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.. questionnaire:: Test Questionnaire :timelimit: 600 :deadline-date: 2006-11-29 23:59 This is a test of the questionnaire handling. With some questions: .. multiple-answer:: compand :question: Which of the following statements about companding are true :choices: :1: Companding is a bit reduction technique :2: Companding increases the quantisation SNR for weak signals :3: Companding degrades the analogue signal :4: The companding characteristic has a linear and a logarithmic proportion :5: Companding is often implemented using a segmented linear quantisation characteristic. :answer: '(list 1 2 4 5) :feedback: Companding does not degrade the analogue signal. Its purpose is to improve the signal to noise ratio, and while the signal to noise ratio for large signals is increased overall the SNR is much improved with companding. .. multiple-choice:: dpcm :question: In differential pulse code modulation (DPCM) do we :choices: :1: Transmit the integral of the signal :2: Transmit differences between actual sampled amplitudes and predicted amplitudes :3: Adapt the quantisation characteristic as the average signal amplitude varies :4: Have a quantisation characteristic which has small steps for small amplitudes and large steps for larger amplitudes :5: Transmit an estimate of the signal :answer: 2 :feedback: In DPCM we use transmit differences between actual sampled amplitudes and amplitudes predicted using a linear combination of previous samples. This difference will be much smaller than the signal amplitude and so will require less bits to represent it. .. numeric:: Nyquist :params: (omega (+ 50 (random 500))) (a (+ 1 (random 25))) (n (/ omega pi)) :question: A waveform, `a`:eval: + `a`:eval: sin(`omega`:eval: t+0.7) is to be sampled periodically and reproduced from these sample values. How many sample values must be stored to reproduce 1 sec of this waveform. :weighting: 0.5 :format: "~,2f" :answer: n :tol: (/ 1.1 n) :feedback: The frequency of this waveform is `omega`:eval: /2 `\pi`:math: = `"~,2f" (* 2 n)`:eval: Hz . We require (from Nyquist sampling theorem) at least 2 samples per period, so the sample frequency must be `"~,3f" n`:eval: Hz., source line 4)