To avoid any possibility of artifacts related to the diphone synthesizer itself, the present study was carried out using the HYBRID and PSOLA methods for pitch modification on digitized monosyllabic words recorded by talkers for this experiment. Forty-nine non-words were selected from the list used by Spiegel, et al. (1990) for assessing consonant intelligibility. The words chosen were those which included the English voiced and voiceless stops, singly or in clusters, in either word onsets or offsets/affixes. The 49 words were recorded by two female talkers, one an adult and one a 10 year old child. With each talker seated in an IAC booth, two channels of data were recorded to DAT tape: the audio signal; and the output of a Glottal Enterprises electroglotagraph (EGG). The EGG output was used to assign pitch period markers for voiced regions of the speech. For processing, the audio output of the DAT recording was filtered and sampled at 20.050 kHz with 16-bit resolution on an SGI Indy computer. Individual tokens were located, excised from the recording, and saved for subsequent processing. Three words were found to contain dysfluencies or were simply mispronounced by one or the other of the two talkers. One of these words was removed from the corpus of one talker, but the other words remained in the corpus for the listening sessions. None of the three words for either talker were included in the final data analysis.
Four F0-shifted stimuli were generated from each natural token by shifting the F0 of the original up by a factor of 1.6, or down by a factor of .7 using each of the two processing methods (PSOLA and HYBRID). In all there were thus 485 stimuli (2 TALKERS by 5 F0-SHIFT conditions (original speech plus two shift directions and two shift methods) by 49 WORDS for one talker and 48 for the other). Examples of the syllable "blerk" as produced by each talker, and in each of the shifted F0 conditions, are audible via Table I.
|F0 * 1.6||Hybrid||PSOLA||Hybrid||PSOLA|
|F0 * 0.7||Hybrid||PSOLA||Hybrid||PSOLA
Table I: Examples of the syllable "blerk" in each condition.