Click here to down load the Delta Modulation files (dm.tar).
Click here to down load the Delta Modulation files (dm.zip).
Delta modulation (DM) may be viewed as a simplified
form of DPCM in which a two level (1-bit) quantizer is used in conjunction
with a fixed first-order predictor. The block diagram of a DM encoder-decoder
is shown below.
The "dm_demo" shows the use of Delta Modulation to approximate a input sine wave signal and a speech signal that were sampled at 2 KHz and 44 KHz, respectively. The source code file of the MATLAB code and the out put can be viewed using MATLAB. Notice that the approximated value follows the input value much closer when the sampling rate is higher. You may test this by changing sampling frequency, fs, value for sine wave in "dm_demo" file.
To view these you need to download the zip or tar files and sound file into a directory. if you wish you may modify the dm_demo file any time to see the effect of sampling rate and stepsize, then run demo file on MATLAB. To run the demo file, type "dm_demo" at the MATLAB prompt. (Remember to change directory into the same directory that the files were placed in.) Since DM (Delta Modulator) approximate a waveform Sa(t) by a linear staircase function, the waveform Sa(t) must change slowly relative to the sampling rate. This requirement implies that waveform Sa(t) must be oversampled, i.e., at least five times the Nyquist rate.
"Oversampling" means that the signal is sampled
faster than is necessary. In the case of Delta Modulation this means that
the sampling rate will be much higher than the minimum rate of twice the
bandwidth. Delta Modulation requires "oversampling" in order to obtain
an accurate prediction of the next input. Since each encoded sample contains
a relatively small amount of information Delta Modulation systems require
higher sampling rates than PCM systems. At any given sampling rate, two
types of distortion, as shown below limit the performance of the DM encoder.
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