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Volume, level, loudness, subjective loudness - are they all the same, or subtly and importantly different?

There is nothing in audio more important than how loud or how quiet a sound or signal is. So exactly how should we describe this vital feature of sound?

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I remember reading some time ago the historical reason why the volume control on a television or radio is so called. Unfortunately, although I remember reading it, I can't remember what I read. My bad. But I can refer you to a review of a performance of Handel's Messiah in The London Review in 1784...

Review of Handels Messiah

And congratulations to Mr. Atbridge for perhaps being the first drummer in history to receive a credit (I hope I spelled his name correctly!)

So 'volume' it is then, and there is something about this word that conveys the weight of sound and how a really high volume (large volume?) can pummel the whole body, where a sound that merely has a lot of loudness can feel like being poked in the ear with a sharp stick.

You may, or should I say probably, have noticed that on many devices from television sets through radios to car audio to mobile phones, the only audio control the user has is volume. Perhaps other controls are hidden away under menus, but volume is always very easily accessible.

This shows that nothing is more important than volume, and that volume must always be under the ultimate control of the listener. OK, so the listener doesn't have control in a movie theatre, but if anyone is going to complain about any aspect of the audio it will almost certainly be the volume. So let's consider this for a while...

Volume

'Volume' is not a word that is considered in sound engineering, other than 1. In a theatre or movie theatre referring to the sound volume heard by the audience, and 2. The monitoring or foldback volume in the studio. While the sound is being processed as a signal either electronically or digitally the word 'volume' is not often used. This doesn't mean you can't use it, and I wouldn't go so far as to say that it is wrong to use it, but it just isn't often used. Indeed, volume implies something with three dimensions and an audio signal only has two - amplitude and time. (Oh dear, I've just introduced yet another term, so I guess I'll have to add that to my list to consider.

I think we may conclude therefore that volume refers to the quantity of sound in an auditorium, domestic living room, or heard through headphones or earbuds, and is the experience of the listener rather than the product of the producer or engineer.

Amplitude

Amplitude, which clearly I need to cover, refers to the 'height' or 'strength' of the sound waveform - in fact any waveform and not just sound. I put these words in inverted commas because neither really defines amplitude, but both give a good feeling for what it is, particularly when amplitude is displayed as a graph, as it is in the edit screen of digital audio workstation software. Greater amplitude will lead to louder sound, although amplitude refers more to how loud the raw signal is because it will always be controlled by a fader during production and the volume control on listening.

Level

Level is certainly related to volume, but level can apply to an electronic or digital signal, as well as to actual sound in air. So in audio we talk a lot about level because control of level is vitally important all the way from the microphone, though the preamp, into the DAW, through EQ and compression plug-ins, all the way through mastering plug-ins or processors to the final audio file. Changes in level are measured in decibels and there are a variety of ways of measuring absolute level.

If we're talking Venn diagrams, then we can say that volume is a subset of level. I can't think of any way that volume is not part of level, other than in the subjective experience.

Loudness and subjective loudness

(To keep things concise, I'm going to say that loudness = subjective loudness. Loudness is an intrinsically subjective experience, but it doesn't hurt to include the word subjective to emphasise that this is so.)

If things were not interesting already, this is where they get really interesting. It's easy to measure level, but does that measurement always correspond to how loud we think a sound is? Up to the mid 1990s we would probably not have given this a second thought. More level = more loud, simple as that.

But then some clever people idiots realized that even when the level was as high as it could possibly get, it was possible to achieve a greater degree of subjective loudness.

One way to explain this is that in an audio file, the waveform can occasionally hit full level, which we call 0 dBFS, but it can't go any higher than this. It just can't, no matter how much you might want it to.

But what about the rest of the time when it is lower than 0 dBFS? If it can be increased during these periods, then the sound will be louder overall, and appear louder to the listener.

Believe it or not, until recently this was considered a good thing, apparently forgetting that the listener has a volume control and can set whatever listening volume he or she likes.

Subjective loudness is immensely important because, as I have said, nothing in audio is more important than volume, and subjective level affects the perception of volume.

One example of the importance of subjective level is how people have been annoyed by TV ads being so much louder than the programmes, presumably to gain attention. This even resulted in legislation, the CALM Act in the United States for instance.

But at the other end of the scale, if people can't hear and understand dialogue properly because its subjective level is too low, then that is an equally important issue.

So technical measurements of volume, amplitude and level are all very well, but it's how people hear things that matter.

Conclusions

While I'm not saying that anyone should use this article as their only source for their degree dissertation, there are some clear points...

  • Amplitude is technically relevant, but in sound engineering practice isn't much mentioned.
  • Level is significantly relevant all the way through the recording (or cinema or live sound) process.
  • Subjective level affects the listener, i.e. the person who is paying for all of this to happen and therefore should be considered your lord and master.
  • Every listener has a volume control (or is able to complain) and is ultimately in control of how loud they hear your work.

P.S. Actually there is one thing more important than how loud a sound or signal is, and that is the information or entertainment value it contains. It's easy to think that when every technical factor is optimized, then the audio is as good is it can be, but if the information or entertainment value is low, then the work is of little worth to anyone. The moral therefore is to provide great content, and get the technical aspects right.

By David Mellor Wednesday July 4, 2018
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