Fidelity: Faithful to
What?
In November, I discussed
some of the terminology of audio and how it relates to the performance of stereo
components, but I rather glossed over one vital term that deserves special treatment.
Central to the whole field of sound reproduction is the notion of fidelity, from
the Latin word for "faithful."
Historically, music was meant to be performed and listened
to in the same acoustic environment. Symphonies were written to be played in large spaces,
and acoustic designers go to considerable lengths to make sure that the halls where they
are performed offer an appropriate sonic environment, because the acoustics are an
integral part of the music itself. Jazz, on the other hand, is usually performed in
smaller areas -- clubs, for example -- with less carefully designed acoustics, but there
too the ambience is part of the musical experience. The nominal aim of sound reproduction
equipment in the home, therefore, is to recreate as closely as possible the aural
impression of attending a live performance. "Concert-hall realism" has been the
touchstone ever since sound started to be recorded.
In reality, it's an impossible goal. The overall sound of a
concert hall, for instance, is made up of a complex blending of the direct sound from the
instruments themselves with numerous reflections off the walls, floor, and ceilings. The
size, shape, and furnishings of the hall all determine the nature of these reflections. No
two halls are physically identical, so no two sound exactly alike.
Other factors affecting sonic character at any given time
are the position of the orchestra and the number of people in the hall, both of which are
usually quite different in a recording session than during a live performance: the
musicians are frequently placed elsewhere than on the stage, and there is rarely an
audience (the larger the number of people present, the less reverberant the sound).
Finally, no two positions in the hall are exactly the same
distance from the individual musicians or the reflecting surfaces, so every point has its
own distinctive characteristics; where you sit during a concert, or where an engineer
chooses to place his microphones while recording, will have a significant effect on the
sound.
So even a perfect system could only have
"fidelity" to the sound in a specific location in a particular hall on one
unique occasion. Without very specific information about what these conditions were, and
an intimate familiarity with them, a listener would have no way of judging whether or not
the recording was faithful or not.
Fortunately for lovers of the classics, however, the range
of acoustic characteristics that work for that sort of material is fairly narrow, so
conductors and engineers can choose their halls and position their musicians and
microphones -- or even use multiple microphones and after-the-fact processing -- to
simulate a believable sound.
When it comes to other sorts of music, things are much more
complicated. Popular music, rock, country, jazz -- all are typically recorded contrived
environments where natural acoustics have been deliberately suppressed. Any sense of
"space" included in such recordings is artificially added by electronic or
mechanical means.
Similarly, the use of multiple microphones -- sometimes
several for one instrument -- means that there is no natural sonic point of view; spatial
relationships between instruments are created in the control room. In the most complicated
productions, the various elements are recorded on different tracks at different times --
occasionally even in a variety of separate studios -- to be mixed later. Some sounds are
totally artificial, such as those made by synthesizers or electronic instruments.
In such recordings, the producer's creative intent, rather
than an actual performance, is the controlling factor, brought together in the final
mixing stage from a number of elements. The "sound" that results from this
rather arbitrary process is further influenced by the conditions under which the producer
makes his final choices: the acoustics of the mixing room and the characteristics of the
speakers used there both contribute to the artistic decisions made, and neither will be
exactly the same as those in the room of the ultimate listener.
So "fidelity" is really a misnomer, as there is
no real live reference for a system to be faithful to, even in the "purest" sort
of recording. But if there's no reality, there can still be realism. We do have a fairly
definite idea of how a particular sort of music should sound -- a generalized live
reference -- and it is this that record producers and musicians cater to. The aim is not
to reproduce a specific acoustic environment exactly, but rather to create a plausible
illusion of the sound a particular piece of music should have.
But true fidelity and high fidelity are very
different things. The latter phrase became common in the 1950s to describe a series of
improvements that brought a much higher level of performance into the reach of the general
public. There was no single breakthrough, but the introduction of the long-playing record
in the late 1940s made high-quality recorded material available, and brought with it a
demand for equipment that could take advantage of the new medium. The term continues in
use today, even though it is no more precise now than when it was first coined; "high
quality" would probably be a better term, but habits die hard so "high
fidelity" it remains.
...Ian G. Masters
ian@mastersonaudio.com
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