PT101 - Lesson 1a

Audio Basics

• The three critical parts of audio are:
  • Waveform: the shape of a sound
  • Frequency: the pitch of a sound
  • Amplitude: the energy level of a sound

Waveform

• A waveform represents the tone or timbre of a sound
• Waveforms have a compression phase and a rarefaction phase
• A compression phase is when the energy increases, and a rarefaction phase is when the energy decreases
• The combination of compression and rarefaction phases creates a cycle
• A waveform with a shorter compression phase and a longer rarefaction phase will have a different tone than a waveform with a longer compression phase and a shorter rarefaction phase
• Examples of waveforms include:
  • Sine wave: a simple and pure sound
  • Square wave: a sound with a more complex waveform
  • Triangle wave: a sound with a triangular waveform

Frequency

• Frequency refers to the pitch of a sound
• It is measured in Hertz (Hz) and represents the number of cycles per second
• A higher frequency means a higher pitch, while a lower frequency means a lower pitch
• The human range of hearing is from 20 Hz to 20,000 Hz
• Different animals can hear different frequencies
• The frequency range of human hearing can vary depending on age and listening habits

Amplitude

• Amplitude refers to the energy level of a sound
• It is visually represented in a waveform by its height
• A sound with a greater amplitude will be a taller waveform, while a sound with a lower amplitude will be a shorter waveform
• Amplitude can be affected by the force of a sound, such as hitting a drum harder or softer
• The unit of measurement for amplitude is Decibel (dB)
• The human range of hearing is from 0 dB (silent) to 120-130 dB (painful)

Audio in the Digital Domain

• Audio can be recorded and stored on a digital medium
• The process of converting analog audio to digital audio is called analog-to-digital (A/D) conversion
• The process of converting digital audio back to analog audio is called digital-to-analog (D/A) conversion

Samples and Sample Rates

• A sample is an instantaneous measurement of an audio signal
• A sample rate is the number of samples taken per second
• Common sample rates include:
  • 44.1 kHz (44,100 samples per second)
  • 48 kHz (48,000 samples per second)
  • 88.2 kHz (88,200 samples per second)
  • 96 kHz (96,000 samples per second)
• The sample rate must be at least twice the highest frequency of the sound to accurately record or reproduce it
• The Nyquist-Shannon sampling theorem states that the sample rate must be at least twice the highest frequency of the sound

Bit Depth

• Bit depth refers to the number of bits used to measure the amplitude of a sound
• Common bit depths include:
  • 16-bit: 65,536 possible amplitude values
  • 24-bit: 16,777,216 possible amplitude values
• A higher bit depth allows for more accurate measurements of amplitude and a greater dynamic range
• The formula for calculating the dynamic range of a bit depth is: 6 dB per bit
• 16-bit audio has a maximum dynamic range of 96 dB, while 24-bit audio has a maximum dynamic range of 144 dB

The Impact of Sample Rate and Bit Depth on File Size

• The choices of sample rate and bit depth will influence the file size of a digital audio file
• A higher sample rate and bit depth will result in a larger file size
• The following chart lists sample rates, bit depths, and their corresponding file sizes for a mono, one-minute audio file:
  • 44.1 kHz, 16-bit: 5.3 MB
  • 48 kHz, 16-bit: 5.8 MB
  • 88.2 kHz, 16-bit: 10.6 MB
  • 96 kHz, 16-bit: 11.5 MB
  • 176.4 kHz, 16-bit: 21.1 MB
  • 192 kHz, 16-bit: 23.0 MB
  • 44.1 kHz, 24-bit: 7.9 MB
  • 48 kHz, 24-bit: 8.6 MB
  • 88.2 kHz, 24-bit: 15.9 MB
  • 96 kHz, 24-bit: 17.2 MB
  • 176.4 kHz, 24-bit: 31.8 MB
  • 192 kHz, 24-bit: 34.6 MB

Learn about the concept of amplitude in sound waves and how it is visually represented in waveforms. Explore how different amplitudes affect the energy level of sound and the height of waveforms in this informative quiz.