Photoshop Designer

6 November 2010

Digital Audio And Sound Application

Sample Rate
Taking more samples allows the “sampling" process to more closely approximate the curve of the original, analog wave, and therefore get closer to reproducing the sound digitally

Also known as Sampling Frequency
E.g:
  • 44KHz: CD quality sound
  • 22KHz: OK for music
  • 11KHz: OK for voice
  • 5 KHz: A.M. radio
Sample Size
  • Sample size is either 8-bit or 16-bit; this naming scheme describes the amount of computer space allotted to store data gathered in each sample
  • Also known as Bit Depth / Sample Resolution
  • The more bits used to represent the amplitude, the greater the dynamic range that can be represented

Analog To Digital Converter


1. Here is an analog sound wave. Analog sound is continuous variation in air pressure.
2. To digitize sound, samples are taken at even intervals of time.
3. These samples are trimmed to the nearest value and encoded in binary.

Sound File


  • Sound files contain large amounts of data, and uncompressed, they are huge.
  • A sound file generally has audio data and metadata
  • Audio data is the sound that you hear
  • Metadata can include the name of the sound file, its size, duration, number of channels, resolution or sample size (in bits), sampling rate (in kilohertz), type of compression, information about licensing or streaming, special instructions, or other text or graphics.

Amplitude Envelope
  • When a mechanical musical instrument produces sound, the relative volume of the sound produced changes over time
  • The way that this varies is different from instrument to instrument
  • Example: A guitar, by contrast, is loudest immediately after it is played, and fades with time
  • Shaping of the sound's amplitude profile is realized with an "ADSR" (Attack Decay Sustain Release) envelope model
  • The ADSR envelope is a parameter used in synthesizers to control the sound produced




  • Attack: How quickly the sound reaches full volume after the sound is activated (the key is pressed).
  • Decay: How quickly the sound reduces in volume after the initial peak.
  • Sustain: The "constant" volume that the sound takes after decay until the note is released.
  • Release: How quickly the sound fades after the end of the note (the key is released). Often, this time is very short.
Stereophonic
  • It is the study of multichannel, 3D sound and the electronic audio equipment used to reproduce it.
  • It is a way to recreate a sound stage, including the ability of the listener to determine the original source location of specific sounds.
  • (stereois ‘3D’ and phonicis ‘the science of sound’)
  • Before stereophonics, there was monophonicwhich only utilized one channel of recording and playback

Channels
  • A channel is a single path for transmitting electrical signal
  • One channel audio system = 1 source, 1 recording channel, 1 amplifier & 1 speaker
  • Multichanneling makes several recordings of the same sounds
  • Its like having two or more tape running simultaneously
  • The channels are recorded with more than one microphone thus the channels are not exact duplicates of each other.

Creating Stereo
  • Stereo theoretically separates each sound source and places it in 3 dimensions
  • E.g. Guitar on the left, piano to the right and a singer centered.
  • Two microphones are recording the sound pressures which placed at a distance from each other
  • Usually reside in front of instruments or voices being recorded
  • Each microphone is recording one track on the same audio tape. The two tracks then played by two separate speakers.
Law of the First Wave Front
  • The first sound to arrive at the ears determines the perception of direction to the source.
Reverberation
  • Reverberation consists of the random sounds that surround the listener in a live concert hall experience
  • It is the hidden equation in stereo imaging
  • These are the sounds that are launched out to the audience, auditorium, concert hall or studio and are bounced back to the microphones that are recording two tracks.
Surround sound

  • Surround sound is a system that enhances the spatial imaging capabilities of the playback system
  • To create a sound field that can surround the audience with direct and ambient sound from all directions
  • Example:  Pro Logic, 4 Channel and 5, Speaker-Dolby Digital
Speech Synthesis
  • Speech synthesis is the artificial production of human speech.
  • It can be implemented in software or hardware.
  • Speech synthesis systems are often called text-to-speech (TTS) systems in reference to their ability to convert text into speech
  • TTS is composed of two parts: a front end and a back end

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