Page 173 - The Master Handbook Of Acoustics

148 CHAPTER SEVEN

4. Integrate the squared signal with a resistance-capacitance circuit.
5. Record this integrated signal as it builds up during the reversed
decay. Turn it around and this trace will be mathematically identi-
cal to averaging an infinite number of traditional decays. Program-
ming this operation into a computer would be easier and more
satisfactory.

Influence of Reverberation on Speech

Let us consider what happens to just one tiny word in a reverberant
space. The word is back. It starts abruptly with a “ba...” sound and
ends with the consonant “...ck”, which is much lower in level. As
measured on the graphic-level recorder, the “ck” sound is about 25 dB
below the peak level of the “ba” sound and reaches a peak about 320
milliseconds after the “ba” peak.
Both the “ba” and “ck” sounds are transients that build up and decay
after the manner of Fig. 7-3. Sketching these various factors to scale
yields something like Fig. 7-12. The “ba” sound builds to a peak at an

0.32

Sec
0
25
dB
Relative sound pressure level, dB 40 “...CK” RT60=0.5
20
“BA...”

RT60-1.5 Sec

60
0 0.5 1.0 1.5
Time - seconds
FIGURE 7-12

An illustration of the effects of reverberation on the intelligibility of speech. Under-
standing the word “back” depends on apprehending the later, lower level consonant
“....ck,” which is masked by reverberation if the reverberation time is too long.