Tyco 579-769 specifications Distortion

Influences on Intelligibility, Continued

Distortion	Distortion of the speech waveform can come from many sources, however it is usually exhibited
	by an overdriven signal, causing the peaks of the waveform to be clipped. “Clipping” is caused by
	some part of the electrical signal path within the fire alarm system exceeding the capacity of the
	components. The most common cause of clipping is improper use of the microphone, where the
	operator is shouting into the microphone, overdriving the system. Because clipping itself does not
	reduce modulations, the intelligibility effects of clipping are generally not as severe as noise and
	reverberation effects. A properly installed, operated, and maintained Simplex Fire Alarm Audio
	System has minimal distortion and reproduces speech with excellent clarity.

Microphone Technique

Proper microphone technique can be a major speech intelligibility factor in emergency voice/alarm communications systems. Unfortunately, this is one area over which the system designer has no control. Although this is not normally considered during the measurement of speech intelligibility or during system acceptance testing, it should be considered in the training and use of the system.

For this reason, when possible, use of pre-recorded messages or digitally compiled phrases may be preferred. These messages provide a consistent sound level output and a controlled speech pattern and pace that may be more intelligible than an unpracticed announcement via microphone.

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