Physics of Sound and Decibels

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Questions and Answers

Which microphone type is known for its ability to record high sound pressure levels (SPL) effectively?

Dynamic Mic (correct)

Condenser Mic

Electret Mic

Ribbon Mic

What is a primary characteristic of a condenser microphone?

Is the most durable microphone type

Has a heavy diaphragm

Requires no power supply

Utilizes phantom power (correct)

What is the typical frequency response range for a dynamic microphone?

10-20 kHz

5-8 kHz (correct)

0-5 kHz

12-22 kHz

Which microphone type is characterized by its bi-directional pickup pattern?

Ribbon Mic Signup and view all the answers

What disadvantage is most commonly associated with ribbon microphones?

Require extensive power supply Signup and view all the answers

What is the effect of increasing track width on the signal to noise ratio in analogue tape recording?

It improves the signal to noise ratio by 3dB for each doubling of track width. Signup and view all the answers

Which term describes the slow dragging effect experienced during playback on an analogue tape machine?

Wow Signup and view all the answers

What is the primary concept of multitrack recording?

To record multiple tracks independently in synchronicity. Signup and view all the answers

What is the minimum recommended rotation speed for Hard Disc Drives used in HD recording?

7200 rpm Signup and view all the answers

What does PCM stand for in the context of digital recording?

Pulse Code Modulation Signup and view all the answers

What role do the ossicles play in the ear's function?

They amplify and transmit vibrations to the inner ear. Signup and view all the answers

What happens to the tympanic membrane when atmospheric pressure varies?

It disrupts the action of the ossicles. Signup and view all the answers

How are hair cells arranged in the cochlea?

They respond to a range of frequencies split into 24 bands. Signup and view all the answers

What is the function of the Eustachian tube in the ear?

To maintain equal pressure on both sides of the tympanic membrane. Signup and view all the answers

What frequency corresponds to the first band of hair cell responses in the cochlea?

50Hz Signup and view all the answers

What term describes the time delay between the direct signal and the first early reflection?

Pre-delay Signup and view all the answers

Which type of reverb leverages impulse responses to mimic real acoustic spaces?

Convolution reverb Signup and view all the answers

What is the main characteristic of a cardioid microphone?

Focuses on sound from the front with reduced sensitivity at the sides and rear Signup and view all the answers

Which of the following best describes the function of diffused reflection in sound?

Bouncing sound waves between multiple surfaces before reaching the listener Signup and view all the answers

What is the purpose of a bucket brigade delay (BBD) in audio processing?

To store and play back audio signals in sequence Signup and view all the answers

How does a super cardioid microphone compare to a standard cardioid microphone?

It has better side rejection but increased sensitivity at the rear Signup and view all the answers

What is the characteristic sound effect achieved by phasing in audio processing?

Subtle pitch modulation creating a swirling sound Signup and view all the answers

What type of microphone is best suited for a live performer who moves a lot?

Super cardioid microphone Signup and view all the answers

What does the inverse square law describe in relation to sound?

Sound intensity decreases with the distance to the source squared. Signup and view all the answers

Which of the following statements is true about decibels?

Decibels are compared to a fixed reference level of 0 dB. Signup and view all the answers

How is wavelength calculated for a given frequency?

Wavelength = Speed of sound / frequency Signup and view all the answers

What is NOT a characteristic of the decibel scale?

It measures the loudness directly. Signup and view all the answers

Which statement about sound phase and frequency is true?

Phase differences help establish directivity in sound perception. Signup and view all the answers

What happens to the energy level of sound as the distance from the source increases?

The energy level decreases exponentially. Signup and view all the answers

Which of these options best describes why the human brain struggles to detect low frequencies?

Long sound waves have less distinct phase differences. Signup and view all the answers

What is the approximate speed of sound in meters per second?

340 m/s Signup and view all the answers

What is one advantage of Solid State Drives (SSD) compared to traditional Hard Drives?

They have no mechanical restrictions on access times. Signup and view all the answers

Which type of equalizer offers full control of the entire frequency range?

Fully-parametric EQ Signup and view all the answers

What effect does the Fletcher Munson curve illustrate regarding human hearing sensitivity?

Humans hear best at frequencies around 1-4 kHz. Signup and view all the answers

What is the primary function of a compressor in audio processing?

To limit the dynamic range of a signal. Signup and view all the answers

Which dynamic control system specifically reduces noise below a certain level?

Noise Gate Signup and view all the answers

In the context of audio equalization, what does a peaking filter do?

Enhances or attenuates frequencies at a specific point. Signup and view all the answers

What is meant by 'attack' in dynamic processing?

Time taken to apply changes to the output. Signup and view all the answers

What is the purpose of using limiters in audio processing?

To reduce the dynamic range significantly. Signup and view all the answers

Study Notes

The Physical of Sound

Sound is created by a source disturbing air molecules, causing fluctuations in air pressure.
Sound energy propagates through compression and rarefaction of air molecules, forming a sound pressure wave.
The intensity of sound in a free field decreases in proportion to the square of the distance from the source. Sound energy spreads uniformly in all directions, like an expanding sphere.

The Decibel

Decibels (dB) measure the difference in intensity between two sound levels, not volume.
0dB is a reference point; other values are compared to this.
Doubling sound power increases loudness by 3dB in intensity, but a 10dB increase is perceived as twice as loud.
Human hearing sensitivity varies logarithmically, with maximum sensitivity to quieter sounds and minimum sensitivity to louder sounds. Hearing range is 10,000,000,000,000: 1.

Speed of Sound

340 meters per second.

Calculating Wavelength

Wavelength = Speed of sound / frequency.

Auditory Perception & Psychoacoustics

Sound arriving at the right ear slightly later than the left ear provides brain with the differences needed to establish directivity. The brain interprets short sound waves (high frequency) more accurately and precisely than long sound waves (low frequency) direction.
The pinna, ear drum (tympanic membrane), and ossicles (hammer, anvil, stirrup) all contribute to sound transduction and transfer to the inner ear, where the variation of atmospheric pressure is converted into neutral signals.
The inner ear (cochlea) processes sound vibrations with fluid-filled chambers and thousands of hair cells, which are structured along 24 frequency bands, responding to specific frequency ranges.

Room Acoustics

Three types of room modes exist: axial, tangential, and oblique, with axial being the most influential. Axial modes occur between two surfaces (the worst), tangential modes involve four surfaces (½ the power), and oblique modes contain all six surfaces (¼ the power).
The problem frequencies are low, in the range of 200Hz to upwards.
Room modes, when combining, will boost certain frequencies.

Sound Pressure Levels

Sound pressure levels lose 6dB for every doubling of distances.
Reflections, absorption, and transmission all affect the way sound propagates in a room.

Audio Signals and Interconnectivity

Electrical Current: Audio equipment uses alternating current (AC) to represent changes in air pressure. AC is the flow of electrons periodically reversing direction.
Direct Current (DC) is used as the signal ground for equipment and flows in a unidirectional manner.
Units used to measure signals include volts, amps, and ohms.
Impedances matching (guitar high impedance, mic low impedance)
- High impedance above 1k ohms
- Low impedance below 1k ohms.

Reverb

Reverb is the persisting sound of reverberation which decays by 60dB below the original sound level.
Types of Reverb: early reflections, late reflections, diffuse reflections, decay, and pre-delay
Components of reverberation measurement that are discussed include room interaction through absorption, transmission, and reflection.

Microphones

Microphones convert sound waves into electric signals, with categories like dynamic, condenser (capacitor), and ribbon mics each with a different method of transferring the sound wave into corresponding current.
Directivity describes how a microphone responds to sound from different directions.

Recording Formats, Multitrack, and Digital Audio

Sonic attributes include tape width, signal-to-noise ratio, and tape speed.
Digital recording: PCM, sampling, A/D and D/A conversion, audio interfaces, hard drive storage (HDD).

Equalisation

Filter Types: Hi-shelf, low-pass, high-pass, peaking (bell curves).
Full and semi parametric Equalization (EQ)

Dynamic Control System

Dynamic control systems like compressors, limiters, gates, and expanders adjust the dynamic range of an audio signal by compressing, attenuating, or equalizing loud or quiet sections of the audio signal to achieve acceptable sound performance levels.

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Description

This quiz explores the physics behind sound, including how it is created, measured, and propagated. Learn about sound intensity, decibels, and the speed of sound, as well as the fundamentals of calculating wavelength. Test your knowledge and understanding of these essential concepts in acoustics.