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Topic: Companding

	Companding Encyclopedia
		Companding can also refer to the use of compression, where gain is decreased when levels rise above a certain threshold, and its complement, expansion, where gain is also decreased when levels drop below a certain threshold.
		Companding is used in professional wireless microphones to improve the dynamic range of the microphone (the dynamic range of the microphone itself is higher than the dynamic range of the radio transmission).
		Companding is sometimes used in digital systems, compressing before input to an analog-to-digital converter, and then expanding after a digital-to-analog converter.
	www.hallencyclopedia.com /topic/Companding.html (569 words)

	Audio-Technica - Microphones, headphones, wireless microphone systems, noise-cancelling headphones & more : Companding
		The purpose of the companding process is to preserve the signal-to-noise ratio of the original audio.
		Companding is also effective in reducing buzz, hiss and low-level audio tones caused by mild interference.
		However, the quality of the audio is highly dependent upon the specific companding circuitry employed, the precision of the circuit components and the care with which the system is designed and manufactured.
	www.audio-technica.com /cms/site/490e7be64dfcaa53 (618 words)

	Near-instantaneous companding PCM involving accumulation of less significant bits removed from original data - Patent ...
		However, it is difficult that the conventional near instantaneous companding PCM transmission is applied to the DPCM transmission in an unaltered fashion, as the DPCM can achieve the data compression to a greater extent.
		In the near-instantaneous companding system, the provision of an accumulator in the transmitting side is effectively combined with DPCM system, thereby achieving a high quality transmission of data.
		As a further effect of the provision of the accumulation in the transmitting, a shift and fluctuation of DC level caused by removed bits is eliminated and, when a muliplex signal comprising a plurality of sinusoidal waves having different frequencies is transmitted, the low frequency component can be transmitted effectively, thereby enabling a multiplex signal.
	www.freepatentsonline.com /4633483.html (13489 words)

	Companding - Wikinfo
		In telecommunication, signal processing, and thermodynamics, companding (occasionally called compansion) is a method of reducing the effects of a channel with limited dynamic range.
		It is a combination of compressing and expanding (the word companding therefore is a portmanteau word), and is a variant of audio level compression.
		Companding reduces the noise and crosstalk levels at the receiver.
	www.wikinfo.org /wiki.php?title=Companding (1009 words)

	Digital to analog converter with improved companding - Patent 3997892
		A digital to analog converter includes nonlinear and linear cascaded resistive voltage dividers the nonlinear divider having its resistors valued to approximate a desired transfer characteristic.
		A converter as in claim 1 where said first switching means includes buffer amplifiers for connecting said resistor of said first voltage divider to said second voltage divider.
		The segment itself is linear and thus the linear voltage divider 16 locates the point on the segment 11, for example, which has the proper equivalent analog level to the digital code which as discussed above provides for 256 digital code levels; that is, 2 raised to the eighth power.
	www.freepatentsonline.com /3997892.html (2028 words)

	Analog Devices: Technology Leadership: Tutorial MT-018: Intentionally Nonlinear DACs
		In effect, this reduces the quantization noise associated with small signals (where it is most noticeable) and increases the quantization noise for larger signals (where it is less noticeable).
		The term "companding" is generally used to describe this form of encoding.
		The µ-law or A-law companded input data is mapped into data points on the transfer function of a high resolution DAC.
	www.analog.com /jp/content/0,2886,758%255F%255F92067,00.html (1129 words)

	Companding - ITtoolboxWiki
		Companding is a signal processing technique used in the digital systems primary in audio such as microphones (more effectively in wireless) to reduce the noise levels in the sound quality mainly owing to low-level radio frequency interference in the frequency channel.
		The objective of the companding process is to preserve the signal-to-noise ratio of the original audio.
		The Companding is also used in the digital systems by compressing the signals before input to an analog-to-digital converter, and then expanding after a digital-to-analog converter.
	wiki.ittoolbox.com /index.php/Topic:Companding (421 words)

	Shure - Products
		Shure's patented Audio Reference Companding is currently featured in many Shure Wireless Systems, and in some PSM 700 Personal Monitor Systems (H3 and L2 bands).
		Companding is the process of compressing the audio signal prior to transmission and expanding it after reception.
		Instead of companding across the entire dynamic range like most wireless systems (causing a whooshing audio artifact known as "breathing"), companding only occurs at high audio levels.
	www.shure.com /ProAudio/Products/WirelessMicrophones/ssLINK/us_pro_product_wireless_ARC (169 words)

	Companding (Site not responding. Last check: )
		Companding, means compression and expansion of a signal or sample.
		It forms part of the PCM (Pulse Code Modulation) process, whereby analogue signal values are logically rounded on a nonlinear scale.
		The process is reversed at the receiving terminal using the same nonlinear scale.
	www.mpirical.com /companion/Multi_Tech/Companding.htm (58 words)

	Background Method
		The word "companding" stands for compression and expansion, which is a process to reduce the number of bits required to encode a voice signal.
		In telephony systems, compander is used to reduce quantization noise in speech coding and to reduce the number of bits required to encode a voice signal.
		Let the speech voltage level into the compander be x(t) and the speech output voltage be F(x).
	www.egr.msu.edu /~leejinyo/ee490/490back.html (856 words)

	ezln23: Synthetic Morpheme
		After reading Chris' comments to my post yesterday [comments], I decided to find out what companding is all about.
		However, in addition to the companding process, which is used to supress noise introduced into the signal, there is another type of dynamic range compression used in cellular phones.
		Before the companding process, the audio signal is "compressed" to equalize volume levels.
	radio.weblogs.com /0107035/2003/04/02.html (232 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal
		In this, the 'ranging' was to be applied to the analogue signal before the ADC and after the Digital to Analog Converter (DAC).
		The application of this to broadcasting, in which the companding was to be done entirely digitally after the ADC and before the DAC, was described in a 1972 BBC Research Report.
		Digital companding (using a CCITT J.17 pre-emphasis curve) ensures that the encoding and decoding algorithms can track perfectly.
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=NICAM (1421 words)

	Companding a Signal :: Source Coding (Communications Toolbox)
		The combination of a compressor and expander is called a compander.
		function supports two kinds of companders: µ-law and A-law companders.
		Mu = 255; % Parameter for mu-law compander sig = -4:.1:4; sig = exp(sig); % Exponential signal to quantize V = max(sig); % 1.
	www.mathworks.com /access/helpdesk/help/toolbox/comm/ug/fp6570.html (185 words)

	Software Configuration (Site not responding. Last check: )
		Actual companding refers to the state of the hardware bits.
		DB Companding is displayed by digroup (D0 means digroup 0, and D1 means digroup1) and refers to the Mu-law or A-law parameter setting in the software.
		This indicates the companding mode selected when the card was installed in the configuration database.
	www.net.com /support/manuals/html/idnx/vm/vm_21.html (1457 words)

	DSP Voice Frequency Compandor
		Simply put, frequency companding is a method of removing the most unused frequency components from a given source and then shifting the remaining components together.
		Part of their companding technique was to simply remove this band of frequency components as well as those below 100 Hz and above 2500 Hz.
		The compander definitely helped to lessen the co-channel interference from this interfering signal transmitting at the same signal strength.
	www.wwc.edu /frohro/qex/qex-art.html (2443 words)

	MPRG - Research Thrust Areas
		From these reasons, a concatenated scheme for PAPR reduction that employs interleaving followed by non-uniform quantization (i.e., companding) of the OFDM waveform was developed at MPRG, which is classified into a symbol scrambling method.
		As seen in the figure, the performance gap between the various curves is relatively small and hence significant reductions in PAPR can be realized with the synergistic use of interleaving and companding (non-uniform quantization) but with only negligible loss in receiver performance.
		From these observations, it can be clearly seen that the synergistic use of symbol scrambling and companding provides significant reductions in PAPR with relatively small loss in receiver performance.
	www.mprg.org /research/OFDM/ofdm_papr.html (434 words)

	Companding: Definition and Links by Encyclopedian.com
		In telecommunication, a companding is an operation in which the dynamic range of signals is compressed before transmission and is expanded to the original value at the receiver.
		Note: The use of companding allows signals with a large dynamic range to be transmitted over facilities that have a smaller dynamic range capability.
		Post a link to definition / meaning of " Companding " on your site.
	www.encyclopedian.com /co/Companding.html (107 words)

	Location Sound Corp. -- Tech Tips
		The incoming audio signal is compressed in the transmitter, used to modulate the RF carrier, and again transmitted.
		However, because the compressor limiters are externally adjustable on the transmitter, poor dynamic range and/or distortion can occur as a result of misinformed use.
		Routine inspection, cleaning, and calibration is your best assurance to continued, trouble-free operation of your microphones.
	www.locationsound.com /proaudio/ls/tips/techtips18.html (324 words)

	App Note Abstract: mu-Law and A-Law Companding Using the TMS320C2xx DSP
		Companding (compression and expansion) is a method commonly used in telephony applications to increase dynamic range while keeping the number of bits used for quantization constant.
		Mu-law is a companding standard commonly used in the United States.
		This application note describes subroutines for performing mu-law and A-law companding using Texas Instruments (TI)(tm) TMS320C2xx ('C2xx) DSP.
	www.ti.com /sc/docs/psheets/abstract/apps/spra349.htm (178 words)

	Narrow-band companding
		A compander is a tool that amplifies a signal with a variable gain, depending on the signal's measured amplitude.
		Frequently the gain depends not only on the immediate signal level but on its history; for instance the rate of change might be limited or there might be a time delay.
		The patch diagrammed in Figure 9.8 shows one very useful application of companding, called a noise gate.
	crca.ucsd.edu /~msp/techniques/v0.06/book-html/node162.html (384 words)

	NICAM 728 Digital TV Sound
		One bit of parity protection is added to each sample, and the 3 bits of "range bits" (which convey to the decoder what companding factor was used so that the companding can be reversed) are cunningly added too by twiddling some of the parity bits.
		This process is course reversed at the decoder, and its purpose is to reduce the effects of noise modulation which occur as a result of the companding procedure's block-by-block processing.
		The first 11-bit word of the payload is word 0 of the left channel companding block, this is followed by word 0 of the right channel companding block, then word 1(L), 1(R), 2(L)...
	www.qsl.net /zl1vfo/nicam.htm (5653 words)

	How the Companding Calculator Works
		The calculator is supplemented with a graphical display of companding functions.
		This can help you visualize and understand what these functions mean, in an intuitive sense.
		The question often arises, "What value for gamma gives a companding function that most closely represents the CIE L* function (i.e.
	www.brucelindbloom.com /CompandCalcHelp.html (626 words)

	Shure PGX-14 Guitar Set
		All pro audio wireless needs companding to deliver a wide dynamic range (greater than 100dB).
		Audio Reference Companding is a level-dependent companding scheme.
		These levels are high enough to make the companding artifacts inaudible.
	www.musik-service.de /wireless-microphone-Shure-PGX-14-Guitar-Set-prx395744235en.aspx (250 words)

	App Note Abstract: TMS320C6000 u-Law and a-Law Companding with Software or the McBSP
		This document describes how to perform data companding with the TMS320C6000(tm)digital signal processors(DSP).
		This application report discusses how to use the McBSP to perform data companding in both the mu-Law and A-Law formats.
		The appendix provides software companding codes and a brief discussion on the companding theory.
	www.ti.com /sc/docs/psheets/abstract/apps/spra634.htm (156 words)

	Glossary
		ITU-T companding standard used in the conversion between analog and digital signals in PCM systems.
		A-law is used primarily in European telephone networks and is similar to the North American µ-law standard.
		North American companding standard used in conversion between analog and digital signals in PCM systems.
	www.cisco.com /univercd/cc/td/doc/product/voice/ata/ataadmn/ata_h323/h3288gls.htm (1725 words)

	AES Barcelona 2005: Paper Session B
		A new IC for implementing companding noise reduction in professional wireless microphone applications is described.
		Unlike existing devices designed primarily for the cordless telephone market, the new design allows straightforward, repeatable implementation of companding schemes incorporating ratios greater or less than 2-to-1, level-dependent ratios, limiters, and noise gates.
		The overall device architecture and design and performance of individual functional blocks is described.
	www.aes.org /events/118/papers/session.cfm?code=B (327 words)

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