Audio and Psychoacoustics Notes

What is Audio

• Definition: Transmission, reception, or reproduction of sound.
• Frequencies: Acoustic, mechanical, or electrical frequencies corresponding to audible sound waves.
• Description: Audio refers to any sound or noise within the range of human hearing and reproduction.

Psychoacoustics

• Definition: Objective study of how sounds affect humans and how the human brain interprets sound.
• Key Researchers: Harvey Fletcher and Wilden Munson of Bell Laboratories in the 1930s.
• Fletcher/Munson Curves: These curves demonstrate the principle of equal loudness.
  • Principle of Equal Loudness: Mid-range frequencies are perceived as louder than low and high frequencies.
  • Amplitude Adjustment: To perceive all frequencies as equally loud, amplitudes of frequencies outside the mid-range (roughly 50 Hz to 350 Hz and 1 kHz to 6 kHz) must be increased.
  • Practical Implication: Listeners must boost bass and treble to balance loudness with mid-range frequencies.

Sound Envelope

• Components:
  1. Attack: Changes occurring before the sound reaches its intensity; the build-up of sound.
  2. Decay: The steady state of sound at maximum intensity.
  3. Sustain: The rate at which sound fades to silence.
  4. Release: The final fade or reduction in amplitude over time.

Acoustics/Psychoacoustics

• Acoustics: Properties of a room determining how sound is transmitted.
• Key Elements:
  1. Early Reflection: Initial reflections reaching the ear immediately.
  2. Late Reflection (Reverberation): Prolonged duration of reflected sound - example: cathedral or gym.
  3. Echo: A sound returning with a delay after the direct sound.

Echo/Delay

• Definition: Distinct repetitions of sound, where the echo can be undeniably heard. Examples include utterances in vast canyons or large rooms.
• Effect of Parallel Walls: Parallel walls create resonance issues, as sound waves travel the same path.
  • Result: An increase in problematic frequencies both at the resonant frequency and its multiples.

Frequency Considerations

• Wave Behavior: A wave half the length of its original frequency allows two wavelengths to fit in the same space, increasing the sound level at that frequency.
• Solution to Resonance: Non-parallel walls cause sound pressures to bounce off in varied paths, reducing resonant problems.

Pro Tools

• Sample Rate: The number of audio samples captured per second, measured in Hertz (Hz).
  • Options include recording at 44.1 kHz, 48 kHz, and 96 kHz.
  • Recommendation: Use 44.1 kHz for a balance of quality and sample size.
• Bit Rate: Pertains to the dynamic range in audio.
  • Bit Depth: The number of bits in each sample; more bits equate to greater dynamic range.
    • CD Quality: 16-bit
    • iTunes and DVD Quality: 24-bit
  • Recommendation: Opt for 24-bit to accurately capture the dynamics in music or recordings.