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. What is needed is a scheme for breaking down sound quality into components that we can more accurately listen for when we are critically evaluating our systems.

Using a sound quality measurement framework allows us to score a system against each element, make changes and then revisit it to rescore it. By doing this we can turn a subjective 'it sounds better' into an objective 'dynamics has improved from C to A'. It also provides a mechanism for even relatively unskilled critical listeners to judge improvements to sound quality.

The HAA breaks up sound quality into five key metrics: Clarity, Focus, Envelopment, Dynamics and Response. The following table links these sound quality metrics to some typical issues that people hear.

Metric Typical sound quality issues
Clarity Lyrics are unclear
Lack of tonal color
Focus Individual instruments can’t be located in the soundstage.
Instruments are blurred together
Images (e.g. a singers voice) aren’t fixed and seem to wander
Envelopment Soundstage is flat or two dimensional
Holes in the soundstage
Imbalance in the soundstage
Dynamics There are echoes
Sounds take a long time to die down
Response Bass is boomy
Treble is abrasive
Instruments do not sound real

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 reverberation levels, ambient noise levels, and listener position among others.



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. While envelopment requires three-dimensional imaging of all sonic cues, of pivotal importance is the realistic recreation of the ambient sound field of the recorded venue. Focused sounds become more realistic as they move side to side and front to back with the backdrop of the ambient sounds of the intended venue.

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.

These sound quality metrics are copyright of the Home Acoustics Alliance.