Language as a carrier of information - Signals, Processes, and Systems - page 95

2,5
2,0
1,5
1,0
0,5
0,0
-0,5
-1,0
-1,5
-2,0
-2,5

Time domain

H..... i................ s............. t........ o......... r....... y

0.25 0.50 0.75 1.00

s

3,00

2,25

1,50

0,75

0,00

250 500 750 1000 1250 1500 1750 2000 2250 2500

Hz

Illustration 72: The word "history" as a waterfall representation and frequency-time landscape

At the top you can see the complete sequence of the word in the time domain, at the bottom the waterfall
representation (time domain). Please note the overlapping sections of signals in the waterfall representa-
tion. They are marked by the two arrows. The sequence starts with the plosive "h", followed by the vowel
"i". The vowels "i"and "o" are clearly distinguishable since they both have a distinctive near-periodic
structure. The sibilant "s" can also be clearly recognized in time domain, but hardly in frequency domain..

The waterfall representation is used for a frequency analysis in order to resolve the non-periodic and near-
periodic characteristics more effectively. These are clearly recognizable in the frequency-time landscape.

This type of signal analysis should be used in connection with acoustic pattern and voice recognition in
order to be able to identify a specific word by its characteristic sequence of consonants and vowels.