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ECE 5325 Wireless CommunicationsVocoders, quantization and compressionQ1: Which of the following consonants are voiced?B, p, t, s, z, v, f, m, p, j, ch, sh, thGo to <http://www.spsc.tugraz.at/courses/scl/download> and download “vocoder.zip” Extract it to a local directory and open “index.html”Read the text in the left-hand panel.Q2: Which excitation method in Figure 4b (right-hand panel in the browser) is used to produce a “d” (tone generator or noise generator)? How is that excitation expressed in Figure 5?Read the instructions for using the vocoder simulation program in section 4 of the left hand panel. Then do the following:- Load the pre-recorded text “He caught them at your house”.- Click on “Analyze.”- Click on “Synthesize”- Switch the view mode to the left-most choice.Q3: Do the original and synthesized images look identical?Q4: Do they sound the same? (Click the Audio speaker button.)Q5: How would you rate the quality according to Table 8.2 in Rappaport?Switch the view mode to the colored middle button.Q6: What are the red bars?Q7: What does it mean to see 2-4 parallel bars stacked above each other?Q8: Did you expect to see this based on the model descriptions?Q9: What does this tell you about which LPC vocoder approach is used from Section 8.7 in Rappaport?Now, do the following:- Switch to the right-most view mode and do the following:- Click the pencil button at the far left of the synthesis panel.- Click the “down arrow” at the far right.- Click “Synthesize”- Play the signal.Q9: Why did the pitch bars disappear?Q10: How does the speech differ with this setting? What is the model doing to achieve this sound?Q11: Is it still intelligible?Now do the following:- Click the undo arrow at the far right.UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 | www.ece.utah.edu1ECE 5325 Wireless Communications- Select the “up-down” arrow button.- Move the pitches to 200 Hz- Click “Synthesize”- Play the signal.Q12: How does the speech differ with this setting? What is the model doing to achieve this sound?Q13: Is it still intelligible?Q14: Assuming speech covers a dynamic range of up to 40 dB, how many bits of quantization are required to reproduce speech? (Rely on your textbook, section 8.3.)Q15: If compact discs (CDs) use 16-bit quantization, what dynamic range can they reconstruct?Suppose that you wanted to transmit a sequence {bi} of ones and zeros where p(bi = 0) = p(bi = 1) = 0.5. (Rely on the MacKay textbook.)Q16: What is the entropy of this signal?Q17: How many bits of information does each element of the sequence contain?Q18: How much can this signal be compressed according to the Entropy law (see MacKay textbook)?Suppose you wanted to transmit a sequence {bi} of ones and zeros where p(bi = 0) = 0.1 and p(bi = 1) = 0.9.Q19: What is the entropy of this signal?Q20: How many bits of information does each element of the sequence contain?Q21: How much can this signal be compressed according to the Entropy law?Q22: What does the Entropy law tell you about how much an LPC coder can compress speech?UNIVERSITY OF UTAH DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 50 S. Central Campus Dr | Salt Lake City, UT 84112-9206 | Phone: (801) 581-6941 | Fax: (801) 581-5281 |


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U of U ECE 5960 - Vocoders

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