Talk:Linear pulse-code modulation

Merge with Pulse Code Modulation

I don't think the LPCM article should be merged with Pulse Code Modulation. It is a computer media format, like MPEG, not just a data encoding format. Readers need to access it in relation to MPEG, not just in relation to PCM. ___ —Preceding unsigned comment added by 67.122.114.28 (talk) 03:02, 19 August 2005 (UTC)

I agree -- I'm after a standard, ISO something something -- very much related to computer audio (DLNA specifically) so it's computer-type information that I'm after. —Preceding unsigned comment added by 210.11.153.86 (talk) 09:16, 31 August 2005 (UTC)

I support a merge. I don't see much support for LPCM being a distinct file format. The references cited use the term "linear audio" but not "linear PCM". These are generic audio formats and the individule files already have their own articles, e.g. WAV, AIFF, Au file format -—Kvng 13:47, 27 September 2012 (UTC)

 Done ~KvnG 00:27, 2 March 2014 (UTC)

Source of the LPCM stub

The stub for LPCM was taken from an ad for a computer program from the company Cyberlink. This is the website:

http://www.cyberlink.com/english/dv-entertainment/articles/lpcm.jsp

—Preceding unsigned comment added by 65.87.26.127 (talk) 17:31, 28 September 2006 (UTC)

vs. PCM

I think this article should explain the difference between PCM and LPCM.

— Preceding unsigned comment added by Joachim Michaelis (talk • contribs) 08:30, 25 October 2006 (UTC)

I tried to make clear the distinction between LPCM as a method of encoding and a file format, and added links to information about particular specifications. The existing article was referring to some particular implementation of LPCM used on DVD players which I was not aware of and don't know much about. But I wasn't really happy just removing this. This explains the bizarre section on standard sampling rates. Alexwright 14:37, 19 November 2006 (UTC)

Most DVD players only support 48 kHz/16-bit capability. Only more high-end players have built-in 96 kHz/24-bit capabilities.

"Most DVD players only support 48 kHz/16-bit capability. Only more high-end players have built-in 96 kHz/24-bit capabilities." is not correct. The official allowed formats for the PCM audio tracks on a DVD Video are:

* PCM: 48 kHz or 96 kHz sampling rate, 16 bit or 24 bit L-PCM, 2 to 6 channels, up to 6144 kbit/s

This means that there has to be a 24 bit decoder. But probably only with 16 bit accuracy in reallity. (8 bit of noise at the LSB)

But I'm not absolutely sure.

--helohe (talk) 16:19, 21 April 2007 (UTC)

Sampling Resolution and Rates

Quote from the article:

Standard sampling resolutions and rates

Common sample resolutions for LPCM are 8, 16, 20 or 24 bits per sample.

While two channels (stereo) is the most common format, some can support up to 8 audio channels (7.1 surround).

Common sampling frequencies are 48 kHz as used with DVD format videos, or 44.1 kHz as used in compact discs. Sampling frequencies of 96 kHz or 192 kHz can be used on some newer equipment, with the higher value equating to 6.144 megabits per second per audio channel.

It seems to me that the 6.144 mbps figure is arrived at by multiplying 192 kHz and 32 bits. This gets you 6144000 bits per second. It is not clear that 32 bit samples were used in this calculation, especially since it isn't listed in the list of common sample resolutions.

Furthermore, 6144000 bps is equal to 5.859375 mbps, not 6.144 mbps. It is unfortunate that the example used here is so similar to the max bitrate for PCM tracks on a DVD - 6144 kbps.

—Preceding unsigned comment added by 128.111.117.22 (talk) 16:04, 13 May 2008 (UTC)

6144000 bps = 6.144 Mbps (megabit per second), but 5.859375 Mibps (mebibit per second). This is the usual use of Mbps in computing and engineering in data communications including discussions of audio bitrates (the exception being Microsoft software like Windows Media Player). It appears that 6.144 x 10⁶ bit/s is the maximum total audio data rate in DVD-Video for ALL channels put together, implying that 192 kHz/16-bit stereo is at maximum bitrate for DVD-video (because 6144 kbps = 6.144 Mbps), but more usefully, 8 channels (7.1 surround) of 48 kHz/16-bit audio can be used, which is surely where the bitrate ceiling came from. It's tough to prove that greater bit-depth or sampling frequency could be useful in an 8-channel LPCM audio content delivery system for humans (though it's useful in the recording/mixing/mastering process that precedes it). —Dynamicimanyd (talk) 17:14, 6 January 2009 (UTC)

Incorrect Shannon Theory Claim

The article said this:

Theoretically, there is no loss or error in conversion and reconstruction, as long as the sampling rate is just over twice the highest desired frequency component of the recorded signal [Claude Shannon; Harry Nyquist]. For example, if you want to record audio at up to 20 kHz, you would need a frequence of sampling (F/s) of a little more than 40 kHz.

But this is wrong. The Nyquist Theorem says that the highest frequency of signal that CAN be recorded is 1/2 the sampling rate. It does not say that a sampling rate of R will accurately record a signal of frequency R/2. For example, to accurately record a frequency of, say, 22 kHz with a 44 kHz signal requires that the samples be taken at exactly the maximum of the peak and exactly the minimum of the valleys; if the 22 kHz signal is phase-shifted at all from the period of the sampling, then the 22 kHz will be aliased as a lower-frequency signal by the 44 kHz model. —Preceding unsigned comment added by MarkRLindsey (talk • contribs) 01:06, 2 February 2009 (UTC)

Zero value in signed code

The article sais If the sample is 16-bit signed, the sample range is from -32768 to 32767, with a centerpoint of 0. If the entire range $[-2^{N-1},2^{N-1}-1]$ is allowed, then the zero value actually is (assuming the zero value is the average of maximum and minimum)

${\frac {-2^{N-1}+2^{N-1}-1}{2}}=2^{N}{\frac {-2^{-1}+2^{-1}-2^{-N}}{2}}=-2^{N}2^{-N}/2=-1/2\neq 0$

—Preceding unsigned comment added by 90.229.142.67 (talk) 14:09, 31 December 2010 (UTC)

Strictly speaking, the term "linear quantization" is self-contradictory

This article says that "LPCM is PCM with linear quantization". However, there is no such thing as linear quantization. Quantization is an inherently non-linear process. Linear processes are (ordinarily) invertible. Quantization is not invertible. No quantizer is linear. Some abuse of basic mathematical concepts is necessary to come up with such a term. This strange term "linear quantization" should be removed, or at least explained. The referenced document does not provide a definition of this self-contradictory term. —SudoMonas (talk) 16:51, 25 April 2011 (UTC)

Linear here refers to the step size use for encoding. An example on non-linear PCM is something encoded using Mu-law. -—Kvng 13:47, 27 September 2012 (UTC)

Contributions needing work

Doorknob747 contributed the following to the article. I'm pulling these contributions here for discussion before inclusion.

I'm not aware of 32-bit linear PCM in consumer applications. 32-bit floating point is a thing. Do you have a citation?

As for the second contribution, discussion of subjective sound quality doesn't usually lead anywhere productive. Especially so for uncited discussion. ~KvnG 20:30, 21 December 2013 (UTC)

==Linear 32bit PCM== There is a L32 bit PCM, and there are many sound cards that support it. ===Similar effects of DTS-HD master audio (192kHz DTS)=== It is said that there is no difference at all that can be heard from a Linear 32 bit PCM at a 96 kHz sample rate playback sound to a, high quality DTS-HD Master Audio (192 kHz DTS). They both sound the same because, of the extremely high quality sound playback from these two types of codecs. But, in reality the 192 kHz DTS sound file has actually 1.45 times better quality than a sound file of L32 at 96 kHz.