The procedure of generating a discrete-time signal from an analog signal is shown in the
following block diagram. In the digital signal processing course we are mostly dealing with
discrete–time rather than digital signals and systems, the latter being a subset of the former.
The three boxes shown above can be represented by an analog to digital converter
(ADC). A complete digital signal processing (DSP) system consists of an ADC, a DSP algorithm
(e.g., a difference equation) and a digital to analog converter (DAC) shown below.
(Diff. Eq. or
As the name implies discrete-time signals are defined only at discrete instants of time.
Discrete-time signals can arise by sampling analog signals such as a voice signal or a
temperature signal in telemetry. Discrete-time signals may also arise naturally, e.g., the number
of cars sold on a specific day in a year, or the closing DJIA figure for a specific day of the year.
AT&T’s T1 Stream The voice signal is band limited to 3.3 kHz, sampled at 8000 Hz (8000
samples per second), quantized and encoded into 8 bits per sample. Twenty four such voice
channels are combined to form the T1 stream or signal.
= 0.125 msec.
Sampling interval =
Bit rate for each channel = 8000
= 64000 bits/sec.
Bit rate for T1 = 64000 bits/sec per channel x 24 channels = 1 544 000 bits/sec.
Commercial examples CD, Super Audio CD (SACD), DVD Audio (DVD-A), Digital audio
broadcasting - 32 kHz, and Digital audio tape (DAT) - 48 kHz.
Commercial Audio Examples
Super Audio CD
16-bit PCM per sample
With 2 channels the bit rate is 1.4112
Mbits/sec, but additional error control
bits etc., raise it to 4.3218 Mbits/sec.
Digital – like Delta
3 of 77
44.1, 88.2 or
48, 96, 192
12-, 20-, 24bit