Caution Compression Formats! – By Dr. Phil
Do you usually use MP3, WMA, or AAC files for your audio compression when ripping cds to Itunes or Windows Media Player; or when your final production is ready for uploading to the internet? That’s great, but have you ever wondered about other types of compression formats such as Ogg Vorbis, RMA, or FLAC? When would it be useful to use these formats? We will explore these less common compression formats, and the different categories of compression they fall under: Lossy and Lossless, in this article.
Lossy? Lossless? Let’s learn more …..
Lossy File Formats:
Most people think that MP3 just means ‘music file’. In fact, MP3 means MPEG Audio Layer 3, and is only one way of converting music into digital files. There are many audio formats, and almost all of them compress the audio data so that it takes up less digital space, that’s less room on your hard drive, or less space on your portable music player.
The MP3 format is one that uses lossy compression. This means that it loses some of the audio information found in the original to make the compressed file much smaller. The information that lossy compression loses is the information deemed least important to the file. In music, this tends to be the very high and very low harmonic frequencies that are not considered to add as much to the music as the range of frequencies in between.
Many audio formats use lossless compression. This means that they retain every bit of information that is found in the original, so nothing is lost at all. Because of this, lossless compression cannot make the compressed file as small as it would be using lossy compression. However, lossless compression means that you get a smaller file without losing any information, and so is the only method that can be used when absolute fidelity is required.
What’s wrong with MP3 as a format?
Nothing. But MP3 is already being replaced by other lossy formats that claim to offer better sound quality while creating smaller files.
Creating a collection of your music in digital form, you may end up with a huge number of files in MP3 format, and then realize that nobody uses MP3 files anymore. So you’d have to start again and create all your music again in the latest format.
The advantage to creating your collection using a lossless compression format is that each file will be identical, in terms of information, to the original. The music stored in a lossless audio file will be exactly the same as the music stored on the CD (or other audio source) you created the file from.
So technically, the definition of MP3 is:
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented encoding format for digital audio which uses a form of lossy data compression. It is a common audio format for consumer audio storage, as well as a de facto standard of digital audio compression for the transfer and playback of music on most digital audio players.
Other Lossy Compression Formats Include:
Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates.
Vorbis is a free software (open source) project headed by the Xiph.Org Foundation (formerly Xiphophorus company). The project produces an audio format specification and software implementation (codec) for lossy audio compression. Vorbis is most commonly used in conjunction with the Ogg container format and it is therefore often referred to as Ogg Vorbis.
RMA, RA or RM:
Rea lMedia is a proprietary multimedia container format created by RealNetworks. Its extension is “.rm”. It is typically used in conjunction with RealVideo and RealAudio and is used for streaming content over the Internet. Typically these streams are in CBR (constant bitrate), but a container for VBR (variable bitrate) streams, named RMVB (RealMedia variable bitrate), has been developed.
Windows Media Audio (WMA) is an audio data compression technology developed by Microsoft. The name can be used to refer to its audio file format or its audio codecs. It is a proprietary technology that forms part of the Windows Media framework. WMA consists of four distinct codecs. The original WMA codec, known simply as WMA, was conceived as a competitor to the popular MP3 and RealAudio codecs.WMA Pro, a newer and more advanced codec, supports multichannel and high resolution audio. A lossless codec, WMA Lossless, compresses audio data without loss of audio fidelity (the regular WMA format is lossy). WMA Voice, targeted at voice content, applies compression using a range of low bit rates.
Lossless Compressed formats:
Even though lossless audio is a perfect copy of the original, a file created with lossless compression will not be as small as a file created with lossy compression. So if you have a limited amount of data storage on, for example, your portable music player, smaller files will mean you can fit more files on your player storage. That is, using lossy compression may reduce the quality of the music slightly, but it allows you to take a greater number of music tracks (or albums) on the bus to work.
When is Lossless Audio Useful?
Lossless audio files are great for archiving your music. A while ago this would have been possible only for a small number of audio tracks, or for professionals who could afford a lot of storage devices.
However, hard drives are now so large that it is possible to store your entire CD, tape, and vinyl collections in the form of lossless audio, and still have space left to run your operating system, word processor, and games.
Because lossless audio files are an exact copy (in information – music – terms) of the original source, you can then use software that will process any of those lossless files into a lossy, smaller copy. So if the MP3 format stops being the standard, you can just delete all your MP3s, and use software to create lossy copies of a different format, using the archive of lossless files you have built up.
Can’t I just convert my MP3 files to another format if necessary?
Yes, you can convert MP3 files into any other format that you can find software for. But because MP3s are created with lossy compression, the information they contain about the music is not a perfect copy of the original. So you would be working from an imperfect source. Even if the format you were converting to allowed better audio quality than MP3, your converted files would not be able to make use of this extra quality, because you would be working from an MP3 file. Conversion and compression can only ever make quality stay the same or get worse; they can never make quality improve.
The only way to get more purity would be to delete all your MP3 files and start all over again, creating new files from the original audio source.
Some Lossless File Formats:
(Free Lossless Audio Codec) is a codec (compressor-decompressor or coder-decoder) which allows digital audio to be losslessly compressed such that file size is reduced without any information being lost. Digital audio compressed by FLAC’s algorithm can typically be reduced to 50–60% of its original size, and decompressed into an identical copy of the original audio data.
FLAC is an open format with royalty-free licensing and a reference implementation which is free software. FLAC has support for metadata tagging, album cover art, and fast seeking.
Though FLAC cannot store floating-point data, and playback support in portable audio devices and dedicated audio systems is limited compared to lossy formats like MP3 or uncompressed PCM, FLAC is supported by more hardware devices than competing lossless compressed formats like WavPack.
MPEG-4 Part 14 or MP4 (formally ISO/IEC 14496-14:2003) is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images. Like most modern container formats, MPEG-4 Part 14 allows streaming over the Internet. A separate hint track is used to include streaming information in the file. The only official filename extension for MPEG-4 Part 14 files is .mp4.
Some devices advertised as “MP4 Players” are simply MP3 Players that also play AMV video or some other video format, and do not necessarily play the MPEG-4 part 14 format.
WMA Audio 9:
Windows Media Audio 9 Lossless is a lossless incarnation of Windows Media Audio, an audio codec by Microsoft, released in early 2003.
It compresses an audio CD to a range of 206 to 411MB, at bit rates of 470 to 940 kbit/s. The result is a bit-for-bit duplicate of the original audio file; in other words, the audio quality on the CD will be the same as the file when played back. WMA Lossless uses the same .WMA file extension as other Windows Media Audio formats. It supports 6 discrete channels and up to 24-bit/96kHz lossless audio. The format has never been publicly documented, although an open source decoder has been reverse engineered for non-Microsoft platforms by the libav and ffmpeg projects.
I hope you enjoyed this look at Audio Compression Formats and what they do. If you stick with me, I am going to take you step by step through Phil’s Audio Production Course. You will become a Pro! Sign Up Now Here
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