Audio : Physics

audio

changes in air pressure

waveform

amplitude v. time

amplitude

amount of change

frequency

• "rate" of change
• number of repetitions per second = Hertz (Hz)

phase

offset in starting time (cancellation at 180 degrees (1/2 cycle))

periodic sounds

"tonal" or "pitched", repeats the same or similar waveform many times

aperiodic sounds

"noise", random waveform

spectrum

• describes amplitude of each frequency present in a sound
• harmonic spectrum: has components at integer multiples of a "fundamental" frequency (musical instruments, voice) (figure)
• inharmonic spectrum: not harmonic (clangs, noise) (figure)

envelope

• amplitude envelope: changes in loudness over a sound's duration: attack, decay, sustain, release (ADSR)
• Besides the sound's overall amplitude envelope, each spectral component of a "real" sound has a different envelope
• Fig 4.6, Buford, p.72

sinusoid

sine wave = A sin ( f t + phi )
where A = amplitude, f = frequency, phi = phase offset
(figure)