Preliminary Descriptive F0-statistics for Young Male Speakers
Jonas Lindh · 2009
This paper presents preliminary descriptive statistics for 109 young male speakers’ fundamental frequency. The recordings were taken from the Swedia dialect database with speakers from different geographical areas of Sweden. The material consisted of spontaneous speech ranging between seventeen seconds and approximately two minutes. F0 mean, median, baseline and standard deviation distributions in Herz are described using histograms. It is suggested to use median instead of mean when measuring F0 in for example forensic cases since it is more robust and not as affected by octave jumps. 1 Background and introduction 1.1 Why young male speakers? Young males aged 20-30 were chosen as a group because they exist as such in the Swedia database ( ) and because they stand for 62% of the convicted criminals in Sweden last year ( ), which was important due to the forensic implications of the descriptive statistics. 1.2 F0 and forensic phonetics The within-speaker variation in F0 is affected by an enormous amount of factors. In Braun (1995), she categorizes them as technical, physiological and psychological factors. Tape speed, which surprisingly still is an issue for forensic samples, and sample size are examples of technical factors. Smoking and age are examples of physiological, while emotional state and background noise are examples of psychological factors. However, fundamental frequency has been shown to be a successful forensic phonetic parameter (Nolan, 1983). To be able to study differences it is suggested to use long-term distribution measures such as arithmetical mean and standard deviation (Rose, 2002). The duration of the samples should be more than 60 seconds according to Nolan (1983), but Rose (1991) reports that F0 measurements for seven Chinese speakers stabilised much earlier, implying that the values may be language specific (Rose, 2002). Positive skewing of the F0 distribution is typical (Jassem et al., 1973) and an argument for considering a base value (Fb) for F0 (Traunmuller, 1994). This base value is also described here together with mean, median and standard deviation for the whole group. There are no Swedish statistics on F0 found after Kitzing (1979), where he reports a mean of 110.3 Hz and a standard deviation of 3 semitones (in Traunmuller & Eriksson, 1995a) for 51 male speakers ranging between 21-70 years of age. 2 Method The software Praat (Boersma & Weenink, 2005) was used to collect F0 data from 109 young male speakers (20-30 years old). The recordings were taken from the Swedia database JONAS LINDH 90 ( ) and the durations of the recordings range from 17.4 to 116.8 seconds with a mean duration of 52.3 and standard deviation of 15.2. The parameters extracted from the recordings were F0 mean, median, average baseline value (Fb), standard deviation, maximum and minimum in Hz. The range for the F0 tracker was set to 75 350 Hz to be able to cover all possible frequency excursions but at the same time avoid octave jumps. 3 Results and discussion 3.1 F0 means, medians and average baselines This section contains five histograms showing F0 distributions using mean, median, and baseline in Hz. Figure 1. Histogram showing the distribution of F0 means for 109 young male speakers. Approximately 65% of the speakers have a mean fundamental frequency between 100-130 Hz. The mean of the means is 120.8 Hz. There is a positive skewing (0.6) with five extreme outliers between 150-170 Hz. Since the automatic analysis had a tendency for making positive octave jumps it is suggested to use median as it is more robust (see Figure 2 below). Figure 2. Histogram showing the distribution of F0 medians for 109 young male speakers. The median distribution still has a positive skewing (still 0.6), but the mean (of the medians) has moved down to 115.8 Hz. There is now approximately 68% that has a median between 100-130 Hz. Mean distribution of F0 for YM