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 DIGITAL SOUND

FOUNDATIONS OF THE DIGITAL SOUND

1. Nature Of The Sound

To understand (include) the characteristics of the digital, first sound there will be done a small introduction of the characteristics of the sound and his concepts mass basic.

The sound they are vibrations of the air particles that propagate across the air, thanks to these particles of the air that move, the vibrations come to our ears(hearing). The hearing in the human beings, happens providing that a vibration has a frequency understood (included) between(among) approximately 15 and 20.000 hertz, and his intensity is the sufficient one to come to the internal ear(hearing).When the vibrations spend(pass) these margins one ultrasound speaks and they are not perceptible to the human being.
The characteristics of the sound it is possible to measure and for it there are used the units of hertzes (Hz) that measure the frequency of a sound or all the times vibrate in a second, and the decibels (Db) that there measures the intensity (extent) of a wave.
The ear(hearing) and a microphone incorporated into the sound card have a similar functioning. Both transform the vibrations of the air into an electrical sign that can be understood(included) and stored by his(her,your) respective brains. This sign can be guarded, manipulated or reproduced by the electronic suitable means.

 

Muestra de cuatro sonidos con distinta frecuencia

Tabla de frecuencias

TECHNOLOGIES OF COMPRESSION

The technologies (skills) of compression are an object of other one of the works of the subject; nevertheless they are very related to the formats of digital audio for what I will treat them as a brief form.

The technologies (skills) of compression are the fundamental tool of the one that prepares to reach the commitment adapted between(among) capacity of storage and of processing needed

                                          

ADPCM (Adaptative Differential Touches Code Modulation). It is a question of a differential codification: instead of representing the samples of the sign, there is stored the difference between consecutive samples, which for signs audio, it(she) is in the habit of being small. ADPCM is articulated in the standards CCITT G.721, CCITT G.723 and in the CCITT G.726, which replaced both previous ones defining standards for 16, 24, 32 and 40 kbits in second (that they correspond(fit) to sizes of sample of 2, 3, 4 and 5 bits respectively).

LPC - 10E (Linear Predictive Coder This algorithm makes correspond (fit) the sign audio with a linear simple model and obtains the parameters that better fit the model to the sign. The generated sign is slightly faithful to the original one. It is in use in some services of voice.

      CELP (Code Excited Linear Prediction). It is similar to LPC-10E, but beside assigning the parameters of the model, bears the mistake in mind between(among) the original sign and the approximate one, creating a table of mistakes. The sign consists of the parameters of the model more the index of the mistake in every sample. The table is common to codifier and Decoder.

      GSM 06.10. It is LPC's modification named RPE-LPC (Regular Touch Excited - Linear Predictive Coder). The compression is very high but it   needs also of very much processing.

      MPEG. It is a standard both for audio and for video. It obtains high compression in the information and needs of a lot of power of calculation, especially in the codification. It has defined three layers for the versions MPEG-1 and MPEG-2:

          Or Layer I: from 32 to 448 kbps

          or Layer II: from 32 to 384 kbps

           Layer III: from 32 to 320 kbps 

DirectSound

DirectSound is a software component of the DirectX library, provided by Microsoft, which resides on a computer with the Windows operating system.

 Provides a direct interface between applications and drivers for your sound card, allowing applications to produce sounds and music. Besides providing the essential service to pass data to the audio sound card, it provides many needed capabilities such as recording and mixing sound, adding sound effects like reverb, echo, flanger, using hardware controlled buffers for extra speed; position sounds in 3D space (3D audio spacing), capture sound from a microphone or another input capture and control of effects during audio capture. Of these, the sound mixing and volume control of audio are essential.



DirectSound also allows multiple applications in a convenient way to share access to the sound card simultaneously. His ability to play the 3D sound adds a new dimension to games. It also provides the ability to change games a musical sequence in response to events of the game in real time, the music could accelerate as the action increases.

After many years of development, DirectSound API is now a very mature, and provides many other useful capabilities, such as the ability to reproduce the sounds of multichannel sound and high resolution. While DirectSound was designed to be used in games, a number of audio professionals now take advantage of its diverse capabilities.