Implementation Of Graphical Equaliser Using Labview Computer Science Essay

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Abstract: Graphical equaliser is a method to obtain desired tuning of an audio signal like producing various audio effects. The project aims to implement a 5-band graphical equaliser on TMS320C6713 DSK- KIT, which is accomplished by using real time data communication between host PC and DSK (DSP Starter Kit) with RTDX (Real Time Data Exchange) using Lab view in CCS (Code Composer Studio). Digital signal processor is very useful in fine tuning and to overcome the acoustic and other problems. A channel is created for transferring data between host PC and DSK using RTDX.

Index terms: CCS, RTDX, TMS320C6713 and Lab View.

INTRODUCTION

The Graphical equalizer is a method of fine tuning an audio signal by altering the characteristics of active and passive components in a desired way of a audio system. It is an audio controller which facilitates to control various frequency bands in graphical equalizer and observe variations in audio effects. This method helps in overcoming various audio effects such as distortion, echo and reverb, and harmonics. The project aims to implement a 5-band graphical equaliser on DSP-KIT using CCS and Lab View.

Code Composer Studio provides an integrated development environment (IDE). DSP processors are concerned primarily with real-time signal processing[1]. Real time processing requires processing of some external event like input signal. CCS provides an easy to use software tool to build and debug program. Real time data exchange(RTDX) allows the exchange of data between the host PC and DSK. Lab View (Laboratory Virtual Instrument Engineering Workbench) is a platform which provides a graphical user environment.

PRESTUDY

The equalizer can be implemented by graphical interface method and parametric method depending on the application.

The project is implemented in CCS which helps to drive the DSP-KIT, Lab View provides graphical user interface with which user can drive the kit through CCS. A universal synchronous bus is used to connect DSP kit to the PC.

Digital Signal Processor

DSP based systems are less affected by environmental conditions, easy to use, flexible and economical. They are more compact with specialized type of architecture as it uses microprocessors and an instruction set suitable for signal processing[1]. Digital signal processors are used for a wide variety of applications in communications, speech and image processing.

The DSK support tools consists of [1]

Code Composer Studio: It provides an integrated development environment (IDE), which links compiler, linker, assembler and debugger.

A board that contains a digital signal processor and 32 bit stereo codec.

A universal synchronous bus.

5V power supply.

In CCS, C compiler compiles a C program (.C) to produce assembly source file (.asm). Assembler produces a machine language object file (.obj). The linker combines object files and object libraries to produce an executable file (.out). This executable file can be loaded and run in a digital signal processor.

The supporting file in CCS include

C6713dskinit.c

C6713dskinit.h

C6713dsk.cmd

Vectors_intr.asm

And libraries include

rts6700.lib, dsk6713bsl.lib, csl6713.lib.

The figure shows different parts in digital signal processor block diagram.

Fig. 1. Block diagram of DSK 6713

The onboard codec AIC23 [37] uses a sigma-delta technology that provides ADC and DAC. The kit includes 16MB synchronous dynamic ram access memory, 256KB of flash memory and four connectors. MIC-IN for microphone input, LINE IN for line input, LINEOUT for line output and HEADPHONE for headphone output.

RTDX

Real time data exchange (RTDX) provides an interface between the pc and processor.via onboard Joint Test Action Group (JTAG) interface. RTDX library is included in the target application. A channel is created and enabled using RTDX. When target application calls the libraries API, data is transferred to/from the host without interfering with the target application. On the host, RTDX libraries work in combination with code composer studio. DSP/BIOS make use of RTDX to transfer data for its real-time analysis tools and allows the user to insert and configure RTDX by providing an RTDX interface in its configuration tool[2]. RTDX works according to the routines defined in the RTDX user interface as shown.

"if(!RTDX_channelBusy(&control_channel1))

RTDX_readNB(&control_channel1,&250slid_gain,sizeof(250slid_gain)); " .

LAB VIEW

Lab view is platform and environment for visual programming. Programs written in lab view are called as virtual instruments(VIs). The basic elements are front panel and block diagram, controls and indicators. Front panel provides graphical interface for the user to interact with the system i.e., it contains all the inputs and outputs. Block diagram is made of functional code. These two windows contain two bars which gives control of the execution and also basic editing features. Run and Abort buttons are used to control the program. Controls and indicators are added by using control palette. Controls are added by simply dragging and dropping them on to the front panel. All controls are of same data type. Block diagram creates icons of the controls that are added in front panel. Function palette can be used to add controls in block diagram. This palette consists of functions and structures that are useful in coding an application.

Fig. 2. Block diagram of interface between Pc and DSK 6713

Fig. 3. Front panel of user interface

PROCEDURE

The Graphical Equalizer implemented here consists of 5-bands, which include different frequency bands like 250 Hz, 1 KHz, 2 KHz, 4 KHz and 16 KHz. It is set of filters centred at some fixed frequency. The frequencies are attenuated and boosted to desired frequencies with the help of knobs. The responses are linked to the knobs, the amount of boosting or attenuating reflects in the form of audio effects. Altering one knob reflect changes in the particular frequency band leaving other bands unchanged.

Gain

Band pass

0

frequency

Fig. 4. Frequency response of ideal band pass filter

The figure represents the characteristics of a band pass filter which is incorporated in the equaliser. when the audio signal is passed through equalizer, the audio effects can be varied by varying the filter characteristics which can be better described as shown.

Fig. 5. Graphical Equalizer With 5-Bands Band pass filter.

The filter is designed by generating suitable coefficients. This is done using mat lab FDATOOL.

Selecting a Sampling frequency of 48 kHz and order of 64, filter coefficients are generated for each band of frequency. These coefficients are included in "GraphicEQcoeff.h".

Few filter coefficients are shown here

//GraphicEQcoeff.h Filter coefficients for Graphic Equalizer obtained with Matlab fir1()

float coeff250[] = { -0.0008590809713742, -0.0143116925756, -0.01518090922791, 0.009425519212295, 0.004176276216806, -0.00230315728735, 0.00729984247155, -0.00118715484374, 0.003333815042436, 0.002576743628741,-0.0002010089148403, 0.004211039430268, -0.0009095937362588, 0.003194515325537,0.0004212568292968, 0.001065601657562, 0.001991114366024,-0.0005015981116225, 0.002515457546672,-0.0007519175968182,0.001791368704721,

3.132749263639e-005,0.0004563676999373, 0.001016753572365, -0.0006306812989271, 0.001458811582498,-0.000943397388763, 0.001103803536151,-0.0005095992885592,

0.0002221521815682,0.0002239892466348,-0.0006525502191852, 0.0006855094694644,-0.0009056383424007 }.

e. Procedure Of Equalizer

The process can be better illustrated with a flow chart which shows how digital signal processor takes action to apply equalization on input signal

Start

Initialize: gain parameters and delay parameters

Input_sample

5-Band FIR filter

Output sample

Fig. 4. Flow chart of the 5-Band Graphic Equalizer

In this process, the gain parameters and the delay parameters are initialized first. The input audio signal is applied to the DSP processor and then applied to the 5-band graphical equalizer. And sends the output audio signal, after processing according to the generated filter coefficients.

f. Interfacing DSK with PC

CCS and Lab View are run on host PC. DSK is connected to PC by using a universal synchronous bus. The connections are as shown below.

CPU

PC

USB cable

DSK

6713 Line out

Conclusion

The main aim of the project was to implement a 5 band graphical equalize, which is accomplished by loading an executable file in to the DSK and driving it from lab view through CCS. The result shows the necessary implementation of graphical equalizer.

Acknowledgment

This paper is a part of project in course digital signal processors. We are very much thankful to Mr. Kristain Nilsson for his esteemed supervision and support.

5. References

[1] Rulph Chassaing and Donald Reay"Digital Signal processing andApplication with the TMS320C6713 and TMS320C6416 DSK"2nd Ed. pp 125-150.

[2] Harish Thampi S / Jagan Govindarajan

available:http://focus.ti.com/lit/an/spra895/spra895.pdf

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