Chapter 1: Notes - Posted on 2016-11-23 by Nicholas Casas

CHAPTER 1 BOOK NOTES

• Notice how the higher pitched tones vibrate faster to match the frequency that is produced!
• Compression is the motion of air molecules forcing into other air molecules. Rare-faction is the exchange of energy between the two and the adjustment of space from the aftermath. The inverse- square law explains the rate of energy lost with distance.
• Sound from a popped balloon is created through the atmospheric pressure being rapidly altered due to the sudden diffuse of gases.
• Sinewave: "perfect wave". Only has 1 fundamental frequency
• Rare-faction: Low pressure are of the wave. (bottom)
• Sound waves are "periodic". They happen in interludes of different time.
• Amplitude = Loudness +Pressure; +Amplitude -Pressure = +Amplitude
• Ways to measure amplitude: 1. Acoustic Standpoint 2. SPL (Sound Pressure Level) 3. Electrical Standpoint (Voltage)
• Peak Amplitude: Maximum absolute value of a signal. Peak-to-Peak Amplitude: the change between peak and trough values.
• RMS: Root means square amplitude determines a meaningful value level of a waveform over time. (INT) An area of time where the most value from a wave is sensed.
• Decibels are measured relatively to the unit that they are compared to.
• Decibel measurement is the ratio of two logarithms taken from two sound energy sources. A logarithm (ln) is taken to control for the psychoacoustic effect that sound is perceived logarithmically; it takes 4x the sound pressure to hear a pitch as twice as loud. So by taking the logarithm, the effect is cancelled out, and a simple numeric ratio (dB) can be expressed to relate the two power levels.
• We measure the amplitude of sounds in the world in "dB SPL". This allows us to value what may or may not be considered loud or damaging for our ears.
• Optimal mixing level: 85-95 dB SPL
• Every instrument on earth has the same Tonal Factors. They just differ in harmonics, overtone, and physical structure.
• Overtones of an instrument, often reproduce the fundamental frequency at a higher rate. EX: Fundamental fqz=100-114. Overtone fqz= 300-314, 500-514, 600-614 etc. Duplicating a fundamental fqz level is raising it an octave. EX: FF=600 fqz; OctF=1200
• The speed of sound is directly affected by temperature
• Low fqz= bigger wavelengths. Vice Versa.
• Lower fqz waveforms can travel around obstacles better due to their larger size.
• Soundwaves can be reflected based on the physical properties of near by objects. Some items can absorb sound more than others, reflecting less sound back.
• Diffusive, or uneven surfaces distribute sound waves in an uneven matter.
• Phase shift is the occurrence of one waveform delayed from another and both of them being mixed together. This is common with a sound is being recorded and its reflections are picked up as well.
• Envelope is the design of the waveform that aides to its distinctive sound. I.e. Sine, Triangle, Square, Saw
• Simple Waveforms: Sine, Triangle, Square, Saw
• Complex wave forms: Sound waves that are altered by several different variables. Real world sounds are complex wave forms.
• Sine waves are created through AN OSCILLATOR, a circuit that converts direct current to alternating current. OSCILLATORS FUNCTION THE SAME WAY EVERY TIME IT IS TURNED ON. That's why they produce simple wave forms.
• The complex aspects of real world sound, help us invoke emotion through dynamics and tonal changes.
• ASDR: A wave’s envelope can be broken down into Attack, Sustain, Decay, and Release.
• Attack: The time it takes for a sound to build up to its full amp.
•  Decay: The time taken for the subsequent run down from the attack level to the designated sustain level.
• Sustain: The primary duration of a note occurring after the attack decay until the note is released by the musician.
• Release: The amount of time it takes after the musician has stopped playing for a sound to return to silence
• Pinna: The outer ear, helps localize sound and filters out certain frequencies due to its shape
• Sound Localization: Distance, direction, time, and proximity help determine this. The design of our pinna is especially designed to produce phase cancellations under certain circumstances. The cave like structure of the pinna amplifies and directs a sound source through the external ear canal and into the tympanic membrane, or eardrum.
• The Eardrum is a small flap of skin which vibrates back and forth with the wave vibrations. Ruptured eardrums can cause hearing loss. It also separates the outer ear from the middle ear. The back of the ear drum has the Malleus, Incus, and Stapes bones attached to it.
• The three bones act as a hydraulic lever system.
• The malleus rotates back and forth with the vibrations from the ear drum, which then causes the incus to push on the stapes accordingly so it can communicate with the cochlea.
• The cochlea is lined with tiny reed-like fibers connected to hair follicles. Just as a piano keyboard, there are different sets of follicles designated to specific frequencies. As sound travels through the ear canal, it enters the cochlea and moves the liquid inside that sends different vibration signals to the follicles. The follicles then send their specific frequency information to nerve endings for sound to be perceived by the brain.
• High SPL situations can speed up hearing loss. We tend to lose higher frequency hair follicles first.
• Hearing loss is due to how high the decibel level is and how long the duration is you're listening to it. Government research suggests the safe exposure limit is 85 decibels for eight hours a day.
• Pyschoacoustics: The scientific study of sound perception
• Fletcher-Munson Curve: Bell Lab. in 1933 determined the frequency and decibel level of sounds and how that impacts our perception. Ex: 100Hz @ 40 dB SPL is the same as 1000Hz @ 10 dB SPL
• The difference becomes less drastic as amplitude increases.
• 2-7kHZ is the most sensitive hearing range.
• Optimal mixing level falls between 85-95dB
• Auditory Masking: When the perception of one sound is affected by the presence of another.
• Acoustic beats are two sounds with slight frequency differences interacting with each other.
• Music production was played on monaural, or monophonic sound reproductions until the late 1950s. Monophonic sound reproduction is sound listened to on a single speaker. It is difficult to perceive spatial elements and depth through this
• Stereophonic sound reproduction involves recording on two speakers. This allows us to assign sounds to different places within the stereo image. Stereo image: The perception of depth, space, and the ability to locate individual elements of a mix within a two-channel stereo recording.
• IMPORTANT! Lower volume of Stereo track to match the level of the Mono one - don’t let volume trick you
• Panning can separate instruments and create space Reverb and delay can create depth and more space between instruments giving each instrument a distinct place in the mix.