Using the audiorecorder() function in MATLAB, make a recording of your voice. Use a sample rate of 8kHz, 16 bits per sample, and aim to record around 2 seconds worth. Part (a) — 20 Marks Quantize the audio samples down from the original 16 bits by removing the least-significant bit (LSB) from the waveform, to make a 15 bit recording. Repeat for 14, 13, 12 bits, down to 1 bit. Explain how you would do this in MATLAB, and implement your approach. Part (b) — 20 Marks Listen to the recordings, and make a table with the number of bits and the corresponding quality assessment. This can simply be a subjective assessment; use terms such as 'no perceptual difference', 'minor noise present', 'quite noisy', 'poor quality' etc. Calculate the signal-to-noise ratio in each case, and add that to your table. Explain how you calculated the SNR. (a) Explanation & MATLAB coding 20 (b) Subjective assessment table with SNR 20 Total 40 Question 2 — 80 Marks This question examines the addition of a (synthetic) echo to the voice recording, such as would be found in a reverberant room. To do this, use a difference equation of the form y(n) = x(n) + αy(n − D) (1) where x(n) is the input audio, y(n) is the output (echoed) audio, D is the echo delay (in samples), and α governs the amount of echo fed back. Part (a) — 20 Marks Explain how to convert the above equation into a form suitable for passing to MATLAB's filter() command. Use α = 0.8 and D = 2 samples to explain your reasoning. . . . / 5 Signal Processing Signals and Systems Page 5 Part (b) — 20 Marks A delay of 2 samples (as in the previous part) would not be audible. Select an echo delay of 0.2 seconds, and α = 0.4. Using your reasoning above, implement the reverberation equation, and listen to the result. Experiment with different values of the parameters α and D. In your report, include a plot of the waveform, and explain in your own words the physical significance of these parameters. Part (c) — 20 Marks Convert equation (1) to a z transfer function. Where are the poles located (i) for D in general? (ii) for the value of D found in part (b) above? Part (d) — 20 Marks Suppose the equation governing the reverberation is y(n) = x(n) + αx(n − D) (2) What is the physical significance of this form, as opposed to that used in equation (1) ? Implement an audio echo system based on equation (2), and listen to the results. (a) Explain use of filter command 20 (b) Implement realistic filter, show waveform 20 (c) z transfer function and poles 20 (d) Explain nonrecursive transfer function 20 Total 80