Each um in the original materials used for Experiment 1 was replaced with a sine wave tone of the same duration, and with a frequency (400 Hz) chosen to approximate the baseline frequency of the recorded speaker.
The volume of the box thus acts as a type of Helmholtz resonator, with a resonant frequency that is determined by the geometry of the hole or tube and is deliberately chosen so that it extends the frequency range of the speaker system smoothly to a significantly lower value.
The frequency response curves of the speakers for frequencies ranging from 1 to 40 kHz were determined by measuring the output of the speakers using this set-up, while a Gaussian white noise stimulus was played at the maximum voltage (±10 V for the TDT system), and the power spectral density of the recorded output was then obtained.
The frequency response curves of the speakers resulting from this calibration were used for setting of the level of the sound stimuli (Rajan et al., 1991).
Each speaker is designed to handle different ranges of frequencies, and the speakers are often powered by 1 or more amplifiers that are also housed within the enclosure.
We also measured speaker output at approximately the same position where the beak was during recordings in order to correct for frequency response deviations of the speaker system by subtracting the dB values of the speaker output from the measured spectrum.
Nevertheless, itinerant scientists coming from large metropolitan areas such as Paris, London, Tokyo, or Boston will quickly realize that the frequency of foreign seminar speakers can be quite low in comparison to what they are used to.
"Especially in the low-frequency region, placement of the speaker has a big influence on sound," said Poul Praestgaard, senior technology manager of Bang & Olufsen, which is based in Struer, Denmark.
The character himself does not roll but the ball inside him does, creating a particular narrative or pragmatic impetus to depict the manner of movement, an impetus which could account for the high frequency of speakers using gestures depicting both manner and path information.
To obtain the input features of a sentence, the speech signal is pitch-asynchronously processed and analyzed in the frames of constant duration corresponding to the mean fundamental frequency of a speaker group (different for male/female speakers).
