# PT101 - Lesson 1a

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## 42 Questions

Waveform

### Which part of an audio waveform is referred to as the compression phase?

When energy reaches its peak and then goes back down

Smooth curve

### Which common feature do different waveforms share in terms of energy?

Horizontal line indicating zero energy

### What behavior is seen in all naturally occurring audio waveforms?

Ascending from the zero energy line

### How would a silent audio waveform appear on a graph?

Straight horizontal line at zero energy

Energy level

Taller

Decibel

120-130 dB

dB SPL

Volume

### What does loudness deal with in relation to sound?

Perceived sound level

### What is needed to properly record or reproduce a sound using digital audio?

Several samples spaced evenly in time

### Analog-to-digital (A/D) conversion refers to which process in the recording of audio?

Conversion of sonic to electrical energy

### What is the term used to describe the part of an audio wave where the air pressure increases?

Compression phase

Tone or timbre

Frequency cycle

### How is frequency measured in sound waves?

In cycles per second (Hertz)

20 Hz to 20 kHz

Presbycusis

### What represents a low-frequency sound compared to a high-frequency sound?

Fewer cycles per second

'Pure' sound

### 'Two cycles of a sine wave' represents what aspect of sound?

'Temporal' property

### According to the Nyquist-Shannon sampling theorem, how many samples per second are needed to accurately record or reproduce a sound?

At least twice the highest frequency of the sound

### What happens when there are less than two samples per cycle when recording a sound?

Lower frequency is created

22.05 kHz

### Why is a high-frequency distortion near the Nyquist frequency audible in digital recordings?

The distortion is within the audible range

### What is the significance of a 16-bit audio in terms of amplitude representation?

A maximum of 65,536 discrete amplitude levels

24-bit

48 kHz

16,777,216

### How does increasing bit depth affect the dynamic range in audio recording?

Increases the dynamic range

144 dB

### How does a 24-bit audio file compare to a 16-bit audio file in terms of dynamic range?

24-bit has a higher dynamic range than 16-bit

~3 MB

Doubles

32-bit float

### What impact do higher sample rates and bit depths have on Digital Audio Workstations?

Can handle more tracks and plug-ins

~10.6 MB

### What valuable resources are recommended for those interested in diving deeper into digital audio science as per the text?

Digital Domain and Principals of Digital Audio by Ken Pohlmann

## Study Notes

### 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.

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