[...]... soon as the disk rotates a little, such that the hole no longer faces the mechanism blowing the air If the propagation speed of the sound is high with respect to the speed of the holes, by the time new air injection takes place, the air density in the neighborhood of the hole will be similar to the density that we had at the beginning of the process The recurrent passing of holes in front of the air... as the one displayed in Fig 1.3b, the amplitude is the number that measures the maximum value of the departure from the average of the oscillating quantity Since, for a gas, the pressure is a function of the density, we can perform a description of the sound in terms of the fluctuations of either quantity Traditionally, the option chosen is to use the pressure Therefore, we have to describe how much the. .. attached to the wall In the case of the tube, the pressure at the open end is “tied” to the atmospheric pressure Notice that the fact that the pressure fluctuation is zero does not mean that the interior of the tube is isolated from the exterior The displacement D, as seen in Chap 1, satisfies ∂D/∂x ∼ −p and therefore it oscillates with the maximum possible amplitude at the open end These fluctuations of the. .. sequence of holes close to the edge, as displayed in Fig 2.1a The disk faces the mechanism that blows the air, so that the air jet can pass through one of the holes of the disk If the disk is set into a rotating motion (for example, with the help of a motor), there will be an airflow through the device that is sequentially established and interrupted as the holes pass in front of the mechanism blowing the. .. rotation speed, the siren produces a note (a sound of constant frequency), and the frequency of the note is the frequency at which the holes pass in front of the air jet (b) A recorder Very close to the mouthpiece, there is a sharp edge that breaks the otherwise smooth, constant airflow into vortices, creating turbulence The frequency of the resulting sound is related to the effective length of the tube, which... cube of size ∆x, and our portion of air enclosed in this imaginary volume Before the sound phenomenon is established, the air is at a given pressure P0 , and the density ρ0 is constant (in fact, the value of the pressure is a function of the value of the density) Before a perturbation of the density is introduced, the forces acting on each face of the cube are equal, since the pressure is uniform Therefore,... of the air jet as the disk rotates then generates a note The frequency of such a note will be the frequency at which the holes pass in front of the air jet For example, if the disk rotates at such a speed that 261 holes pass in front of the air jet per second, then the frequency of the note is 261 Hz (the middle C) The flute works in a different way It consists of an open tube made of wood or metal,... components of a complex sound are usually enumerated in order of decreasing period (or increasing frequency): the first component is the one with the largest period of all the components, the second component is the one with the second largest period, and so on Note that the period of the complex sound is equal to the period of its first component The frequency of the first component is also called the fundamental... 151 1 Elements of the Description There is a wide range of physical phenomena behind birdsong Physics allows us to understand what mechanisms are used in order to generate the song, what parameters must be controlled, and what part of the complexity of the sound is the result of the physics involved in its generation The understanding of these processes will take us on a journey... et al 1970] The key quantities for establishing this strong signal in the neighborhood of the membrane are the characteristic times of the problem In order to construct such a signal, the action of the membrane must be helped by the reflected wave For this to occur, there must exist a particular relationship between the period of the signal generated by the membrane and the time it takes the signal to . fact, the value of the pressure is a function of the value of the density). Before a perturbation of the density is introduced, the forces acting on each face of the cube are equal, since the pressure. parameters must be controlled, and what part of the complex- ity of the sound is the result of the physics involved in its generation. The understanding of these processes will take us on a journey. sampling fre- quency, the larger the number of data points representing the same total time of recording, and therefore the better the quality. This record corresponds to the song of the great grebe