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DC215 Basics of Sound

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by

Mike Mitchell

on 11 January 2016

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Transcript of DC215 Basics of Sound

Speed of Sound

• 344 meters/sec in air at 20°C


Basics of Sound

• The theory states that, in order to avoid unwanted
digital artifacts (aliasing) when recording audio,
you must use a sample rate that is double that of
the highest frequency recorded.

• Since we hear up to 20 kHz, we must use a sample
rate of at least 40 kHz.

• To make up for digital errors, among other things,
we generally start off with a sample rate of 44.1 kHz.


• NYQUIST THEOREM

Sample Rate

• At 48kHz, for example, you’re getting 48,000
samples a second.

• You can think of this as thousands of audio snapshots
per second. The greater the number of snapshots,
the closer the digital audio sounds to the original
source.

•The Sample Rate is the number of times your audio
is measured (sampled) per second.

Sample Rate

• In other words, we perceive amplitude as loudness.

• The amplitude of a wave is closely related to how
loud it sounds.

Amplitude

• The range of human hearing is
20 Hz - 20,000 Hz (20 kHz)

• Just under 262 Hz = middle C

• For example, 110 cycles per second, or 110 Hz = a low A

Frequency

• BIT DEPTH

• SAMPLE RATE

• Digital Audio is greatly affected by two factors:

Audio Resolution

• A 6dB increase results in a doubling
of perceived volume

• It expresses a ratio between two given amplitudes.

• The decibel (dB) is used to describe gains and losses
in signal power within an audio system.

Decibels

• Frequency determines the pitch or the
highness or lowness of a sound.

• Frequency is measured in Hertz (Hz).

• Frequency is the number of complete wave
cycles (one compression and one rarefaction)
that occur in one second.

• Also referred to as cycles per second.

Frequency

Human Hearing

converted to nerve impulses in cochlea

amplified by bones

vibrates ear drum

sound wave

• 16 bits gives us 65,536 possible levels. 24 bits gives
us 16,777,216.

• Dynamic range, simply put, is the difference between
loud and soft sounds.

• The greater the bit depth, the greater the dynamic
range.

• On a graph, the sample rate is a vertical
measurement and bit depth is a horizontal measurement.


Bit Depth
refers to the measurement or sampling
of a sound wave’s amplitude.

Bit Depth

0

10

18

40

120

110

100

80

70

Decibels

• The wavelength of 60 Hz (a bass drum fundamental)
is about 19 feet.

• The wavelength of 1,000 Hz (1kHz) is about 1.1 ft.

• Wavelengths are measured in distance units, such
as inches or feet.

Wavelength

• Measure of the distance that sound will take to complete
a single cycle.

Wavelength

Point of rest

Rarefaction

Compression

Sound Wave

Frequency

Speed of sound

Depends on:
• Type of medium
• travels better through liquids and solids
• can’t travel through a vacuum
• Temperature of medium
• travels faster at higher temps
Full transcript