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1: Introduction to Sound - 1 1: I NTRODUCTION TO S OUND S IGNALS I NTRODUCTION Most of the labs will 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). Today, you will talk into a microphone, which 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" Time (s) 0 1.53977 -0.6258 0.6766 0 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. R ECORDING SOUND A. Let's try it out. 1. Turn on the computer if it is not already on. After a short time, the computer monitor will light up and you will see the "desktop." Using the mouse, point the cursor arrow
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Introduction to Sound - 2 at the symbol in the lower left that is labeled "Praat." Then, quickly click the mouse button twice [i.e., "Double-click"]. This automatically starts up the program called PRAAT . PRAAT is a computer application that phoneticians and other researchers use to analyze, synthesize, and manipulate speech and other sounds 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 , 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. 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 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 your voice for now. 5.
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