Introduction to Digital Signal Processing - Digital Signal Processing: Fundamentals and Applications - page 4

Noisy signal

2

1

0

-1

-2

0 0.005 0.01 0.015 0.02 0.025 0.03

2

1

0

-1

-2

0 0.005 0.01 0.015 0.02 0.025 0.03

Time (sec.)

FIGURE 1.3

(Top) Digitized noisy signal. (Bottom) Clean digital signal using the digital lowpass filter.

Analog
input

x(n)

Time domain display

Analog
filter

DSP
Algorithms

ADC

Frequency content display

FIGURE 1.4

Signal spectral analysis.

As another practical example, we often perform spectral estimation of a digitally recorded speech
or audio (music) waveform using the FFTalgorithm in order to investigate spectral frequency details of
speech information. Figure 1.6 shows a speech signal produced by a human in the time domain and
frequency content displays. The top plot shows the digital speech waveform versus its digitized sample
number, while the bottom plot shows the frequency content information of speech for a range from 0 to
4,000 Hz. We can observe that there are about ten spectral peaks, called speech formants, in the range
between 0 and 1,500 Hz. Those identified speech formants can be used for applications such as speech
modeling, speech coding, speech feature extraction for speech synthesis and recognition, and so on
(Deller et al., 1993).