Input and Output with the DSK • • Input and output with the onboard AD535 codec (alternative input and output with the stereo codec PCM3003 are described in Appendix F) Programming examples using C code INTRODUCTION Typical applications using DSP techniques require at least the basic system shown in Figure , consisting of analog input and output. Along the input path is an antialiasing filter for eliminating frequencies above the Nyquist frequency, defined as one-half the sampling frequency Fs. 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 | DSP Applications Using C and the TMS320C6x DSK. Rulph Chassaing Copyright 2002 John Wiley Sons Inc. ISBNs 0-471-20754-3 Hardback 0-471-22112-0 Electronic 2_ Input and Output with the DSK Input and output with the onboard AD535 codec alternative input and output with the stereo codec PCM3003 are described in Appendix F Programming examples using C code INTRODUCTION Typical applications using DSP techniques require at least the basic system shown in Figure consisting of analog input and output. Along the input path is an antialiasing filter for eliminating frequencies above the Nyquist frequency defined as one-half the sampling frequency Fs. 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 so that Fs 2 f which is also 1 Ts 2 1 t where Ts is the sampling period or Ts T 1 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 can 33 34 Input and Output with the DSK FIGURE . DSP system with input and output. t ms FIGURE . Aliased sinusoidal signal. use a lowpass input filter with a bandwidth or cutoff frequency at 20 kHz to avoid aliasing. We can then sample a music signal at Fs 40 kHz typically or 48 kHz and remove frequency components higher than 20 kHz. 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- or 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 aliased signal. Similarly a 9-kHz signal would also appear as a 1-kHz aliased signal. TLC320AD535 AD535 ONBOARD CODEC FOR INPUT AND OUTPUT The DSK board includes the TLC320AD535 AD535
