Talk:Dolby Digital

Patents?
The AC-3 codec is at least 18 years old and patents were for 17 years following the date of issuance back then. Does this mean all the foundational patents have expired and it is legal to use a free encoder/decoder now? Is there a list of patent numbers somewhere? This is not clear cut because Dolby still licenses AC-3, but that may simply be for the use of their logo for all I know; also, submarine patents were still legal so they could have been granted additional patents on AC-3 much later than 1992. 96.57.9.142 (talk) 13:58, 28 October 2010 (UTC)

The patents are now expired: https://ac3freedomday.org/ — Preceding unsigned comment added by 70.35.217.14 (talk) 18:24, 22 March 2017 (UTC)

Dates?
What is the timeline on Dolby Digital? Where does it fit in with the other Dolby codecs?

technical details?

 * I'd like to see a bit more technical detail here. It should *at a very minimum* at least be mentioned that it uses a logarithmic scale for quantization rather than the more standard linear scale. As far as I know it is significantly different from standard PCM-based encoders that some in-depth discussion would be useful.
 * Dolby TrueHD's sample rate is listed as being 96 khz; however this is only the case when encoded over 8 channels or more (as listed here with 14), but can actually sample at rates up to 192 khz when encoded over 6 channels. --Photoactivist (talk) 01:37, 3 September 2008 (UTC)
 * Is 24 frames (sound delay) really 2 seconds? A frame rate of 12 per second seems implausible. — Preceding unsigned comment added by 89.246.150.136 (talk) 13:03, 21 January 2015 (UTC)

Naming
I'm pretty sure that Dolby Digital EX and Dolby Digital Surround EX (Or Dolby SEX as some projectionists have dubbed it) are different names for the same system - one that matrix decodes additional rear channels from the surround channels.

Also, the article mentions the term SR-D as referring to sources that are compatible with dolby surround technology. I do not think this is correct. Dolby SR means Dolby Spectral Recording - a new method of noise reduction introduced in the late 1980s for use on analogue film soundtracks, also backwards compatible with Dolby A. Dolby SR-D therefore means Dolby Spectral Recording - Digital, since SR-D is the replacement for SR and SR-D soundtracks on films ALWAYS have a Dolby SR track as a backup. The name has nothing to do with Dolby Surround, and soundtracks featured surround channels long before Dolby SR or SR-D came out.

"Dolby Technologies in Packaged Media Formats" question
What does the "mandatory" vs. "optional" in the status column in the "Dolby Technologies in Packaged Media Formats" table refer to? Does this refer to whether players of the particular media format (e.g. DVD) require a Dolby decoder?--GregRM 01:19, 14 August 2006 (UTC)


 * Mandatory means that the specifacations requires that all players MUST decode that kind of codec. Optional means that the player manufacturer can choose whether to add that decoding functionalty to their player.  Example: all blu-ray players must decode Dolby Digital.  But, lets say that Sony wanted to add Dolby TrueHD decoding to only their high-end players.  They could still do that because the blu-ray spec gives them the option to add it.  -- Sam916 02:08, 14 August 2006 (UTC)
 * OK, that makes sense...thanks.--GregRM 14:14, 14 August 2006 (UTC)

Bitrates

 * The bit rates are unclear. It would be nice to see both the compressed data rate encoded onto the media, and the per channel PCM rate (such as 96hkz/24 bits or whatever.)
 * Dolby Digital's bit depth is not mentioned, in comparison to Dolby TrueHD which is listed as having 24 bit depth.
 * The bit rate on Laserdisc is 384 kbps for all the extra channels combined (i.e. surround L/R, center and subwoofer). That is 96 kbps per channel, theoretically. 44.1 kHz and 16 bits. Same on DVD but 448 kbps total there, so 112 kbps per channel. -- Alexey Topol (talk) 23:14, 10 February 2019 (UTC)

Opening sentence correct?
I am not an expert but is the opening sentence correct in stating that Dolby is as series of "lossy audio compression" given Dolby TrueHD? —Preceding unsigned comment added by 92.5.2.87 (talk) 16:55, 3 August 2008 (UTC)

You're right; with the addition of Dolby TrueHD, they are no longer lossy-only compression codecs.--Photoactivist (talk) 01:31, 3 September 2008 (UTC)

Comparison Chart Width
The comparison chart is too big to fit on 1024px and narrower displays without scrolling. Maybe we can shorten the word "Mandatory" or get rid of one of the categories(HDDVD)? —Preceding unsigned comment added by Drizek (talk • contribs) 22:18, 27 March 2009 (UTC)

Dolby Digital Live: not always in hardware
This section needs a rewrite regarding hardware DDL support by some sound cards. X-FI's DDL support is software based, and I believe this is also the case for C-Media cards. It may be true for some other cards mentioned there, too. I will try and edit this section, at least as far as X-Fi sounds cards are concerned. Any comments? --Piotr Wwa (talk) 22:10, 31 August 2010 (UTC)

What is relationship with MP3?
This article mentions that "Dolby is part of a group of organizations involved in the development of AAC (Advanced Audio Coding), part of MPEG specifications, and considered the successor to MP3. AAC outperforms MP3 at any bitrate, but is more complex.[19]". But what has this to do with AC3? The section doesn't explain the relationship of AC-3 to MP3, or say whether AAC outperforms AC-3. FurrySings (talk) 22:51, 20 February 2011 (UTC)

Original logo missing
I think the article should include all the official logos used by Dolby Labs. for Dolby Digital. They can include a short description, like "Original logo, used from 1995-1999" ... here's a reminder of how the original logo looked like, just a low-quality pic of it: http://imageshack.com/scaled/large/32/k7tj.gif It would be great if somebody could create a high-res vector graphics version of that and put it into the article. -- Alexey Topol (talk) 23:17, 21 October 2013 (UTC)

Dolby digital
What is AC-3 in this context? The acronym(?) is used without any reference or explenation. Theking2 (talk) 15:05, 25 April 2015 (UTC)

According to "AC-3: Flexible Perceptual Coding for Audio Transmission and Storage" (1994) this is the third attempt by Dolby at creating an audio coder for HDTV, and the first truly multi-channel one. Apparently, AC-1 and AC-2 existed but weren't practically used for much of anything, aside from testing. -- J7n (talk) 06:21, 29 August 2015 (UTC)

At midnight on March 20, 2017, Dolby's last relevant patent on Dolby Digital expired.
"ac3freedomday" --Hong620 (talk) 15:56, 21 March 2017 (UTC)

Original logo "DOLBY SURROUND AC-3 DIGITAL" is missing
The original logo should be added to the article. -- Alexey Topol (talk) 20:40, 10 February 2019 (UTC)