Delta modulation
Delta modulation (DM, ΔM, or Δ-modulation) is an analog-to-digital and digital-to-analog signal conversion technique used for transmission of voice information where quality is not of primary importance.
DM is the simplest form of differential pulse-code modulation (DPCM) where the difference between successive samples is encoded into n-bit data streams.
An optional low-pass filter will remove high frequency zigzags (see the blue output signal of Fig.
But a 1971 study shows that slope overload is less objectionable compared to granularity than one might expect based solely on SNR measures.
While slope overload (also referred to as slope clipping) can be avoided by increasing the quantum step size or sampling rate, very high sampling rates, typically 20 times the highest frequency of interest, are required to achieve the same quality as pulse-code modulation (PCM).
[1][2] The seminal[5] paper combining feedback with oversampling to achieve delta modulation was by F. de Jager of Philips Research Laboratories in 1952.
A February 1966 paper by H. Inose "Asynchronous delta-modulation system"[9] uses Schmitt triggers to detect when the input signal exceeds the local demodulator by a predetermined difference, with the benefit of reducing the number of output pulses.
Adaptive delta modulation (ADM) was first published by Dr. John E. Abate (Bell Labs Fellow) in his doctoral thesis at NJ Institute Of Technology in 1968.
In the mid-1980s, Massachusetts audio company DBX marketed a commercially unsuccessful digital recording system based on adaptive delta modulation.
Rather, when several consecutive bits have the same direction value, the encoder and decoder assume that slope overload is occurring, and the step size becomes progressively larger.
The Nintendo Entertainment System's audio processing unit (the Ricoh 2A03 chip) includes a Delta Modulation Channel (DMC) to demodulate percussion and sound effects.
[12][13][14] Delta modulation was used by Satellite Business Systems (SBS) for its voice ports to provide long distance phone service to large domestic corporations with a significant inter-corporation communications need (such as IBM).
The original proposal in 1974, used a state-of-the-art 24 kbit/s delta modulator with a single integrator and a Shindler Compander[definition needed] modified for gain error recovery.
In 1977, one engineer with two assistants in the IBM Research Triangle Park, NC laboratory was assigned to improve the quality.
The complete function of delta modulation, VAC and Echo Control for six ports was implemented in a single digital integrated circuit chip with twelve bit arithmetic.
A single digital-to-analog converter (DAC) was shared by all six ports providing voltage compare functions for the modulators and feeding sample and hold circuits for the demodulator outputs.
A single card held the chip, DAC and all the analog circuits for the phone line interface including transformers.
