Contains reports on two research projects

Cohen, A. J.

Halle, Morris

Hughes, G. W.

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XIII. SPEECH ANALYSISProf. M. HalleA. CohenG. W. HughesJ.-P. A. RadleyA. INVESTIGATIONS OF FRICATIVE CONSONANTS1. Spectral MeasurementsThe aim of the work reported here was to establish criteria by means of which itwould be possible to decide whether a fricative consonant belonged to one of the followingclasses: /f/ or /v/; /s/ or /z/; /f/ or /3 /. (When talking of these classes in whatfollows, we shall designate them by the voiceless member; thus /f/ will mean both /f/and /v/. )Available evidence indicates that the desired information is contained in the spectrumof the sound and that relatively little is contributed by the behavior of the formants in theadjacent vowels. (See the experiment reported below.) The measurements were madeon 50-msec gated central portions of fricative consonants in about 200 English wordsspoken by four subjects (2 females and 2 males).For purposes of filtering we used the set of low- and highpass filters with the verysteep skirts which was described in the Quarterly Progress Report of April 15, 1955.The particular bands to be measured were selected after an examination of a largenumber of detailed energy spectra of fricative consonants. To eliminate the voicingcomponent, all measurements were made with a 720-cps highpass filter. The followingmeasurements were actually made.1. The difference (in db) between the total energy in the sound (720 cps to 10, 000cps) and that in the band from 4200 cps to 10, 000 cps.2. The difference (in db) between the energy in the band from 720 cps to 6500 cpsand the energy in the band from 720 cps to 2170 cps.3. The frequency location of the maximum in the spectra between 1500 cps and 4000cps.4. The difference (in db) between the energy in a 500-cps band centered about themaximum (located in measurement 3) and that in the band from 720 cps to 1370 cps.Measurement 1 indicates the presence or absence of a peak above 4 kc/sec. Withthe exception of samples from male speaker E, all /s/ had peaks above 4 kc/sec.Several /s/ of speaker E had peaks in the region between 3 and 4 kc/sec. No /j/ hadpeaks in that region. Some /f/ also had peaks above 4 kc/sec. Thus, if measurement1 was small, this could be taken as an indication that the sound was either /s/ or /f/; ifit was large, this would indicate that the sound was either /f/ or /f/.Sounds giving small values for measurement 1 could be uniquely determined as beingeither /s/ or /f/. Small values for measurement 2, reflecting a concentration of energy66-(XIII. SPEECH ANALYSIS)in the frequency region below 2 kc/sec, were always /f/; large values, /s/.Sounds giving a large value for measurement 1 could be uniquely determined as beingeither /f/ or /f /. Large positive values for measurement 4, reflecting the presence ofa strong maximum in the region between 1500 cps and 4000 cps, were always producedby /f /; small positive or negative values were produced by /f/.The difficulty with speaker E resulted from the fact that most of his spectra for /s/were shifted downward by about 1 kc/sec (if compared with /s/ of other speakers), oftenplacing them in the region between 3 kc/sec and 4 kc/sec. If this fact is taken into con-sideration and measurement 1 is adjusted to compare the total energy in the sound withthat in the region above 3 kc/sec (instead of 4 kc/sec as for the remaining speakers),then the data can be made to fit all the other criteria. That his speech is somewhatat variance with that of the other speakers can be seen in the results of the perceptualtests discussed in the following section.M. Halle, G. W. HughesB. PERCEPTUAL TEST1. Purposes and ProcedureAn experiment was set up to determine the identifiability of gated portions of voice-less fricatives and to establish correlations between certain spectral properties of thesound presented and its identification by a group of listeners. Gated portions, each 50msec long, of 46 /s/, 32 /f/, and 22 /f/, taken from isolated words spoken by 1 femaleand 3 male speakers were recorded twice in random order on a test tape. This tape,containing 200 samples in all, was played through a sound system having a reasonablyflat response up to 10 kc/sec and presented to a group of 10 listeners under conditionsof high S/N ratio, with instructions to identify every sample as one of the three frica-tives /f/, /s/, or /f /. The samples were spaced at 6-sec intervals with a 45-sec pauseafter each group of 25.2. LearningSince each stimulus was presented twice, the change in agreement among listenersfrom the first presentation to the second presentation was taken as a rough indication ofthe learning that had gone on in the interim. In 51 out of 100 cases there was an increasein agreement; in 23 cases there was a decrease in agreement, while in 26 cases therewas no change; thus we conclude that a certain amount of learning took place.3. IdentificationThe following table shows the degree of agreement between the judgments of thelisteners and the intention of the speaker.-67-(XIII. SPEECH ANALYSIS)In 26 cases2241303715610 (all) listeners agreed with speaker98766 or moreIn the remaining 44 instances there were 16 cases in which 6 or more listeners agreedon the identity of a sound, but disagreed with the speaker.We conclude from this that it is possible to obtain correct identifications of fricativeconsonants in isolation.4. SpeakersTable XIII-1 presents the responses of the listeners to the different phonemes utteredby the speakers.Speaker ETable XIII-1Speaker T Speaker R Speaker Hs f f s f f s f f s f f107 23 13 184 52 22 112 26 22 175 27 1317 143 6 26 97 7 13 111 29 29 109 8156 14 61 10 11 71 75 23 89 16 4 99280 180 80 220 160 100 200 160 140 220 140 120Table XIII-i shows that with theity of the judgments agreed withreasons for the deviations in theexception of /s/ uttered by speaker E the great major-the speakers as to the identity of the phonemes. Thecase of speaker E are advanced in the first part ofthis report. Identical reasons hold for the relatively high number of / f/ judgments for/s/ uttered by speaker R (who was not among the speakers studied in the first part ofthis report). The high number of /s/ judgments for /f/ uttered by speaker T (female)is due to the presence of peaks in the region above 4 kc/sec in many of T's /f/.5. Physical Properties of StimuliIn this section we shall discuss the listeners' responses in terms of the physicalproperties of the stimuli as' represented by the four measurements described in thefirst part of this report.-68-StimuliResponsesTotal(XIII. SPEECH ANALYSIS)a. Measurement 1Value of measurement 1 Responses/f/ /s/ /f / Total0 102 216 22 3400.1-1.9 169 343 88 6002.0-3.9 195 85 100 3804.0-5.9 67 52 161 2806.0-7.9 40 45 115 200>, 8.0 28 42 130 200It appears from this table that the percentage of /f/ responses increases with anincrease in measurement 1, whereas the percentage of /s/ responses decreases. Thepercentage of /f/ responses increases initially, and after reaching a maximum valuebetween 2. 0 and 3.9, decreases. The interpretation of the data is quite simple ifwe recall that low values of measurement 1 show a concentration of energy in fre-quencies above 4 kc/sec, while high values show a concentration of energy below4 kc/sec.b. Measurement 2Value of measurement 2 Responses/f/ /s/ /f// Total< 5 401 134 185 720>5 5 10 102 59 79 240> 10, 15 17 87 176 280> 15 < 20 26 195 139 360> 20 46 314 40 400Predominance of energy in the low-frequency region is indicated by small values ofmeasurement 2; /f/ was the most frequent response for stimuli where the energy wasconcentrated in the area below 2000 cps. For high values of measurement 2, where,in other words, there was a great amount of energy in the high-frequency region, themost frequent response was /s/. For intermediate values of measurement 2, /// wasthe most frequent response.-69-(XIII. SPEECH ANALYSIS)c. Measurement 3Peak frequency Responses/f/ /s/ /f/ Total> 1000 < 1500 180 44 56 280> 1500 < 2000 35 19 46 100> 2000 < 3000 19 30 151 200> 3000 < 4000 38 117 225 380As was to be expected from measurement 2, peak frequencies in the low region wouldlead to frequent /f/ responses and peaks in intermediate regions would lead to /f/responses. The absence of a large number of /s/ responses results from the fact thatpeaks above 4 kc/sec were not considered in this tabulation (see discussion of measure-ment 1).d. Measurement 4Value of measurement 4 Responses/f/ /s/ / f/ Total< 0 178 39 23 240> 0 10 53 32 95 180> 10 20 15 46 159 220> 20 26 93 201 320Again we see that the predominance of energy in the low-frequency region favors /f/judgment. A strong concentration of energy round the peak frequency region, indicatedby high values for this measurement, gives rise to a majority of /f / judgments.A. Cohen-70-

Speech Analysis

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Speech Analysis

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