Real Time Digital Audio Processor System Computer Science Essay

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The main aim of project is to design a real time digital audio processor system, which performs 5 band graphic equalizer operated at a rate of 48000 samples and it eliminates two interference tones when connected to a NI SPEEDY-33 target board, which is connected via graphical user interface running on a personal computer. Two interference tones at which the tone is to be removed is 5KHz and 10KHz. Based on the design conditions four possible operations can be achieved which is analysed on a bode plot for mono and stereo audio channel.

2. INTRODUCTION:

The real time audio processor system is designed with help of LabVIEW and is tested with a NI SPEEDY-33. LabVIEW is a graphical programming environment used to develop sophisticated measurement, test and control systems with software for advanced control algorithms, dynamic simulation, and motion control.

NI SPEEDY-33 can be referred as National Instruments Signal Processing Engineering Educational Device for Youth. NI SPEEDY-33 is an high performance digital signal processor.

Fig 1: Structure of NI SPEEDY-33.

The operating and hardware details of NI SPEEDY-33 are shown below:

This device contains on board flash memory and also supports DSP processing. It features 34 k* 32 words on chip memory. Consists eight lines of digital I/O arranged in eight-bit switch input port and eight digital output LEDs.

Fig 2: Hardware functioning and interfacing details of NI SPEEDY-33 device.

3. PROCEDURE FOR DESIGNING FILTERS:

For the implementation of system design we required to design filters, in order to design filters we have to go to LabVIEW installation folder. We can find the 'vi' file in the path "National instruments\LabVIEW\examples\Digital Filter Design\Design StepByStep\Design a Filter Step by Step.vi". By selecting the 'vi' we can design filters.

vi.JPG

Fig 3: VI file for Design of Filter

By selecting the floating-point filter design & analysis button, the design of filters can be started.

3.1 DESIGNING PROCESS OF HIGHPASS FILTER:

The following frequency specifications are to be made in the VI window to configure highpass filter.

Type

Highpass

Passband Edge Frequency 1

4 khz

Stopband Edge Frequency 1

3.9 khz

Sampling Frequency

48 khz

Passband Ripple

0.1 dB

Stopband Attenuation

80 dB

Design Method

Butterworth

Fig 4: Specifications of Highpass Filter.

Fig 5: Simulation of Highpass Filter.

Click on the design button to see the characteristics of filter as seen in the figure 5. And then click on the structure selection and coefficients quantization to study the effect of quantization. Press the fixed-point modelling and simulation to simulate the filter. We can see the simulation process as shown in the figure 5. And click on the save filter to file to save the filter design to hard drive.

3.2 DESIGNING PROCESS OF LOW PASS FILTER:

The following specifications are to be made to design a lowpass filter.

Type

Lowpass

Passband Edge Frequency 1

22 hz

Stopband Edge Frequency 1

30.5 hz

Sampling Frequency

48 khz

Passband Ripple

0.1 dB

Stopband Attenuation

80 dB

Design Method

Butterworth

Click on the design button to see the characteristics of filter as we followed for highpass filter

Fig 6: Specifications of Lowpass Filter.

Fig 7: Simulation of Lowpass Filter.

3.3 DESIGNING PROCESS OF NOTCH FILTERS:

To eliminate the interference tones present at 5 KHz and 10 KHz frequency, band stop filters are to be designed. The following frequency specifications are to be made in the VI to configure the bandstop filter at 5 KHz.

Type

Bandstop

Passband Edge Frequency 1

4 khz

Passband Edge Frequency 2

6 khz

Stopband Edge Frequency 1

5 khz

Stopband Edge Frequency 2

5.5 khz

Sampling Frequency

48 khz

Passband Ripple

0.1 dB

Stopband Attenuation

80 dB

Design Method

Butterworth

Fig 8: Specifications of 5 KHz Bandstop Filter.

Fig 9: Simulation of 5 KHz Bandstop Filter.

To configure the bandstop filter at 10 KHz, the following frequency specifications are to be made in the VI window:

Type

Bandstop

Passband Edge Frequency 1

9.5 khz

Passband Edge Frequency 2

10.5 khz

Stopband Edge Frequency 1

10 khz

Stopband Edge Frequency 2

10.003 khz

Sampling Frequency

48 khz

Passband Ripple

0.1 dB

Stopband Attenuation

80 dB

Design Method

Butterworth

Fig 10: Specifications of 10 KHz Bandstop Filter.

Fig 11: Simulation of 10 KHz Bandstop Filter.

3.4 DESIGNING PROCESS OF BAND PASS FILTERS:

Type

Bandpass

Passband Edge Frequency 1

85 hz

Passband Edge Frequency 2

102 hz

Stopband Edge Frequency 1

63 hz

Stopband Edge Frequency 2

155 hz

Sampling Frequency

48 khz

Passband Ripple

0.1 dB

Stopband Attenuation

80 dB

Design Method

Butterworth

The above frequency specifications are to be made in the VI window to configure bandpass filter 1.

Fig 12: Specifications of Bandpass Filter 1.

Fig 13: Simulation of Bandpass Filter 1.

The following frequency specifications are to be made in the VI window to configure bandpass filter 2.

Type

Bandpass

Passband Edge Frequency 1

465 hz

Passband Edge Frequency 2

670 hz

Stopband Edge Frequency 1

350 hz

Stopband Edge Frequency 2

1 khz

Sampling Frequency

48 khz

Passband Ripple

0.1 dB

Stopband Attenuation

80 dB

Design Method

Butterworth

Fig 14: Specifications of Bandpass Filter 2.

Fig 15: Simulation of Bandpass Filter 2.

The following frequency specifications are to be made in the VI window to configure bandpass filter 3.

Type

Bandpass

Passband Edge Frequency 1

2.5 khz

Passband Edge Frequency 2

3 khz

Stopband Edge Frequency 1

1.5 khz

Stopband Edge Frequency 2

3.9 khz

Sampling Frequency

48 khz

Passband Ripple

0.1 dB

Stopband Attenuation

80 dB

Design Method

Butterworth

Fig 16: Specifications of Bandpass Filter 3.

Fig 17: Simulation of Bandpass Filter 15.

4. DESIGNING PROCESS OF 5-BAND GRAPHIC EQUALIZER:

Initially a mono channel system is designed and then it can be extended to stereo channel system. A mono channel system is shown in the below fig.

Fig 18: Block Diagram of a Mono Channel 5- band Equalizer.

After designing the Mono channel 5-band equalizer in LabVIEW, it is connected to NI SPEEDY-33 . The system mainly consists of an analog input, high pass filter, band pass filter, low pass filter ,notch filters in which the analog input and notch filters are connected to 5 kHz, 10 kHz which are further connected to the low pass filter, 3 band pass filter and high pass filter. Analog output is connected at the end of the circuit to have the output of the system. The whole system is comprised in while loop. And another channel is created which is named as right channel and is connected to existing left channel to make the mono system as stereo system.

Fig 19: Block Diagram of a Stereo Channel 5-band Equalizer.

And the front panel window of the LabVIEW is shown in the fig below which contains slides and waveform graphs.

Fig 20: Front panel Window of Stereo channel 5-Band Equalizer.

By clicking the arrow to run, we can verify the working of the designed audio processor system.

5. IMPLEMENTATION OF THE SYSTEM:

Oscilloscope and signal generated are connected to the serial ports of the computer by means of an USB to serial port adaptor and NI SPEEDY-33 is connected to the oscilloscope to have the input. 1 kHz of frequency and 500mv of p-p voltage is set from signal generator. Now the bode plotter is to be opened to have the gain and phase plots. The bode plot settings can be changed as per the requirement. After setting the values for lowest frequency, highest frequency, number of points and p-p voltage click on the acquire button to sweep from given value of frequencies. The gain plot and phase plot have to be taken from the bode plotter. And the process is repeated for specified conditions.

6. RESULTS:

The following are the bode plots obtained from the bode plotter.

Case 1: When only 5 KHz tone is removed.

Fig 21: When 5 KHz tone is removed

.

Case 2: When only 10 KHz tone is removed.

Fig 22: When 10 KHz tone is removed.

Case 3: When both tones are removed:

Fig 23: When both tones are removed.

Case 4: When No tones removed.

Fig 24: When No tone is removed.

7. CONCLUSION:

A 5-band graphic real time digital audio processor is designed which is functioning as a high quality stereo music signal which is implemented on NI SPEEDY-33 device. Depending up on the two interference tones present at 5 KHz and 10 KHz, which are eliminated by the system and by using bode plotter diagrams we can easily verify the operation and finally system is successfully designed and verified using bode plotter.

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