تقنيات الوسائط المتعددة - المحاضرة 7

Multimedia Technologies - Lecture (7)

• The lecture focuses on sound, sound properties, sound wave properties, sound representation in a computer, and calculating sound volume.
• Sound is a set of invisible waves that living creatures perceive through their sense of hearing.
• Scientifically, sound is the physical effect on the ears that allows them to distinguish and recognize surrounding sounds, based on the brain's interpretation of sound waves transmitted by the auditory nerve.
• Sound encompasses everything audible through hearing, including speech, music, and even noise (though undesired).
• Sound is vibration that travels through air or another medium until it reaches a person's or animal's ear.
• Human perception of sound is a complex process involving three systems: the source of the sound, the medium for transmission (e.g., air), and the receiver that captures and interprets the sound.
• Sound waves are the form sound takes when it moves from the source to the receiver through a medium (a series of frequencies interacting with air molecules, which separate after the sound passes).
• Engineers represent these vibrations visually as waves to make calculating the number of vibrations and theoretically studying the nature of sound easier.
• Every wave consists of several vibrations, which shape the wave.
• Multiple vibrations vary in pitch, timbre, and loudness, resulting in different sounds.

Sound Properties

• Sound is characterized by three properties:
  • Sound Pitch: The distance the frequency of sound waves travels, depending on the sound source. Sounds can be soft or very loud, producing screams—the rapid movement of sound waves through air molecules increasing their intensity and spread. A higher pitch is associated with greater dissonance if various sounds are made simultaneously.
  • Sound Intensity: The increase in the energy used to transmit sound, the compression of sound particles. A microphone, amplifies sound to increase its frequency.
  • Sound Quality: Measures how clearly the sound reaches listeners. Clear and distinct sound without interference is considered high quality. Factors like frequency boosters (used by radio stations) affect quality. Equipment errors during recording, and file formats used for storing digital sound, can reduce quality. Geographical location also affects quality based on coverage.

Sound Wave Properties

• Period: The time span for a periodic signal to repeat.
• Frequency: The rate at which vibrations occur per second, measured in Hertz (Hz). Higher frequency corresponds to a higher pitch.
• Amplitude: The maximum displacement of a wave from its equilibrium position. The larger the amplitude, the louder the sound.
• Bandwidth: The range of frequencies a device or person can produce or hear.
• Dynamic: Not further defined in the provided text.

Sound Representation in a Computer

• Converting analog to digital.
  • Digitalization: Converting analog signals to digital.
  • Sampling (rate & size/depth): Taking samples at intervals. Rate (samples per second/Hz) and Depth (number of bits per sample, e.g., 8, 16 bits) affect quality.
  • Quantization: Assigning numerical values to samples.
  • Encoding: Converting the numbers to a computer-readable format (e.g., binary).

Calculating Sound Volume

• Formula: Size = Time (seconds) x Sample Rate (Hz) x Sample Depth (bits) x No. of Channels (mono/stereo)
• Variables:
  • Time: Duration of recording.
  • Sample Rate: Sample-taking frequency.
  • Sample Depth: Number of bits used to represent each sample.
  • Number of Channels: Number of audio channels (e.g., 1 for mono, 2 for stereo)
• Conversion to kilobytes (KB) or megabytes (MB) may need division by 1024.

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