Audio Engineering concepts

• These notes cover essential audio engineering concepts

Line Check

• Ensures all individual inputs are functioning correctly
• Involves testing connections by unplugging, replugging, and turning them

Sound Check

• The artist listens to the overall sound while the engineer monitors each headphone (HP) cue mix

PAFL

• Pre or After Fader Listen allows monitoring of signals

Redundancy

• Using multiple devices as backup in case of failure
• Avoid cheap wireless systems, opting for mid-range or higher quality (never fixed frequency) because they are not as reliable as cables

MIDI Controllers

• MIDI controllers have only 128 positions due to being 8-bit technology, limiting their resolution

Middle C

• Middle C has a fundamental frequency of 261.5 Hz, which determines its pitch

Overtones

• Different instruments produce different overtones, which are additional pitches above the fundamental frequency
• Overtone frequencies exist above the fundamental frequency

Harmonics

• Harmonics are a specific type of overtone that is a multiple of the fundamental frequency

Odd Harmonics

• Add a sharper, more distinct quality to the sound due to brightness or edginess

Even Harmonics

• Offer warmth and fullness to the sound, due to pleasing and harmoniousness

Audio Phase

• Audio phase indicates a point in time within a sound wave
• Sound waves comprise three primary components: amplitude, wavelength, and frequency
• Amplitude describes the loudness of the wave at a specific point in time

Acoustics

• Acoustics includes reflection, diffusion, and absorption
• Specular Reflection occurs when a sound wave bounces off a hard, flat, nonporous surface
• Diffusion involves sound waves encountering a hard, nonporous, irregularly shaped surface, reflecting at seemingly random angles
• Diffusion aids in managing standing waves and reverberation and is good for open rooms
• Absorption is self-explanatory, with varying effectiveness based on frequency and equipment and is optimal for smaller rooms

Materials

• Fiberglass Corning 703 (from Home Depot) is used for professional wall panels but requires an acoustic panel to function
• Auralex offers equipment and room analysis services
• Acoustiblok is for blocking sound

Speaker Dispersion

• Speaker dispersion is measured in horizontal and vertical planes
• Horizontal dispersion is assessed by viewing speaker spacing from above
• Vertical dispersion is assessed from the side to see the angle towards the audience
• Place speakers above the audience if possible because crowds block sounds waves
• Dispersion patterns depend on frequency, with low end being more omnidirectional and high end more directional

Sound Indoors

• Reverberation and echo differ because an echo has distinct, separate sounds
• Reverberation consists of multiple delays within 35ms, meshing together and decaying
• RT60 is the time it takes for a sound to decrease by 60dB

Inverse Square Law

• Doubling the distance from a sound source results in a 6dB reduction in sound pressure level (SPL)
• Vocalists should keep the microphone within two fingers' distance from their mouth

Critical Distance

• Critical distance is the point where direct sound and reverberant/ambient sound are equal, resulting in reduced clarity

Aux Speakers

• Aux speakers may be necessary for the audience and must be delayed based on their distance from the main speakers
• Sound travels at 1130 ft/sec, or 1 foot per 0.88 milliseconds
• Formula to workout the speaker delay needed is: 60ft x .88ms/ft = 52.8ms if the aux speaker is 60ft from the main speaker

Sound Outdoors

• Environmental factors impact inverse square law calculations

Crosswind

• Crosswind can shift the direction of sound propagation
• Phase cancellation and oscillation can occur when wind causes sounds from two speakers to combine, resulting in some phase cancellation depending on wind speed.

Wind

• Sound going against the wind propagates upwards, while sound moving with the wind refracts downwards

Temperature Gradients

• Sound travels faster through hot air but slower through cold air
• In colder air, sound propagates downwards, and in warmer air, sound propagates upwards

Humidity

• Sound attenuates (loses energy) as it travels through the air, especially at frequencies above 2kHz
• Dry air absorbs more sound than moist air due to its higher density

Noise Types

• Real-time analyzers (RTAs) tune sound systems by attenuating or boosting frequencies
• White noise has equal energy per frequency, causing the high end to dominate
• Pink noise has equal energy per octave

Doppler Effect

• The Doppler effect causes pitch to sound higher as a sound source approaches and lower as it moves away, due to wave compression

TRS Cables

• TRS cables act as splitters, with the tip serving as the left cable
• One cable sends the signal to the input of a compressor, and the other returns the output of the compressor to the TRS.

These notes cover essential audio engineering concepts. It includes line checks, sound checks and PAFL to ensure optimal performance. Redundancy is crucial, recommending mid-range or higher-quality wireless systems over cheaper fixed-frequency options. It also explains MIDI controller limitations and Middle C frequency.