Input and Output with the DSK - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 40

FIGURE 2.1. DSP system with input and output.

FIGURE 2.2. Aliased sinusoidal signal.

The sampling period T s 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
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 F s >

40 kHz (typically, 44.1 or 48 kHz)
and remove frequency components higher than 20 kHz. Figure 2.2 illustrates
an aliased signal. Let the sampling frequency F s = 4 kHz, or a sampling period of

T s 0.25 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.

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2.2 TLV320AIC23 (AIC23) ONBOARD STEREO CODEC FOR
INPUT AND OUTPUT

The DSK board includes the TLV320AIC23 (AIC23) codec for input and output.
The ADC circuitry on the codec converts the input analog signal to a digital repre-
sentation to be processed by the DSP. The maximum level of the input signal to be