Sound Learning for Field Recording

Understanding the structure and properties of the “sounds” we handle daily in field recording allows us to engage more deeply with them, enhancing the quality of recording, editing, and creation. This knowledge is also beneficial from the perspective of sound visualization and audio-reactive expressions.

What is Sound? The Three Elements of Sound

Sound is a vibrational wave that propagates through a medium such as air, water, or solids. The sounds we hear daily are longitudinal waves (compression waves) traveling through the air, where vibrations emitted from a sound source compress and expand air molecules as they propagate.

Visualizing these air pressure changes as waveforms reveals the “shape of sound” over time. The processes of recording, visualization, and analysis capture this physical phenomenon.

The fundamental structure of sound is determined by three elements: frequency (pitch), amplitude (volume), and waveform (timbre).

Element	Description	Impact on Recording
Frequency	Number of vibrations per second (Hz)	Distinguishes high and low sounds; significantly affects microphone and recording equipment frequency response.
Amplitude	Magnitude of vibration	Volume; susceptible to distance, environmental noise, and wind.
Waveform	Shape of the sound wave (sine, square, etc.)	Determines timbre; closely related to harmonic structure.

These elements combine to form a diverse array of sounds, from environmental noises to musical instruments and voices. In field recordings, the subjects often have non-periodic and complex waveforms, making spectral analysis (FFT), which will be discussed in future installments, crucial.

Decibels and Audible/Inaudible Sounds

What is dB?

The unit dB (decibel), which expresses sound intensity, is represented on a logarithmic scale because the human ear perceives changes in sound intensity logarithmically. For example, a tenfold increase in sound pressure is perceived as twice as loud, and a hundredfold increase as four times as loud.

• 0 dB SPL (Sound Pressure Level): Threshold of hearing
• 20–40 dB: Quiet environments (libraries, forests)
• Above 85 dB: Risk of hearing damage with prolonged exposure
• 130 dB and above: Painful sound pressure (e.g., near jet engines)

There are two different concepts of “loudness”: SPL and loudness.

Term	Description
SPL	Actual sound pressure; a physical measurement by devices
Loudness	Subjective perception of sound volume by humans

These concepts exist because human hearing sensitivity varies across different frequencies. For instance, even at the same dB level, certain frequencies may be perceived as louder due to the characteristics of human hearing.

When recording, it’s important not to dismiss inaudible sounds as unnecessary but to approach them as traces of sound existence, leading to more delicate creations.

Characteristics and Limits of Human Hearing – Audible and Inaudible Sounds

Sound is captured by the ears and processed through the eardrum, ossicles, and cochlea (inner ear), ultimately being interpreted by the brain as “sound.” This auditory system has the following characteristics:

• Peak sensitivity in the mid to high-frequency range (2kHz–5kHz), aligning with consonants and alarm sounds, considered evolutionarily important.
• Equal-loudness contours (Fletcher-Munson curves): Perception of loudness varies with frequency, even at the same dB level.
• Masking effect: One sound can obscure another; wind noise and low-frequency noise can act as both “nuisances” and “concealers” in recordings.

Audible Range and Beyond

The typical human audible frequency range is approximately 20Hz to 20,000Hz (20kHz).

Range	Frequency	Examples
Audible	20Hz–20kHz	Human voice, bird songs
Infrasound	Below 20Hz	Earthquakes, wind, elephant communication
Ultrasound	Above 20kHz	Bat sounds, dolphin communication

In field recording, microphones can capture a broader frequency range, including inaudible sounds, which may influence recordings. Therefore, it’s essential to be aware of this during recording and editing.

RMS, Peak, and Loudness – Understanding “Loudness”

In recording and mixing, “loudness” is a crucial factor, but it has multiple definitions: physical sound pressure, instantaneous peak values, and human perception (loudness). Let’s clarify these differences.

Peak: Instantaneous Maximum Sound Pressure

Peak refers to the momentary maximum amplitude of a sound wave. Sounds with high peaks are described as having strong attacks. While peaks add dynamics to sound, excessively high peaks can be jarring, so balance is vital.

Monitoring peak values is fundamental in recording and mastering to prevent clipping (distortion). Since peaks represent instantaneous amplitude, they don’t necessarily correspond to perceived loudness.

RMS (Root Mean Square): Average Energy Level

Humans require about a second to perceive the loudness of a sound. RMS represents the average amplitude over time, aligning more closely with perceived loudness. It’s calculated by squaring the amplitude, averaging it, and taking the square root.

Unlike peak values, RMS corresponds more accurately to how humans perceive loudness. The term “volume” often refers to controlling the loudness at a specific moment.

Loudness: Subjective Perception

While peak and RMS are based on physical measurements, loudness pertains to human auditory perception. It’s influenced by factors like frequency composition and duration.

Characteristics:

• Due to equal-loudness contours, the human ear is most sensitive to mid to high frequencies (2–5kHz).
• Sounds with the same dB level may be perceived differently in loudness depending on their frequency.
• Perception of loudness is affected by frequency composition and duration.

In recording and editing, it’s important to note that “audible” sounds and “physically loud” sounds don’t always align. Adjusting sound balance involves considering peaks, RMS, and loudness.

Types of Noise and Spectral Structure

“Noise” present in natural and urban sounds can be categorized by frequency composition into different “colors”:

Noise Type	Characteristics	Impression/Usage
White Noise	Equal energy across all frequencies	Harsh “shh” sound; used in measurements and masking.
Pink Noise	1/f spectrum (emphasized low frequencies)	Common in nature; pleasant for listening; resembles rain or rustling leaves.
Brown Noise	Further emphasized low frequencies	Resembles thunder or heavy rain; has a warm, heavy feel.

Comparing white and pink noise reveals tendencies in what humans perceive as “natural” sounds. This understanding aids in interpreting the texture of recording subjects.

Experimental Listening: Sound and Its Contours

Engaging in experiential learning can help redefine “audible” sounds:

• Fill a room with self-generated white noise and observe how surrounding sounds change.
• Use high-resolution microphones to record sounds above 20kHz and analyze them spectrally.
• Intentionally create situations to feel sound through the body, such as by blocking ears and sensing vibrations through the floor.

The skill of recording is often supported by the ability to “listen as if seeing.”

Understanding Sound Before Recording

Knowing the properties of sound isn’t just theoretical knowledge; it’s practical wisdom that directly influences equipment selection, setup angles, recording positions, and post-processing.

Moreover, how we engage with “inaudible sounds” can transform recording from mere collection to creative expression.

Recommended Book

The Soundscape – R. Murray Schafer 

This book introduces the idea of the “soundscape”—a term the author created—to describe the sounds that surround us in everyday life. From the natural sounds of the past to the noise of modern cities and machines, our acoustic environment has become increasingly complex.

The author argues that as noise levels rise, our ability to truly listen and notice subtle sounds has declined. He encourages us to become more aware of the sounds around us, to listen more closely, and to recognize the difference between enriching sounds and harmful noise.

Just as we’re concerned about air and water pollution, we should also care about sound pollution. The book offers ways to classify sounds, judge their quality, and includes simple exercises and “soundwalks” to help us tune in. It’s a thoughtful guide to understanding our sonic world—past, present, and future.

—–
► The Soundscape – R. Murray Schafer 
Publication date: October 1, 1993

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BGD_SOUNDS (barbe_generative_diary SOUNDS)

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