What is volume?
This seemingly obvious question is quite difficult to formalize, as completely different things are understood in different cases.
The meaning of loudness is more obvious when we talk about sound pressure, since it is something that is perceived directly by the ear.
Sound pressure: the pressure that additionally arises during the passage of a sound wave in a liquid and a gaseous medium. By propagating in the medium, the sound wave forms thickening and rarefaction, which create additional pressure changes relative to the mean pressure value in the medium. Therefore, the sound pressure is the variable part of the pressure, that is, pressure fluctuations with respect to the mean value, whose frequency corresponds to the frequency of the sound wave. (Great Soviet encyclopedia)
Therefore, we can evaluate any sound: loud sounds create a lot of pressure, quiet sounds little. Pressure is measured in pascals, but in acoustics, sound pressure is usually measured in decibels (dB) relative to the threshold of hearing. By definition, the threshold value is taken equal to pt = 0.00002Pa = 20μPa. The threshold of audibility is taken as 0dB and the volume calculated as l = 20 * log (p / pt), where l [dB] – volume (in the sense of sound pressure), p [Pa] – sound pressure, pt [Pa ] – hearing threshold. In this case: all audible sounds have a positive volume value; inaudible (below loudness threshold) – negative; a 6 dB volume change corresponds to twice the pressure change; 20 dB change – pressure change 10 times. Loudness in the sound pressure sense will be referred to below as absolute loudness.
Some typical loudness values:
Sound Volume Pressure
Hearing threshold 0dB 20 μPa
Whisper of foliage and wind
soft The ticking of a wristwatch
Breath 10-20 dB 60-200 μPa
Silent whisper The
wall clock ticking 20-30dB 200 – 600 μPa
Interior noise 30-40dB 0.6 – 2 MPa
Quiet conversation 40-50dB 2-6 MPa
Moderate talk 50-60dB 6 – 20 MPa
Loud talk 60-70dB 20 – 60 MPa
Noisy street 70-80dB 60-200 mPa
Truck motor ~ 80dB 200 mPa
Noise in the subway while driving
Jackhammer ~ 90dB 600 mPa
Noisy disco 100-120dB 2 – 20 Pa
Airplane taking off 120dB 20 Pa
Pain threshold 130dB 60 Pa
Pay attention to the range of perceived pressures: the pressure at the hearing threshold and that created by the aircraft differ by a factor of a million! Therefore, the logarithmic scale is much more consistent with the physiology of hearing: a linear change in sound pressure does not correspond to the sensation of a linear change in volume. For example, a change in sound pressure of 50 MPa during a conversation will be very noticeable, but completely imperceptible when the plane takes off. A change in sound pressure by 6 dB (twice) will be perceived as an approximately equal change in volume in both cases, although in the first case it will correspond to a change in pressure by 25 MPa and in the second – 10 Pa.
Another volume is the volume of the recording (the volume of the signal). This loudness is not sound pressure (it can be voltage, magnetization, etc.), however, the sound pressure is generated according to the loudness of the recording signal by the playback system. Each specific signal volume corresponds to a specific sound pressure. The volume of the signal can also be measured in decibels. However, if sound pressure is generally measured relative to the hearing threshold (minimum audible sound pressure), then the volume of a digital signal is generally measured relative to the maximum digital level taken as 0dB. Thus, the loudness of a digital signal is expressed in negative values (-3dB, -20dB) since the loudness of the recording must always be less than the maximum. The lower the volume value, the lower the signal (-20dB is lower than -3dB). If the volume of a digital signal is positive, it means overflow and, as a result, the appearance of digital distortion. (The essence of these distortions will be discussed later).
The volume controls on the amplifier, in the system settings, on the player do not create sound pressure at all. In the absence of a signal, even with the maximum volume setting, we will not hear anything (as long as the playback system itself does not create noise). Therefore, they affect loudness only indirectly and make sense to amplify the signal. (gain may mean attenuation of the signal). In the following, the term loudness will not be used to denote gain levels, with the exception of system loudness, as it is an established term. The system volume will mean both the gain level set in the operating system settings and the player, amplifier / receiver, etc.
