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Delta modulation
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<p>Delta modulation (DM, ΔM, or Δ-modulation) is an <a href="/facts/Analog-to-digital_converter/8YYNsMFg">analog-to-digital</a> and <a href="/facts/Digital-to-analog_converter/5loEvAeb">digital-to-analog signal</a> conversion technique used for transmission of voice information where quality is not of primary importance. DM is the simplest form of <a href="/facts/Differential_pulse-code_modulation/v8H09k06">differential pulse-code modulation</a> (DPCM) where the difference between successive <a href="/facts/Sampling_(signal_processing)/xxck7aLN">samples</a> is encoded into n-bit data streams. In delta modulation, the transmitted data are reduced to a 1-bit data stream representing either up (↗) or down (↘). Its main features are: </p> <ul><li>The analog signal is approximated with a series of segments.</li> <li>Each segment of the approximated signal is compared to the preceding bits and the successive bits are determined by this comparison.</li> <li>Only the change of <a href="/facts/Information/3LdrzXtJ">information</a> is sent, that is, only an increase or decrease of the signal amplitude from the previous sample is sent whereas a no-change condition causes the modulated signal to remain at the same ↗ or ↘ state of the previous sample.</li></ul> <p>To achieve high <a href="/facts/Signal-to-noise_ratio/qohClhyG">signal-to-noise ratio</a>, delta modulation must use <a href="/facts/Oversampling/9rka4Dpg">oversampling</a> techniques, that is, the analog signal is sampled at a rate several times higher than the <a href="/facts/Nyquist_rate/Xb1v87Bu">Nyquist rate</a>. </p><p>Derived forms of delta <a href="/facts/Modulation/aAXPjINv">modulation</a> are <a href="/facts/Continuously_variable_slope_delta_modulation/EgxgfCzr">continuously variable slope delta modulation</a>, <a href="/facts/Delta-sigma_modulation/QrhBCoUe">delta-sigma modulation</a>, and differential modulation. <a href="/facts/Differential_pulse-code_modulation/v8H09k06">Differential pulse-code modulation</a> is the superset of DM. </p>