For preliminary work in acoustic analysis, we will use a program called Wasp that is provided free of charge by the writer of the program, Dr. Mark Huckvale of University College London. The PHON2 group are very grateful to Mark for his permission to use his software in our material. He has also produced a much more advanced and powerful package called SFS, which is also available free of charge (see information on PHON2 Home Page). Before you can start the practical work for this unit, the WASP package must be installed on your computer.
There is a small problem in working with a different program while studying with PHON2, a problem that will be found in some other lesson units: you need to keep reading the PHON2 pages, but your screen will also be needed to show the Wasp activities. To overcome this problem, you need to learn the skill of making one window small and another large so that you can look first at one window and then at the other. If you already know about this, skip the next paragraph.
At the top right corner of each window on your screen there are three small squares (buttons). If you click once on the left button, this reduces the screen to a little rectangle at the bottom of the computer screen (this is called "minimizing" the screen); if you do this, then you need to click on that rectangle to bring the window back to its previous size. The middle button changes the window size between about half of the screen and full screen - each time you click, the size changes. In this way it is possible to have more than one window visible on your screen. You can "switch" from one window to another by clicking inside the window you want to work with, and you can "drag" a window to a different place on your screen by moving the mouse pointer to the bar along the top of the window, holding down the left mouse button and moving the mouse in the direction in which you want to move the window.
Like most modern acoustic analysis software, Wasp works with files in the .wav format that is the standard for Microsoft Windows applications. For work in PHON2, we provide you with a lot of files that we have recorded, but you can also learn how to record you own files.
When you start up Wasp, the Wasp window will probably appear in a half-size window, and during this training stage it's probably a good idea to leave it that way. When you are using Wasp for your own work, you will want the window to be full-screen size. Sometimes, however, you will need to "minimize" the Wasp window so that you can read your PHON2 screen more easily.
For the first exercise, we will use the demonstration file of a male voice saying [apa] which is provided with the Wasp program. Go to the File menu, click on Open and then select http://www.rdg.ac.uk/~llsroach/phon2/apa.wav . Your Wasp window should then show the acoustic patterns for [apa]: in the upper half of the window is the acoustic waveform, which is a simple representation of what the microphone picked up when the speaker said [apa], starting at the left-hand side and ending at the right side. The lower window shows a spectrogram of the recorded signal. This shows how much energy is present at different frequencies. The frequency scale goes from low (at the bottom) to high (at the top).
If you have studied the material in the Instruction section of this unit, you should be able to recognize what you can see in the spectrogram: firstly, the first [a] vowel, then a gap for the [p] plosive, then the second [a] vowel.
Look at the bar along the top of the Wasp window: there are various buttons there which you will learn to use. The triangular button to the right of the red Record button is the Play button. If you click it, you should hear the recording of [apa] through your loudspeakers or headphones.
As a preliminary exercise, we will measure the time taken by the two vowels. Move your mouse pointer to the beginning of the first vowel and click the left mouse button. A vertical line (the left cursor) should appear. Now move the mouse pointer to the end of the first vowel and click the right mouse button. The right cursor should appear. You have now selected the first vowel. If you click the Play button, you should hear only the vowel. Now look at the bottom of the screen. You will see a time "ruler" , and below that in the right hand corner you should see three figures. The left figure tells you the position of the left cursor in relation to the start of the recording, so if it is showing 0.025, this tells you that the vowel starts 0.025 seconds after the start of the recording. The middle window should be showing a figure in the region of .202. The right-hand figure tells you what the interval between the two cursors is: in this case, it will be in the region of 0.177, and that is the duration of the first vowel. (Ignore for now the other figure expressed in Hz). Now position the cursors at the beginning and end of the second vowel. What duration measurement do you get for the second vowel?
Measuring pitch (fundamental frequency)
Wasp can also display the fundamental frequency (F0) of voiced sounds (people often refer to this as 'pitch', though that is not strictly speaking the correct term). If you click the button to the left of the button labelled An (it has a curved line on it), the F0 traces for the two vowels in [apa] should appear. Notice how the trace is low for the first vowel, and falls gradually from a high start in the second vowel.
To make a recording of your own, you need a suitable microphone connected to the microphone input socket on your computer. If you click the red button, you will get a little panel which lets you check that the recording level is OK. When you click the rectangular Record button, recording will start. You must click 'stop' when you have produced the sounds you wanted to record, otherwise the recording will go on and on and fill up your computer's disk space. Try recording you own pronunciation of [apa] and compare it with the file you have just worked on.
There are many more things for you to learn, but if you have carried out the above exercises, you now have the basic skills to carry out simple acoustic analysis of speech signals.