When finalising the audio for an artist's album the primary focus of the Mastering Engineer is good tonal balance and appropriate dynamic restriction, relative to the genre of music.
With the advent of digital technology in the late 70's there has been a gradual decrease in the relative level of dynamic range in the final product for the consumer. Basically albums have become louder and louder for the simple reason that perceptively (because of the way we perceive audio) a louder product sounds better in comparison to the same audio played quieter. Fundamentally if we turn it up, it sounds like it has more bass/weight, brightness/excitement. This is just a psycho acoustic effect and has led to what audio engineers refer to as 'the loudness wars'.
Prior to this when our output formats were analogue (vinyl or magnetic tape) there was still a push for volume but from a different focus, signal to noise primarily from an engineering perspective.
Nearly all mastering houses of note use an analogue processing path, in which we are concerned with what we call the RMS (Root Mean Squared) of the audio, its weight. With the advent of digital audio this has meant we also need to focus on the peak of a signal to avoid unpleasant digital clipping. To correct this we have use digital limiting. Because this enables the engineer to 'turn up' the volume of the audio – making it perceptibly louder, it has led to the increase in audio playback levels over time or what mastering engineers describe as hyper-compression.
Again – previously in time when we had juke boxes installed for the public consumption there was no volume control. If a record sounded louder, it perceptively sounded better.
This need for volume has not been a mastering engineer led phenomenon historically but one driven by records labels and sometimes artists naivety in the perception their music will be better received if it's louder when played against another production.
In some ways this is true in an online consumer environment, where people are auditioning clips of music on i-tunes/U-tube. Also, the previous juke box style of delivery. In making a comparison, without subconsciously realising, they may buy a louder production as they think they can hear it sounds better. Hence the record company perception that louder sounds better.
The reality at home is we just turn our album to an appropriate listening level. On the radio or live any DJ would balance their tunes for equal playback level and so on. This is why perceived output volume should not be a consideration in the process of finalising the album.
Volume is a decision for playback, not delivery. Thus, bringing us back to the job of the mastering engineer; to make an album sound balanced or 'fit for purpose' in any playback environments. Not just to make music sound louder.
If we actual play the audio at the same volume, what engineers call 'equal loudness', we can hear the actual difference between the compared audio. If we do this with a 'loud' album (what mastering engineers would describe as 'hyper-compressed' or over limited) and the original session mixes often we can hear unpleasant distortion, dulling of the transients and the audio can sound tiring because of the lack of dynamic range. This means we have not done our job as a mastering engineer – make the audio sound better!!!
This is not obviously a good outcome for the audio but unfortunately the purpose of dynamic range in music has become blurred by commercial pressures. Some would say, why not have an 'industry standard' dynamic range to avoid this, but, music is art. Should we be really forcing a standard upon it? As what is appropriate - surely this depends on the 'art', the music itself!
This is why dynamic range is important for music. Each album has an ideal dynamic range relative to it genre/style. There is no standard. We should deliver an album at its optimum sound level dynamically, leaving the listener to decide on the playback level.
This is what we should all be interested in, hearing music at it best!