Audio Fundamentals

1. Frequency

1.1. Frequency and period are Inversely Proportional: •T=1/f •f=1/T

1.2. Unit for frequency: Hz (Hertz) 1 Hz = 1 cycle/second

2. SPL

2.1. Example: : - 0 dB SPL - no sound heard – 35 dB SPL - quiet home – 70 dB SPL - noisy street –110 dB SPL - thunder –120 dB SPL - discomfort

2.2. sound pressure level (SPL): SPL is measured in decibels based on ratios and logarithms

2.3. Pitch of Sound : • Sound frequency • Higher frequency: higher pitch • human ear can hear sound ranging from 20 Hz to 20,000 Hz

2.4. Sound Intensity vs. Loudness

2.4.1. Sound intensity: • an objective measurement • can be measured with auditory devices • in decibels (dB) Loudness: • a subjective perception • measured by human listeners •human ears have different sensitivity to different sound frequency •in general, higher sound intensity means louder sound

3. audio digitization

3.1. Two step process for digitizing audio : 1- sample and hold 2- Quantize

3.2. Analog signal (continuous change in both temporal and amplitude values) should be acquired in digital forms (digital signal) for the purpose of – Processing – Transmission – Storage & display

4. Sound

4.1. Acoustics : is the study of sound: generation, transmission, and reception of sound waves

4.2. Sound wave: energy causes disturbance in a medium, made of pressure differences

4.3. Sound : is a continuous wave that travels through a medium

4.4. Sound : is a continuous wave that travels through a medium

5. Signal Fundamentals

5.1. Pressure changes can be periodic or aperiodic Periodic vibrations: –cycle - time for compression/rarefaction –cycles/second - frequency measured in hertz)) –period - time for cycle to occur (1/frequency Human perception frequency ranges of audio [20, 20kHz]

6. Sampling Rate

6.1. : Higher sampling rate : .The reconstructed wave looks closer to the original wave More sample points, and thus larger file size

6.2. Sampling Rate Examples • 11,025 Hz AM Radio Quality/Speech • 22,050 Hz Near FM Radio Quality (high-end multimedia) • 44,100 Hz CD Quality • 48,000 Hz DAT (digital audio tape) Quality • 96,000 Hz DVD-Audio Quality • 192,000 Hz DVD-Audio Quality

6.3. The sampling rate determines how many values of the signal we choose to retain. Sampling Interval (Ts): • Amount of time separating the samples • Also called sampling period Sampling Rate (fs): •Number of samples persecond •Also called sampling frequency Ts = 1/fs or fs = 1/Ts

6.4. Sampling Rate vs. Sound Frequency

6.4.1. • Both uses the unit Hz BUT: • sampling rate =! sound frequency • Sample rate: a setting in the digitization process • Sound frequency: NOT a setting in the digitization process • Sound frequency: the pitch characteristic of sound • Higher sampling rate: NOT the pitch characteristic of sound