there is no difference there is no difference
Adaptive differential pulse-code modulation(ADPCM) is a variant of differential pulse-code modulation (DPCM) that varies the size of the quantization step, to allow further reduction of the required bandwidth for a given signal-to-noise ratio.Typically, the adaptation to signal statistics in ADPCM consists simply of an adaptive scale factor before quantizing the difference in the DPCM encoder.[1]ADPCM was developed in the early 1970s at Bell Labs for voice coding, by P. Cummiskey, N. S. Jayant, and James L. Flanagan.[2]susheelonline.com
in pcm entie sample is sent.. where as in dpcm the difference between the predicted value and the original sample is sent which will be smaller when compared rto the original sample..
ADPCM
Delta modulation is not a type of quality conversion and runs on digital-to-analog, analog-to-digital. Differential pulse code modulation has a higher quality of conversion and runs on a 1-bit data stream.
Let (M) and (D) be the peak amplitudes of signals m(t) and d(t) respectively. If the same quantization level (L), is used to sample both signals. The quantization step (Dv) in DPCM is reduced by a factor of (D/M). The quantization noise power is [(Dv)^2]/2. So we can say, that in DPCM the quatization noise reduces by the factor (M/D)^2. As the SNR is inversely proportional to Noise, this parameter (SNR) increases by the same factor. In Practice the SNR improvement may be as high as 25 dB in such cases as short-term voiced speech spectra. Alternatively for the same SNR, the bit rate for DPCM could be lower than for PCM by 3 to 4 bits per sample. Thus, telephone systems using DPCM can often operate at 32 kbits/s (4 bits * 8000 saples/s) or even 24 kbit/s (3 bits * 8000 saples/s). So DPCM could improve the SNR of the system, using less bandwidth.
Shihab Ahmed Jimaa has written: 'Data transmission over ADPCM links'
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