Dr Md Kabirul IslamProfessor and Head Department of MICA

Daffodil International University

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Contents of Today Lecture Different audio editing softwares List the different audio file formats

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AudioSound is a continuous wave that travels

through the air. The wave is made up of pressure differences.

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Basic Sound Concepts Frequency represents the number of

periods in a second (measured in hertz, cycles/second)

Human hearing frequency range: 20 Hz - 20 kHz (audio), voice is about 500 Hz to 2 kHz.

Amplitude of a sound is the measure of displacement of the air pressure wave from its mean.

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Digital Conversion of Audio • Speech is analog in nature and it is

converted to digital form by an analog-to-digital converter (ADC). • A transducer converts pressure to voltage

levels. (A transducer is a device that converts a signal in one form of energy to another form of energy) • Convert analog signal into a digital stream

by discrete sampling • Discretization both in time and amplitude

(quantization)

Digital Conversiton

Digital audio systems may include compression, storage, processing and transmission components. Conversion to a digital format allows convenient manipulation, storage, transmission and retrieval of an audio signal.

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Digital AudioDigital audio is created when a sound wave is converted into numbers – a process referred to as digitizing. It is possible to digitize sound from a microphone, existing tape recordings, live radio and television broadcasts, and popular CDs.

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Example: A sound wave, in red, represented digitally, in blue (after sampling).

Formula for determining the size of the digital audio• 1. Sampling Rate: rate at which a continuous

wave is sampled (measured in Hertz) Examples: CD standard - 44100 Hz, Telephone

quality - 8000 Hz 2. The sample size is the amount of information

stored. This is called as bit resolution.3. The number of channels is 2 for stereo and 1 for

monophonic.4. The time span of the recording is measured in

seconds.

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Monophonic and Stereophonic sound

Stereo (or Stereophonic sound) is the reproduction of sound using two or more independent audio channels in a way that creates the impression of sound heard from various directions, as in natural hearing.

Mono (Monaural or monophonic sound reproduction) has audio in a single channel, often centered in the “sound field”. i.e. and stereo (Stereophonic) are classification of sound.

Examples Mono: Public address system, radio talk shows, hearing aid, telephone and mobile communication, some AM radio stations

Stereo: Movies, Television, Music players, FM radio stations

Editing Digital RecordingsThe basic sound editing operations that most

multimedia procedures needed are described as follows:

1.Multiple Tasks: Able to edit and combine multiple tracks and then merge the tracks and export them in a final mix to a single audio file.

2.Trimming: Removing dead air or blank space from the front of a recording and an unnecessary extra time off the end is your first sound editing task.

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Editing Digital Recordings

3. Volume Adjustments: If you are trying to assemble ten different recordings into a single track there is a little chance that all the segments have the same volume.

4. Format Conversion: In some cases your digital audio editing software might read a format different from that read by your presentation or authoring program.

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Audio File FormatsA file format determines the application that is to be used for

opening a file. Following is the list of different file formats and the software that can be used for opening a specific file.

1. *.WAV for Windows Systems2. MIDI files – for Windows3. *.WMA –windows media player4. *.MP3 – MP3 audio5. *.RA – Real Player6. *.VOC – VOC Sound

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