gil@limbic.UUCP (Gil Kloepfer Jr.) (10/12/88)
Recently, I have been playing around with sound digitization, and was able
to get a peek at a commerical unit. It had a chip in it that was referred
to as a CODEC. This appears to be a A/D & D/A converter with an audio
compression that they refer to as mu and A law.
Can anyone provide input on what the mu and A law compression schemes are,
and (especially) how I would go about getting a CODEC chip (prices, locations,
etc). Would a company like Motorola, AT&T, or TI provide evaluation kits
with these chips?
It seems like AT&T Microelectronics is the biggest supplier of such chips,
probably because they are used in digital telephone equipment. I really
don't know how to go about getting in touch with them about getting a
single-quantity chip (oh well...).
Thanks in advance for any info. This sounds like a good subject to post
responses to because I think it would be of interest to the net.
Gil Kloepfer, Jr. U-Net: {decuac,boulder,talcott,sbcs}!icus!limbic!gil
ICUS Software Systems Voice: (516) 968-6860 [H] (516) 746-2350 x219 [W]
P.O. Box 1 Internet: gil@icus.islp.ny.us
Islip Terrace, NY 11752 "Life's a ... well, you know..."pfales@ttrde.UUCP (Peter Fales) (10/13/88)
In article <375@limbic.UUCP>, gil@limbic.UUCP (Gil Kloepfer Jr.) writes: > Can anyone provide input on what the mu and A law compression schemes are, > and (especially) how I would go about getting a CODEC chip (prices, locations, > etc). Would a company like Motorola, AT&T, or TI provide evaluation kits > with these chips? All the companies you mention as well as others make CODEC chips. However, most of them share a common drawback for experimenter's use in that the digital information is input and output serially. I have used a chip made by National Semiconductor which is much nicer for microprocessor use because it has a parallel data interface (though the data bus does use a somewhat non-standard clocking and chip selection scheme). It comes in two versions: the TP3051 uses mu law and the TP3056 uses A law companding. Companding is explained in any reference book on digital telecommunications. Simply put, it is a method of improving the sigal-to- noise ratio without increasing the number of sampling bits by using finer sampling for low amplitude signals. In other words, the relationship between analog input and digital output is not a straight line, but a curve, and the shape of that curve is defined by the mu law or A law equation. My source is National's 1984 Telecommunications Databook. There are probably more recent devices out there that I am not aware of. -- Peter Fales AT&T, Room 2F-217 200 Park Plaza UUCP: ...att!ttrde!pfales Naperville, IL 60566 Domain: pfales@ttrde.att.com work: (312) 416-5357
barry@crcmar.uucp (Barry Mclarnon) (10/17/88)
From article <375@limbic.UUCP>, by gil@limbic.UUCP (Gil Kloepfer Jr.): > Recently, I have been playing around with sound digitization, and was able > to get a peek at a commerical unit. It had a chip in it that was referred > to as a CODEC. This appears to be a A/D & D/A converter with an audio > compression that they refer to as mu and A law. > > Can anyone provide input on what the mu and A law compression schemes are, > and (especially) how I would go about getting a CODEC chip (prices, locations, > etc). Would a company like Motorola, AT&T, or TI provide evaluation kits > with these chips? > I'm not sure about evaluation kits, but you probably won't need one once you get the applications info on the chips. The best source for this is the data books from the various manufacturers. They can usually be had for free if you contact the nearest sales office or distributor and ask nicely. Here are several to look for, so you should be able to hit on at least one of them: Motorola: Telecommunications Device Data National Semiconductor: Telecommunications Databook Intel: Telecommunication Products Handbook Hitachi: CODEC/Filter Combo LSI Data Book TI: Telecommunications Circuits Data Book Good luck! -- Barry McLarnon Communications Research Center Ottawa, ON Canada UUCP: uunet!ai.toronto.edu!utgpu!bnr-vpa!bnr-rsc!crcmar!barry Compu$erve: 71470,3651 Packet radio: VE3JF @ VE3JF
nat@bales.UUCP (Nathaniel Stitt) (10/19/88)
In article <375@limbic.UUCP> gil@limbic.UUCP (Gil Kloepfer Jr.) writes: >Recently, I have been playing around with sound digitization, and was able >to get a peek at a commerical unit. It had a chip in it that was referred >to as a CODEC. This appears to be a A/D & D/A converter with an audio >compression that they refer to as mu and A law. > >Can anyone provide input on what the mu and A law compression schemes are, Here is a look up table I created a while back for going from 8-bit mu-law encoded samples to 13-bit signed linear samples. I generated this table from a description of mu-law from a book I got at Radio Shack, so no guarantees. You should use the 8-bit mu-law value as an unsigned 8-bit index into the table. Here is the table: short u2norm[256] = { -4016, -3888, -3760, -3632, -3504, -3376, -3248, -3120, -2992, -2864, -2736, -2608, -2480, -2352, -2224, -2096, -2000, -1936, -1872, -1808, -1744, -1680, -1616, -1552, -1488, -1424, -1360, -1296, -1232, -1168, -1104, -1040, -992, -960, -928, -896, -864, -832, -800, -768, -736, -704, -672, -640, -608, -576, -544, -512, -488, -472, -456, -440, -424, -408, -392, -376, -360, -344, -328, -312, -296, -280, -264, -248, -236, -228, -220, -212, -204, -196, -188, -180, -172, -164, -156, -148, -140, -132, -124, -116, -110, -106, -102, -98, -94, -90, -86, -82, -78, -74, -70, -66, -62, -58, -54, -50, -47, -45, -43, -41, -39, -37, -35, -33, -31, -29, -27, -25, -23, -21, -19, -17, -15, -14, -13, -12, -11, -10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 4016, 3888, 3760, 3632, 3504, 3376, 3248, 3120, 2992, 2864, 2736, 2608, 2480, 2352, 2224, 2096, 2000, 1936, 1872, 1808, 1744, 1680, 1616, 1552, 1488, 1424, 1360, 1296, 1232, 1168, 1104, 1040, 992, 960, 928, 896, 864, 832, 800, 768, 736, 704, 672, 640, 608, 576, 544, 512, 488, 472, 456, 440, 424, 408, 392, 376, 360, 344, 328, 312, 296, 280, 264, 248, 236, 228, 220, 212, 204, 196, 188, 180, 172, 164, 156, 148, 140, 132, 124, 116, 110, 106, 102, 98, 94, 90, 86, 82, 78, 74, 70, 66, 62, 58, 54, 50, 47, 45, 43, 41, 39, 37, 35, 33, 31, 29, 27, 25, 23, 21, 19, 17, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 }; > >Gil Kloepfer, Jr. U-Net: {decuac,boulder,talcott,sbcs}!icus!limbic!gil >ICUS Software Systems Voice: (516) 968-6860 [H] (516) 746-2350 x219 [W] >P.O. Box 1 Internet: gil@icus.islp.ny.us >Islip Terrace, NY 11752 "Life's a ... well, you know..." -- Nathaniel Stitt | This life is a test. It is only a test. Had Guidelines Software, Inc. | this been an actual life, you would have received ucbvax!ucbcad!z!nat | further instructions as to what to do and where (415) 376-1395 | to go.