Audio Engineering & Music Technology Midterm Review

Comprehensive practice flashcards covering the fundamentals of acoustics, analog recording history, digital audio principles, MIDI standards, microphone technologies, spectral processing, dynamics processing, and temporal effects.

Sound

An alteration in pressure, particle displacement, or particle velocity propagated in an elastic medium, or the auditory sensation produced in the ear by moving particles.

Compression (Sound Wave)

A region in a longitudinal sound wave where air molecules are forced together by greater atmospheric pressure.

Rarefaction (Sound Wave)

A region in a longitudinal sound wave where air molecules are pulled apart due to lower atmospheric pressure.

Period

The time required for one complete cycle of a sound wave to pass by a given point.

Hertz ($\text{Hz}$)

The standard unit of frequency in sound, representing one complete repetition or cycle of a wave per second ($1\,\text{kHz} = 1{,}000\,\text{Hz}$).

Phase

The timing and angular relationship between two or more interacting sound waveforms, measured in degrees ($0^\circ, 90^\circ, 180^\circ, 270^\circ, 360^\circ$).

Decibel ($\text{dB}$)

A logarithmic unit of measurement used to describe sound ratios relating to sound pressure level, voltage, power, or intensity.

Speed of Sound (Velocity)

The distance travelled per unit of time by a sound wave through an elastic medium ($c = \sqrt{\frac{K_s}{\rho}}$), which equals approximately $1{,}125\,\text{feet per second}$ ($767\,\text{mph}$ or roughly $1\,\text{foot per } 1\,\text{millisecond}$) at sea level at $68^\circ\text{F}$.

Refraction (Acoustics)

The directional variation or bending of a sound wave resulting from changes in environmental velocity conditions, such as bending upward when cooler air sits above warmer air.

Fletcher-Munson Equal Loudness Curve

An acoustic graph mapping the human auditory system's perceived loudness relative to intensity across varying audible frequencies.

Fundamental

The lowest resonant pitch or frequency produced within a complex sound wave.

Harmonic Series

The natural sequence of overtone frequencies vibrating at whole-number multiples above the fundamental pitch.

Phonautograph

An analog instrument created by Édouard-Léon Scott de Martinville in $1857$ that mechanically tracked sound vibrations onto smoke-blackened paper or glass without playback capability.

Phonograph

The sound recording and playback device invented by Thomas Edison in $1877$ that utilized a rotating tin foil cylinder.

Gramophone

An analog recording playback device patented by Emile Berliner in $1887$ that utilized flat, grooved shellac discs instead of cylinders.

Magnetophon

An early magnetic tape audio recording machine created in Germany in $1935$ by BASF and AEG using ferrite-coated recording tape.

Three Tape Heads

The sequential components across an analog open-reel tape path consisting of the Erase head (clearing previous magnetization to zero), Record head (converting electrical signal into magnetic tape patterns), and Playback head (reading magnetic domains for amplification).

Tape Saturation

The condition in analog magnetic tape recording when all available magnetic domains are oriented, resulting in a progressive and musically warm distortion when input levels increase.

Tape Bias

An inaudible, ultrasonic high-frequency alternating current signal mixed with the audio signal during recording to overcome tape hysteresis and achieve linear magnetization.

Pulse Code Modulation (PCM)

A digital audio representation patented by Alec Harvey Reeves in $1938$ where analog signal amplitude is sampled at regular time intervals and quantized into discrete binary numeric values.

Nyquist-Shannon Theorem

A foundational digital audio sampling theorem stating that the sampling rate must be at least twice the highest frequency intended to be accurately reproduced ($\text{Sample Rate} \ge 2 \times f_{\max}$).

Aliasing

A digital sampling error and distortion occurring when audio frequencies exceeding the Nyquist frequency enter the system unattenuated, creating false mirror frequencies in the audible spectrum.

Quantization

The stage in analog-to-digital conversion where continuously measured instantaneous sample amplitudes are rounded to the nearest discrete numeric bit depth interval.

Dither

A low-level randomized noise intentionally added to an audio signal to mask and decorrelate quantization distortion when reducing bit depth.

Dynamic Range (Digital Audio)

The theoretical maximum decibel span between the loudest unclipped signal and the noise floor, determined by multiplying the bit depth by $6.02\,\text{dB}$ ($16\text{-bit} = 96\,\text{dB}$, $24\text{-bit} = 144\,\text{dB}$).

Jitter

Time-based errors or clock inaccuracies in the synchronization and placement of samples during digital encoding, transmission, or playback.

Broadcast Wave (.wav)

An advanced variation of the standard .wav audio format allowing embedded metadata (such as iXML and original recording timecode) that can use RF64 to exceed the standard $4\,\text{GB}$ file size limit.

MIDI (Musical Instrument Digital Interface)

A standardized serial data communications protocol that enables synthesizers, controllers, sequencers, and computers to transmit and synchronize musical performance instructions.

MIDI Thru

A physical MIDI port that directly passes an identical copy of data incoming from the device's MIDI In port without modification, allowing sequential chaining of multiple hardware units.

Microphone

An electroacoustic transducer that converts mechanical acoustic pressure waves into an analogous electrical audio signal.

Proximity Effect

An acoustic phenomenon characteristic of directional microphones (such as cardioid and figure-8) where low-frequency bass response substantially increases as the microphone gets closer to the sound source.

Dynamic Microphone

A rugged microphone operating on electromagnetic induction, where a mylar diaphragm attached to a wire voice coil vibrates within a magnetic gap to produce signal voltage.

Ribbon Microphone

A velocity-sensitive microphone that produces an electrical signal via electromagnetic induction using a thin, corrugated aluminum foil strip suspended between two magnetic poles.

Condenser Microphone

An electrostatic microphone featuring a movable diaphragm and a stationary backplate acting as a capacitor ($Q = CV$), requiring an external polarizing voltage ($+48\,\text{V}$ Phantom Power) to operate.

Cardioid Polar Pattern

A unidirectional microphone pickup pattern that exhibits maximum sensitivity directly on-axis ($0^\circ$) and maximum acoustic rejection at the rear ($180^\circ$).

Figure-8 (Bi-Directional) Polar Pattern

A microphone polar pattern that picks up acoustic energy equally from the front ($0^\circ$) and back ($180^\circ$) while rejecting sound originating from the sides ($90^\circ$ and $270^\circ$).

Sennheiser MD421

A large-diaphragm cardioid dynamic microphone frequently used on guitar cabinets, toms, kick drums, and brass.

Audix i5

A durable cardioid dynamic instrument microphone commonly utilized for snare drums and instruments.

Shure SM57

A widely used cardioid dynamic instrument microphone with a rotating plastic capsule screen, standard on snares and guitar amplifier speakers.

Sennheiser e604

A compact cardioid dynamic microphone outfitted with an integrated rim-mounting clip, designed primarily for toms and snare drums.

AKG C1000 S

A handheld cardioid condenser microphone with internal battery capability and a built-in power switch.

Shure SM81

A small-diaphragm end-address pencil cardioid condenser microphone known for flat frequency response, often used for cymbals and acoustic instruments.

MXL 4000

A blue-bodied, multi-pattern side-address large-diaphragm condenser microphone.

Audio-Technica PRO 35

A small clip-on cardioid condenser microphone attached to a gooseneck, designed for brass, woodwinds, and percussion.

Spectral Processing

Audio signal manipulation designed to modify or balance the frequency response and timbral characteristics of an audio signal, most commonly via equalization.

Cutoff/Corner Frequency ($f_c$)

The specific frequency boundary at which an audio filter attenuates signal amplitude by $-3\,\text{dB}$.

Filter Slope

The rate of signal roll-off or attenuation occurring past the filter cutoff frequency, generally quantified in $\text{dB per octave}$.

High Pass Filter (HPF)

A filter topology that allows frequencies above a set cutoff frequency to pass unhindered while progressively attenuating frequencies below it.

Q (Quality Factor)

The ratio of center frequency to bandwidth ($Q = \frac{f_c}{\text{Bandwidth}}$), where higher numerical values produce narrower frequency bell curves and lower values yield broader curves.

Dynamics Processing

The process of controlling or adjusting an audio signal's amplitude and dynamic range to manage headroom, perceived loudness, and timbre.

Compressor

A dynamic processor that automatically attenuates signal peaks that exceed a user-defined threshold, narrowing dynamic range and allowing subsequent make-up gain.

Threshold (Dynamics)

The user-set input amplitude level at which dynamic gain reduction or processing begins taking effect.

Compression Ratio

The ratio of input decibel change to output decibel change for signal levels exceeding the processor threshold (e.g., a $2:1$ ratio halves signal increases above the threshold).

Limiter

A compressor configured with an extreme ratio of $20:1$ or higher, preventing an audio signal from surpassing an absolute ceiling threshold.

Temporal Processing

Time-based audio effects processing—such as delay, reverb, flanging, chorus, and phasing—that manipulates time relationships of a signal.

RT60

The duration of time in seconds required for a reverberant decay to drop by $60\,\text{dB}$ below its initial sound pressure level, effectively falling into inaudibility.

Pre-Delay

The time delay in milliseconds between the occurrence of direct source sound and the audible onset of early reverberation reflections.

Flanger

A time-based modulation effect that splits an audio signal, delays one path by $1\text{ to }20\,\text{ms}$, and continually modulates that delay time to produce sweeping comb filter cancellations.

Chorus (Effect)

A modulation effect that splits an audio signal and applies a modulated delay between $20\text{ and }50\,\text{ms}$ to duplicate voices, simulating the subtle timing and pitch discrepancies of multiple performers.