Talk:Pulse-code modulation

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Concerning the possible copyright violations noted by User:Muriel Gottrop on 11:57, 19 Oct 2003 (UTC). I have cowritten much of this article, it has partial histories at Pulse-code modulation and Pulse code modulation.

The history section was directly copied from: http://www.derivaz.fsnet.co.uk/ahr/pcm.htm

The document at http://ccc.inaoep.mx/~cferegrino/cursos/comprcrip/Lossy_Methods.pdf seems to have copied the article literally from Wikipedia without a proper attibution or an acknowledgement of the license under which Wikipedia is distributed. -- Ap 14:21, 19 Oct 2003 (UTC)

• So is reversed copy violations. I'm glad. :) Muriel Gottrop

PCM also stands for phase change material, disambiguation needed?. Thadk 00:12, 2004 May 14 (UTC)

Contents 1 Number format 2 This article badly needs an illustration or two 3 Nomenclature? 4 Bell Labs also invented PCM 5 Nyquist limit 6 Paul M. Rainey, 1926 7 Cathode Ray Tube Encoders 8 Attribution to Rainey? Not resolved on talk. 9 History of PCM and SIGSALY

[edit] Number format

Does PCM imply or mandate anything about the number format? Fixed vs floating point? u-law vs linear quantization levels? — Omegatron 19:49, 22 November 2005 (UTC)

[edit] This article badly needs an illustration or two

Twang 00:58, 11 March 2006 (UTC)

Well, it has one now. If I have time maybew I'll make a DPCM one too.

Shouldn't the current image go beside the input section since it starts with "In the diagram to the right" Adam Bryzak 10:53, 8 October 2006 (UTC)

Also, the image does not show a discrete time samples but continous time stairsteps. This is a common source of confusion for people. The usual and correct way to illustrate discrete time sampling is with pulses (perhaps I should just make a new image?). IMO there is not enbough emphasis on the *pulse* nature of PCM i the article. AL - 15:45 4 March October 2007 (UTC)

The image currently in the article matches the text I have on hand (Stallings). I do, however think you may have a point as this image illustrates the result of decoding PCM, not the process of encoding it. Perhaps a larger image with 3 panels (source, pcm, output) could be created and added to the article? --Ktims 04:19, 7 March 2007 (UTC)

[edit] Nomenclature?

The word pulse in the term Pulse Width Modulation is somewhat confusing, as there appear to be no "pulses" per se anywhere to be found.

I believe this should read 'Pulse Code Modulation'. Please confirm.

[edit] Bell Labs also invented PCM

While I understand that Reeves is widely known as the inventor of PCM, it was also invented independently at Bell Labs as part of X System (aka SIGSALY). An important aspect of the work at Bell Labs is that it was implemented and used in securing Allied communications in WWII. [1]

Because this information was classified for 30 years it has naturally not become as widely known as Reeves' work. Miller is probably the only remaining member of the team at Bell Labs and some of his knowledge needs to be included in this article and the one on SIGSALY.

For external confirmation of Miller's role at Bell Labs, please refer to "National Service in War and Peace (1925-1975), Volume II of A History of Engineering and Science in the Bell System (Bell Telephone Laboratories, 1978)" p. 297. Table 5.5 mentions R. L. Miller as inventor on four of the patents related to the X System.

• It would be of interest to list the patent number, grant date etc of Miller's US patent. I am familiar with the sigsaly system and I admire it very much. It is a matter of debate to say that sigsaly is pcm (I think it is a digital compressed vocoder, and not pcm). If you submit the patent number I will take a look at the patent, and will try to find out what it means. Unfortunately, I do not have a copy of the work you referenced. By the way, according to the US Inventors Hall of Fame, [2], normally a relaible source, Claude Shannon is the inventor of PCM as granted in 'Communication System Employing Pulse Code Modulation,' US Patent Number 2,801,281. It was granted in 1956 (20 years after Reeves PCM patent was granted). Sorn67 14:47, 9 July 2006 (UTC)

• I did some searching and found [3] on Miller's home page. From it, I quote the following relevant text:

It was not until about the middle of 1943 that Bell Labs people became aware of the use of binary coding as already proposed by Alec H. Reeves, of The International Telephone and Telegraph Co. Reeves had filed for a French patent in 1938, but his U.S. patent had not been issued until late 1942. In describing his invention, Reeves later wrote, "Having had it patented, for understandable reasons I then let the invention slip from my mind until the end of the war. It was in the United States during World War II that the next step in PCM's progress was made, by the Bell Telephone Laboratories." Reeves was referring in particular to work carried out by H. S. Black and W. M. Goodall during and after 1943 (a part of the work being for the U.S. government) and described after the war by the first technical publications on PCM.

This emphasis on binary PCM, which was mainly pointed toward wideband circuits, did make the personnel working on the X System take another serious look at the coding arrangement to be sure that something had not been overlooked. H. L. Barney carried out a series of extensive tests with various possible combinations but came to the conclusion that for the situation it faced, the multilevel arrangement used was better.

I conclude that the PCM by Reeves was strictly binary, and sigsaly was a multi-channel vocoder with 6 levels of quantization. Sorn67 15:37, 9 July 2006 (UTC)

That's consistent with my understanding. Bell Labs' patent was for "N-ary" not just binary. I'm trying to get more info about the patents. --Dobbse 21:17, 10 July 2006 (UTC)

I'm working from the same source as you mention above [4]. There's a disclaimer in that PDF about possible errors due to limits of OCR. This table is subject to that same disclaimer and I'll see what I can do to verify the patent numbers and dates for accuracy. --Dobbse 21:54, 10 July 2006 (UTC)

Table 5-5. Patents Related to Project X Research
U.S. Patent No.	Inventor	Filing Date	Issue Date
3,024,321	K. H. Davis, A. C. Norwine	12/29/44	3/ 6/62
3,076,146	M. E. Mohr	12/27/45	1/29/63
3,188,390	M. E. Mohr	12/20/43	6/ 8/65
3,193,626	H. L. Barney	12/29/44	7/ 6/65
3,340,361	R. K. Potter	7/ 9/45	9/ 5/67
3,373,245	N. D. Newby, H. E. Vaughan	8/27/42	3/12/68
3,394,314	L. G. Schimpf	7/17/43	7/23/68
3,405,362	R. H. Badgley, L. G. Schimpf	12/20/43	10/ 8/68
3,470,323	H. W. Dudley	6/30/44	9/30/69
3,967,066	R. C. Mathes	9/24/41	6/29/76
3,967,067	R. K. Potter	9/24/41	6/29/76
3,985,958	H. W. Dudley	12/18/41	10/12/76
3,897,591	A. A. Lundstrom, L. G. Schimpf	8/27/42	7/29/75
3,912,868	R. H. Badgley, R. L. Miller	7/17/43	10/14/75
3,937,888	O. Myers	7/17/43	2/10/75
3,991,273	R. C. Mathes	10/ 4/43	11/ 9/76
3,979,558	E. Peterson	6/30/44	9/ 7/76
3,976,839	R. L. Miller	6/30/44	8/24/76
3,965,296	R. L. Miller	6/30/44	6/22/76
3,887,772	R. L. Miller	6/30/44	6/ 3/75
3,891,799	A. E. Melhose	9/27/44	6/24/75
3,893,326	D. K. Gannett	9/27/44	9/28/76
3,968,454	A. J. Busch	9/27/44	7/ 6/76
3,944,744	D. K. Gannett	5/10/45	3/16/76
3,944,745	D. K. Gannett	5/10/45	3/16/76
3,953,677	D. K. Gannett	5/10/45	4/27/76
3,953,678	D. K. Gannett	5/10/45	4/27/76
3,924,074	E. Peterson	5/19/45	12/ 2/75
3,983,327	D. K. Gannett, A. C. Norwine	7/ 9/45	9/28/76
3,934,078	D. K. Gannett	5/ 1/46	1/20/76
3,965,297	D. K. Gannett	5/ 1/46	6/22/76
3,924,075	D. K. Gannett	3/20/47	12/ 2/75

[edit] Nyquist limit

I just edited a typo in the introduction, but I'm not sure that what's being said is accurate. It's said that "the frequency range of the analog signal is higher than half the sampling rate". This sounds like a reference to the Nyquist limit, but the picture shows a signal with a much lower frequency than the sampling frequency.

Stuarta 10:30, 13 July 2006 (UTC)

[edit] Paul M. Rainey, 1926

Hi, I was wondering why this page has no mention of Paul M. Rainey. I quote from an introductory book on speech recognition tecnology called "Spoken language processing" by Xuedong Huang, Alex Acero and Hsiao-Wuen Hon (Prentice Hall, 2001), p.271: "Pulse Code Modulation (PCM) had been invented by Paul M. Rainey in 1926 and indepently by Alan H. Reeves in 1937, ..."

Anonymous user, 17:22, 29 October 2006 (UTC)

There seems to be some limited debate surrounding this. Rainey's patent that this text seems to be referring to is not what I would call an invention of PCM. His patent describes a system by which paper can be scanned and transmitted by encoding it using an elaborate electro-mechanical arrangement. Though the end-result is essentially a signal modulated in PCM, I wouldn't consider it an invention of PCM as it doesn't realize the general applicability of the technology. It is a very specific case and the patent applies more to the device itself than the encoding used. Reeves' patent describes PCM in detail as a way to encode arbitrary waveforms with virtually no noise. It details the specifics of PCM, its limitations, and how these can be overcome. Since Rainey doesn't describe a general case, I don't think I'd personally give him credit for inventing PCM, since his writings and work didn't contribute to today's use of the technology. It may, however, be worth mentioning in the article. For reference, Reeves' US patent is viewable at the USPTO website as patent number 2,272,070. --Ktims 01:26, 19 December 2006 (UTC)

[edit] Cathode Ray Tube Encoders

Is there a page about these on Wiki? I think the mention of gray coding and these primitive encoders is worthy of the page - but we need to reference these a bit more than calling them out by name. At least a brief description of their operation should be added.

Additionally, I don't think gray codes are limited to cathode ray encoders, either. During transitions and with uncertain inputs, digital devices would have the same problems, possibly oscillating between vastly different values. It's my understanding that most digital ADCs internally use a gray code in their detection element, with the simple decoder in the digital domain on the output.

Anyone feel like writing this? I'm uninspired lately... —The preceding unsigned comment was added by Ktims (talk • contribs) 21:27, 29 December 2006 (UTC).

Gray Code nicely explains a variety of modern uses of the code, and if you read Flash ADC alongside it you can figure why one kind of modern coder can work just as well with Gray as with straight binary. Analog-to-digital conversion also explains a few kinds that don't need Gray. I do not see a Wiki explanation of the ancient sweep coder tube, but I remember the basic theory and will write it up this weekend if nobody beats me to it. Jim.henderson 00:39, 30 December 2006 (UTC)

[edit] Attribution to Rainey? Not resolved on talk.

There is unresolved discussion on the topic of whether or not Rainey invented PCM. I disagree with the change made to the article and move that it be reverted. --Ktims 04:00, 21 February 2007 (UTC)

[edit] History of PCM and SIGSALY

Please see Talk:SIGSALY#Accurate_to_call_it_PCM.3F for my concerns related to the claim that SIGSALY was an early example of the use of PCM for the transmission of speech. --Gmaxwell 19:36, 19 March 2007 (UTC)

The history section already mentions early developments that were TDM but not PCM, I think appropriately. Certainly if the frequency components were encoded by PCM, then PCM is what it was. Seems to me, the SIGSALY article should make clearer the distinction between PCM and samples that were quantized but not coded, and the distinction should be mentioned here as well. Jim.henderson 17:42, 23 March 2007 (UTC)