This is an important question.
Is it the absolutely faithful reproduction of the initial audio, with no degradation or distortion? That is certainly interesting and important, although it is effectively unrealistic as an engineering exercise as there is as yet no perfect technology capable of achieving that, and any attempt to copy and reproduce a real world phenomenon is unlikely to be able to capture every detail of that phenomenon without some loss.
In any case, as Hi-Fi is essentially a domestic entertainment technology, it will be used in environments that are acoustically very different from the location where the music was performed or “constructed”. So even if the chain from storage of the encoded acoustic material is absolutely faithful, the moment the system produces a sound, the acoustics of the listening environment will alter that sound and give the listener a completely different experience.
This perhaps suggests an alternative aim. Perhaps the task of the system is to not only capture and deliver the music as it was performed, but also to reproduce it as if it were being experienced in the venue where it was being performed. That is certainly an interesting challenge, because not only should the music itself be captured, but also the acoustic signature of the performance venue. For the listener, the acoustics of the listening space will need to be overridden and replaced with those of the performance venue so that the experience for the user is of music being performed in a different place.
Whilst these goals are functionally laudable, and represent interesting and rewarding engineering challenges, I feel that this misses something of the essence of what music is. If music is form of artistic expression, a form of story telling produced by an artist, a storyteller, perhaps the goal is to experience as much as possible of the story that the artist is telling.
Let me illustrate this with a simple concrete example. In the song Someone saved my life tonight, sung by Elton John on the album Captain Fantastic and the Brown Dirt Cowboy there seems to be an anger, a crying out with emotion. This is evident, for example in the way that the voice and instruments work together in the lines it’s 4 o’clock in the morning, damm it, listen to me good … But when the song is played on a system that is able to convey the full spectrum of instruments and sounds, the bass notes being played on the piano add a level of ominous foreboding that can be felt as well as heard. It is simply missing when listened to on small speakers or on systems that have limited ability to convey and produce lower frequencies. The artist added that detail, and the song is a different song when when that it is missing, so it seems a different version of the story is being told. I can’t claim to know what the artist meant by constructing and singing the song in the way he did, but when the song is reproduced using a chain of technologies, elements can be removed or become unbalanced, changing how the song is presented and seemingly changing how it is received and understood. It is no longer the whole story as told by the artists.
So I would propose that the goal for user experience engineering of hi-fi music systems is preserving the story as told by the artists, and faithfully reproducing it so as much of the story as told by the artist is reproduced. It is a window into the story as told by the artist. We cant be transported to the story as lived by the artist, but we can be given a window through which we can hear the story.
The outcome is not simply therefore an engineering solution where the success can be measured by how close we can get to a set of measurable attributes. It is a solution that yields a human response through a human experience. If the technologies impede or dilute any aspect of the music as performed they risk reducing the human experience of the music, of hearing the whole story as presented by the artist. Where technical solutions involve compromises, those compromises can be understood and evaluated in terms of the impact they will have on the user’s ability to have a full experience.
To help explore whether Hi-Fi technologies enables this or intrudes in such a way as to evidently add artefacts or compromises to the channel between the artist and the listener, I have assembled a list of pieces of music that have an attribute that is remarkable or vulnerable to being lost by poor technologies.