Difference between Level, Signal Strength, Amplitude and Volume?

Question

It seems impossible to find a precise answer to this question. I researched for quite some time but different sources come up different definitions, that sometimes disagree or contradict with each other.

So far, I got the following answers:

Level refers to the loudness or intensity of a signal. It is measured in decibels (dB). Wether peak level or RMS level is used in metering in a DAW or both simultanously, is sth. I was not able to find out.

Signal Strength refers to the intensity of a signal as well. Although some sources say that it refers to the amplitude, and others say level refers to amplitude while signal strength refers to intensity. Contradiction it seems.

Amplitude is the displacement of air molecules from their resting position.

Volume is defined as either the perceived loudness of sound OR the level of a signal as it leaves the output.

Is anybody here well versed in audio terminology and can clearly define each term and highlight the differences?

Answer 1

I'm afraid there is no easy "one size fits all" answer to this. While most of these terms do have well defined scientific definitions, they are often used as "slang" where the specific meaning depends a lot on the context and the "slang" is not particularly consistent.

Level refers to the loudness or intensity of a signal. It is measured in decibels (dB). Wether peak level or RMS level is used in metering in a DAW or both simultanously, is sth. I was not able to find out.

Level is simply a measure of RELATIVE intensity, amplitude, power etc. Level is always context dependent and always requires a REFERENCE for 0 dB which needs to be stated explicitly or implicitly. For example on a meter bridge or for a DAW 0dB typically means the "clipping point". The reference can also be a certain voltage (dBV, dBu) or power (dBm). For measurements of sound pressure (dBSPL) level the common reference is a pressure of $20\mu Pa$.

Signal Strength refers to the intensity of a signal as well. Although some sources say that it refers to the amplitude, and others say level refers to amplitude while signal strength refers to intensity. Contradiction it seems.

Signal Strength isn't commonly used in audio (it's more of a Radio term). It would help if you could provide a reference.

Amplitude is the displacement of air molecules from their resting position.

The definition of Amplitude is simply the value of a signal (physical quantity or digital signal) as a function of time. If you want to describe a physical sound wave you would typically use two different signals: the particle velocity (the speed with which the air molecules move) and the pressure. The signal you describe the "particle displacement". All of these signals have different amplitudes which are related by more or less complicated physical mechanisms. For example the particle velocity is the first derivative of the displacement.

Volume is defined as either the perceived loudness of sound OR the level of a signal as it leaves the output.

The most common use of "volume" that I have encountered is a gain control with a scale on it. This maps numbers (for example from 0-100) to a physical gain that's applied to a signal to adjust it's power, loudness, clipping etc.

I should note that all of these are only loosely related to perceived loudness. Perceived loudness is a rather complicated phenomenon and depends on a lot of different factors. Perceived loudness will scale with most of the terms above but ONLY if "all other things are equal", i.e. it will only scale for the same signal in the same context.

A simple example: a sine with a frequency of 1kHz and a level of 40 dBSPL will be louder than the sine wave with a frequency of 100Hz and a level of 60 dBSPL.

Answer 2

In audio terminology, these terms are often used interchangeably. They all influence each other (I’d say the term volume is easier to differentiate because it is a subjective quantity whereas the others are well-defined).
Here is an attempt (see Hilmar’s great answer as well) at differentiating them.

1. Level: This term is generally used to describe the magnitude or intensity of a sound or an electrical signal. In audio engineering, it often refers to the power or voltage level of an audio signal, and is usually measured in decibels (dB), with respect to some reference. There are various types of levels, such as peak, RMS, and average levels.
2. Signal Strength: usually refers to the power level of an electrical signal (representing sound for example). It is a measure of the electric current or voltage induced by a signal (like audio) in a circuit, and it’s often associated with how well a signal can be perceived or processed in a given system. Higher signal strength generally means a clearer, more robust signal, which is less susceptible to noise or distortion.
3. Amplitude: in the context of audio, amplitude is a measure of the size of the vibration or oscillation of a sound wave over time. It can also refer to the maximum extent of a vibration or oscillation, measured from the position of equilibrium. In the latter case it is typically measured in terms of peak-to-peak, peak, or RMS values.
4. Volume: when it is not referring to a “gain control” (see Hilmar’s answer), Volume sometimes refers to the perceived loudness of a sound as heard by the human ear. In electronic devices, it is controlled by amplifying or attenuating the signal’s amplitude. It’s an interpretation of the amplitude by a listener and can be affected by factors like the listener’s hearing sensitivity, the acoustics of the environment, and the quality of the audio playback system among other things.

Answer 3

Many of these are borrowed from frequency/hertz theory (after all sound is just vibrations) so I can help:

Amplitude is the displacement of air molecules from their resting position.

Amplitude is simply how far from 0 is y at a given x position.

You can see them in the Wikipedia image for wave height.

Every sound produces a vibration (whether it travels through air, wood or water). The amplitude is how high is the vibration at that point.

Signal Strength refers to the intensity of a signal as well. Although some sources say that it refers to the amplitude, and others say level refers to amplitude while signal strength refers to intensity. Contradiction it seems.

Signal Strength and Amplitude are strongly related but are not the same.

Signal is the message I'm trying to convey. Let's say that I want to say "Dinner is served" and I yell it so loud that you hear it perfectly clear.

• We can then say that the Signal is strong. Because I yelled it very loud, the sound I produced will also have a high amplitude.

Now let's say that I whisper "Dinner is served".

• If you heard it fine, then Signal is still strong.
• If you couldn't hear it or you had to guess half of what I said, then we say signal is weak.

But in both cases, the amplitude is low, because I was whispering.

Now let's say I wanted to say "Dinner is served", but in the middle of it I sneeze really loud. I couldn't finish my sentence.

• We can say that Signal is weak (the message didn't get across 100%) but the amplitude is high (my sneeze was really loud, but it wasn't what I wanted to say).

Often times, if you yell (high amplitude) then the message will be received better (strong signal); thus they're related. But they're not the same.

Level refers to the loudness or intensity of a signal. It is measured in decibels (dB). Wether peak level or RMS level is used in metering in a DAW or both simultanously, is sth. I was not able to find out.

That's right. Level is scientific and it relates to power.

If I yell, I will create sound waves with high amplitude. But in order to yell, I need a lot of energy. To whisper, I don't need that much energy.

Thus, amplitude and levels are linked together. The main differences is that while Amplitude cares about the wave height at a single point, levels cares about the sum of each height at all points (i.e. the surface area).

In English, amplitude cares about eating a very, very thin slice of cake (so thin that it weights milligrams), while level cares about the whole cake (which weights multiple kg) or at least a big chunk of it.

With level, you can tell if the cake has 1, 2, 4, or 10 cherries. But for amplitude, it matters only if the very thin slice you got has got cherry traces in it.

Note: Level doesn't mean it measures a whole song. That depends on how the machine measuring it is defined, but usually around a second is analyzed.

Volume is defined as either the perceived loudness of sound OR the level of a signal as it leaves the output.

AFAIK this is correct. Volume is basically the level but perceived.

The thing about perceived volume and levels; is that volume is subjective.

A person who got lucky and got all the slices of cake with cherry in it will say it was tasty (loud), while a person who didn't get those cherries will say it wasn't as good (not as loud). Or maybe he got the cherries but can't savour them anymore (i.e. our ears become deaf to certain frequencies as we age).

In general we tend to agree about volume, thus levels and volume are often treated as synonyms.