Delta Modulation (DM) is a fast but error-prone method of converting analog signals to digital signals for short-range transmission. Pulse code modulation (PCM) and adaptive delta modulation (ADM) are variations of DM that produce better signal-to-noise ratio output rates. PCM is still used to encode audio signals on various forms of electronic media. Alec Reeves is credited with inventing PCM in 1937, which led to the development of DM and all its variations.
Delta Modulation (DM) is a method of taking an analog signal and converting it into a digital signal for data processing. It is primarily used for voice communications, but can also be adapted to transfer video and other forms of data. Because the digital version of a converted signal is merely an approximation of the original analog signal, degradation occurs in the conversion process and increases with the distance the signal has to travel from transmitter to receiver. The primary use of delta modulation technology has been in short-range transmission for devices such as cordless telephones and bamonitors. Other forms of wireless transmission also use delta modulation, such as wireless headphones, but the heavier the noise level in an analog transmission, the more the quality of the digital output signal is reduced.
Modulation is a process with any wireless audio signal in which the transmitting radio frequency carrier wave has a change in amplitude in relation to the input signal it carries. In the delta modulation process, this analog signal is sampled at a high rate, and for each sampling instance, one bit of data is recorded. This data stream is then composed into a digital signal that approximates the original analog signal. Because the analog delta modulation process creates only one bit of data for each sample instance, the analog signal is not represented very accurately, making the process a fast but error-prone method of transmission.
Both pulse code modulation (PCM) and adaptive delta modulation (ADM) are variations of the DM process that are believed to produce better signal-to-noise ratio output rates than DM. Pulse code modulation is the original process, which can be traced back to before the invention of the modern computer. ADM and DM are more modern transmission schemes developed as methods to streamline the transmission process for large amounts of data.
While pulse code modulation is the original process, it is still the method used to encode audio signals on various forms of electronic media, such as compact discs (CDs), digital video discs (DVDs), and Blu-ray Discs. Variations on PCM now include Delta Pulse Code Modulation (DPCM) and Delta Adaptive Pulse Code Modulation (ADPCM). These recent applications of pulse code modulation use mathematical algorithms and more sophisticated analog signal sampling methods for accurate digital output.
Alec Reeves, an engineer from the UK, is credited with inventing pulse code modulation (PCM) in 1937, which led to delta modulation and all the variations on the process that now exist. His ideas are believed to have made the digital age possible. The motivation behind PCM was to remove errors from analog signal transmissions by converting them into discrete digital data packets. He was ahead of his time, however, as electronic technology did not yet exist to make his ideas practical. The transistor would not be invented until 1947, and it would not be miniaturized and mass-produced for the first integrated circuits until 1958-1959.
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