🔊Sound Design Unit 2 – Sound Physics: Waves, Frequency, and Amplitude

What's the Big Deal?

• Sound is a fundamental aspect of our daily lives and plays a crucial role in communication, entertainment, and even survival
• Understanding the physics behind sound waves, frequency, and amplitude is essential for sound designers, engineers, and musicians
• Mastering these concepts allows for the creation of immersive audio experiences in movies, video games, and live performances
• Knowledge of sound physics enables the development of advanced audio technologies like noise-canceling headphones and acoustic levitation
• Studying sound physics provides a deeper appreciation for the complexities of the auditory world around us

Key Concepts Breakdown

• Sound waves are longitudinal pressure waves that propagate through a medium (air, water, or solid materials)
  • Compression: regions where particles are closer together, resulting in higher pressure
  • Rarefaction: regions where particles are farther apart, resulting in lower pressure
• Frequency is the number of wave cycles that pass a fixed point per second, measured in Hertz (Hz)
  • Higher frequencies produce higher-pitched sounds, while lower frequencies produce lower-pitched sounds
  • The human ear can typically hear frequencies between 20 Hz and 20,000 Hz (20 kHz)
• Amplitude is the maximum displacement of a wave from its resting position, determining the loudness of a sound
  • Measured in decibels (dB), a logarithmic scale that represents the intensity of a sound relative to a reference level
  • Every 10 dB increase in amplitude is perceived as a doubling of loudness by the human ear

Math Behind the Music

• The speed of sound (v) is determined by the properties of the medium it travels through and can be calculated using the equation: $v = \sqrt{\frac{K}{\rho}}$
  • K is the bulk modulus (stiffness) of the medium
  • $\rho$ is the density of the medium
• The wavelength ($\lambda$) of a sound wave is the distance between two consecutive compressions or rarefactions and is related to frequency (f) and speed (v) by the equation: $\lambda = \frac{v}{f}$
• The relationship between amplitude (A) and intensity (I) of a sound wave is given by: $I = \frac{1}{2}\rho v\omega^2A^2$
  • $\rho$ is the density of the medium
  • $\omega$ is the angular frequency ($\omega = 2\pi f$)

Real-World Applications

• Acoustic design in architecture and construction to optimize sound quality and minimize noise pollution (concert halls, recording studios)
• Development of high-quality audio equipment (microphones, speakers, amplifiers) for professional and consumer use
• Sound synthesis and manipulation in music production, allowing for the creation of unique and innovative sounds
• Sonar technology uses sound waves to navigate, communicate, and detect objects underwater (submarines, marine research)
• Medical applications, such as ultrasound imaging and lithotripsy, which use high-frequency sound waves for diagnostic and therapeutic purposes

Cool Experiments to Try

• Create a simple wave machine using a slinky or a rope to visualize the propagation of longitudinal waves
• Explore the relationship between frequency and pitch by building a homemade guitar using rubber bands of varying thicknesses
• Demonstrate the Doppler effect by having a friend ride a bicycle with a sound source (bell or horn) and observe the change in pitch as they approach and move away from you
• Build a rudimentary speaker using a paper cup, a magnet, and a coil of wire to understand how sound is produced by vibrating surfaces
• Investigate the effects of different materials on sound absorption and reflection by creating a small-scale anechoic chamber using egg cartons or foam

Tech and Tools

• Digital Audio Workstations (DAWs) like Ableton Live, Pro Tools, and FL Studio for recording, editing, and producing audio
• Spectrum analyzers and oscilloscopes to visualize and measure the frequency and amplitude of sound waves
• Microphones with various polar patterns (omnidirectional, cardioid, figure-8) for capturing sound in different recording situations
• Audio plugins and software synthesizers that utilize sound physics principles to generate and manipulate sounds
• Acoustic modeling software (EASE, CATT-Acoustic) for simulating and optimizing the acoustic properties of rooms and spaces

Common Pitfalls and How to Avoid Them

• Confusing frequency with pitch
  • Remember that frequency is an objective measure of the number of wave cycles per second, while pitch is a subjective perception of how "high" or "low" a sound is
• Neglecting the importance of phase in audio recordings and sound system setups
  • Ensure that multiple microphones or speakers are properly aligned in phase to avoid cancellation or undesired interference
• Overloading audio equipment by exceeding their maximum amplitude capabilities
  • Use proper gain staging and monitor levels to prevent clipping and distortion
• Ignoring room acoustics when setting up a recording or listening environment
  • Treat the room with acoustic panels, bass traps, and diffusers to minimize unwanted reflections and standing waves
• Relying too heavily on digital processing without understanding the underlying physics
  • Develop a strong foundation in sound physics principles to make informed decisions when using audio software and plugins

Beyond the Basics

• Psychoacoustics: the study of how the human brain perceives and interprets sound, including topics like auditory illusions and spatial hearing
• Fourier analysis: a mathematical technique used to decompose complex sounds into their constituent frequencies, essential for audio processing and synthesis
• Wave interference and superposition: understanding how sound waves interact with each other, leading to phenomena like constructive and destructive interference
• Room modes and standing waves: exploring the impact of room dimensions and geometry on sound propagation and the formation of resonant frequencies
• Advanced audio coding and compression: investigating the algorithms and techniques used to efficiently store and transmit digital audio data, such as MP3 and AAC formats