Speech Quality

It is common practice in audio to use the term "music quality" to describe the upper tier of sound system products. The alternative term -- "speech quality," is typically used to denote systems that are capable of little more than supermarket paging. While this may allow very general references to be made regarding the suitability of products, especially loudspeakers, to a particular application; it is very misleading when judging the needs of a specific sound reinforcement application.

The human voice is the single most recognizable sound we can perceive. The universal access we have to this source allows it to become the most stringent test signal we can subjectively evaluate. While everyone working with sound reinforcement systems will have a collection of "critical listening discs," a familiar voice can most quickly highlight deficiencies in the path between microphone and listener. A voice may not always indicate whether the subwoofers are too boomy or if there is enough sizzle from the compression drivers. It can definitely make bumps in the bass and mid-range apparent to the qualified listener and it can also call attention to the stridency of high-frequency problems faster than hemi-demi-semiquavers on a highhat.

There are a number of excellent time-domain analyzers available to quantify the sound reaching listeners in a venue, but no sound reinforcement system can be regarded as complete until you have heard it reinforce a familiar voice while sitting in the audience area. Ironically, the way we judge the quality of music is far more adaptable to common problems in room acoustics and loudspeaker systems. A notch in the frequency response may be masked by the broad spectrum that music encompasses. We can forgive variations in reverberation and often we prefer to hear some music in the reverberant field. However, speech is traditionally an intimate sound that degrades rapidly when reverberation or poor coverage is an issue. You can identify a familiar tune even in the worst circumstances but you may not be able to tell if you are hearing a quote from Hamlet or the National Enquirer if the system is only marginal.

When earnest sound system users are asked whether their new upgrade will be for music or speech, they hesitate to even mention speech. They envision a series of re-entrant paging horns being the solution for their "speech" requirement. The system designer views this problem very differently. A speech system must provide direct sound to each listener with the least amount of energy bouncing off the walls and ceilings. This can be far more stringent than a "music only" system would require. A loudspeaker array can be designed for intelligible speech that also sounds great for music. An array configured strictly to achieve excellent music reproduction may never provide adequate speech intelligibility.

These distinctions in between music systems vs. speech systems have cultural implications and a long history that predates sound reinforcement systems. For thousands of years, music has been generated by anything from a few tapping fingers to several hundred instruments. The singing voice, as soloist or choir, has more in common with the musical instruments than with the speaking voice. Until this century, speech was only heard emanating from a mouth, a single point source.

Our current understanding of the human brain indicates that we analyze sounds very differently when they are considered musical than when they are expected to be conveying the specific information of speech. Our ability to extract content from speech sounds has been a decisive factor in our ability to adapt and prosper. While music may soothe the spirit, speech can warn of unseen danger. It's easy to see why our hearing system is so highly adapted to speech communication.

Professionals in the sound reinforcement industry must never fall prey to the misconception that speech requires less rigor than music. Even a sound system that is used exclusively for concerts cannot be forgiven if the audience does not understand a word said during the band's introduction.

United Entertainment Media Inc.
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New York, NY, 10016
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FAX 212-378-2160

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