_Signal_LabS1 - N ATIONAL U NIVERSITY of S INGAPORE...

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N ATIONAL U NIVERSITY of S INGAPORE DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING Course: EE2009 - SIGNALS E XPERIMENT S1 S IGNALS A ND S PECTRA L ABORATORY M ANUAL ________________________________________________________________________________ IMPORTANT! READ THIS MANUAL CAREFULLY AND PREPARE FOR THE EXPERIMENT BEFORE YOU ATTEND THE LABORATORY SESSION. SUBMIT THE LABORATORY REPORT ON THE SAME DAY OF THE EXPERIMENT, BEFORE LEAVING THE LABORATORY. SOME PARTS OF THE EXPERIMENT NEED EXPLANATIONS BASED ON THEORETICAL UNDERSTANDING. STUDY THE NECESSARY THEORETICAL CONCEPTS BEFORE COMING TO DO THE EXPERIMENT. ________________________________________________________________________________ 1
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1. Introduction In our daily life and in most scientific and engineering applications, we encounter many forms and types of signals. We produce and send speech signals as we use our mobile-phones, we listen to music created from audio signals, we watch TV from signals on our VCD or DVD players, our hearts and brains generate biomedical ECG and EEG signals for our bodily functions, and so on. There are many ways to classify a signal. One simple method is to consider whether it is non-periodic or periodic . In the latter case, the signal exhibits a repetitive pattern and this repetition occurs at a fixed interval of time called a period . This is illustrated in Fig. 1 where the period is seconds. 0 T t 0 0 T 0 T LL t 0 (a) A non-periodic signal Fig. 1. Non-periodic and periodic signals (b) A periodic signal Another way of classifying a signal is to see whether it is a continuous-time ( analog ) signal or a discrete-time ( digital or sampled ) signal. Fig. 2 shows an analog signal and a sampled signal. A sampled signal is obtained by sampling, or taking snapshots, of the analog signal at fixed instants of time known as sampling instants . In Fig. 2, the sampling is carried out at instants uniformly spaced with a sampling period of seconds or at a sampling frequency of s T s s T f 1 = Hz. In practical systems such as digital camera and digital audio recorder, an appropriate A/D ( analog to digital ) converter is used to realise the process of sampling. 0 s T t t 0 (a) An analog signal Fig. 2. Analog and digital signals (b) A digital or sampled signal An important issue is whether the sampled signal can be used to faithfully recover the original analog signal. Consider, for example, the distribution of music produced by a pop group. The recording will be carried out in a studio and will give rise to a number of sound tracks of analog audio signals. These signals are then converted to digital form by sampling at 44.1 kHz, processed, burned on CD and sold. To the pop fan who buys the CD, the most important question is: can the digital signal stored on 2
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the CD be used to reproduce the original analog recording? Hopefully, as you perform this experiment, you will be able to answer this question yourself. Figs. 1 and 2 show signals in the time-domain. However, describing signals in the frequency or spectral domain is also very useful. In fact, many human perceptions are based on analysing signals in the frequency-domain. For example, we recognise
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This note was uploaded on 08/02/2009 for the course ECE EE2009 taught by Professor Prof.c.c.ko during the Fall '07 term at National University of Singapore.

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_Signal_LabS1 - N ATIONAL U NIVERSITY of S INGAPORE...

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