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Delta-sigma (ΔΣ; or sigma-delta, ΣΔ) modulation is an oversampling method for encoding signals into low bit depth digital signals at a very high sample-frequency as part of the process of delta-sigma analog-to-digital converters (ADCs) and digital-to-analog converters (DACs).
To achieve high signal-to-noise ratio, delta modulation must use oversampling techniques, that is, the analog signal is sampled at a rate several times higher than the Nyquist rate. Derived forms of delta modulation are continuously variable slope delta modulation, delta-sigma modulation, and differential modulation.
The following digital model of pulse-density modulation can be obtained from a digital model of a 1st-order 1-bit delta-sigma modulator. Consider a signal x [ n ] {\displaystyle x[n]} in the discrete time domain as the input to a first-order delta-sigma modulator, with y [ n ] {\displaystyle y[n]} the output.
Direct Stream Digital (DSD) is a trademark used by Sony and Philips for their system for digitally encoding audio signals for the Super Audio CD (SACD).. DSD uses delta-sigma modulation, a form of pulse-density modulation encoding, a technique to represent audio signals in digital format, a sequence of single-bit values at a sampling rate of 2.8224 MHz.
Pulse-frequency modulation (PFM) Pulse-position modulation (PPM) Analog-over-digital methods. Pulse-code modulation (PCM) Differential PCM (DPCM) Adaptive DPCM (ADPCM) Delta modulation (DM or Δ-modulation) Delta-sigma modulation (ΣΔ) Continuously variable slope delta modulation (CVSDM), also called adaptive delta modulation (ADM) Pulse ...
Digital eXtreme Definition, used for recording and editing Super Audio CDs, as 1-bit Direct Stream Digital (DSD) is not suited for editing. 8 times the frequency of 44.1 kHz. 2,822,400 Hz SACD, 1-bit delta-sigma modulation process known as Direct Stream Digital, co-developed by Sony and Philips. 5,644,800 Hz
On the contrary, delta modulation and delta-sigma modulation are random processes [clarification needed] that produces a continuous spectrum without distinct harmonics. While intersective PWM uses a fixed period but a varying duty cycle, the period of delta and delta-sigma modulated PWMs varies in addition to their duty cycle.
This results in a broadband dynamic range of only 7.78 dB, but it is not consistent among frequency bands, and in the lowest frequencies (the audible range) the dynamic range is much greater — over 100 dB. Noise shaping is inherently built into the delta-sigma modulators. The 1-bit converter is the basis of the DSD format by Sony.