Chap62

DIGITAL MEDIA FUNDAMENTALS

Compare the advantages and limitations of various audio files format.


In This Chapter, you’ll learn on: The following file formats.

o RAWo MP3o AIFFo MPEGo WAVo ACTo WMA

The characteristics of these formats. The advantages and limitations of these formats.


What is a “Raw” Audio? It’s hard to talk about “Raw” because it’s not really

the name of a file format. Originally the term was used within Photoshop for doing a desperation import of a mystery file that contains no metadata whatsoever, not even the most basic facts such as file format, size, color mode, etc.

A newer (and basically unrelated) meaning of “raw” — more formally called Camera Raw — has become very common with the rise of digital photography.


What is a “Raw” Audio? Raw Audio is any recorded audio that is unedited

and unprocessed. The advantage of raw audio means it can provide clients with audio exactly as it was recorded. However when a file is defined as “raw”, it also means that the file size can be too big to be easily transferred.


MP3 MP3 is the name of a type of audio file extension and also the

name of the type of file for MPEG (Audio layer 3). Layer 3 is one of three coding schemes (layer 1, layer 2 and layer 3) for the compression of audio signals. Layer 3 uses perceptual audio coding and psychoacoustic compression to remove all superfluous information (more specifically, the redundant and irrelevant parts of a sound signal. The stuff the human ear doesn't hear). It also adds a MDCT (Modified Discrete Cosine Transform) that implements a filter bank, increasing the frequency resolution 18 times higher than that of layer 2.

The result in real terms is layer 3 shrinks the original sound data from a CD (with a bit rate of 1411.2 kilobits per one second of stereo music) by a factor of 12 (down to 112-128kbps) without sacrificing sound quality.


MP3 Because MP3 files are small, they can easily be transferred

across the Internet, which really is a plus point as compared to the other audio formats. MP3 files are played on the computer via media player software, such as Apple's iTunes and Microsoft's Windows Media Player, as well as in countless iPods and other handheld players. MP3 sound quality cannot fully match the original CD, and true audiophiles complain bitterly, but millions of people consider it "good enough" because they can pack thousands of songs into a tiny pocket-sized player.

Converting a digital audio track from a music CD to the MP3 format (or other audio format) is called "ripping" or "importing," and this conversion function is built into iTunes, Windows Media Player and other jukebox software. Stand-alone rippers are also available.


MP3 While 128 Kbps (kilobits per second) is considered the norm for

MP3 files, MP3s can be ripped to bit rates from 8Kbps to 320 Kbps. The higher the bit rate, the better the sound and the larger the file.

According to CNN, any artists, execs and labels in the music

industry have lashed out at the MP3 format due to the fact that it doesn't offer much security and is, therefore, very easy to pirate. Another potential disadvantage to MP3 format is that at lower bitrates the MP3 format's quality has been known to suffer, while WMA sounds much better at comparable low bitrates. Finally, MP3 files do not support 5.1 Surround Sound, which the WMA format does support.


AIFF Short for Audio Interchange File Format, a common format for

storing and transmitting sampled sound. The format was developed by Apple Computer and is the standard audio format for Macintosh computers. It is also used by Silicon Graphics Incorporated (SGI).

AIFF files generally end with a .AIF or .IEF extension.

The AIFF format does not support data compression so AIFF files tend to be large. However, there is another format called AIFF-Compressed (AIFF-C or AIFC) that supports compression ratios as high as 6:1.


AIFF

The extension for this file type is ".aif" when it is used on a PC. On aMac, the file extension is not needed. A Mac file uses a Type and Creatorresource to identify itself to the operating system and the applicationsthat can open it.

An AIFF file contains the raw audio data, channel information (monophonic orstereophonic), bit depth, sample rate, and application-specific data areas. Theapplication-specific data areas let different applications add informationto the file header that remains there even if the file is opened andprocessed by another application.


MPEG Moving Pictures Experts Group is an ISO/ITU standard for

compressing digital video. Pronounced "em-peg," it is the universal standard for digital terrestrial, cable and satellite TV, DVDs and digital video recorders (DVRs).

MPEG uses lossy compression within each frame similar to JPEG, which means pixels from the original images are permanently discarded. It also uses interframe coding, which further compresses the data by encoding only the differences between periodic frames (see interframe coding). MPEG performs the actual compression using the discrete cosine transform (DCT) method (see DCT).


MPEG

MPEG is an asymmetrical system. It takes longer to compress the video than it does to decompress it in the DVD player, PC, set-top box or digital TV set. As a result, in the early days, compression was perfomed only in the studio. As chips advanced and became less costly, they enabled digital video recorders, such as Tivos, to convert analog TV to MPEG and record it on disk in real time (see DVR).


The major MPEG standards include the following:

MPEG-1 (Video CDs) - Although MPEG-1 supports higher resolutions, it is typically coded at 352x240 x 30fps (NTSC) or 352x288 x 25fps (PAL/SECAM). Full 704x480 and 704x576 frames (BT.601) were scaled down for encoding and scaled up for playback. MPEG-1 uses the YCbCr color space with 4:2:0 sampling, but did not provide a standard way of handling interlaced video. Data rates were limited to 1.8 Mbps, but often exceeded. See chroma subsampling.

MPEG-2 (DVD, Digital TV) - provides broadcast quality video with resolutions up to 1920x1080. It supports a variety of audio/video formats, including legacy TV, HDTV and five channel surround sound. MPEG-2 uses the YCbCr color space with 4:2:0, 4:2:2 and 4:4:4 sampling and supports interlaced video. Data rates are from 1.5 to 60 Mbps. See chroma subsampling.


MPEG-4 (All Inclusive and Interactive) MPEG-4 is an extremely comprehensive system for multimedia

representation and distribution. Based on a variation of Apple's QuickTime file format, MPEG-4 offers a variety of compression options, including low-bandwidth formats for transmitting to wireless devices as well as high-bandwidth for studio processing. See H.264.

MPEG-4 also incorporates AAC, which is a high-quality audio encoder. MPEG-4 AAC is widely used as an audio-only format (see AAC).


MPEG-4 (All Inclusive and Interactive)

A major feature of MPEG-4 is its ability to identify and deal with separate audio and video objects in the frame, which allows separate elements to be compressed more efficiently and dealt with independently. User-controlled interactive sequences that include audio, video, text, 2D and 3D objects and animations are all part of the MPEG-4 framework. For more information, visit the MPEG Industry Forum at www.mpegif.org.


MPEG-7 (Meta-Data)MPEG-7 is about describing multimedia objects and has nothing to do with compression. It provides a library of core description tools and an XML-based Description Definition Language (DDL) for extending the library with additional multimedia objects. Color, texture, shape and motion are examples of characteristics defined by MPEG-7.

MPEG-21 (Digital Rights Infrastructure)MPEG-21 provides a comprehensive framework for storing, searching, accessing and protecting the copyrights of multimedia assets. It was designed to provide a standard for digital rights management as well as interoperability. MPEG-21 uses the "Digital Item" as a descriptor for all multimedia objects. Like MPEG-7, it does not deal with compression methods.


MPEG-2 and MPEG-4 are international standards for compressing video signals; they are widely used in digital television broadcasting, DVD discs, and mobile videophony. Using these standards, video can be compressed in an encoder before transmission or storage, perhaps to 1/50 of the original size, and then decompressed in a decoder for playback.

Like the JPEG (Joint Photographic Experts Group) standard for

compressing still images, the MPEG-2 and MPEG-4 standards exploit redundancies in the original signal and limitations of human vision to discard unnecessary information. Depending on the compressed bitrate selected, the decoded image can be imperceptibly different from the original or badly flawed with visible artifacts.


MPEG-2 and MPEG-4 offer several advantages over proprietary codecs. The standards process allows careful, open, and objective tests of competitive ideas and approaches to find the best mix of efficiency, latency, and implementation complexity for a codec.

WAV The format for storing sound in files developed jointly by

Microsoft and IBM. Support for WAV files was built into Windows 95 making it the de facto standard for sound on PCs. WAV sound files end with a.wav extension and can be played by nearly all Windows applications that support sound.


This is a high-quality audio file type generally used for applications that require high quality, such as CDs. WAV files are uncompressed, and therefore take up some disk space, unlike MP3s or AACs, which are compressed.

Because WAV files are uncompressed, they contain more data and produce better, more subtle, and more detailed sounds.

A WAV file generally needs 10MB for every 1 minute of audio, whereas an MP3 needs about 1MB for every 1 minute.


ACT ACT is a lossy ADPCM 8 kbit/s compressed audio format

recorded by most Chinese MP3 and MP4 players with a recording function, and voice recorders. However, many models of recorder that use the ACT format do so only for their lowest-quality recording setting; if the quality setting is increased then a different format such as WAV is used instead (albeit at the expense of using up recorder memory more quickly).

There are different versions of ACT; files produced by later devices cannot as of June 2009 be read by any free standard audio player and converter software, only by the supplied MP3 utilities.


WMA Short for Windows Media Audio, a file format developed by

Microsoft for encoding digital audio files similar to MP3 though can compress files at a higher rate than MP3. WMA files, which use the ".wma" file extension, can be of any size compressed to match many different connection speeds, or bandwidths. Known originally as MSAudio, this proprietary format competes with the MP3 and AAC methods. WMA encodes rapidly and is known to be especially effective at low bit rates.


WMA One of the largest advantages to the WMA format is the

format's support of DRM, or Digital Rights Management. This is an anti-piracy procedure that allows for much more security to surround a given music file. Although it doesn't completely make it pirate-proof, it makes pirating in this method much less common; MP3 offers no DRM and is therefore much easier to steal.

One of the largest disadvantages associated with the WMA format is the lack of support from third party devices such as MP3 players. Although some support WMA files, such as Microsoft's own Zune, many do not. The Apple iPod does not support WMA and, as the market's dominant MP3 player, compatibility can be a huge issue if you own one. Also, many media players for the computer do not play DRM protected WMA files, making this format's biggest advantage also a disadvantage, in some cases.


WMA When it comes to WMA and MP3, both sacrifice sound quality to

save space. With WMA Lossless this sacrifice is not made but the sound file is still condensed down to about half of its original size. The file extension for WMA Lossless is still .WMA. This format is less popular than other lossless audio formats, such as FLAC.

Chap62

Technology

digital rights

specific data

windows media

ycbcr color

data rates

interframe

bit rate

mp3 files