It should be obvious from the word "fidelity" (defined as exactness, or accuracy in details) that high fidelity means "like the original." In this case, a high degree of accuracy in music reproduction.

A high fidelity home music system should reproduce music that sounds (as near as physically possible) identical to the information on the recording. If it is a recording of live music, it should sound like live music when played back. When listening to a studio recording, the home stereo system should accurately reproduce the music on the original recording.

In the case of a studio album, that may or may not resemble live music, so it is not correct to say that a high fidelity stereo system sounds like live music. It is correct to say that a high fidelity home music system can faithfully reproduce recorded music, whatever it may be.

Important (and measurable) elements in a HiFi system are a wide, flat frequency response and inaudible distortion. "Distortion" means falsified reproduction of an audio signal caused by change in the wave form of the original signal.

Ideally, we would like to have a frequency response from 20-20,000 Hz (+/- no more than 3db variation in amplitude) and less than 0.5% total distortion in our HiFi system when measured in an anechoic chamber. Human hearing is not perfect, so we can allow a little tolerance in our specifications. The +/- 3db in frequency response and 0.5% distortion are levels of imperfection that generally go unnoticed by human listeners.

Frequency response and distortion are just the most obvious measurable factors in a music system. There are many others, some quite subtle. It is possible for a system to measure well and still not sound good. However, I have never heard a system that measured bad and sounded good.

Many individual high fidelity components boast specifications that are within, or better, than those parameters. However, distortion and other errors are cumulative.

The weak link in most home music systems is the loudspeakers. Very few loudspeakers can meet those specifications. If you can achieve a useable frequency response of 30-15,000 Hz at your listening position in your home without intrusive distortion, I'd say you have a HiFi system (and a listening room) to be proud of.

In a concert setting, the musicians are in front of the audience. From the perspective of someone in a center seat in the audience, the direct sound of the music comes to the listener from straight ahead. In an outdoor venue, the direct sound is about all there is. In an indoor venue, there is also reflected sound (reflecting off the walls and ceiling) and reverberant sound bouncing off the back wall of the concert hall.

At home, a two channel stereo system in the front of the listening room also produces direct, reflected and reverberant sound. Sound from the Hi-Fi system's loudspeakers goes directly to the listener's ears, but sound waves also bounce off the side and back walls of the room. Thus, a good listening room is analogous, on a much smaller scale, to an indoor concert experience.

A moderate percentage of reflected sound gives the music a "lush" sound. A little reverberation sounds spacious, but too much muddies the aural information.

Bad concert venues usually have too much reverberant sound and most multi-channel home sound systems simulate too much reverberant and reflected sound. That is why a two channel stereo system typically reproduces music more accurately than a home theater system that has additional speakers to the sides of and behind the listening position.

Adding inferior, usually smaller, loudspeakers with a restricted frequency response to the back and sides of a high fidelity stereo (two channel) system merely muddies the sound and increases distortion. (Remember, the room itself is also creating reflected and reverberant sound waves and these reach the listener's ears out of phase with the simulated reflected and reverberant sound from the home theater speakers.) The net result is usually fuzzy or blurred music with excessive "boom" and lower fidelity. In a sentence, less accurate music reproduction.

Multiple channel sound systems can be great for reproducing movie sound tracks, which are mostly dialogue and ambient sounds. (Movie music is incidental to the viewing experience.) Movie sound might be anything, such as waves rolling onto a beach, wind in the trees, traffic sounds, city noise, police sirens, rockets blasting off, screams, gunfire and explosions. In the real world (and in a surround sound movie theater), such noise can come from any and all directions. However, this bears scant resemblance to a normal concert experience, which is why a high fidelity, home stereo system remains the best way to listen to recorded music.