A Matter of Opinion
One thing that makes it difficult to define high fidelity is that sound quality is somewhat subjective. One person might think a sound system stresses the treble range of sound too much. But another person might think the sound is perfect. There may even be psychological factors that influence how an audiophile perceives the quality of a particular sound system.
What makes a system hi-fi? An audiophile would tell you that a good hi-fi system would reproduce sounds that were identical to the original sound. In other words, a hi-fi system would pick up every nuance of the original performance. It's easier to understand this with an example.
Imagine that you're recording a live performance of a touring symphony orchestra at the Sydney Opera House in Australia. You're using the best audio recording equipment on the market. After the performance, you follow the orchestra to its next destination -- the Lincoln Center in New York City. Again, you record the orchestra's performance with the same equipment.
Later, you decide to listen to the two performances. An audiophile would suggest that you use the best audio systems you could afford to play back the music. That's because the higher-end equipment is usually better at recreating the sound generated from the original performance. On low-end equipment, you might not be able to tell the difference between the two performances. High-end equipment can be another story entirely.
Using the right equipment, you might be able to tell a lot about the original recording conditions. Even if the orchestra was able to perform exactly the same way both times, there would be differences. The acoustics of the two venues wouldn't be the same. Sound would carry in slightly different ways, and this would affect the recording. Some audiophiles say that certain venues imbue recordings with a particular sound or mood, and with hi-fi equipment you can recreate the sensation of actually being at the venue during the performance.
For an audiophile, such considerations are important. The skill and performance of a musician are still critical, but so are many other factors. An audiophile might even claim that he or she could identify the brand of guitar played by a musician based on how it sounds on a hi-fi system.
The ultimate high-fidelity system would recreate sound perfectly. Were you blindfolded, you'd be unable to tell if you were listening to a recording or if a musician were in the room playing right next to you. For some audiophiles, the quest to achieve perfect sound reproduction verges on an obsession.
What about high-definition audio? Is it a meaningful term? Keep reading to find out.