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Different frequency bands

Abstract

This paper accounts to analyze and implement the Graphic Equalizer with 5 different frequency bands on TMS320C6713 digital signal processor. The Graphic interface is built using the LabVIEW, which is the graphical programming language from National Instruments. The interface designed is compatible to draw results from the DSK processor. The FIR filter coefficients are resulted using MATLAB. Finally, the performance of Equalizer is analyzed using an audio signal as an input and the variations are observed at different frequency levels.

INTRODUCTION

GRAPHIC equalizer controls different frequency bands and it is an audio controller. The use of Graphic equalizers is found in many user applications like in sound systems and in audio recording studios. The controllers are in the form of sliders and the amplitude levels of particular frequency are varied just by moving the sliders up and down.

The Graphic equalizer which was designed is a 5-band equalizer. The five different levels are 250Hz, 1 kHz, 2 kHz, 4 kHz and 16 kHz. The analysis is involved in designing 5 different filter coefficients using MATLAB, and a GUI is designed using LABVIEW for the equalizer. The source code is written in C and the code is managed to compile and run using Code Composer Studio (CCS). All the functionality is implemented on Digital Signal Processor kit (DSK) along with TMS320C6713.

The flow analysis of this paper involves in studying the behaviour of the equalizer and DSK-TMS320C6713 processor and LabVIEW. Later, the performance of the equalizer is also analyzed.

PRE-STUDY

Equalizer

The process of Equalization varies the characteristics of the frequency for a given audio signal. The amplitude levels of particular frequency can be varied for a given sound signal. The audio signal is generally a mixture of many frequency bands. Here , in this paper, we try to amplify only certain specified frequency notes.

The amplitude levels are changed in accordance to change in slider's position. The sliders control the amplitude in order to either amplify or decimate the signal point. We designed a graphic equalizer with five different sliders. The first slider was designed to change the amplitude levels of those, whose frequencies are at 250 Hz. The second one was for 1 kHz, third for 2 kHz, fourth for 4 kHz and the last one for 16 kHz.

DSK-TMS320C6713 Processor

The C6713 DSK is a low-cost standalone development platform that enables users to evaluate and develop applications for the TI C67xx DSP family. The DSK also serves as a hardware reference design for the TMS320C6713 DSP. Schematics, logic equations and application notes are available to ease hardware development and reduce time to market.[2]

The DSP on the 6713 DSK interfaces to on-board peripherals through a 32-bit wide EMIF (External Memory Interface). The SDRAM, Flash and CPLD are all connected to the bus. EMIF signals are also connected daughter card expansion connectors which are used for third party add-in boards. [2]

LabVIEW

LabVIEW is a graphical programming environment used by millions of engineers and scientists to develop sophisticated measurement, test, and control systems using intuitive graphical icons and wires that resemble a flowchart. LabVIEW offers unrivalled integration with thousands of hardware devices and provides hundreds of built-in libraries for advanced analysis and data visualization. The LabVIEW platform is scalable across multiple targets and operating systems [3].

The front panel window of LabVIEW is displayed with a gray coloured background and the block diagram is displayed with a white coloured background. The GUI built front panel consists of the controllers and the signal displays which act as inputs and outputs. The controls used in this project, such as sliders and other inputs helps to simulate the input data and will supply that data to the block diagram. The graphic source code is contained along with the block diagram of the VI. The front panel objects are controlled by the graphical represented functions of the code. The control and indicator terminals are connected to VIs and functions using wiring tool. The execution order of the VI and its functions are determined by the flow of the data through the nodes of the block diagram.

Template Design in LabVIEW

LabVIEW was launched and a new VI was opened to design the graphic equalizer. The „Show Block diagram? option was selected from the windows menu on the template to open the block diagram with white background. In our project, three Stacked Sequence Structures were used in the block diagram where each stacked sequence structure contains one or more sub-diagrams or frames that execute sequentially. All the necessary VIs and functions were added in these structures to create and control the objects in the front panel.

Compiling, Linking and Rebuilding in CCS:

TMS230C6713 kit was tested and connected to PC through CCS by selecting the option „connect? in the „Debug? menu. The project file with .pjt extension was opened in code composer studio and the source code files GraphicEQ.c along with all necessary support files were added. The build options were modified by selecting C6710 in the „basic? category, selecting the path of dsk6713.h file and writing CHIP_6713 in the necessary fields of the „pre-processor? category. The project was compiled and built with all necessary executable files by selecting the option „rebuild all? in the „project? menu. The source code written in C enables the user to run the project in the LabVIEW. Thus the CCS and the LabVIEW acts as back-end and front-end respectively.

Run project in LabVIEW:

The equalizer project designed in LabVIEW was opened and an audio signal from PC was given as input to the equalizer by connecting input to the connector LINE IN on the DSP board. Speaker was connected to the LINE OUT connector on the DSP board. The option „run? on the template was selected to load and run the project. While running the project, the positions of the sliders were altered for tuning the audio signal and the sound from the speaker was observed. The project was stopped by pressing the push button STOP on the template.

CONCLUSION

A Graphic Equalizer is designed with five sliders using LabVIEW and is analysed perfectly using TMS320C6713 DSK processor. Five different FIR filter coefficients with respect to each slider were resulted using MATLAB. An audio signal was given as input and the equalizer has been tested in order to undergo fine tuning. The performance of equalizer was good and variations in the sound levels are observed.

References

  1. Digital Signal Processing and Applications with the C6713 and C6416 DSK by Rulph Chassaing.
  2. TMS320C6713 DSK Technical Reference 506735-0001 Rev. May 2003 by Spectrum Digital
  3. http://www.ni.com/labview/whatis/