239 Midterm Flashcards
What is sound?
vibrations that travel through the air or another medium that can be heard when they reach a person/animal’s ears
Features of a Soundwave?
2 defining features: frequency (pitch) and amplitude (volume)
What is frequency?
the number of vibrations that occur in one second
What is period?
the amount of time that passes during one cycle of vibrations (seconds per vibration)
What is the range of human hearing?
20Hz to 20,000Hz (20kHz)
What is the speed of sound?
approx. 760
What is amplitude?
volume, the extent of the change in air pressure from the surrounding level of air pressure
What are decibels?
(measure of amplitude) a logarithmic-based unit of power relative to a reference point of 0dB which is set at the typical threshold of perception of an average human
What is loudness?
relates to psychoacoustics– the study of the perception of sound (in comparison to amplitude which relates. to acoustics– the study of the physical properties of sound
Amplitude envelopes
describe a sound’s variation in amplitude over time (Attack silence to peak, Decay diminishes, Sustain remains constant)
Transients?
sudden bursts of amplitude, often with chaotic frequencies– typically occur at the beginning of a sound and help define a sound’s timbre/sound quality
What is phase?
the position of a sound wave in time
What is constructive interference?
occurs when amplitudes of sound waves combine to create the impression of a single sound with even greater amplitude
destructive interference
can occur if one sound begins when another sound of the same frequency is half a cycle ahead, then the two sounds are being described as being 180 degrees out of phase WHICH MEANS the amp of one sound will subtract from the amp of the other
beating
two sounds, slightly different frequencies, impression of a single sound that pulsates as they move in and out of phase
overones
partials that are higher than the fundamental frequency, sounds are a combination of frequencies and overtones
timbre
the overall impression we have of a collection of frequencies and overtones– helps identify what instrument is being played
Harmonic series
not exactly sound but a mathematical relationship between frequencies and dynamics
Consonance
combo of notes that are in harmony due to their frequencies
dissonance
lack of harmony among music notes, freq’s clash– sounds harsh
acoustical basis of harmony
interference, beating, and overtones are the fundamental principles of harmony in the west, based on the alternation of dissonance (tension) and consonance (release).
Samples are
periodic measurements of the instantaneous amplitude of the electrical signal
sampling rate
the number of measurements take of an analog signal in one second
bit depth?
amplitude resolution of the signal– the # of binary digits used to encode the voltage level for each sample
ADC
analog to digital converter- converts electrical signals into numbers
audio interface features (5)
1) built into computer 2) a simple two I/O audio device 3) multichannel offering 8 analog I/Os and expansion options D) fitted with MIDI I/O ports E) fitted with a controller surface (with or without motorized faders)
WAV
Waveform Audio File Format – lossless uncompressed, versatile, windows
AIFF
Audio Interchange File Format– uncompressed, lossless, used by apple
AAC
Advanced Audio Coding– lossy, compressed, but better than MP3, default for itunes
MP3 (MPEG)
Moving Picture Experts Group- lossy, compressed audio
