Digital Signal Processing Reference
In-Depth Information
Delta-modulator
Delta-demodulator
analog
digital
transmission
+
³
TP
1 Bit ADC
+
Integrator
-
delta-modulated signal
³
Integrator
Rec or der
Signal
S& H
Dif f erence
1 Bit DA C
* C
Offset
Sum
Delay
Difference signal
A
B
C
Delta-modulated e.g. delta-coded signal
Illustration 226:
Schematic block diagram, DASYLab circuit and signals in
Δ
-encoding
In this form of encoding or modulation only the
change
in the audio signal is transmitted. In a way the
original signal is differentiated digitally, i.e. the gradient is measured. The way the circuit functions is
explained in detail in the text.
The (digital) differentiation must be reversed in the receiver by (digital) integration. You remember: inte-
gration reverses differentiation and vice versa (see Illustration 133 and Illustration 134).
In the case of screencam video it is therefore sufficient to register
changes
in the picture
- i.e. the cursor movement and change of picture. For this only a fraction of storage
capacity is needed compared to saving all the pictures.
This
-encoding can be used efficiently if the signal only changes slightly between two
measurements or within the time segment
Δ
Δ
t = T
S
= 1/f
S
(f
S
is the sampling frequency).
