Using Creaky Voice Index in Forensic Phonetics – Is it valid and is it reliable?

Using Creaky Voice Index in Forensic Phonetics – Is it valid and is it reliable? ____________________________ Tuija Niemi-Laitinen Forensic Scientist/Technical Department Crime Laboratory National Bureau of Investigation

Creaky voice… • Is a voice of an “expert” • Sounds more mature • Sounds more “relaxed” (not much muscle action) • Reflects “cool” attitude - ” - • Is a social marker of “educated speech” in Finland? • Is a marker of Swedish speaking person in Finland? • When female speakers try to imitate male voice? • Signals uncertainty and/or nervousness • F-072 Finnish Police National Bureau of Investigation

Creaky voice is thought to involve high adductive tension and medial compression, but little longitudinal tension Finnish Police National Bureau of Investigation

Finnish Police National Bureau of Investigation

Creak phonation • is produced with vibrating vocal folds but at a very low frequency • pitch has been observed to be extremely low, and would appear to be controlled by aerodynamic factors and not by varying the longitudinal tension (like other qualities, Ní Chasaide & Gobl 1999). Finnish Police National Bureau of Investigation

Creak phonation • the F0 and amplitude of consecutive glottal pulses is further known to be very irregular • because of the high adductive tension, only the ligamental part of the vocal folds is vibrating • the folds are relatively thick and compressed, and the ventricular folds may also be somewhat adducted, so that their inferior surfaces come in contact with the superior surfaces of the true vocal folds • this would thus create an even thicker vibrating structure Finnish Police National Bureau of Investigation

Creak phonation • the mean airflow rate has been observed to be very low (Ní Chasaide & Gobl 1999) • the resulting low tension and heavy vibrating mass are responsible for the slower and irregular vibration • both subglottal pressure and the glottal airflow are lowered compared to modal phonation • creak is produced at a flow rate of 12-20 cc/s while pulses are produced in a frequency range from 25 to 50 Hz (male) and 50-130 (female). Finnish Police National Bureau of Investigation

Potentially functional, idiolectal or emotional use of creaky voice • Lexically distinctive feature in some languages • Laryngealisation before vowel onset • Word boundary marker between two vowels (/-V#V-/) • Filler in filled pauses • Utterance or turn final preboundary marker • Occurring only in unstressed vowels in some speakers • Overall idiolectal feature in some speakers (Iivonen, Nordic Prosody 2004) Finnish Police National Bureau of Investigation

Study of creaky voice index • How much creakiness there is among Finnish female speakers in both reading and spontaneous speech • 33 female speakers • Age 18-61 (mean 36.1) • Speech samples were recorded via GSM phones and stored on a computer Finnish Police National Bureau of Investigation

Analysis • For the F0 analysis I used the Praat program • Manually-set analysis range (70-300 Hz) • Praat program was used to create PitchTiers • SPSS program was used to calculate the statistics and F0 histograms from the PitchTiers Finnish Police National Bureau of Investigation

Creaky voice limits for female speakers • 140 Hz (Moosmüller 2001) • 100 Hz ("Finn-voice-limit") Finnish Police National Bureau of Investigation

RESULTS • Results show the percentages how often a certain speaker used creaky voice • Results show the difference in using creaky voice between the spontaneous speech and text reading tasks intra-individually • Inter-individual differences can also be seen Finnish Police National Bureau of Investigation

F0 Statistics with SPSS, speaker F072, spontaneous speech, with F0 script Finnish Police National Bureau of Investigation

F0 Statistics with SPSS, speaker F072, spontaneous speech, F0 analysis range 70-300 Finnish Police National Bureau of Investigation

Hypothesis-1 • Some female speakers use creaky voice (less than 140 Hz) almost 50% of the total amount of the measured F0 points. • Answer-1: This study shows that the minimum percentage was 2.4, maximum 81.3 and average 18.7 with 33 speakers in spontaneous speech. • With the text reading task, the values were 0.7, 80 and 13.8%, respectively. Finnish Police National Bureau of Investigation

Hypothesis-2 • About one half of the Finnish female speakers use creaky voice (less than 140 Hz) at least 10% of the total amount of measured F0 points • Answer-2: The result in this study show that 21 out of total 33 female speakers (63.6 %) used creaky voice at least 10% of the total amount of measured F0 points Finnish Police National Bureau of Investigation

Hypothesis-3 • All Finnish female speakers have measured points less than 100 Hz. • Answer-3: Yes. • Minimum percentage was with the speaker no. 88=0.8, the maximum value was with the speaker no. 72=34.9, and the average was 9.2%. • For nine speakers out of 33, the percentage was over 10%. Finnish Police National Bureau of Investigation

Hypothesis-4 • Spontaneous speech is creakier than read speech. • Answer-4: Yes. • Only two speakers showed the opposite tendency • Nine out of 33 speakers had a very small difference (less than 1%) between these two speech styles (limit 140 Hz) • With the limit of 100 Hz the results were as follows: • Read speech was creakier only with four speakers • Nine out of 33 speakers had a very small difference (less than 1%) between these two speech styles Finnish Police National Bureau of Investigation

Hypothesis-5 • If the average F0 value is over 200 Hz, the CVI is 1-2% (limit 140 Hz). • Answer-5: In this study there are five speakers whose F0 average is over 200 Hz with spontaneous speech, and five with read speech. This hypothesis is true only for two of them with spontaneous speech and three with read speech. Finnish Police National Bureau of Investigation

Hypothesis-6 • If the average F0 value is less than 160 Hz, the CVI is over 20% (limit 140 Hz). • Answer-6: In this study there are eight speakers whose F0 average is less than 160 Hz (spontaneous speech) • This hypothesis is true for seven out of eight persons with spontaneous speech and none with read speech. Finnish Police National Bureau of Investigation

CONCLUSION • The speakers differ greatly from each other in respect with the use of creaky voice. The percentages vary from 0.2 to over 80% • There is also a huge variation between the speakers in the way they use creaky voice (only in the final falls of utterances, final falls of every sentence, in every word final, throughout the speech) Finnish Police National Bureau of Investigation

VALIDITY • Validity of the measurements is a relevant question in respect with the extent in which the use of creaky voice signals uncertainty or nervousness of the speaker • This question is relevant also in forensic phonetics • When a suspect is being recorded, does his/her voice get creaky because s/he knows much about the case (cf. the idea of lie detectors) or that s/he is uncertain or just nervous? • If a person's voice is creaky due to uncertainty and/or excitement, it is definitely an area that has to be studied in forensics due to the fact that suspects often are under severe stress when they are accused of committing a crime (if they are guilty, of course) • Then the reference speech samples should deviate from the incriminating speech samples in the level of stress and uncertainty Finnish Police National Bureau of Investigation

RELIABILITY • All the recordings were made via GSM phones • The samples were band-pass filtered without the actual fundamental frequency values • The auto-correlation method for F0 measurements still can be used for measuring using the upper harmonics • This can be checked by inspecting the spectrogram • Reliability is going to be checked by analysing simultaneous GSM and microphone recordings Finnish Police National Bureau of Investigation

COMPARISON QUALITY • Questioned sample(s) • ( ) large amount of personal features • ( ) small amount of personal features • ( ) few words (words_______) • ( ) too short sample • ( ) poor technical quality • Reference samples • ( ) natural variation of the speech is well represented • ( ) natural variation of the speech is poorly represented • ( ) not verbatim text_________ • ( ) poor technical quality _________ Finnish Police National Bureau of Investigation

COMPARISON QUALITY • Comparison quality • ( ) good • ( ) inadequate • Similarities • ( ) no significant similarities • ( ) are concerned to be idiolectal speech features • ( ) are concerned to be ordinary speech features • Other: • ( ) different speech style • ( ) time between the recordings • ( ) different channels of the recordings • Possible voice disguise • ( ) not recognized • ( ) recognized Q ( ) R ( ) Finnish Police National Bureau of Investigation

( ) no significant differences ( ) significant differences ( ) do not fit within the range of natural variation observed in the reference sample Estimation of differences ( ) time between the recordings ( ) physical/psychological state ( ) voice disguise ( ) medicine/alcohol/drugs ( ) speech situation DIFFERENCES Finnish Police National Bureau of Investigation

Using Creaky Voice Index in Forensic Phonetics – Is it valid and is it reliable?