0.6 Dsp laboratory: iir filter design via the bilinear transformation  (Page 9/3)

Iir filter design via the bilinear transformation

The purpose of this lab is to examine IIR filter design/implementation using LabVIEW DSP. Particularattention is drawn to the comparison between theoretical filter characteristics and actual filter performance. In this lab, it isassumed that the student is already familiar with the basic operation of LabVIEW DSP.

Create a vi for plotting time and frequency domain data

• Open Surround Mixer, a program which controls the input/output operation of the sound card. Make sure that theWave/mp3 and Line-in volumes are set to approximately 75%. Make sure that all source buttons are muted for now. Keep the SurroundMixer open throughout the lab. You will be selecting various inputs (Wave and Line-in) throughout the lab.
• Start LabVIEW Embedded Edition (Start»All Programs»LabVIEW Embedded Edition) and open a blank VI (Virtual Instrument).

• We will build the VI whose Block Diagram is shown in Figure
  • Switch execution target to your hardware by going to Operate»Switch Execution Target in LabVIEW Embedded.
  • Go to the Block Diagram of the blank VI, navigate the function palette to the Analog Input, click and drop an analoginput element on the Block Diagram. It is located under Functions»Elemental IO»Analog Input. See Figure 2.

  • Double-click on the Analog Input elemental I/O for configuration. In the configuration window, select the “General”tab. Click on the drop down under resource and select 2 channel Multiple Samples. On the Configuration tab, set the Sampling Rateto 16000 Hz and the Framesize to 256. Click “OK” to close the window.
  • Drop an Add function located on the Numeric sub palette of the Functions palette: Functions»Numeric»Add.
  • Drop an Analog Output elemental I/O. Functions»Elemental I/O»Analog Output. Double click on the Analog Output you justdropped on the Block Diagram and set the Sample Rate to 16000 Hz on the Configuration tab. Click “OK” to close.
  • Drop a “Spectral Measurement” Express VI on the block diagram. Functions»Signal Processing»Frequency Domain»SpectralMeasurements. This VI will allow us to build the power spectrum of the sound signal. Double click on the Spectral Measurements ExpressVI to open its configuration window. In the window, select Power Spectrum for Spectral Measurements and dB for results (See Figure)
  • Click “OK” to validate the configuration.

  • Now let’s switch to the Front Panel (Windows»Show Front Panel) and drop two Waveform Graphs. The Waveform Graph is locatedon the Graph Sub palette: Controls»Graphs»Waveform Graph. Name one “Time Domain” and the other “Power Spectrum.” Do not add the stopbutton yet.

  • Let’s switch back to the Block Diagram and wire everything already on the diagram as shown in Figure 1.
  • Select the while loop from Functions»Structures»While Loop, click and drag to enclose everything on the Block Diagram withinthe loop. You Block Diagram should now be similar to the one in Figure 1 and the Front Panel similar to the one in Figure 4.
  This setup is similar to that found in the “DSP Laboratory: Time and Frequency Displays” Module except that the Left and Right channels are being combined into a single channel.
• In Surround Mixer activate the Wave/mp3 source and put a CD into the computer’s CD-ROM drive. Run theWindows Media Player program in the EE 453 folder to start the CD. Finally, press the Run icon and you should hear your music throughthe headphones. If there is distortion/clipping (due to the volume being too high), adjust the CD volume on the Surround Mixer tolower the volume until the clipping stops. Now adjust the two displays to make one a time-domain display and the other afrequency-domain display. Remember how to set/unset the automatic scaling on the displays. It is usually best to use Auto scaling onthe frequency-domain display but not the time-domain display.
• Once you have verified that everything is working properly, stop the CD, then stop the LabVIEW program (butdon’t exit LabVIEW).
• 11. Save the VI by selecting File»Save As. Make sure to save the file in your personal directory -- Desktop\ee453\<folder name>. You can give the file any name you want (such as lab2setup).