NATURE OF SPEECH AND ITS INTERPRETATION 



141 



housed in two boxes. The switching mechanism was arranged so 

 that by turning a dial the condensers and coils were connected in 

 such a way that the filter transmitted different frequency bands. 



In Fig. 7 are shown the transmission properties of the low pass 

 filter when the dial is set to transmit frcciuencics from to 1500. 

 It is seen that for frequencies below 1400 the amplitudes of the trans- 

 mitted tones are always greater than .8 of their initial values, while 

 for frequencies above 1500 the amplitudes are decreased to less than 

 .001 of their initial values. These electrical filters were connected 

 into the high quality circuit between the third and fourth stages 



400 



1200 1600 



Frequency 



Fig. 7. 



zooo 



2400 



2800i 



of the amplifier as indicated in Fig. 1. This combination formed a 

 system which would pick up a complex sound wave and transmit 

 faithfully to the ear those component frequencies in any desired 

 region and eliminate all other frequencies. 



Results of Articulation Tests with Filter Systems 



Articulation tests were made with these filter systems and the 

 results analyzed as described above. In Fig. 8 the syllable articu- 

 lation results are shown in graphical form. The ordinates for the 

 solid curves represent the per cent of the articulation syllables called 

 into the system which were correctly recorded at the observing end. 

 The abscissas represent the so-called "cut off" frequency of the 

 filter. For example on the curve labelled "Articulation L" the 

 point (1000, 40) means that a system w^hich transmits only frequencies 



