18. Playtime: Virtual Theremin (and a little about frequency and amplitude)

     We've been having fun all along, but this unit is especially fun (there will be more extra-fun units!!!). We have started using Wasp to analyze and visualize speech as a waveform. We noticed that the more densely the vertical lines are crowded together, the higher the pitch 音高 or frequency 頻率 of a sound is. The horizontal axis 橫軸 records the passing of time. Frequency is measured in cycles per second (that is, how many times your vocal folds, and thus the outside air, vibrate in one second), or hertz 赫茲 (or just 赫; named after Heinrich Rudolf Hertz). Pitch is our perception 感知 of a sound, of how 'high' or 'low' a note it is. In general, the higher the frequency of vibrations, the higher the pitch our ears perceive, though frequency and pitch are not perfectly matched – we'll discuss that another time.

     We have also seen that the taller or longer the vertical waveform lines are, the louder the sound seems to be. The vertical axis 縱軸 of a waveform records the amplitude 振幅 of a sound. Amplitude is the measure of pressure variations in the air made by sound vibrations; if you use more lung power when speaking, for example, the air pressure change for each vibration will be greater. Our ears hear this as greater loudness 音量.

    Loudness is usually measured in decibels 分貝, which compare the intensity of one sound to another – a big subject in and of itself that is covered in another unit. Don't worry about any of this at this point. For now, we'll just consider amplitude as a general indicator of how loud or prominent a particular sound is, remembering that we'll have to come back to this sometime later and sort it out a bit more.

     (Ahem) We said this was going to be fun. Well, here's the more fun part.

     Back in 1919, a Russian named Lev Termin (later called Leon Theremin) invented an electronic musical instrument called the theremin (a mainland dictionary calls it 泰勒明電子琴!). The theremin is basically an oscillator 振盪器 (a scientific instrument that produces a sound wave of the frequency and amplitude you choose) controlled by signals received by two antennas. The vertical antenna is for changing the frequency of the sound, and the horizontal antenna is used to vary the amplitude of the sound. You manipulate the frequency and amplitude of the sound produced by the oscillator by waving your arms near the two antennas. The music produced is often described as "other-worldly", "weird" or "eerie". Theremin music has been used in science fiction movies.

     You can link to a brief, illustrated introduction to the theremin here: http://www.thereminworld.com/learn.asp and here: http://theremin.info

Link to videos and MP3 files of theremin playing:



     Now, the really fun part (finally): you don't have to spend US$$279 + S&H (shipping and handling), for a kit you have to build yourself, to play the theremin. All you have to do is download the following application:


and play away! Just move your mouse right and left to control the frequency, up and down to control the amplitude. This nice thing about this application is that it shows the changes in the waveform as you play.

     For a simpler online virtual theremin you don't have to download to your computer, try this:


Again, you control the frequency and amplitude by moving your mouse around your computer screen, but for this version, the further away from the antenna your "right hand" goes, the higher the frequency and thus the pitch; and the further away from the antenna your "left hand" goes, the higher the amplitude or volume.

     And here is a link to iPad and iPhone virtual theremin apps:


    The TED talks site has a fascinating video in which musician Pamelia Kurstin plays the "violin" and "double bass" parts of "The Autumn Leaves" and other tunes on a theremin, and also provides a clear (and giggly) explanation of what's going on:


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