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Basic Physics of Sound

P105 E XTRA C REDIT A SSIGNMENT : U SING F REE P RAAT S OFTWARE TO RECORD & A NALYZE S OUND – S PRING 2015 Introduction We can use various tools to visualize sounds. For example, we will record sound with computers that store the recording as a list of numbers (similar to the way a CD represents sound). The web page ( ) has other sound resources, links to download this free software, and links to other .WAV files. When you talk into a microphone, it converts the sound pressure into an electrical signal, and the computer will measure the strength of that electrical signal about 22,000 times each second. The result is that each second of recorded sound is represented by a time-series of 22,000 numbers that we will call a "sound signal". Once the sound data is stored on the computer, there are many things that the computer allows us to do to analyze or modify the sound recording. One thing the computer can do is to make a graph of this data. Here is how the computer graphs a part of the recording of the word "hello". The vertical axis is the strength of the electrical signal that is proportional to sound pressure, and the horizontal axis is time. The computer connects the points on the plot to help us to see the patterns. Time (s) 0 1.53977 -0.6258 0.6766 0
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Downloading the software Go to the web site In the upper left corner are links for downloading the software to Macintosh, Windows, or even a Linux box and simply follow the instructions. This is the advantage of this software, i.e., that it is freeware and available for a wide variety of platforms. Recording sound A. Let's try it out. 1. Start up the program called P RAAT . P RAAT is a computer application that phoneticians and other researchers use to analyze, synthesize, and manipulate sounds and speech as well a providing high quality figures to document their work. Wait a minute for the program to load itself. Two windows should appear: a Praat objects window and a Praat picture window. B. To record from the microphone (most computers have an internal microphone), perform the following steps: 1. Choose Record mono Sound… from the New menu in the Praat objects window . A SoundRecorder window will appear on your screen. If you don't have an internal microphone, you can hit a radio button indicating "line in" and connect an external microphone. Record some sustained, fairly constant sound, like playing a note on an instrument or saying/singing a constant vowel like "eeeee" or "aaaaaa". 2. Press the button on the computer’s microphone to activate the microphone. Use the Record and Stop buttons to record a few seconds of sound or your speech. Experiment with how loud to speak and how close to the microphone. The level meter will indicate the appropriate combination, i.e., you want to maintain the level to show green with the rare “spike” into the yellow or red levels. 3. Use the Play button to hear what you have recorded. 4. Repeat the two steps above until you are satisfied with what you have recorded. To make sure that the sound file does not get too large, don’t record more than a few seconds of the sound or your voice for now. 5. Type in a name for your sound file in the text box below the Save to list: button. Hit the Save to list: button and the text string “Sound name” should appear in the Praat objects window that indicates file where your sound is recorded.
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Physics P105: Basic Physics of Sound Spring 2015 Homework Assignment #8 (Due 11:59 p.m., Monday, March 23 ) Make sure you show your work online where relevant for full points. 1. (3 pts) Speech sound is a product of the source (_____ flow), the filter (______ tract), and the radiator (_______ opening). 2. (2 pts) A tone of 6000 Hz is presented at a sound intensity level of 60 dB. If the sound intensity is increased, then the perceived pitch is lower/higher than the original tone. 3. (2 pts) Speech sounds originate in the with vibrations of the vocal . 4. (1 pt) Resonances of the vocal tract, called , are tuned by changing the length and cross- sectional area of the vocal tract. 5. (3 pts) The individual units of sound that make up speech are called . They are divided into two groups: (that are voiced) and (that are voiced or unvoiced). 6. (2 pts) To analyze speech, it is desirable to display sound level as a function of and . 7. (2 pts) Such a display for analyzing speech is called a . 8. (1 pt) The first two or three are usually sufficient for the recognition of vowel sounds. 9. (2 pts) How long must a tone be heard to have an identifiable pitch (and not just a “click”)? (a time). The voice spectra for two vowels are shown below. In each spectrum, the vertical lines under the envelope curve represent the strengths of the harmonics of the fundamental pitch of 150 Hz. 10. (4 pts) The formant frequencies for spectrum #1 are: F 1 = _ ______ Hz , F 2 = _______ Hz , and F 3 = ____ Hz. Using Rossing, Table 15.3, the vowel best representing this picture is ( __ ). Each vertical line is at an increment of 150 Hz. Using this information, you can estimate the formant frequencies. 11. (4 pts) The formant frequencies for spectrum #2 are: F 1 = _________ Hz , F 2 = _ __ Hz , and F 3 = _ ____ Hz and the vowel best representing this picture is ( ____ ).
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12. (3 pts) Assume that a “singer’s formant” at 3000 Hz is due to a resonance on part of the larynx above the vocal cords. Using a cylindrical-closed-pipe model for the upper-larynx tube, we estimate the length of this region to be _____ m or ______ cm. 13. (2 pts) If you wanted to record music in a room that has a constant noise of 60 Hz. The best way to remove this (and close by) frequencies is using a filter. 14. (2 pts) The filter function below is an example of a filter. 15. (2 pts) If the time between puffs of air coming through the vocal folds is 10 msec, then the fundamental frequency of any vowel resulting after it passes through the vocal tract is Hz.
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