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Assignment 1: Fundamentals of Speech Sciences and Signal Processing

1. Exploring constructed signals with Praat:

1.1. Create a complex wave (a) consisting of three sinusoids of the following characteristics:

· 200 Hz, amplitude 0.5, phase 0 pi

· 400 Hz, amplitude 0.5, phase 0 pi

· 600 Hz, amplitude 0.5, phase 0 pi

1.2. Create a complex wave (b) consisting of the same three sinusoids but now give the second one (400 Hz) a phase of 1 pi.

1.3. Do the waveforms of (a) and (b) look different?

1.4. Do (a) and (b) sound different?

1.5. Describe and explain your observations.

1.6. From these observations, what can you conclude about the relationship between the wave shape and the perceived quality of the sound? What can you conclude about the phase changes in a complex signal and vowel sounds.

2. Construct signals with Praat: When you open Praat, two windows will be displayed: the Praat Objects window and the Praat Picture window. As you do not need the Praat Picture window for now, you can close it. Click New, and then Record mono sound. . . in the upper part of the Praat Objects window in order to record a new sound.

2.1. Record yourself producing the word ‘seashore’ and and make sure you produce a long /i:/ (the vowel in the first syllable). Save it to the list, and then click View & Edit in the Praat Objects window. In the lower left corner of the new window, you can find buttons to zoom in and out. If you zoom in, you will recognize a more or less regular pattern. Select one period of the /i:/ in your signal and measure its duration. Using the formula frequency = 1/period, calculate the repetition frequency (number of periods per second).

2.2. Please indicate both the duration of one period and the calculated frequency.

2.3. Record yourself producing the same sound with either a higher or a lower pitch than before. Calculate the repetition frequency (number of periods per second).

2.4. In what unit is frequency measured?

3. Explore real signals with Praat: Record the word ‘see’. Zoom in to a 0.1 sec selection of the waveform in the fricative /s/ and then look at the same amount of the vowel part.

3.1. What differences do you observe between the fricative part and the vowel part in the waveform?

3.2. What signals that we discussed in class in week 2 do you see in there? Do you find sinusoids in the signal? Do you find complex signals? If yes, which type? Complex periodic? Complex aperiodic? Transient?

4. Exploring the spectra of sounds: Produce spectra of the different parts in the word ‘see’ in the following way. Go to ‘view & edit’, select a part of the signal you want to produce a spectrum of and then go to ‘Spectrogram’ -> ‘View spectral slice’.
Task: Produce a spectrum of the entire word and then only one of the consonant /s/ and another one of the vowel /i/. How do the two spectra compare? Explain the differences based on what we discussed in class.

5. Solve the following amplitude tasks:

5.1. Why is does a sound of -20 dBSPL still have an amplitude? How much is that same sound in Pa or microPa? What does the negative sign in front of the number tell us about the sound in worldly terms?

5.2. Someone adds 0.5 Pa to a sound of 25 dBSPL. How much is the resulting sound in dBSPL. Show how you calculated this.

5.3. I asked ChatGPT the question in 5.2 and it came up with the answer below. What is wrong with this answer? Why did ChatGPT not get it right? There are relatively simple ways of explaining this.