Into the wild of Alaska..

I always want to know the audio format in which the sound can be produced in a better quality. I do know couple of formats but i cannot order the same based on their quality. So i started to search and found a lot details. Hope this will give a basic idea about formats.

The first CD format was of course that which defined the audio CD used in all regular CD players, called CD Digital Audio or CD-DA for short. The specifications for this format were codified in the first CD standard, the so-called "red book" that was developed by Philips and Sony, the creators of the original compact disk technology. The "red book" was published in 1980, and actually specifies not just the data format for digital audio but also the physical specifications for compact disks: the size of the media, the spacing of the tracks, etc. In a sense, then, all of the subsequent standards that came after CD-DA build on the "red book" specification, since they use the same specifications for the media and how it is read. They also base their structure on the original structure created for CD audio.

Data in the CD digital audio format is encoded by starting with a source sound file, and sampling it to convert it to digital format. CD-DA audio uses a sample rate of 44.1 kHz, which is roughly double the highest frequency audible by humans (around 22 kHz.) Each sample is 16 bits in size, and the sampling is done in stereo. Therefore, each second of sound takes (44,100 * 2 * 2) bytes of data, which is 176,400 bytes.

Audio data is stored on the disk in blocks, which are also sometimes called sectors. Each block holds 2,352 bytes of data, with an additional number of bytes used for error detection and correction, as well as control structures. Therefore, 75 blocks are required for each second of sound. On a standard 74-minute CD then, the total amount of storage is (2,352 * 75 * 74 * 60), which is 783,216,000 bytes or about 747 MB. From this derives the handy rule of thumb that a minute of CD audio takes about 10 MB, uncompressed.

Using special software, it is possible to actually read the digitally-encoded audio data directly from the CD itself, and store it in a computer sound format such as a WAV file. However, while every CD-ROM drive will play standard "red book" digital audio, not every drive will allow you to read the digital audio data directly, which is sometimes called CD-DA extraction. Sometimes the reasons are technical, but more often they are political; some drive manufacturers intentionally program their drives not to allow data extraction, in order to avoid possible copyright infringement by their owners!

Digital audio comes in many different formats, and multiple formats will be a fact of life for the foreseeable future. Groups like MPEG have created open standards, but even formats based on the same MPEG standard may not compatible with each other because of proprietary components.

Fortunately for consumers, many hardware and software players are able to support multiple formats—so if you purchase digital music in any of the major formats (MP3, WMA, etc.) you will be in a good shape. If a format does become obsolete, plenty of tools are available for converting digital audio to different formats.

Digital Audio Files

An audio file has two main parts: a header and the audio data. The header is used to store information about the file, including the resolution, sampling rate and type of compression. Often a “wrapper” is used to add features, such as license management information or streaming capability, to a digital audio file.

The format of a digital audio file refers to the type of audio data within the file. The file type refers to the structure of the data within the file. It is common for the same format to be used by more than one file type. For example, the PCM format is found in both WAV and AIFF files.

WAV

WAV is the default format for digital audio on Windows PCs. WAV files are usually coded in PCM format, which means they are uncompressed and take up a lot of space. WAV files can also be coded in other formats, including MP3.

AIFF and AU

AIFF is the default audio format for the Macintosh, and AU is the default format for SUN systems. Both of these formats are supported on most other platforms and by most audio applications. Each of these formats can be compressed, but compression sometimes creates compatibility problems with other platforms.

Streaming Audio

Streaming audio avoids many of the problems of large audio files. Instead of having to wait for the entire file to download, you can listen to the sound as the data arrives at your computer. Streaming audio players store several seconds worth of data in a buffer before beginning playback. The buffer absorbs the bursts of data as they are delivered by the Internet and releases it at a constant rate for smooth playback.

Many digital audio formats can be streamed by wrapping them in a streaming format, such as Microsoft ‘s ASF (Active Streaming Format), which can be used to stream MS Audio, MP3 and other formats.

Standard Formats

Standard formats make it easier for software developers and equipment manufacturers to produce products that are less costly and more compatible with each other. The compatibility provided by standard formats helps assure consumers that their music and equipment won’t become obsolete. Cassette tapes, compact discs and PCM are examples of standard audio formats that benefit both consumers and manufacturers.

PCM

PCM (Pulse Code Modulation) is a common method of storing and transmitting uncompressed digital audio. Since it is a generic format, it can be read by most audio applications—similar to the way a plain text file can be read by any word-processing program. PCM is used by Audio CDs and digital audio tapes (DATs). PCM is also a very common format for AIFF and WAV files. PCM is a straight representation of the binary digits (1s and 0s) of sample values. When PCM audio is transmitted, each “1” is represented by a positive voltage pulse and each “0” is represented by the absence of a pulse. Figure 26 shows how binary data is converted to a PCM signal.

DPCM

DPCM (Differential Pulse Code Modulation) is a simple form of lossy compression that stores only the difference between consecutive samples. DCPM uses 4 bits to store the difference, regardless of the resolution of the original file. With DCPM, an 8-bit file would be compressed 2=1, and a 16-bit file would be compressed 4=1.

ADPCM

ADPCM (Adaptive Differential Pulse Code Modulation) is similar to DCPM except that the number of bits used to store the difference between samples is varied depending on the complexity of the signal. ADPCM works by analyzing a succession of samples and predicting the value of the next sample. It then stores the difference between the calculated value and the actual value.

u-law Compression

u-law (pronounced “mew-law”) is a common lossy compression scheme, similar to ADPCM, which can be used on AU, AIFF and WAV files.

MPEG Audio

MPEG Audio is a family of open standards for compressed audio that includes MP2, MP3 and AAC.

MPEG-Based Proprietary Formats

Several proprietary formats are based on MPEG audio. Some of these are used in special applications, such as voice mail systems, high definition TV and satellite radio. Others compete directly with MP3 and are based on AAC or MP3, with proprietary wrappers. The sound quality of some of these is very good, but their proprietary nature makes them incompatible with many programs and portable players.

a2b

AT&T’s a2b music is a sophisticated music distribution system with many features, such as watermarking and encryption, to support copyright protection and royalty tracking. It is based on the MPEG-2 AAC Low Complexity Profile. The Policy Maker feature of a2b is a flexible electronic licensing system, which can control how music is used and distributed. Music encoded with a2b can include artwork, credits, lyrics and links to the artist’s Web site.

Proprietary Formats

Even though MPEG Audio formats are based on open standards and widely used, many companies continue to develop proprietary digital audio formats. Proprietary formats can generate enormous profits for the developer if the format becomes a de facto standard. The marketplace, which tends to favor open standards like MPEG, will ultimately decide which formats will prevail.

MP4

Global Music Outlet uses the term MP4 to describe its proprietary music delivery system. It’s based on an enhanced version of MPEG AAC and includes an embedded player (each song is an .EXE file). Album graphics and links to the artist’s Web site can be embedded in the file.

Liquid Audio

Liquid Audio is a sophisticated music distribution system based on Dolby Digital and MPEG AAC. It supports both downloadable and streaming audio and uses watermarking and encryption for copyright protection. Music encoded with Liquid Audio can include artwork, lyrics, notes and pricing, along with links to a Web site where the song or album can be purchased. Liquid Audio has a playlist feature and allows you to burn songs to a CD if you have a supported CD-R drive.

Apple QuickTime

QuickTime is a widely used multimedia format from Apple Computer that supports both streaming audio and streaming video. Much of the MPEG-4 standard is based on QuickTime, and it is widely used for streaming video on the Web.

Non-MPEG Proprietary Formats

Several digital audio formats exist that are entirely proprietary. Many of these are quite good and are widely used.

Dolby Digital (Formerly AC-3)

Dolby Digital is a very high quality audio encoding and noise reduction system that is the audio component of High Definition Television (HDTV) and digital broadcast TV (DTV). It is also used in DVDs, laser discs, digital cable and direct broadcast satellite (DBS) systems.

EPAC

EPAC is a perceptual audio encoding scheme based on PAC—developed by Bell Labs, the research and development arm of Lucent Technologies. EPAC is reported to produce quality indistinguishable from the original CD at 128 kbps. However, I participated in one listening test where the audience was able to consistently tell the difference between original CD tracks and the same tracks encoded in EPAC at 160 kbps.

Windows Media Audio

Microsoft’s Windows Media Audio (WMA) format is a relatively late entry into the field of proprietary audio formats. WMA performs very good at lower bit-rates and is reported to produce quality indistinguishable from the original CD at 128 kbps. WMA is supported by most full-featured player programs and by many portable players. WMA is royalty-free when incorporated into software that runs on the Windows platform.

RealAudio

RealAudio was the first widely used system for streaming audio and video over the Internet. It is a proprietary format, but it is used by many online music stores for sample clips of songs. The RealPlayer also provides support for MP3.

TAC

TAC (Transparent Audio Compression) is a high-quality perceptual encoding scheme developed by K+K Research. TAC uses Adaptive Bit-rate Management (ABM), which is similar to VBR (variable bit-rate) encoding. TAC was developed as part of K+K Research’s MP02 (Music Publisher 02) software.

TwinVQ (VQF)

TwinVQ (Transform-domain Weighted Interleave Vector Quantization) is an encoding scheme developed by the NTT Human Interface Lab in Japan. TwinVQ is reported to provide higher quality than MP3, but encoding times are reported to be much longer, and CPU utilization is reported to be higher during playback.