Introduction to Sound and Hearing

What You’ll Learn

Basics of sound: amplitude, frequency, phase, and harmonics
How the ear processes sound
Introduction to psychoacoustics: How we perceive sound
Practical implications for audio production

Why It Matters

Understanding sound and hearing is foundational for anyone working in audio production, from recording and mixing to synthesis and sound design.

Sound areas

The basics of sound
The characteristics of the ear
How a sound stimulates the ear
The psychoacoustics of hearing

The Transducer

device -> energy conversion -> resulting energy

https://commons.wikimedia.org/wiki/File:Django_Reinhardt_(Gottlieb_07301).jpg

The basics of sound

Understanding Amplitude

Key Concepts

Amplitude measures the strength or intensity of a sound wave.
It directly relates to perceived loudness.

Amplitude

Amplitude in the Real World

Example: Think about the difference in loudness between a whisper and a shout.
Interactive Example amplitude
Tip: When recording, always monitor amplitude levels to avoid distortion.

Understanding Frequency

Key Concepts

Frequency refers to the number of cycles per second in a sound wave.
It determines the pitch of the sound.

Frequency in Action

Example: A bass note versus a high-pitched whistle.
Interactive Example frequency
Tip: Different frequencies interact in complex ways in a mix.

Phase Relationships

Key Concept: Phase refers to the timing relationship between two sound waves.
Impact: Out-of-phase waves can cancel each other out, leading to a reduction in sound.
Sound Demo: Phase

Random phases - square and sawtooth

Harmonic Content

Key Concept: Harmonics are additional frequencies in a sound that define its timbre.
Real-World Example: Why a guitar and piano sound different, even when playing the same note.
Sound Clips: Fourier Series 3D interactive demonstration

The Decibel

The Ear

Introduction to Psychoacoustics

What Is It? Psychoacoustics explores how our brain interprets sound.
Key Concepts: Pitch perception, loudness perception, and spatial hearing.

Auditory Perception

What sound comes into your ears is not always what you “hear”; your brain completes the picture. Our ears perception of timbre and frequency changes with the loudness of a perceived signal

This image is known as the Fletcher-Munson curve or equal-loudness contour. It’s a graph that shows how the human ear perceives loudness at different frequencies and volumes.

Breaking It Down:

Horizontal Axis (X-axis):
- This represents the frequency of a sound, measured in Hertz (Hz). The frequency ranges from low (20 Hz) to high (10,000 Hz). Lower frequencies are bass sounds, while higher frequencies are treble sounds.
Vertical Axis (Y-axis):
- This represents the sound pressure level (SPL) in decibels (dB SPL), which is a measure of how loud a sound is.
Curves on the Graph:
- Each curve shows the ear’s sensitivity to different frequencies at various loudness levels.
- The numbers on the right represent loudness levels in phons, which correspond to the perceived loudness of a 1,000 Hz tone at different decibel levels.
- For example, the 60-phon curve means that all the frequencies on that line sound equally loud to our ears as a 1,000 Hz tone at 60 dB SPL.

Key Points:

Threshold of Hearing:
- The dotted line near the bottom represents the quietest sound that the average human ear can hear at each frequency. This is known as the threshold of hearing.
Sensitivity Variation:
- The ear is most sensitive to frequencies between 1,000 and 5,000 Hz. Sounds in this range are perceived as louder compared to lower or higher frequencies at the same SPL.
Practical Implications:
- This means that a low-frequency sound (like a deep bass) needs to be much louder than a mid-frequency sound (like a human voice) for us to perceive them as equally loud.

In simple terms, this graph tells us that our ears don’t hear all frequencies equally well, especially at lower volumes. This is why, for instance, bass might seem softer at lower volumes and why sound engineers compensate for this in their mixing.