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	  Text			  "What are DM, LDM, CVSD, and ADPCM?\n\nDelta"
"-modulation (DM) is a differential waveform quantization\n(or coding) techniq"
"ue.  A DM encoder uses the error between\nthe original signal to be coded and"
" the coded signal itself to create\na differentially-quantized data stream.  "
"This data stream (usually\nthe computed error signal) is a lower-bit-rate sig"
"nal that can be\ndecoded by a matched decoder on the receiver side in order t"
"o\nachieve data compression and hence low data transmission rates.\n\nLinear "
"Delta-modulation (LDM), Continuously Variable Slope\nDelta-modulation (CVSD),"
" and Adaptive Differential Pulse Code Modulation\n(ADPCM) are each differenti"
"al waveform coding techniques.  Each employ\ntwo-level (i.e. one-bit) encoder"
"s, and may be performed at many different\nsampling/data rates.  The encoded "
"bit rate is usually directly proportional\nto the input signal sample rate.  "
"For example, in both LDM and CVSD\none-bit per sample is used to compute the "
"encoded data stream.\n\nIn LDM, a constant step-size is used to approximate t"
"he input signal with\na single-bit per signal sample.  In the encoded bit-str"
"eam, each \"1\" bit\nmeans \"increase the amplitude\" by the step-size (as co"
"mpared to the\nprevious decoded signal sample), while a \"0\" bit means \"dec"
"rease the\namplitude\" by the step-size (as compared to the previous decoded"
"\nsignal sample).  Using LDM, the encoder performance can suffer due to\na co"
"ndition known as \"slope-overload\", when the input signal slope\n(such as du"
"ring high frequency content) changes too rapidly for the\nencoder to track it"
" accurately.\n\nCVSD is basically LDM with the addition of an adaptive step-s"
"ize.\nBy adjusting (adapting) the step-size to the changes in slope of the\ni"
"nput signal, the encoder is able to represent low-frequency signals\nwith gre"
"ater accuracy without sacrificing as much performance due\nto \"slope-overloa"
"d\" at higher frequencies.  When the slope of the\ninput signal changes too q"
"uickly for the encoder to keep up with it,\nthe step-size is increased.  Conv"
"ersely, when the input signal slope\nchanges slowly, the step-size is decreas"
"ed.  A slope-overload detector\nand syllabic filter is used in conjunction wi"
"th a pulse amplitude\nmodulator (PAM) to accomplish the step-size adaptation."
"\n\nCVSD is used in both commerical and military communications where\n\"toll"
" quality\" or \"communications quality\" is required, yet low computation\nco"
"mplexity and low memory requirements are desirable.  Two examples\nof this te"
"chnique are U.S. MIL-STD-188-113 (16 kbs and 32kbs CVSD)\nand U.S. Federal St"
"andard 1023 (12 kbs CVSD).  In addition, encoded\nCVSD data can be encrypted "
"and made more secure - desirable for\nmany wireless communications applicatio"
"ns (including speech\nand general-purpose audio coding).\n\nADPCM is a lot li"
"ke CVSD, however it provides more accuracy (and thus\npreserved frequency ban"
"dwidth) at the expense of additional computational\nrequirements for the adap"
"tation step-size calculations."
	  FontName		  "Arial"
	  FontSize		  14
	}
      }
    }
    Line {
      Name		      "Decoded CVSD"
      Labels		      [1, 0]
      SrcBlock		      "CVSD Decoder"
      SrcPort		      1
      DstBlock		      "Mux1"
      DstPort		      2
    }
    Line {
      Name		      "Decoded LDM"
      Labels		      [1, 0]
      SrcBlock		      "LDM Decoder"
      SrcPort		      1
      DstBlock		      "Mux"
      DstPort		      2
    }
    Line {
      SrcBlock		      "LDM Encoder"
      SrcPort		      1
      DstBlock		      "Transmission\nChannel"
      DstPort		      1
    }
    Line {
      SrcBlock		      "CVSD Encoder"
      SrcPort		      1
      DstBlock		      "Transmission\nChannel"
      DstPort		      2
    }
    Line {
      SrcBlock		      "Bandlimited\nAnalog Input Signal\n(linear freq "
"sweep)"
      SrcPort		      1
      DstBlock		      "8-bit Linear ADC"
      DstPort		      1
    }
    Line {
      Name		      "Raw Digital Input"
      Labels		      [0, 0]
      SrcBlock		      "8-bit Linear ADC"
      SrcPort		      1
      Points		      [0, 0; 80, 0]
      Branch {
	Points			[410, 0; 0, 30]
	Branch {
	  DstBlock		  "Mux"
	  DstPort		  1
	}
	Branch {
	  Points		  [0, 75]
	  Branch {
	    DstBlock		    "Mux1"
	    DstPort		    1
	  }
	  Branch {
	    Points		    [0, 75]
	    DstBlock		    "Mux2"
	    DstPort		    1
	  }
	}
      }
      Branch {
	Points			[0, 45]
	Branch {
	  DstBlock		  "LDM Encoder"
	  DstPort		  1
	}
	Branch {
	  Points		  [0, 75]
	  Branch {
	    Points		    [0, 75]
	    DstBlock		    "ADPCM Encoder"
	    DstPort		    1
	  }
	  Branch {
	    DstBlock		    "CVSD Encoder"
	    DstPort		    1
	  }
	}
      }
    }
    Line {
      SrcBlock		      "Transmission\nChannel"
      SrcPort		      1
      DstBlock		      "LDM Decoder"
      DstPort		      1
    }
    Line {
      Name		      "Original and LDM"
      Labels		      [0, 0]
      SrcBlock		      "Mux"
      SrcPort		      1
      DstBlock		      "Scope"
      DstPort		      1
    }
    Line {
      SrcBlock		      "ADPCM Encoder"
      SrcPort		      1
      DstBlock		      "Transmission\nChannel"
      DstPort		      3
    }
    Line {
      Name		      "Decoded ADPCM"
      Labels		      [0, 0]
      SrcBlock		      "ADPCM Decoder"
      SrcPort		      1
      DstBlock		      "Mux2"
      DstPort		      2
    }
    Line {
      SrcBlock		      "Transmission\nChannel"
      SrcPort		      2
      DstBlock		      "CVSD Decoder"
      DstPort		      1
    }
    Line {
      Name		      "Original and CVSD"
      Labels		      [0, 0]
      SrcBlock		      "Mux1"
      SrcPort		      1
      Points		      [95, 0; 0, -60]
      DstBlock		      "Scope"
      DstPort		      2
    }
    Line {
      Name		      "Original and ADPCM"
      Labels		      [0, 0]
      SrcBlock		      "Mux2"
      SrcPort		      1
      Points		      [110, 0; 0, -120]
      DstBlock		      "Scope"
      DstPort		      3
    }
    Line {
      SrcBlock		      "Transmission\nChannel"
      SrcPort		      3
      DstBlock		      "ADPCM Decoder"
      DstPort		      1
    }
    Annotation {
      Position		      [454, 27]
      Text		      "Delta-modulation (DM) Waveform Codecs"
      FontName		      "Arial"
      FontSize		      20
      FontWeight	      "bold"
    }
  }
}