity for each input. Some may remember that at the time when Hi-Fi equipment came to our country through the Beryozka store, the amplifier of the well-known West German company Uher was popular. The distinguishing feature of this unit was the small sensitivity knobs for each input, which were located right on the bottom edge of the front panel, which made it possible to always have a signal with the same level from all sources. In some modern expensive devices, such level matching can be carried out even from the remote control, as we observed, for example, in TEAC A-V3000P or Yamaha DSP-A3090. And in the case of a more affordable price category, you need to make sure that the individual components have, in addition to a fixed, also an adjustable output.

Fixed loudness, which is turned on by a button, is designed for a certain position of the volume control. If the regulator has a scale, then -30 dB mark corresponds to this position. Sometimes this limitation creates insurmountable difficulties, and the tone compensation has to be turned off, and a compromise solution is tried to be found using simple tone controls. Smooth, independent loudness control, found in Denon, Yamaha, and some third-party amps, allows you to not only always set the desired volume, but also get natural tonal coloring of music over a wide range of volume levels. Therefore, the presence or absence of loudness must always, of course, taking into account the operating conditions, be taken into account when choosing an amplifier.

Author: Alexey Grudinin

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