Us7602320b2 systems and methods for companding adcdsp. A law and u law are two algorithms that are used in modifying an input signal for digitization. Companding is a common technique for reducing the data rate of audio signals by making the. Routines are developed and an application is shown to implement a. Mulaw encoding law is a nonlinear companding method that can be used to reduce the bit depth of a digital audio signal in a way that preserves the dynamic range of samples at low amplitudes. In the webui, click the settings tab in the left navigation pane, go to system system companing law. The two algorithms have a fairly minimal difference and most people would not know the difference. An expanding dac is also developed that restores the compressed digital value back to an analog value. In the alaw companding, the compressor characteristic is piecewise, made up of a linear segment for low level inputs and a logarithmic segment for high level inputs.
Using modern video terminology the difference between alaw and mulaw is analogous to that of mpeg and avi. Pdf correlation power analysis with companding methods. Us7602320b2 systems and methods for companding adcdspdac. Limiting the linear sample values to magnitude bits, the law compression is defined by equation 2, where m is the compression. Alaw is similar to the law mulaw algorithm used in north america and japan. This is equivalent to using a nonlinear adc as in a tcarrier telephone system that implements alaw or. Format description for alaw standard companding algorithm used in european digital communications systems telephones, for the most part to optimize the dynamic range of an analog signal generally a voice for digitizing, i. Using a bspcm block scaled pulse code modulation method, in each block of nominally 246 eightbit pcm. Both use a logarithmic nonlinearity, since this is what converts the spacing detectable by the human ear into a linear spacing. These algorithms are implemented in telephony systems all over the world. Abstract this paper describes how to use a codec coderdecoder to encode, decode, synthesize and play auformat audio data. The word companding is used because this method works by compressing.
Pcm a law and u law companding algorithms in ansi c the pulse code modulation pcm, also known as g. Different types of nlcts are described in the literature, such as the mu law and a law companding method, exponential companding, errorfunction companding, tanh companding, and arct 22, 33. An analog speech signal is sampled of a nominal rate of 6 kilohertz and digitized in a mu law encoder. So, the mulaw companding produces low out of band oob spectrum and provides good spectrum characteristic than other nonlinear companding techniques.
Mu law signals typically ride on a single 64 kbps ds0 channel in a t1 line. Consider for a moment the fact that alaw and mulaw both take a 16bit value and crunch it down to an 8bit value. Companding is used in digital telephony systems, compressing before input to an analogtodigital converter, and then expanding after a digitaltoanalog converter. Alaw companding is used for pcm telephone system in europe. Mulaw uses a companding technique that provides more quantization steps at lower amplitude volume than at higher. The mc14lc5480 is a general purpose per channel pcm codecfilter with pin selectable mulaw or alaw companding, and is offered in 20pin dip, sog, and ssop packages. Format description for a law standard companding algorithm used in european digital communications systems telephones, for the most part to optimize the dynamic range of an analog signal generally a voice for digitizing, i. Consider for a moment the fact that a law and mu law both take a 16bit value and crunch it down to an 8bit value. The combination of a compressor and expander is called a compander the compand function supports two kinds of companders. Change mulaw to alaw for systems using alaw companding. The reverse of that is to take an 8bit value and turn it into a sixteen bit value. An2095 algorithm logarithmic signal companding not just.
Is there any good methods that can effectively utilize and implement the mulaw logarithm characteristic and the standard mulaw ccode in web and as the same. Format description for alaw standard companding algorithm. An alaw algorithm is a standard companding algorithm, used in european 8bit pcm digital communications systems to optimize, i. Routines are developed and an application is shown to implement a law compressor that converts an analog voice band signal and produces a digitized 8bit compressed value. Law and alaw companding with software or the mcbsp pdf. Alaw and mulaw companding implementations using the tms320c54x 7 alaw and mulaw companding implementations using the tms320c54x abstract presented in this application note is the implementation of alaw and law companding routines for the tms320c54x. Mu law uses a companding technique that provides more quantization steps at lower amplitude volume than at higher. The digital output of the mulaw encoder is converted by a microprocessor performing table lookup to linearized pulse code modulation pcm samples nominally of eight bits per sample. Mulaw contains a good logarithm curve for compressing the signal. Home proceedings volume 9902 proceedings volume 9902. Law compressor that converts an analog voice band signal and produces a digitized 8bit compressed value.
Mulaw signals typically ride on a single 64 kbps ds0 channel in a t1 line. Modified square rooting companding technique to reduced. Modified square rooting companding technique to reduced papr. This page on companding vs expanding describes difference between companding and expanding techniques. The european telephone system uses a system of companding known as a law whereas north america uses mu law. Systems and methods for resizing a signal for use with a fixedpoint dsp are provided. The inverse operation of a compressor is called an expander. You will write the inverse expansion function as part of your prelab report. Different types of nlcts are described in the literature, such as the mulaw and alaw companding method, exponential companding, errorfunction companding, tanh companding, and arct 22, 33. Theoretical material regarding companding and speech signals is provided. Castellano, todd hiers, and rebecca ma, tms320c6000 mulaw and alaw companding with software or the mcbsp, texas instruments application report, spra634, april 2000. The first difference between the two is the dynamic range of the ouput.
Hence because one uses alaw, then all calls from the usa to uk or uk to usa must use alaw. The lecture discusses mulaw companding used in the us and japan u 255 and alaw companding in europe a 87. Is there any good methods that can effectively utilize and implement the mu law logarithm characteristic and the standard mu law ccode in web and as the same. Thus the mu law companding is more localized in frequency domain compared to other companding techniques. Mc14lc5480 view datasheet pdf freescale semiconductor. Difference between alaw and ulaw difference between. This method is also used in digital file formats for better signaltonoise ratio snr at. In some embodiments, companding is used to improve the signaltonoise and distortion ratio. The european telephone system uses a system of companding known as alaw whereas north america uses mulaw. More specifically, a process called companding is used in conjunction with fixedpoint devices to resize a signal to make use of the available range of these devices. Alaw and mulaw companding free download as word doc. Here a is known as compression parameter and its value is about 87.
Source code mulaw or alaw compressor or expander matlab. A law and u law pronounced mu law are socalled companding compression expanding schemes that are used in telephone networks see figure below. Nov 14, 2018 now, the most obvious way to decompress a compressed mu law or a law sample would be to reverse the algorithm. Media in category mu law the following 5 files are in this category, out of 5 total. Sep 11, 2015 this matlab exercise illustrates the impact of mu law companding compressing and expanding and quantization of a speech signal. Two nearly identical standards are used for companding curves. Applicable both for uniform and nonuniform quantizers how to find the partition and reconstruction levels for mulaw quantizer apply inverse mulaw mapping to the partition and reconstruction levels of the uniform quantizer for y.
Table 5 input bit values for law compression bit1514 12 3 2 1 0 value s x12 x11 x10. A law is used across europe as companding standard recommended by ccitt. Using modern video terminology the difference between a law and mu law is analogous to that of mpeg and avi. The following matlab function quantizes a signal with a range of 1 to approximately 8. The program quantizes a speech file using a mu law quantizer with a bit rate of nbits per sample, where nbits is typically in the range of 210. Oct 09, 2006 mu law contains a good logarithm curve for compressing the signal. An analog speech signal is sampled of a nominal rate of 6 kilohertz and digitized in a mulaw encoder. Whereas a law is widely used by european digital communication systems, u law is used widely throughout north america and japan. Hence they use ulaw companding on calls between the two countries becuase neither uses alaw. Therefore, it is advisable that when the sound input is very soft, alaw is the best algorithm to be utilized.
Papr reduction for fbmcoqam using hybrid scheme of different precoding transform and mulaw companding. Pcm alaw and ulaw companding algorithms in ansi c the pulse code modulation pcm, also known as g. In certain applications, such as speech processing, it is common to use a logarithm computation, called a compressor, before quantizing. In this lab you will study the effect of companding on the quantization snr of. By limiting linear sample value equivalent to 12 bits we can obtain a law equation as mentioned below. Alaw and ulaw pronounced mulaw are socalled companding compression expanding schemes that are used in telephone networks see figure below. Now, the most obvious way to decompress a compressed mulaw or alaw sample would be to reverse the algorithm. Integrated circuits, transistor, semiconductors search and datasheet pdf download site.
There are two basic types of companding in telephone systems across the world viz. The program illustrates the impact of mu law companding on a speech signal, showing the signal histograms of the original speech signal along side of the histogram of the mu law encoded signal. Performance evaluation of papr reduction in fbmc system. An anechoic chamber has about a 10 db spl noise floor. Also, with regards to the countries that utilize a law and u law, the two algorithms vary. Pdf this paper describes how to use a codec coderdecoder to encode, decode, synthesize and play auformat audio data.
An2095 explains how logarithmic signal compression works. Change mulaw to alaw for systems using alaw companding only return to task list. Find out inside pcmag s comprehensive tech and computerrelated encyclopedia. Busyout the trunk group associated with the ip trunk by typing busyout board uucss and pressing enter. No system being perfect, both have their advantages and disadvantages. An example of a peak reduction associated with a data symbol before and after companding with mu 255 is shown in fig. Pin selectable mulaw alaw companding with corresponding data format onchip precision reference voltage 3. Pulse code modulation pcm is a common method of digitizing or quantizing an analog waveform. Therefore, it is advisable that when the sound input is very soft, a law is the best algorithm to be utilized. The other useful difference between terms are also provided here. Nonetheless, in a linear quantization scheme, we assign as many reconstruction levels for larger amplitudes as for smaller amplitudes, which are more probable to occur.
Alaw and ulaw are two algorithms that are used in modifying an input signal for digitization. Performance evaluation of papr reduction in fbmc system using. Mc145480motorola15 v pcm codecfilterthe mc145480 is a general purpose per channel pcm codecfilter with pinselectable mulaw or alaw companding, and is offered in 20pin dip, sog,and ssop packages. Alaw and mulaw companding implementations using the.
This device performs the voice digitization andreconstruction as well as the band limiting and smoothing required for pcmsystems. The digital output of the mu law encoder is converted by a microprocessor performing table lookup to linearized pulse code modulation pcm samples nominally of eight bits per sample. Mulaw pcm is used in north america and japan, and alaw used in most other countries. Pcm is based on an nonuniform 8 bits quantization who is used for representing each sample took from an continuous analog signal. In the left navigation pane, go to system system companing law. The word companding is used because this method works by.
Pdf papr reduction for fbmcoqam using hybrid scheme of. For systems using alaw companding, an additional procedure is necessary. However, zero code suppression is applied to the compressor that makes a discontinuous output at zero input value. This device performs the voice digitization and reconstruction as well as the band limiting and smoothing required for pcm systems. A proposed approximation for u mu for mu law companding scheme is given by 33 u mu. An2095 algorithm logarithmic signal companding not. Page 3 of 4 mlaw compander the united states and japan use law companding. Sep 11, 2015 the program illustrates the impact of mu law companding on a speech signal, showing the signal histograms of the original speech signal along side of the histogram of the mu law encoded signal. Mu specifies, and v is the input signals maximum magnitude.
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