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Digital Audio : Players & FORMATS : ONLINE MUSIC 

If you buy a portable digital music player today, it will likely play a number of different file formats. Among these are MP3, WAV, and one of either WMA or AAC. If your player decodes AAC files, it is most certainly an Apple iPod. If it plays WMA files, it is probably a player from the likes of Creative, Rio, Dell, or any of the other myriad brands in the marketplace. If you download music from online music stores, make sure you get the proper file format for your player. The chart below shows the trend for music files over the last 10 years, starting with WAV files of  1995 and going up to today's WMA files. The tendency has been to create smaller and smaller file formats which take up less space and to also create copy protection schemes.

WAV files: The original digital audio file 

WAV is the file format for sound, and it was built into Windows 95 years ago, which in essence made it the standard for digital audio. Wav files have the file extension .wav in Windows. If you have a Windows personal computer and have the Windows Media Player program (check version), you can listen to this   WAV file   of a violin. This file takes up 250KB of disk space but only plays for 23 seconds. If you rip tracks from a CD with an application like RealJukebox or MusicMatch Jukebox, you'll be converting from source files, which are in the WAV format.

If you're wondering why people didn't share music en masse, as was the case in the glory days of Napster, with WAV file availability, it's because WAV files take up much more memory than files encoded with MP3 or other recent compression standards. For example, an hour of music encoded in the WAV format requires about 600MB of memory when a "CD quality" WAV file is encoded at 1411kbps (kilobits per second). Whereas, to achieve CD-quality sound with an MP3 file, it can be encoded at 128kbps, which requires only 32MB of storage for about an hour of music. Therefore, when WAV files are converted to MP3, it becomes much easier to store these smaller files on your hard drive or transfer them over an Internet connection. 

What’s the difference between WMA and AAC ?

In terms of functionality, there is very little difference. Some audiophiles will tell you one format sounds better than the other, but for most people, the difference is indiscernible.

WMA stands for Windows Media Audio, and was developed by Microsoft. It is a proprietary format owned by Microsoft. In order for developers of software music players or portable music players to include support for WMA in their product, they must pay a license fee to Microsoft. WMA is the format chosen by online music stores including Napster, Wal-mart, and Musicmatch. If you purchase a song from these online stores, it will be in WMA format. Most digital music players sold today can play WMA files — the notable exception is Apple’s iPod, the most popular player on the market today (there are rumors that Apple may add WMA support to the iPod).

AAC stands for Advanced Audio Codec. It is an open standard developed by a committee that included Dolby Labs and AT&T Research. If you are a developer, it does not require a license fee to use in your software application or portable music player. AAC is based upon the same technology as MPEG-4. Apple has chosen a variant of AAC as the file format for their iTunes Music Store, which is one of  the most popular online music store at this time. Apple’s iTunes software and iPod player can play both standard AAC files as well as the variant of AAC provided by the iTunes Music Store. Few, if any, other digital music players can handle AAC files.

What is a DRM?

DRM stands for Digital Rights Management, and is a generic term for a system built into a music file format that aides in preventing piracy. WMA includes an (optional) DRM system. Most WMA-supporting online music stores use this DRM. Apple developed a DRM system called Fairplay, which sets on top of the industry standard AAC format. Fairplay is used in files purchased from the iTunes Music Store.

Why the new file formats? What was wrong with MP3?

Nothing is wrong with the MP3 format, and every digital music player sold today supports MP3 files — including the iPod. However, MP3 does not have a DRM option, and therefore record companies were very skeptical about releasing legal downloadable versions of their music in this format. Doing so would have only increased the level of MP3 piracy. For this reason, record companies did not jump onboard with online music sales until Fairplay and the Windows Media DRM became available.

It’s also worth noting that files saved as AACs or WMAs are typically smaller in size than an MP3 saved at the same bitrate — which means you fit more music on your device.

What are the arguments for and against choosing a WMA store, rather than iTunes (or another AAC store)?

The primary reason you’d choose a WMA store is that you will have more choice in portable music players and music playing software. The downside is that the most popular player, Apple’s iPod, will not be an option for you, as it does not currently support WMA. Additionally, by choosing a WMA store, you are (in a sense) technologically wedding yourself to Microsoft.

What are the arguments for and against choosing iTunes (or other AAC store) instead of a WMA store?

If you choose iTunes Music Store, it will likely be because you want to use the jukebox software Apple’s iTunes and the digital music player Apple iPod. The downside will be less choice when it comes to jukebox software and music players, and also a “technological wedding” to Apple — but only for the moment (see the HP/Apple alliance and the new Real Jukebox for evidence that AAC is starting to branch out beyond Apple).

But isn’t AAC industry standard and WMA proprietary?

Yes, but this is very misleading. Apple fans will tell you that you should choose AAC because it’s an open standard. This is true. However, Fairplay — Apple’s DRM — is not part of that standard. Apple’s products (iTunes and iPod) play both the industry standard AAC (.m4a) files, as well as the Fairplay-enchanced AAC files (.m4p) sold on the iTunes Music Store. While it’s true that AAC is an open standard, the files sold at iTMS are only based on this standard — they do not fully comply with the standard, due to the addition of the Fairplay DRM.

What about the HP and Apple alliance?

HP recently licensed Apple’s iPod player and iTunes software in order to provide HP-branded versions to their customers. This is a huge boost for Apple and the AAC format. Many analysts predict that Apple will be making more deals like this one, and the result will be a day in which AAC and the Fairplay DRM are the de facto standard. Most consumer advocates like this idea, because AAC and Fairplay do not require license fees paid to Apple, and therefore do not marry you to one company, as WMA marries you to Microsoft.

So how do you decide?

The bottom line is that both Apple and Microsoft have their sights set on domination of this market. Until one or the other prevails, consumers will suffer. If Apple adds support for WMA to the iPod, there will finally be one player on the market that can play all major formats.

 Note: Both AAC and WMA files are usually smaller than MP3 files.

Digital audio

MP3 is just one of several digital audio formats. The technical term is MPEG-1, Audio Layer 3. First developed by the Fraunhofer Institut fur Integrierte Schaltungen in Germany back in 1987, MP3 was originally patented in 1989 and incorporated into the Moving Picture Experts Group (MPEG) specifications in 1992. The MP3 standard, or codec, enabled high-quality yet low bit rate compression of digital audio files. In other words, audio files, which were typically large (such as WAV files from CDs), could be compressed to a fraction of their original size without a significantly noticeable loss in quality to the human ear.

However, the power of MP3 did not begin to be harnessed until developers created encoding, decoding, and playing tools for the standard. The original patent holder, Fraunhofer IIS-A, made the technology free for use and development. Therefore, a number of independent developers and companies were working simultaneously to provide MP3 tools. Timing was everything. Just as home PC processing power was exploding and the Internet was taking off in 1997, researcher Tomislav Uzelac introduced the first desktop computer MP3 player known as AMP. AMP became the precursor to Winamp and later MacAmp, the first two widely available MP3 player applications for consumers. Soon, companies such as RealNetworks and MusicMatch jumped on the bandwagon. In May of 1999, RealNetworks introduced RealJukebox, its CD-ripping, encoding, file-management, and player application. Anyone with a personal computer and internet access could share music.

Figure A: The development of Winamp helped MP3s take over the music world.

In September 1998, Diamond Multimedia released its Rio 300 portable MP3 player, and by October, the RIAA battled back with a lawsuit against the company. Eventually, Diamond Multimedia won, and by the summer of 1999, the Rio 300, along with the Creative Nomad and other portable players, became the new, must-have gadgets around the world. 

The Secure Digital Music Initiative (SDMI), which was founded to help regulate the sharing and distribution of copyright protected music, stepped in to establish standards for the portable players. The result was that MP3 files could be downloaded to players, but not uploaded from players to PCs--at least until the SDMI came up with some sort of watermarking system that would make illegal copying extremely difficult.

Figure B: The Rio 300 portable player became a favorite digital music accessory for MP3s.

In January 1999, the RIAA moved on to its next foe--MP3.com, one of the largest MP3 download sites on the Web. Simultaneously, Shawn Fanning, an 18-year-old student at Northeastern University, wrote a program and protocol that allowed peer-to-peer file sharing, or sharing between computers without the need for a centralized server or Web site. This became Napster, and before it knew what hit it, the RIAA had a monster of Godzilla-sized proportions on its hands.

With Napster's peace accord with media giant Bertelsmann (parent company of BMG among others), it seemed that the days of unlimited free music swapping had been dealt a setback.

The MP3 algorithm can compress file size significantly because it uses a psychoacoustic encoding technique. This technique capitalizes on the unique qualities of human hearing by capturing the audio that we hear best while encoding less accurately--or eliminating altogether--the audio that isn't perceptible to the human ear. MP3 files can be encoded at various bit rates, but 128kbps is considered equal to the quality of a Compact Disc even though you can record up to 320kbps with a version of RealJukebox 2 Plus.

The MP3 file format garnered much attention early on because it was one of the first high compression formats available and was supported by numerous developers as well as digital audio player manufacturers. Seeing another opportunity to dominate the world, Microsoft introduced its Windows Media Audio (WMA) file format as a response to the MP3 and RealNetworks G2 formats in the summer of 1999. WMA has one advantage over MP3: It can offer CD-quality sound at an encoding rate of only 64kbps as opposed to MP3's 128kbps, therefore reducing the file size in half. In addition to superior compression, Microsoft appeased the RIAA and SDMI by including the ability for copyright protection in the WMA codec by using a digital certificate to link a song copy to the PC that created it.

The first round of digital audio players that was released--including the Rio 300, Nomad, JazPiper, and others--didn't support files encoded with WMA. Of course, Microsoft changed that by convincing manufacturers of the best players to include WMA as a supported format in its newest products. One benefit of Microsoft's power of persuasion is that the digital audio player companies incorporated upgradable firmware into their portable players. This enabled you to simply download an upgrade from the Web to support WMA instead of having to purchase an entirely new player. One of the first portable players to feature upgradable firmware was the RCA Lyra. The Diamond Rio 500 and Creative Nomad II followed suit. Today, you can download new firmware for most of these players, which will give your player WMA ability. The recently introduced iPAQ digital audio player from Compaq (see Figure C) was the first player to ship with WMA support already included. Now, many CD ripping and player applications also support WMA, as does (of course) Microsoft's Windows Media Player.

Figure C: Compaq's iPAQ digital audio player was the first to come with WMA capabilities.

MP3 and WMA may be the most widely used formats for music sharing, but there are a number of others available, including the widely used RealAudio format, often referred to as RealAudio G2. RealAudio G2, which belongs to RealNetworks, is a proprietary encoding format for audio and video. It is often used for streaming audio found on the Internet, and it works with Real Player or RealJukebox. The RCA Lyra was one of the first portable players to support RealAudio G2, but unfortunately for RealNetworks, few other portable players support its format at this time.

The RealAudio format, unlike MP3, has built-in encryption and security features that allow files to be more easily controlled by the content owner. For instance, RealAudio files can be downloaded, streamed, or previewed depending on settings selected when files are encoded--WMA also has this feature. RealAudio G2 compresses files similarly to the MP3 format, where CD-quality audio is achieved at a 128kbps encoding rate. RealAudio 8 was launched in October 2000, replacing G2 as RealNetworks' standard. RealAudio 8 incorporates Sony's ATRAC3 audio compression technology, which is used with Sony's portable players and VAIO computers. And, like WMA, the new format will be able to deliver CD-quality sound at 64kbps, creating files half the size of those encoded with MP3.

More proprietary formats
RealNetworks and Microsoft aren't the only companies that have proprietary audio encoding formats--there are numerous others. Those you'll most likely run across out there in the wide world of digital audio include ATRAC3 from Sony, LQT from Liquid Audio, and Audible.com's formats. The difference between these formats and MP3, RealAudio, and WMA is that their primary purpose is to protect music and other audio that has been copyrighted.

Sony has always led the way in the world of portable audio by being the first company to introduce the Walkman and, later, the MiniDisc. But unfortunately for Sony, MP3 was nothing but a thorn in its side. Sony, unlike Diamond Multimedia or Creative Labs, is also in the business of music, and the company desperately wanted to find a way to sell portable digital audio players such as the Rio and Nomad without supporting what it saw as the illegal sharing and swapping of music with MP3. Its solution was to adapt two of its previous technologies, MagicGate Memory and ATRAC, for use in its version of "SDMI compliant and secure" portable players.

The first player Sony introduced was the Memory Stick Walkman, which used the MagicGate Memory Stick data storage card also used in Sony's digital cameras. The combination of this proprietary card and a confusing software application called OpenMG guaranteed that rogue MP3 files would be converted to Sony's ATRAC3 format before being stored on its players. The not surprisingly lukewarm reception of the Memory Stick Walkman prompted Sony to release two new players, the Network Walkman and the VAIO Music Clip. Both relied on ATRAC3 and OpenMG as a means of keeping music secure; however, the MagicGate Memory Stick card didn't. 

Sony's ATRAC3 is a sound compression technology based on ATRAC, the technology used in the MiniDisc. ATRAC3 increases the sound compression rate of ATRAC by approximately one-tenth, which makes it more suitable for MP3-like portable players. Meanwhile, the OpenMG software converts MP3 files into ATRAC3 and attaches security features to the files so that they couldn't be shared, downloaded, or even transferred to Sony's own players more than a few times. Needless to say, most consumers weren't too happy about this. ATRAC™ & ATRAC3™  
Short for Adaptive TRansform Acoustic Coding, ATRAC is the digital data compression technology that makes it possible to fit up to 80 minutes of high-fidelity stereo digital audio onto a tiny 2-1/2" disc. Ultra-compact MiniDiscs can hold only about 1/5th of the data of a CD, but thanks to ATRAC, MiniDisc offers CD-like specs for dynamic range, frequency response, and low distortion. ATRAC3 is a newer data compression technology that allows more audio to be stored on a MiniDisc. ATRAC3 recordings are also called MDLP (MiniDisc Long Play) recordings. In LP2 mode, you can record twice as much audio as would normally fit on an MD; in LP4 mode, you can record four times as much. Both modes record in stereo.

Since ATRAC3 uses more compression than ATRAC, the sound quality of MDLP recordings is slightly lower than that of standard ATRAC recordings, and LP2 recordings sound better than LP4. Non-MDLP-capable players cannot play back MDLP (ATRAC3) recordings.

Audible.com sells audio books over the Internet, and, to protect its wares, files can be downloaded in one of four Audible.com proprietary formats. Each format takes into account the source audio, as well as which listening device will be used to play back the encoded file. Formats 1, 2, and 3 use speech compression at varying levels, while format 4 is a version of MP3 encoded at a low bit rate that works better for spoken word than music and is more efficient for downloading over the Internet. Audible makes its own desktop player, called AudibleManager, which lets its files be played on a desktop or transferred to a select group of portable players. If you're satisfied with just hearing Audible.com's content streamed over the Internet, you can use the Windows Media Player or Real Player. 

A few portable digital audio players and handheld PDAs support Audible files. These include the Rio 500, 600, and 800, as well as the Casio Cassiopeia, HP Jornada, and Compaq iPAQ. 

Liquid Audio is one of a number of Web sites that offers downloadable music for a fee. It protects the music it offers by encoding files into its own format. Liquid Audio's format is known as LQT. If you want to play the files on your desktop, you have to use either the Liquid Player or RealJukebox. These files cannot be converted to MP3 or WAV formats, which makes them difficult to share and burn onto CDs. Liquid Audio files can be burned only to a CD if you use its software and a select group of CD recorders that support its format. 

WMA and RealAudio 8 may have the advantage over MP3: Their files are half the size at CD-quality rates. However, a newer standard called Advanced Audio Coding (AAC), or MPEG-2, AAC, may give them a run for their money. AAC was co-developed by the Fraunhofer IIS-A, Dolby, and AT&T, and it is part of the MPEG-2 specification. AAC's algorithm is different from MP3's, and AAC incorporates additional features that boost the efficiency of encoding. Basically, AAC delivers better-quality audio with 30 percent less data than MP3. AAC is widely known to be the best when it comes to audio compression, and a number of desktop players, like the new MusicMatch Jukebox, are beginning to incorporate it into the suite of codecs they support. 

If you're thinking about purchasing a portable digital audio player, and you want to make sure it supports the most number of codecs, definitely invest in one with upgradable firmware. Just because a player has the ability to be upgraded to support new formats doesn't mean that its manufacturer will create the upgrade. Some player manufacturers have more aggressive codec inclusion policies than others. For example, the newer Diamond Rio players (500 and up) support MP3, WMA, and Audible formats. The Rio 600 will also support AAC. The RCA Lyra  was one of the first players to support RealAudio G2 and MP3. 

ADPCM (Adaptive Differential Pulse Code Modulation): If you buy a portable digital audio player and it has a voice recording feature, the recordings you make will be encoded in the ADPCM format. ADPCM encoding creates much smaller files than MP3 does because it's best suited to spoken audio that doesn't have complex sound.

• Bit Rate: The number of bits occurring per unit of time. Bit rate is usually expressed in bits per second.

• CDDB: Now called Gracenote, this Web site provides an online database of information about audio CDs. Virtually every digital audio player has the ability to access information from Gracenote over the Internet. This information includes artist, album title, song title, track length, and other information when you play, record, or rip CDs.

• CD Quality: A term frequently used to describe the minimum bit rate level needed to equal CD-quality sound. A CD-quality MP3 file is encoded at 128kbps and above, whereas a CD-quality WMA file is encoded at 64kbps and above.

• CD Ripper: An application that converts compact disc audio files to MP3 files or other audio encoding formats. Popular CD rippers include RealJukebox and MusicMatch Jukebox.

• Codec: Short for coder/decoder or compression/decompression algorithm. Codecs are used to encode and decode or compress and decompress data.

• Firmware: Firmware is defined as software or data that is in the read-only memory (ROM) of a hardware device. Firmware is found in all types of devices such as printers, fax machines, and portable digital audio players.

• SDMI (Secure Digital Music Initiative): SDMI is a forum that brings together hundreds of companies and organizations. SDMI's goal is to develop open technology specifications that protect the playing, storing, and distribution of digital music.

• Variable Bit Rate: VBR is an encoding method used by popular CD-ripping utilities. It provides a better and more consistent audio quality throughout an entire encoded file than Constant Bit Rate (CBR) encoding. VBR-encoded files are usually larger than CBR-encoded files, but they generally sound better.

Digital Audio Formats

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 be 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 should 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.

Common Digital Audio Formats

* Can be used with other codecs.

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.

Streaming Audio Systems

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.

 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. (See Chapter 13 for more detailed information on MPEG Audio.)

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 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.

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.

Additional Resources