You are always able to tell if sounds are soft or loud, but how much do you know of this phenomenon? The subject of loudness is often discussed even among people who are not audio professionals. As an aspiring audio engineer or producer, you need to understand this scientific concept. Hence, the big question for today is – What is Loudness of a Sound?
Just like other articles on this site, we will cover various relevant topics that surround the main subject of the day, which is the loudness of sound. You will learn more about the misconceptions of loudness, its relation to human perception, and also find out about the negative implications of loudness. So, without wasting precious time, let’s dive right in!
The Loudness Definition
The psychological characteristic of sound that is fundamentally a correlation of its physical strength (amplitude), is known as loudness. A more formal definition of loudness would be “that attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud”.
The measurement of loudness is a subjective one, and totally different from other objective measures of sound strength such as sound pressure, sound pressure level (in decibels), sound intensity and sound power. In an attempt to find out how the typical human perceives loudness, and how this corresponds to sound measurements, filters such as “A-weighting” is used.
However, the psychological interpretation of loudness is a process that is way more complex than what is suggested by “A-weighting”. Loudness is also affected by other scientific factors such as frequency, bandwidth and duration. Hence, a much more thorough analysis is needed in order to understand the perception of loudness by humans.
The topics that we will be looking into today are:
- Loudness concepts
- Hearing loss
- Loudness compensation
Factors such as duration of a sound, frequency content and sound pressure level (SPL), all affect the perception of loudness. For instance, a sound with a constant SPL will appear as if it is increasing in loudness, as samples of duration 20, 50, 100, 200 ms are heard progressively. The perception of loudness will only stabilize when the sample duration reaches about 1 sec.
The phenomenon described above is a result of the human auditory system’s characteristic, which averages the effects of SPL over a 600–1000 ms interval. For any sounds that are longer that 1 sec, the perception of loudness for every moment will be related to the average loudness during the preceding 600–1000 ms.
An equal-loudness graph will show you how the sensitivity of the human ear changes, in relation to different frequencies. Each line on the graph represents the sound pressure level (SPL measured in dB) required for frequencies to be perceived as equally loud. The other variations of curves performs the same function, but at different SPLs.
If you study the graph carefully, it actually shows that humans with normal hearing are most sensitive to frequencies around 2–4 kHz. The sensitivity starts to decline at anything above or below this frequency range. A complete model of the perception of loudness will include the integration of SPL by frequency.
The perception of loudness will not be the same for people suffering from sensorineural hearing loss (damage to the cochlea or in the brain). Low SPL sounds (typically perceived as relatively quiet by people with normal hearing) will not be audible to the hearing impaired, but high SPL sounds will often be perceived to be as loud as how an unimpaired person would hear it.
There are two theories that can explain this hearing loss phenomenon. The first is that loudness grows much more quickly for these listeners, as compared to healthy listeners with changes in level. This is known as the “loudness recruitment” theory and has been largely accepted as the classical explanation.
The second theory is that some people with hearing loss may just have a normal rate of loudness growth, but exhibits elevated loudness at their threshold. This means that the softest sound audible to the hearing impaired will be louder than the softest sound heard by normal listeners. This theory is known as “softness imperception”, a term given by Mary Florentine.
You might be able to find Hi-Fi sound systems in the market, that allows compensation for loudness. The “loudness” control on these sound systems attenuates the frequency response curve, in order to roughly correspond with the equal-loudness characteristic of human hearing.
The purpose of the loudness compensation function is to make the recorded music sound more natural. When music is being played at lower volumes, the ears will become less sensitive to lower frequencies. Hence, the compensation parameter resolves this problem by boosting the lower frequencies.
That is all I have for you people today. I hope you guys now have a better understanding of loudness and its surrounding concepts!
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