Everything about File Compression: Take 4 November 18, 2008Posted by ConnorSmith in : Chit Chat, File Compression, Project Studio , trackback
Definitely wins the award for the weirdest name among digital audio compression formats. However, Ogg Vorbis is arguably one of the best sounding and easiest to access of the bunch (it’s open source, aka FREE)
“Vorbis” is actually the audio compression codec. It was developed as an open source (lossy) compression codec as a substitute for mp3. “Ogg” is simply the file container in which the Vorbis is held, thus “Ogg Vorbis”. (Its worthy to note that you can hold lots of other things in Ogg containers, including FLAC).
So what’s different about Vorbis? For one, its open source. That means there are no licensing costs associated with using it. Unfortunately, since people aren’t making millions of dollars off it, the effort to significantly popularize (or even standardize) the format is a hard sell. MP3 and AAC are very much market-driven formats (i.e. iTunes uses AAC). Since companies and individuals have incentive to make large amounts of money off of their codecs, its no wonder that MP3 and AAC are overwhelmingly more widely used than Vorbis. That being said, it is good to know that Vorbis sounds really good at equivalent bit rates, AND its free. (So although you’d be in the minority, if you are using Ogg Vorbis, you have something that sounds better* and costs nothing to license).
It’s also worth noting that if Vorbis were licensed and AAC open source, we’d likely be saying the same sort of things the other way ’round… this is really just an open discussion.
So, other than being free, what’s good to know about how Ogg Vorbis works?
Vorbis, like AAC, uses an MDCT to begin to break the digital audio into small pieces, and put them through the frequency-analysis process. Vorbis uses its own psychoacoustic model (which theoretically is better than its predecessors). Of course, the implication here is that if the psychoacoustic model is “better” than AAC and MP3, it will be getting better sounding results at the same bit rates.
Vorbis is different too in that it is always variable bit rate. (Click here to revisit the article on VBR encoding) While this will yield more pleasing sonic results for Vorbis, it can make it more difficult to compare MP3 and AAC encoders to Vorbis objectively (as some are not VBR). Now for the big difference…. drum roll please….
Vorbis is different in its “failure mode”. Here, I am using “failure” to describe what happens with the encoder doesn’t have enough available bits to get the good audio encoded above the distortion. Remember, the encoder is inevitably going to have to deal with noise from things like quantization distortion, and ideally, all of that will be below the masking threshold (aka, we won’t hear the bad stuff because the good stuff is loud and covers it up). When, let’s say, and MP3 encoder fails, the distortion gets loud, you may hear metallic swirlies (also called birdies, think “youtube audio”), other non harmonic distortion…
But! When Ogg Vorbis fails, something entirely different can happen. When the audio is initially going through the filterbank in Vorbis, the encoder separates the noise floor from the audio. When the encoder would fail, the noise floor is raised. This gives a much softer (almost analog-noise-like) distortion, rather than birdies and harsh distortions. So, between an improved psychoacoustic model, the inherent VBR, and the nicer-sounding failure mode, Ogg Vorbis seems like a great choice.
Again, problems with Ogg Vorbis mainly stem from the fact that it is not a market driven format. There are many plug-ins and stand alone players that will read and encode/decode Ogg Vorbis files, but they are not nearly as numerous as those of MP3 and AAC files. Most portable music players won’t directly play Vorbis files without some software tweaking.
FLAC is next!
Also coming soon are flipped polarity examples of these encoders with the original files (so you can hear the failure modes, and other “yuck” left over/added from compression conversion)
The Studio Files