When confronted with the task of 'mastering' a track its essence lies in making it 'fit for purpose' i.e. sounding great on all play back systems. However, many engineers get bogged down in a quest for perceived loudness. Which to be fair on many occasions is naively directed from the desire to 'sound as loud as ...' the latest commercial release.
As a Mastering engineer two of the most important considerations working on an album are: ‘Have we improved the aesthetic of the sound overall? Have we taken away or masked anything we liked about the essence of the original session mix?’
A knowledgeable mastering engineer can develop an appropriate chain of processing in seconds from experience and, importantly, an intimate understanding of their processing tools. The latter being a key element in achieving an excellent master. To understand how to approach effective tonal balancing there are a few concepts we must first take on board.
I think it’s a misconception to say we should always use pass filters (High Pass Filter [HPF]/Low Pass Filter [LPF]) at the start of the mastering process to remove unwanted frequency. This should have already been done in the mixing process by the correct application of pass filters to each individual track. I’ll come back to how we do that later.
For those about to submit audio for mastering please read this article
To achieve a mastered sound we need good tonal balance, meaning, to make a track ‘fit for purpose’. It must sound equally weighted within itself on all playback systems. This could be a hi-fi, car stereo, i-pod, mobile phone, sound reinforcement rig and so on. This balancing is also the key element in achieving perceived loudness in a given mixes dynamic range.
I always find it interesting discussing perceived loudness and the use of limiters with my students. In the audio community generally there is a lack of awareness with regards to the effects of peak reduction and its change to the tonality and degradation of mastered material.
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.