Defining Sound Quality

What is Sound Quality?

Sound quality is often a nebulous concept for a lot of people. They can often say that something sounds better than something else but cannot express the qualities that make up this difference. They are often similarly challenged with describing sound quality problems. Luckily the Home Acoustics Alliance have provided a scheme which breaks down sound into understandable components that we can use to critically evaluate our system.

The Sound Quality Metrics

There are five sound quality metrics: Clarity, Focus, Envelopment, Dynamics and Response. The following table links these to some typical problems that exist in the home listening environment.

Clarity

Clarity is the prime acoustical goal because its perfection depends on the successful attainment of all other goals. Of paramount importance is dialogue intelligibility in movies, but one must be able to understand musical lyrics, detect quiet background details, and distinguish the timbre of each instrument.

Elements that affect this goal are varied including equipment quality, room decay times levels, ambient noise levels, early reflections and room modes.

Focus

The ability to precisely locate each reproduced sonic cue or image in a three-dimensional space is defined as acoustical focus. Recordings contain many such images superimposed side to side (2 channel music) and front to back (multichannel music & movies) in every direction for 360 degrees around the listener. A system is said to have pin-point focus if, from the perspective of the listener, each of these images is properly sized, precisely located, and not wandering. Good focus also provides that individual images be easily distinguishable from amongst others within the limits of the recordings quality.

Envelopment

An audio system should reproduce virtual images of each recorded sound presenting the listener with its apparent source location in a three-dimensional space. Each sonic image relates a part of the recorded event and together these sounds compose a wrap- around soundstage that envelopes the listener. Proper envelopment requires that the soundstage be seamless left to right (2 channel music) and front to back (multichannel music & movies) without interruption by holes or hot spots caused by speaker level imbalance or poor placement.

Dynamics

Dynamics is simply defined as the difference between the softest and loudest sounds reproducible by a sound system. While much emphasis is placed on the loudness side, it can be shown that the audibility of the softest sounds is an equal measure of system performance. If low level signals are overwhelmed by excessive ambient noise or reverberation in a room, they will not be audible due to masking effects and will impact focus, envelopment and clarity. At a minimum, a system must be capable of reproducing loud passages with ease and without excess while soft sounds remain easily audible.

Response

The frequency response of a system is a measurement of the relative levels of all reproduced audio frequencies. The smoothness of response can be observed in a variety of ways; as improper tonal balance including boomy bass, excessive treble, improper musical timbre, or a general lack of realism. Factors of importance include selection of high quality components, and proper system set-up including (in a small room) proper listener position, speaker position, and correct use of equalization. At a minimum, the system must be non-fatiguing all sound levels, articulate and faithful to the original signal.

If you've got this far and still want more, consult J Gordon Holt's Sounds Like? An Audio Glossary. You won't be short of descriptive terms after reading that....