SOUND LABORATORY LING123: SOUND AND COMMUNICATION In this assignment you will be using the Praat program to analyze two recordings: (1) the advertisement call of the North American bullfrog; and (2) the song of the male North American black-capped chickadee. You will be asked a number of questions on the acoustic properties of the sounds you will examine. Unlike the other homework assignments, this laboratory assignment does not require a lot of writing (although you may explain your reasoning if you like). Here s a summary of what you need to do to begin: (1) Download Praat if you have not done so already. The link to download the program is http://www.fon.hum.uva.nl/praat/. (2) Download both the bullfrog sound file and the black-capped chickadee sound file. Each file is available for download on the course website, under Resources. If you use your own computer at home, make sure it can produce sound. If you are using a computer on campus, make sure it can produce sound and that you bring (or borrow) a set of headphones. (3) Start Praat by clicking its icon. (4) Once you ve opened the program, you should load the files into the program. To do this, click Read from file... underneath the Read menu in the Praat objects window. (5) Click on the sound file in the objects window and press edit (button on the right). A menu should appear above the waveform of the sound. Make sure Show Spectrum is selected under the Spectrum menu. Make sure Show Pitch is selected under the Pitch menu. Make sure Show Intensity is selected under the Intensity menu. Make sure Show Formants is DE-SELECTED under the Formant menu. Make sure Show Pulses is DE-SELECTED under the Pulses menu. (6) For analyzing each file, you will have to adjust other settings in Praat. Please read the instructions in each section to know how to adjust the settings. Bullfrogs and chickadees sound quite different! (7) It s fine to discuss the questions with your classmates, but make sure you write your own answers in your own words. You may write your answers on this sheet of paper or type up the answers in a separate document. 1. Bullfrog advertisement call In this exercise we ll analyze a recording of the advertisement call of the North American bullfrog, Rana catesbeiana. This recording features a male bullfrog producing a series of eight croaks. The last six croaks in the sequence contain stutters. Males only produce these stutters when no other males are nearby, which suggests that the stutters are flourishes designed to attract females, while plain croaks (without stutters) are more aggressive signals aimed at other males. 1
1.1. Loading and playing the sound You should have already loaded the bullfrog.wav file. Press the Play button (on the right in the objects window) to play the file. 1.2. Settings Select the sound file in the objects window. Click on the edit button on the right. Adjust the following settings when the sound is displayed: Under the Spectrum menu, select Spectrogram settings... The View range should be set to 0-3000 Hz. 1 Under the Pitch menu, select Pitch settings... The Pitch range should be set to 70-300 Hz. Under the Intensity menu, select Intensity settings... The View range should be set to 40-100 db. You can select parts of the sound file by clicking the waveform or spectrogram, and then dragging your cursor to where the sound ends. To zoom-in on the region that you ve selected, press the SEL button at the bottom of the window. To zoom back out, you can either press ALL which shows you the entire sound file or OUT to just zoom out by twice the window duration. Practice this by selecting individual croaks in the bullfrog s advertisement call. Select each individual croak and then press the bar immediately below the spectrogram window. This will play the part that you ve selected. It also gives you the duration of the region you selected (in seconds). 1.3. Measuring Duration Notice the time axis below the spectrogram. If you zoom out all the way (the ALL button), you ll see that the time axis goes from 0 to just under 7 seconds. In other words, this recording is just under 7 seconds long. Now let s measure the durations of the first two croaks. Use the mouse to highlight the first croak. It starts at about the 0.1s mark and ends just after the 0.5s mark. Make sure you are highlighting all of the first croak, but none of the silence (the flat line of the waveform) surrounding it. Press the bar underneath the selected portion or the TAB key to confirm with your own ears that only the first croak is highlighted. On the bar beneath the spectrogram, there should be some numbers indicating the precise duration of the region you highlighted (it should say something like 0.458584 ). Question 1: What is the duration of the first croak? Question 2: What is the duration of all the other croaks? Are they similar in duration? Question 3: Are the croaks with stuttering longer than the ones without the stuttering? 1.4. Measuring Intensity Question 4: Which croak sounds louder, the first one or the second one? 1 TIP! : If you want a clearer picture on the spectrogram, lower the dynamic range under Spectrum: Spectrogram settings to 0.40. 2
Question 5: Look at the waveform window and compare the waveforms of the first and second croaks. Can you tell which is louder just by looking at the waveforms? How is loudness represented in the waveform? Fortunately, there are more accurate ways to determine loudness than eyeballing it. Use the mouse to select all of the first croak again. The average intensity of the portion that you ve selected will appear on the right (on the left side of the window box.) Question 6: What is the mean intensity (in db.) of the first croak? Question 7: What is the intensity of all the other croaks? Are they similar in intensity? Question 8: What is the maximum intensity (in db.) you can find in the first croak? At what time does it occur? Question 9: What is the maximum intensity (in db) you can find in the second croak? At what time does it occur? Question 10: Do these mean and maximum readings of the first two croaks confirm or contradict your subjective loudness judgment from Question 4? 1.5. Estimating the F0 Now highlight the first croak and zoom in on it. From this perspective you can begin to see the individual repetitions that make up the waveform, but we still need to zoom in even closer. Select a region of about 50 ms. (48-52 ms.) in the middle of the croak and click SEL. Examine the waveform inside this region. See if you can tell how many times the wave repeats itself. It s hard to tell exactly, because in real life waves never repeat themselves exactly. But a good way to estimate is to count the number of sharp jags sticking out of the bottom of the waveform in this region. Question 11: How many times does the wave repeat itself inside the highlighted 50 ms. region? Question 12: Now that you know the number of times the wave repeats itself in 50 ms., about how often would this wave repeat itself in 1 second? (You don t have to be exact.) The answer to Question 12 is your estimate of the fundamental frequency (F0) of the bullfrog s croak. 1.6. Examining the pitch contour Luckily, there are more accurate ways to calculate F0 than eyeballing it like we did above. Zoom-out to see each of the frog croaks. Now, if you select each one and zoom in, you will notice the pitch contour plotted as a blue line. All eight croaks have approximately the same pitch pattern. Select about 50 ms. inside of the first croak, roughly about the middle. On the right of the spectrogram window, it will provide you with the mean pitch of the region you ve selected. Question 13: What is the mean pitch value for the selected region? Is this value close to your original F0 estimate in Question 12? Question 14: Do any of the other croaks have a different pitch from the first one? If they do, by how much? 3
2. North American black-capped chickadee Next we will analyze the song of the North American black-capped chickadee. This song transcribed hey sweetie consists of a high first syllable followed by a two-syllable lower whistle. A male sings many renditions of hey sweetie on one frequency before shifting to another. Our recording captures a male switching from a higher frequency hey sweetie to a lower one. Select the sound black-capped-chickadee in the Praat objects window. Press the Edit button on the right to view the sound file. You will now adjust Praat s settings to the following: Under the Spectrum menu, select Spectrogram settings... The View range should be set to 0-10000 Hz. Under the Pitch menu, select Pitch settings... The Pitch range should be set to 100-6000 Hz. Under the Intensity menu, select Intensity settings... The View range should be set to 40-100 db (the same as before). According to spectrogram, it looks like the first hey sweetie starts at a frequency of about 4000 Hz. for the hey part and then drops down to around 3500 Hz. for the sweetie part. However, we can use the Spectrum display to get much more precise frequency measurements. Click on the point of the spectrogram that looks like the middle of the hey part of the first hey sweetie. Now, go to the Spectrum menu and click on View Spectral Slice. Find the largest peak in the spectrum. The greatest peak in the spectrum represents the F0 of the hey part. Question 15: What is the exact reading of the F0 of the first hey? Question 16: What is the exact reading of the F0 of the first sweetie? (It s probably easiest to measure this in the middle of the sweet syllable.) If you subtract the frequency of sweetie from the frequency of hey, this gives you the frequency difference between hey and sweetie. Your answer should be positive, since hey has higher pitch than sweetie. Question 17: What is the frequency difference between hey and sweetie in the first hey sweetie? (Use a calculator, such as the one built in to Windows, if you like.) If you divide the frequency of hey by the frequency of sweetie, this gives you the frequency ratio of hey to sweetie. Use a calculator (such as the one built in to Windows) to get a precise value. (Your answer should be greater than 1.0, since hey has higher pitch than sweetie.) Question 18: What is the frequency ratio of hey to sweetie in the first hey sweetie? Now let s do the exact same calculations for the second, lower-pitched hey sweetie. Question 19: What is the exact reading of the F0 of the second hey? Question 20: What is the exact reading of the F0 of the second sweetie? (Make a measurement in approximately the same spot as you did for the previous sweetie.) Question 21: What is the frequency difference between hey and sweetie in the second hey sweetie? 4
Question 22: What is the frequency ratio of hey to sweetie in the second hey sweetie? Question 23: When a black-capped chickadee switches from a high-pitched hey sweetie to a lowerpitched hey sweetie, which parameter is he keeping constant in his song: frequency difference or frequency ratio? 5