The Theremin was invented by Leon Theremin, a Russian scientist who was working on proximity sensors. It does, in fact, detect your body s proximity

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2 The Theremin was invented by Leon Theremin, a Russian scientist who was working on proximity sensors. It does, in fact, detect your body s proximity to the sensor the antenna and changes the pitch and the volume accordingly. The long, straight antenna is used to control the pitch while the curved antenna is uded to control the volume. There is no reason for the different shapes. 2

3 In order to understand the Theremin, you need to understand sound (a combination of frequencies), but also how to generate oscillating signals. Thus, we will talk a little bit about the science of sound and then about how one would go about developing an instrument that reproduces these sounds. As you will learn, it is all about the frequencies, or combination of frequencies that you will produce with your instrument. We will not really talk about the quality of the sound. As you will readily note when you build your own Theremin, it is fairly straightforward to produce a sound and even to control the pitch, but producing a high quality sound require a much more complex system than you will be able to build. 3

4 Let s first start with sound; sound is a vibration that propagates mechanically through a physical medium. This vibration can only be heard if it occurs at certain frequencies 20 Hz to 20kHz to be exact. If I can generate an electrical signal that oscillates at those frequencies and then use that signal to control the vibrations of a membrane, I can generate an audible mechanical vibration. This is what we are doing with the Theremin we will use the oscillating signal we generate whose frequency we control through the proximity of our hand to the sensor to drive a speaker. 4

5 What do different frequencies sound like? Go to to listen to the rendering of what all frequencies from 20Hz to 20kHz sound like. You could also get onto MATLAB and program a sound using the sound or soundsc command. You will note the vastly different quality of sound when you do that the same frequency can sound like a high pitch squeak or a more mellow sound. The takeaway is, however, that an oscillating frequency can be heard as long as it oscillates within certain frequency ranges. Pay attention to the screen when this youtube clip is playing at what frequency will you start hearing the oscillation and at what frequency do you stop? 5

6 In the lab, you will be designing and building a Theremin that only controls the pitch of the sound you are generating. However, in the digital Theremin lab, you will control both pitch and volume, so let s examine both here. In addition, as you continue in this field and design and build increasingly complex structures, you will discover that these structures are composed of fundamental building blocks that each perform separate functions. It is in how you connect the simpler building blocks that determines the success or failure of your device. In the case of the Theremin, since we need to control pitch and volume, we design and build two separate building blocks one that controls the pitch and the other the volume. The third building block above is the one you have to design in order to combine the signals from the two building blocks into one audible sound. 6

7 The reference oscillator actually oscillates at a much higher frequency than the signal you want to generate this is done purposefully. We will explain why in the ensuing slides. 7

8 In the case of the volume control, one way to implement that is to generate a very high reference frequency and use the antenna to shift it up or down; as this happens, the filter actually changes the shape of the oscillation, so that the higher or lower frequencies are attenuated (thus effecting volume control ). We will discuss this further later. 8

9 In the case of the pitch modulator, you will again generate a very high frequency much higher than the acoustic range. In fact, you will have two oscillators, bot initially oscillating at the same high frequency. One of your oscillators is the reference oscillator while the other is the pitch oscillator. The reference oscillator always oscillates at the reference frequency; the pitch oscillator will oscillate at a central frequency equal to the reference frequency, but its frequency will deviate up and down from the reference frequency as the user approaches the pitch antenna with his or her hand. This change is relatively small and that s why you need to be working at high frequencies. For example, 10% of a big number is still a big number, while 10% of a small number is an even smaller number. In addition, the mixer combines the reference signal (oscillating at f 1 ) and the pitch signal (oscillating at f 2 ), into a third signal, oscillating at and. What is a key objective about this design is its ability to manipulate through the pitch oscillator so that is within the acoustic range, while is high enough to be completely cut out through the lowpass filter. In that way, the user is generating an oscillating signal in the acoustic range that can be used to drive a speaker. 9

10 Between generating the pitch signal and the volume signal, both these signals are used to control the speaker, which will ultimately generate the sound. 10

11 The signal 2 2 is what is generated by the mixer. This signal contains (review trigonometric identities or if you haven t studied trigonometry yet, at least pay a lot of attention to them when you do study them) a component at frequency and one at. A low pass filter will cut off the component, which is at very high frequencies, and will allow the component to pass through to the speaker. 11

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