One of the sites I frequent often is the Anime on DVD forums hosted by Mania (link above). The original creator of the forums tweeted something yesterday that gave me pause about a release I should get tomorow: the first Blu-Ray volume of K-On! by Bandai Enterainment. The text simply states that the audio for the BD is Dolby Digital 2.0 at 192kbps. So what does that mean and why were the forums so upset? Let’s delve into some technical details. Warning: this is going to be somewhat long and dry, but I hope it’s informative.
In 1997 the first retail DVD video discs went on sale. Most consumers typically adapted well to the change and enjoyed the nice clarity of the format compared to past VHS tapes. It gave the ability to have alternative angles, audio streams, and even (optional/multiple) subtitles for a video. How was this accomplished? The makers of the discs were able to compress the audio/video data into a format and decompress it through a player. The terms for this are “encoding” and “decoding” by use of a codec (code/decode).
For DVDs the typical video codec is MPEG-2 while there are a couple of commonly used audio codecs. The best audio codec is one of PCM (typically Linear PCM) which stands for Pulse code modulation. In non-physics terms, this is a method of recording analog (or varying) signals into a digital format. Linear PCM is a way to allow the analog signals to remain uncompressed and offers the highest quality audio on any format. Dolby Digital/AC3 is a format used by Dolby to compress the audio into frames on a disc and decompress it via a player. DTS is a final codec that has a lower compression rate than DD, but is not commonly used to its full capability. When used properly it can be indistinguishable from LPCM. On DVDs each format can support up to 5.1 audio (5 speakers plus a bass).
On Blu-Rays the video is almost always encoded in MPEG-4 AVC. I’ve yet to run across one that is in Microsofts VC-1 personally, but they do exist. For audio purposes, the three mentioned codecs as well as two additional codecs are used on a disc. For Dolby, they have a new codec called Dolby Digital Plus, which replaces the surround sound speakers with higher quality versions that can support upto 7 total channels (plus bass). They also produced a lossless coded entitled Dolby True HD, much like DTS with their codec DTS-HD Master Audio, who both allow for higher quality audio than LPCM on BDs due to higher bitrate. DTS-HD also allows for more channels than just 7.1, which is the most LPCM/DT-HD can do on a BD.
Edit: this is added by relentlessflame from the comments. The lossless codecs don’t actually “allow for higher quality audio than LPCM on BDs due to higher bitrate”, but the compression allows you to fit more audio data in a smaller bitrate without sacrificing quality. The drawback is that it’s not required to be supported on all players/receivers, so it’s not guaranteed compatible (you have to include an additional audio stream that will be compatible). So, we might say LPCM is “best” in the sense that there’s no quality loss and it works everywhere, but it also takes up the most space/bandwidth for the resulting sound, so it’s not necessarily always going to be the “best” in terms of efficiency. For your standard Japanese anime, mastered in 2-channel 48 kHz 16/24-bit, you’re not talking huge files anyway, so there’s no real need to compress (and this way it’s guaranteed to play everywhere). But, if you had to deal with real “HD Audio” (let’s say 8-channel at 24-bit 96 kHz), then the BD authors could benefit from the bitrate savings of that lossless compression (which frees up “bandwidth” for video). Really, the whole authoring process is about the trade-offs between quality, disk space, bandwidth, and compatibility.
DVDs can hold up to 8.5 GB of data for video purposes. Since most Japanese releases only place 1-3 episodes with optional on-disc bonus features, the audio is able to be in LPCM format (with some audio commentaries being in DD like Railgun). For an example: Haruhi 2009’s volume 2 containing Endless Eight I and Endless Eight II plus the textless opening, commercials, location scouting, and a making of Aya Hirano’s Super Driver PV took up 4.07 GB of 4.7 possible GBs (it was a single layer DVD). About 20% of that amount (814 MBs) was LPCM audio with about 79.5% being video and .5% English subtitles. No english audio was included.
Conversely, the trend in the North American market is to fit as many episodes as possible with an English dub. Bandai’s Haruhi 2009 disc 1 (containing 4 episodes, textless ending, two cm packs plus promotional video, two location scouting clips, two PV making clips and a special bonus video) had to be put on a double layer (8.5 GB) disc due to being 7.58 GB big. Since Bandai included a dub, they compressed both audio formats into DD/AC3 format. This allowed them to focus 93% of the data on video and fit each audio track into only 3% of the overall audio. That would be about 227 MBs of data for EACH audio track. The final 1% is likely subtitles and other data overlays. It’s not just Bandai as Sentai used the same ratios on their release of Clannad~After Story~.
So with Blu-Ray discs holding about 25/50 GBs for single/double layer discs, you would be able to fit a lot more data onto a disc; thus NA publishers should be able to take advantage and finally be able to put lossless audio formats on their releases. For the Haruhi BD-Box, the main episodes ranged about 5-6.5 GBs per episode for video files (2006 upscales were slightly smaller on average) and dual LPCM (lossless) audio tracks of 285 MB for each JP/Eng audio track per episode (about 6-7.5 GB per episode). Since Kadokawa used a 50 GB disc for each disc, they could fit 6 episodes on a disc in HD with lossless audio, include the English dub/subtitles, and still have room to spare per disc.
To be honest, most people won’t be able to tell the difference between lossless and lossy (DD, DTS) codecs unless given an immense quality audio system. As a consumer of anime, I would like the best quality product available to me, and for BD audio that tends to be LPCM for TV anime and DTS-HD/DT-HD for movies and such. I can even point to Kadokawa not being able to put higher quality audio on the Haruhi movie BD due to space limitations (the video itself was over 36 GB!).
So once again, I’m sorry for the information dump. It’s a lot to understand and if anyone is confused or can point out where I made a mistake, let me know. I just wanted to lay some background information for my review of K-On! Volume 1 and to give reasons why I’m likely to be disappointed in Bandai for the release. If anyone’s curious as to where I found the information, I used Wikipedia for background sources, the mediainfo program for DVD data information and BDInfo for Blu-Ray data information on my own copies of the releases.