In this module we’ll talk all about loudness and level and all the different ways that
music and audio is perceived and measured. But before we address any of that, we need
to talk about the obscure and often overloaded terminology used in acoustics to represent
the general concept of how loud a sound is. So I’ve listed the following terms here:
Loudness, level, volume, amplitude, gain and drive.
Is there a difference between them? Yes. Are they interchangeable? No. Is the difference
between them important for a regular person to understand? Probably not. Is the difference
between them important for an audio engineer or programmer to understand? Absolutely yes!
The question, how loud is a sound is not an easy question to answer as we’ll soon find
out. but language used to represent this concept can be contained and simplified so that the
discussion becomes easier.
These acoustical terms can be broadly categorized as either objectively measurable or subjectively
perceptible. What does that mean? Objectively measuring something means that you are quantifying
the result as a mathematical formula or a number, and you can repeat the measurements
under the same conditions any number of times, and you should end up getting the same result
every time. Subjective perception is a lot more hairy, it’s how an individual can perceive
something, and it’s more a qualitative measure than something that can be quantified into
a number. You might have heard of these terms in the context of music, that a sound is either
boomy or punchy, muddy or warm, airy or harsh, bright or dark, loud or quiet. What might
appear loud to you, might not for another person. Sure, a certain trend in measurement
can result in a subjective perception to appear. For example, boosting frequencies at around
100Hz to 400Hz could mean a warm sounding track, but if it’s overdone, this range
of frequencies can cause the track to sound muddy. But who’s to judge if a track is
muddy or not? You are, you are the subject who decides adding 3db of gain on a band filter
at 200Hz is muddy or not. When another person is subjected to the same set of objective
parameters applied, he might find it completely different.
Loudness and volume are subjective attributes of audio. Loudness can be thought of as an
auditory sensation where sounds can be ordered on a scale from quiet to loud. It doesn’t
just depend on physical factors such as intensity of pressure waves reaching your ear, but it
also depends on physiological factors like how your ears are designed and the natural
resonance produced within the boundary of the ear. Even physiological factors like how
your brain colors the perception of loudness for different frequencies matter as well.
Volume is quite similar to loudness, but the term is usually used contextually with the
final loudness you can achieve from an amplifier, be it analog or digital. You would’ve come
across volume controls on your radios or speakers or guitar amplifiers, with values ranging
from 0 to 10. You might ask, if you can associate volume with a number, does that not mean it’s
an objective measure? But what does a volume setting of 4 mean when comparing a tiny desk
speaker to a 100W guitar amplifier? It doesn’t translate to the same loudness, it’s just
a convenience measure for consumers.
Gain is an objective measurement, and used in the context of electronics as a measure
of the ability of an amplifier circuit to increase or decrease the electrical power
of the input signal. Gain is the ratio between the electrical power of the signal at the
output stage to the power of the signal at the input stage. If the electrical power of
the output signal is higher after amplification, then the gain is positive and if it is lower,
then the gain is negative. You might have come across gain controls on amplifiers or
audio interfaces. If we look at a guitar amp for example, you have both a gain knob and
a volume knob. Increasing either knobs would increase the loudness of the signal, but what
happens underneath the hood is that a guitar amplifier is made up of a preamplifier stage,
which boosts the weak signal from the input line in, and a power amplifier stage which
drives a loudspeaker. The gain knob is used to control the gain parameter of the preamplifier
stage, and the volume knob is used to control the gain parameter of the power amplifier
stage. As you can imagine, whatever comes out of the preamplifier stage is then blindly
amplified by the power amplifier and the power amplifier determines the final loudness of
the signal. There may be cases where you can increase the gain of the preamplifier to the
point where the signal starts clipping and starts distorting. The preamplifier stage
can be overdriven to produce a warm subtle distortion or harsh and fuzzy distortion,
both of which can be used artistically. The power amplifier is just used to boost up the
loudness of the signal from the output of the pre-amplifier stage, whatever the state
of the signal might be in. Drive is a term that can be used as a synonym for gain in
the context of amplifiers. They’re both the same.
Amplitude and level can be interchangeably used. Amplitude refers to the instantaneous
value of a signal over time. I’ve covered this in considerable detail in the video about
the Properties of sinusoids which you can checkout, if you haven’t already. But in
this module, we’ll talk generally about a few different ways amplitude or level of
a signal can be measured, and its implication with respect to the loudness of the sound
produced. Amplitude as a term is pretty broad and can be used in several different contexts.
It can be used for measuring the strength of pressure waves in the physical world. And
when these pressure waves are captured by a microphone and converted into electrical
signals, we can measure the amplitude of the voltage or current passed through electrical
cables. Even when the signal is converted into the digital domain, we can measure the
amplitude of the sample values of the digitized signal. We can measure the peak value, the
peak to peak values, or the root mean squared or the average magnitude value of the signal,
and is measured on the decibel scale. Generally, as the level of the signal increases, it’s
perceived loudness increases as well. But it’s not necessarily true that 2 different
signals with the same amplitude can be perceived as having the same loudness, as we’ll find
out in the next video.
Alright, that covers all the terms used in the video title. I hear you asking, enough
definitions, can you put them in a single sentence? I can indeed. As I turned the volume
knob down, I reduced the gain of the amplifier reducing the amplitude or level of the signal,
which resulted in the loudness of the sound being lower. If you’re new to this, there’s
no doubt that it’s confusing as hell, with some terms being redundant and ambiguous at
times. It takes a while to use the right terms in the right context. But as you understand
it better, you’ll understand that they are fundamentally different concepts with their
own areas of study. We’ll take a stab at 2 of areas, loudness and levels.
In the next video we’ll get through the perception of loudness, how our sense of loudness
is different for different frequencies and all the nuances associated with hearing. After
that we’ll look at level, and the technical ways of measuring and calculating the amplitude
of signals. And finally we’ll look at a new way of measuring loudness that’s all
the rage at the moment, the Loudness unit. It has redefined the standard used in streaming
and broadcast, and promises to bring an end to the age of super compressed audio and the
so-called loudness war.