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Decoder Circuit for Small Surround Sound

2018-05-03 17:47  
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The circuit has been created to design a decoder circuit that will operate in a module that would produce an audio surround sound.

TL072 – a low noiseJFETinput operational amplifier with features such as common-mode input voltage range, high slew rate, operation without latch up, compensated internal frequency, high input impedance at theJFETinput stage, low noise, low total harmonic distortion, protected from output short circuit, low input bias and offset currents, wide common-mode and differential voltage ranges, and low power consumptionTL074 – low noiseJFETquad operational amplifier with features such as high slew rate, latch up free operation, compensated internal frequency, low harmonic distortion, protection from output short circuit,JFETinput stage with high input impedance, low offset current and input bias, low noise, and wide common-mode and differential voltage rangeMN3101 – aCMOSlarge scale integration generating two phase clock signal of low output impedance used as Bucket Brigade Delay (BBD) clock generator/driver and has features such as 8-lead dual in-line plastic package, single power supply, two phase clock output, separate and self oscillations, andBBDdriving capability up to two MN3005sMN3004 – a 512-stage high performance low noiseBBDthat provides a 85 dB signal to noise ratio (S/N) by increasing the capacity of capacitors with the same chip area, which is enabled by the improvement of Silicon materials and process

Surround sound is a term used to describe several types of processes that makes up an audio output where it enables the sound to come in all directions or surround the listener. This system utilizes front and rear speakers with three or more channels to create directional audio sources and surrounding envelope of sound. It can either be digital or analog as the term becomes widely used in the introduction of home theater systems in recent years. The surround sound system includes a variety of methods where an audio source is being enhanced with a quality sound reproduction with the addition of discrete speakers through the audio channels.

The aim of the construction of this circuit is to provide a decoding scheme using the surround sound system and is not meant to replace the surround sound decoders available in the market since they contain several features and facilities. The circuit however can be used with other basic functionalities as a standard decoder. The first versions of Dolby Digital were being phased out and replaced with Dolby 5.1,DTS, and other succeeding versions which support the transport and management level of digital sound signal. The basics of Dolby Surround process requires four channels of information, the center, rear, front left, and front right surround contained in a signal of two channels. The decoding of four channels is made possible by a decoding chip that sends the signal to the appropriate destination.

The Dolby Digital refers to a brand of technologies developed by Dolby Laboratories for a series of lossy audio compression where the compression and decompression of data results to an output that is fairly distinctive from the original, but still useful in some ways. Dolby Digitals can be made as monophonic, 2-channel, 4-channel, 5.1 channels, or 6.1 channels. However, it must be taken into account that the phrase Dolby Digital does not refer to the number of channels that it contains but on the digital encoding of the audio signal. Although Dolby 5.1 and 6.1 is oftentimes simply called as Dolby Digital in most typical applications.

To enable sounds to propagate in more directions, Dolby Digital 5.1 is adding stereo rear surround channels which make them more accurate and flexible. They can also provide more importance for low frequency effects by adding a dedicated subwoofer channel. The encoding and decoding of Dolby Digital will require the same quantity of frequency range and power output as the main channels unlike the Dolby Pro Logic where there is a limited frequency response and only minimal power for the rear channel.

The other versions of Dolby Digital that follow are Dolby Digital EX which utilizes matrix technology by adding a single rear surround channel to stereo soundtracks and a center channel and functions like the earlier Pro Logic format; the Dolby Digital Surround EX which provides a means for 5.1 soundtracks that is backwards compatible and economical to carry a center back surround channel for enhanced localized results; the Dolby Digital Live (DDL) which is used for interactive media like video games as a real-time hardware encoding by converting any audio signals from a game console into the 5.1 channel Dolby Digital format and transferring it through a Sony/Philips Digital Interconnect Format (S/PDIF) cable ; the Dolby Digital Plus that provides increased bitrates, improved coding techniques to reduce compression artifacts, backward compatibility with existing, and support for more audio channels; and the Dolby TrueHD which is an advanced lossless audio codec that supports codecs mandatory for HDDVD.

The operation of the above circuits starts as the stereo sound signal transports surround sound information on the master volume part of the circuit. This will drive the Left channel Lch attached to Model TL072 IC1A and IC1b in which Right channel Rch is attached. The outputs on these operational amplifiers would serve as the input buffer to the following stages of the circuit. IC2C is responsible for summing up the signals from the left and right channels that will power the central loudspeaker output while IC2D is responsible for increasing the phase difference between left and right channels which is encoded in the two channels and will be fed to the rear loudspeakers. It is necessary to ensure that the negative terminals between the rear speaker is not earthed because they will simply function in parallel with the main speakers.

The output of IC2D will power regulated delay unit of audio to the rear loudspeakers. This would lead to the creation of proper sense of spacing in accordance to the size of the room. This will incorporate op-amp sound delay signal IC5 MN3004 which has 512 stages. Since IC4 MN3101 is a clocking signal, it provides timing to IC5 as it functions as an oscillator in the circuit. Variable capacitor C17 regulates the delay time in the circuit. The presence of filters in the circuit is for the purpose of preventing noise that will be produced during the process. These filters can be regulated to cut the frequencies above 8 KHz and under 100 Hz, to be able to drive the rear speaker. The rear loudspeaker is small in size because its input is encoded with a bandwidth of 100 Hz up to 8 KHz. The filters are built around the IC6A/B which is also an output buffer. A potentiometer is placed in every output to aid in the adjustment and regulation of loudspeakers and amplifiers. The supplied power in the circuit is 15 V and every output can drive a single power amplifier.

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Source:users.otenet.gr/~athsam/surround_sound_decoder.htm


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