. The Bell System technical journal . lled thediscrete sentence intelligibility. It will be seen that for changes in distortion, the changes in thediscrete sentence intelligibility will be small for systems havingsyllable articulations greater than 30 per cent, but very large forsystems having syllable articulations below 20 per cent. It is forsystems in this latter class that these test sentences are useful. Acase in point is the measurement of the degree of secrecy obtained ARTICULATION TESTING METHODS 849 in sound proofing telephone booths, or in dealing with sentences have a
. The Bell System technical journal . lled thediscrete sentence intelligibility. It will be seen that for changes in distortion, the changes in thediscrete sentence intelligibility will be small for systems havingsyllable articulations greater than 30 per cent, but very large forsystems having syllable articulations below 20 per cent. It is forsystems in this latter class that these test sentences are useful. Acase in point is the measurement of the degree of secrecy obtained ARTICULATION TESTING METHODS 849 in sound proofing telephone booths, or in dealing with sentences have also been found to be useful in making quickqualitative tests of the goodness of an audiphone set for a particularcase of deafness. Because of their general usefulness for these purposes, the completelists of sentences are given in the appendix. Due to memory effectsa set of sentences can be used with the same personnel only a veryfew times. The psychological factors are also more prominent withsentences than with simple syllable. 100. 20 40 60 8C SYLLABLE ARTICULATION Fig. 12—Articulation vs. time ratio 100 Sentence lists of the above type have also been used to obtain anotion of how the time taken to transmit an idea correctly over asystem depends upon the articulation. To do this, the observer wasinstructed to reply orally to the question. If the reply indicatedthat the observer failed to understand, the speaker repeated thequestion. Both speaker and observer tried to carry out the test in anormal conversational manner. The observer could ask the speakerto repeat, reword or spell out difficult parts of the sentence. The tests were made on a variety of systems of known syllablearticulation. The results that were obtained are shown in Fig. ordinates of the curve give the ratio of the time required to 850 BELL SYSTEM TECHNICAL JOURNAL transmit correctly one of these test sentences over an ideal systemto the time required over the system under test. With the crew usedin
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