1. Audio Compression Techniques
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2. A computer works in the digital world, a world where everything is discrete. In this world the computer processes data, bit streams of information. The information can be about anything, a command to switch on/off a light, a text file or an audio sequence.
Digital audio compression allows the efficient storage and transmission of audio data. The various audio compression techniques offer different levels of complexity, compressed audio quality, and amount of data compression.
This seminar is a survey of techniques used to compress digital audio signals. Its intent is to provide useful information for readers of all levels of experience with digital audio processing.
Introduction
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3. Definition Of Audio Signals
Audio signals are discrete time and discrete levels (integer or less commonly floating-point valued) one-dimensional data.
The digital representation of audio data offers many advantages: high noise immunity, stability, and reproducibility. Audio in digital form also allows the efficient implementation of many audio processing functions (e.g., mixing, filtering, and equalization) through the digital computer.
The digital audio data consists of a sequence of binary values representing the number of quantizer levels for each audio sample.
Definition Of Audio Signals
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4. When the analog signal is sampled, it results in discrete values that describes the continuous analog signal. By doing this a certain amount of noise is added to the signal.
Hence to maintain the quality of sound the following operations is to be performed on audio signal.
Quantization
Splitting up the signal
Psychoacoustic models/methods
Frequency masking
Temporal masking
AUDIO COMPRESSION
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5. COMMON AUDIO COMPRESSION TECHNIQUE
There are two main techniques of audio compression-
Waveform coding technique-
It further include various coding techniques as follows
PCM
μ- Law audio compression
Silence Compression DM
ADPCM
COMMON AUDIO COMPRESSION TECHNIQUE
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6. 2) Voice coding technique
It further include various coding techniques as follows
LPC
GSM
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7. AUDIO COMPRESSION TECHNIQUES
There are mainly two types of compression techniques-
Adaptive signal segmentation for compression
adaptively split the signal into non-equal frames so that the overall compressed size will be minimized
Compression of floating-point audio
the integer based compression methods is to approximate the floating-point values with integers and also save some additional information needed to correctly restore the values.
AUDIO COMPRESSION TECHNIQUES
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8. AUDIO COMPRESSION AND FORMAT
Here are some of the most important file compression types; there are many more depending on the program you use to create the audio. Followings are the audio compression formats:
.aac = Advanced Audio Coding File
.aif = Audio Interchange File Format
.amr = Adaptive Multi-Rate Codec File
.Mp4 Audio Files
MP3 Audio File
.wav = Windows WAVE Sound File
.mpeg = MPEG Audio File
AUDIO COMPRESSION AND FORMAT
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9. Compression is used in almost all modern digital audio applications
Compression is used in almost all modern digital audio applications. These devices include computer the audio playing devices telephony application and digital recording devices. Many of the devices like the telephone system have been using compression for many years now Others have just recently started using it. The type of compression that is used depends on cost size space and many other factors.
USES OF COMPRESSION
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10. A very good compression ratio was obtained with fairly simple and fast methods. The most compressed signal is audible, but the personality of the person speaking is somehow lost and the background noise is too high for it to be useful.
CONCLUSIONS
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11. REFERENCES
 K. Pohlman, Principles of Digital Audio (Indianapolis, IN: Howard W. Sams and Co., 1989).
Scientist and Engineer's Guide to Digital Signal Processing:
Faculty of Electrotechnics and Infomratics at TUB berlin.de/ RESSION.pdf
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