Pulse-code modulation

Ia early telephoaes, souad (voice) waves caused a carboa microphone s resistance to vary, thus varyiag the current flowing ia a series external circuit. This d-c curreat could thea be used to regeaerate voice waves ia a receiver. Two wires were required to carry a single coaversatioa. With time, telecommunications traffic was eacoded oa a-c carriers, at first usiag ampHtude or frequeacy modulatioa, and more recently pulse code modulation. 

The car truck is also equipped with a power supply soince, an observation system, control equipment including power automatic machinery and a transceiver (another option is also possible of electric-power transmission using trolley or a rail with pulse-code modulation of steering commands). 

We will first discuss studies performed with spectrometers 1 and 2, then with spectrometer 3 and finally spectrometers 4 and 5. In the spectral measurements, data processing is of essential importance. Because, a large amount of experimental data must be quickly and accurately transmitted, a PCM (pulse code modulation) telemetry is indispensable, and will be also discussed. 

We first consider pulse-code modulation where it is the intensity which is modulated. This simple nonorthogonal scheme is frequently referred to as PCM/IM [7.73], The signal is considered to be present when a 1 is transmitted, and absent when a 0 is transmitted. To evaluate system performance, we choose the likelihood-ratio criterion [7.72,73]. If Q represents the a priori probability that a 1 is transmitted, the signal is judged to be present if... 

Analog signals can be converted to digital codes by many methods, including integration, successive approximation, parallel (flash) conversion, delta modulation, pulse code modulation, and sigma-delta... 

Pulse code modulation (PCM) ICs are high-precision A/D converters. The PCM ICis often refered to as a PCM codec with both encoder and decoder functions. The encoder portion of the codec performs the... 

ADPCM Adaptive differential pulse code modulation. 

Pulse code modulation (PCM) Sampling of continuous video signal and coding of samples. (Rabbani and Jones discuss basics of image techniques. See Further Information.)... 

PCM pulse-code modulation plug compatible module process control module... 

Figure 4-1. General flow sheet for analog and digital generation of derivatives. (PCM pulse-code modulator.)...

An easier-to-use op-amp is the LM386. (This is no relation to the Intel 386 micro-processor IC, which is not an op-amp, is digital rather than analog, and has CMOS transistors.) The 386 needs only one power supply and can put out more current — enough to drive a small loudspeaker without a buffer amplifier. The experimenter should build the circuit of Fig. 23.3, with an infrared-sensitive photodiode and a small loudspeaker. It will enable the pulse code modulated (see index if necessary) lightwave signals transmitted by a "remote" control for a TV or DVD set to be made into audible sound signals. (We could use a 4.7 mfd capacitor between pin number 5 and the loudspeaker, to prevent dc output, but that is not necessary in this simplified circuit.)... 

A remote controller for a TV or DVD is aimed at the photodiode, up close, and operated. Pushing various function buttons should cause various clicking sounds to be heard via the loudspeaker. This is digital pulse code modulation, as in Fig. 19.6 on page 211, similar to the coding used in CD or DVD music... 

PCM (uncompressed) stands for pulse code modulation and is a standard lossless format. It is widely used by many formats, notably the Windows. wav format. 

ADPCM (adaptive differential pulse code modulation) is a very popular audio compression system, widely used in telephony, HDTV, and many other applications. It is also a common codec nsed for compressed Windows. wav files. Not all applications can read ADPCM encoded. wav files, but most can. While ADPCM files are nsnally significantly smaller than PCM files, they are still not usually compressed as much as other Internet targeted codecs. 

---