Input and Output with the DSK Input and output with the Analog Interface Circuit (AIC) chip Communication between the PC host and the C31 DSK Alternative memory using external and flash memory Alternative input and output with a 16-bit stereo codec Programming examples and experiments using C and TMS320C3x code | Digital Signal Processing Laboratory Experiments Using C and the TMS320C31 DSK Rulph Chassaing Copyright 1999 John Wiley Sons Inc. Print ISBN 0-471-29362-8 Electronic ISBN 0-471-20065-4 3 Input and Output with the DSK Input and output with the Analog Interface Circuit AIC chip Communication between the PC host and the C31 DSK Alternative memory using external and flash memory Alternative input and output with a 16-bit stereo codec Programming examples and experiments using C and TMS320C3x code INTRODUCTION Typical applications using DSP techniques require at least the basic system shown in Figure consisting of an analog input and analog output. Along the input path is an antialiasing filter for eliminating frequencies above the Nyquist frequency defined as one-half the sampling frequency. Otherwise aliasing occurs in which case a signal with a frequency higher than one-half Fs is disguised as a signal with a lower frequency. The sampling theorem tells us that the sampling frequency must be at least twice the highest frequency component f in a signal or Fs 2f Hence 1 Ts 2 1 T where Ts is the sampling period or 1 2 T Ts and 51 52 Input and Output with the DSK FIGURE DSP system with input and output. Ts 1 2 T The sampling period Ts must be less than one-half the period of the signal. For example if we assume that the ear cannot detect frequencies above 20 kHz we would sample a music signal at Fs 40 kHz typically at kHz or 48 kHz in order to remove frequency components higher than 20 kHz. We can then use a lowpass input filter with a bandwidth or cutoff frequency at 20 kHz to avoid aliasing. Figure illustrates an aliased signal. Let the sampling frequency Fs 4 kHz or a sampling period of Ts ms. It is impossible to determine whether it is the 5-kHz or the 1-kHz signal that is represented by the sequence 0 1 0 -1 . A 5-kHz signal will appear as a 1-kHz signal hence the 1-kHz signal is an Amplitude FIGURE Aliased sinusoidal waveform. The
