0.7 Dsp laboratory: fir filter design  (Page 20/3)

Fir filter design

The purpose of this lab is to examine FIR filter design/implementation using LabVIEW Digital Filter DesignToolkit and LabVIEW DSP Module. In this lab, it is assumed that the student is already familiar with the basic operation of LabVIEW.

Configure sound output on the computer

• Keep the Surround Mixer open throughout the lab. You will be selecting various inputs (wave, microphone, and line-in) throughoutthe lab.
• Select and activate Surround Mixer, a program which controls the input/output operation of the sound card. Beneath each of thevolume bars is a mute box that can be toggled on/off. When checked, the corresponding sound source is deactivated. Make sure that allsource buttons are muted for now.

Create a vi for plotting time and frequency domain data

• Start LabVIEW Embedded Edition and change the target to the SPEEDY-33 board.

• Create a New Blank VI.
• Open the Front Panel and place two All Controls»Graphs»Waveform Graphs
• Label them Time Domain and Frequency Domain.
• Open the Block Diagram and place the following objects in it.
  • All Functions»Elemental I/O»Analog Input node.
  • All Functions»Elemental I/O»Analog Output node.
  • All Functions»Numeric»Add function.
  • All Functions»Signal Processing»Frequency Domain»Spectral Measurements.
  When you place the Analog Input node, it will display only one channel. It is after you configure it that the right and left channels will be shown.
• Double click the Analog Input node and change the Resource under the General Tab to be 2 channel multiple samples.

• Go to the Configuration Tab and set the Sample Rate to 8000 Hz and the Framesize to 256.

• Double click on the Analog Output node and change the resource to 2 channel multiple samples and check that the SampleRate is set to 8000 Hz.
• Double click in the Spectral Measurements Express VI and select Power Spectrum from the type of Measurement.
• Rearrange the objects in the Block Diagram so that you have plenty of space between them. This makes it easier to connect themtogether.
• Connect the 2 outputs of the Analog Input node (Left and Right channels) to the 2 inputs of the Add function. Connect theoutput of the Add function to both inputs of the Analog Output node. What you are doing here is converting the stereo signal intoa mono signal. Then, connect the output of the Add function to the Time Domain Waveform graph indicator and to the Signals Input ofthe Spectral Measurements. Finally, connect the Power Spectrum output to the Frequency Domain Graph.
• Place a while loop around the objects in the Block Diagram to execute this functions continuously.

• In the Surround Mixer activate the Wave/mp3 source and put a CD into the computer’s CD-ROM drive. Run the Windows Media Playerprogram in the EE 453 folder to start the CD. Finally, press the Run button in LabVIEW. You should hear your music through theheadphones. 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.
• Once you have verified that everything is working properly, stop the CD, then stop the LabVIEW VI. (Do not exit LabVIEW)
• Save this VI by selecting File»Save As. Make sure to save the file in your personal directory - - Desktop \ee 453\<folder name>. You can give the file any name you want (such as lab3setup), but use the default extension of .vi