Windows Media Audio Codecs The following audio codecs are automatically downloaded by the latest versions of Microsoft Windows Media Encoder and Windows Media Player, and are supported by the Windows Media Digital Rights Management platform. For more information about Windows Media Audio 9 Series codecs, see Encoding Audio and Video with Windows Media Codecs.
Windows Media Audio 9
 Windows Media Audio 10 Professional
Windows Media Audio 9 Lossless
Windows Media Audio 9 Voice
Compatibility
Windows Media Audio 9This codec samples audio at 44.1 or 48 kilohertz (kHz) using 16 bits, similar to the current CD standard, offering CD quality at data rates from 64 to 192 kilobits per second (Kbps). The resulting sound quality is 20 percent better than audio sampled with Windows Media Audio 8 at equivalent data rates.
The Windows Media Audio 9 codec (WMA 9) supports variable bit rate encoding (VBR), which enables even higher quality audio at smaller file sizes by automatically varying the encoding bit rate according to the complexity of the audio data. With VBR, the encoding bit rate increases to capture complex sections of data and then decreases to maximize the compression of the less complex sections, producing compact, high-quality compression.
WMA 9 is backward-compatible with previous Windows Media Audio-compatible decoders, which means that WMA 9 content can be played with previous versions of Windows Media Player or older consumer electronic devices that support Windows Media. As with all Windows Media 9 Series codecs, it supports the Windows Media digital rights management platform, which is used to securely package and distribute copy-protected digital media.
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Windows Media Audio 10 ProfessionalWindows Media Audio 10 Professional (WMA 10 Pro) is the most flexible Windows Media audio codec available – supporting profiles that include everything from full-resolution 24-bit/96 kHz audio in stereo, 5.1 channel, or even 7.1 channel surround sound, to highly efficient mobile capabilities at 24 Kbps to 96 Kbps for stereo, and 128 Kbps to 256 Kbps for 5.1-channel sound. WMA 10 Pro offers incredible quality for consumers using high-fidelity hardware and 5.1 channel surround sound-equipped computers -– and for consumers playing audio content on their mobile devices. WMA 10 Pro supports streaming, progressive download, or download-and-play delivery at 128 to 768 Kbps.
For more information about the mobile capabilities in WMA Pro and how it compares to other audio codecs, see the NSTL Test Report.
When using 5.1 surround sound audio compressed at 384 Kbps with WMA 10 Pro, most listeners cannot discern any differences between the compressed music and the original pulse code modulation (PCM) files. WMA Pro also offers dynamic range control using the maximum and average audio amplitudes that are calculated during the encoding process. Using the Quiet Mode feature in Windows Media Player 9 and later, users can hear either the full dynamic range, a medium difference range up to 12 decibels (dB) above the average, or a little difference range up to 6 dB above the average.
If a user tries to play back a file that was encoded using the 5.1 channel, 24-bit, 96 kHz sampling capabilities, but does not have a system or sound card that supports multi-channel or high-resolution sound, multiple channels are combined into stereo audio (for example, 16-bit, two channel audio), ensuring that users get the best playback experience their systems can provide.
The following table compares WMA Pro to competing compression technology.
| Audio Data | Industry Compression* | Windows Media* | Compression Savings |
|---|
2 ch x 48 kHz x 16 bits
| Dolby Digital 2.0 at 220 Kbps
| WMA 10 Pro at 128 Kbps
| 1.7:1
| 6 ch x 48 kHz x 20 bits
| Dolby Digital 5.1 at 384 Kbps
| WMA 10 Pro at 192–256 Kbps
| 1.5–2:1
| 6 ch x 48 kHz x 24 bits
| DTS 5.1 at 1,536 Kbps
| WMA 10 Pro at 768 Kbps
| 2:1
|
*Content dependent
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Windows Media Audio 9 LosslessThe audio quality of content that is compressed using this codec is the best of all Windows Media Audio codecs. It creates a bit-for-bit duplicate of the original audio file so that no data is lost, which makes it ideal for archiving content masters.
Depending on the complexity of the original, content will be compressed at a 2:1 or 3:1 ratio. Although this is lower than the ratio achieved with other Windows Media Audio 9 Series codecs, it provides the same benefits of compression while leaving the data intact.
Like Windows Media Audio 9 Professional, the Windows Media Audio 9 Lossless codec also offers dynamic range control using the maximum and average audio amplitudes that are calculated during the encoding process. Using the Quiet Mode feature in Windows Media Player 9 and later, users can hear the full dynamic range, a medium difference range up to 12 dB above the average, or a little difference range up to 6 dB above the average.
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Windows Media Audio 9 VoiceThis low-bit-rate codec is primarily targeted for speech content, but performs very well with mixed-mode content that includes both voice and music. In voice mode, the codec takes advantage of the relatively less complicated and narrower frequency range of the human voice to maximize compression. In music mode, the codec operates like the standard Windows Media Audio 9 codec. Encoded content can be configured to switch between voice and music modes automatically.
The Windows Media Audio 9 Voice codec offers superior quality for low-bit-rate streaming scenarios (less than 20 Kbps), such as radio broadcasts, advertising, e-books, podcasts, and voiceovers. The voice codec can also compress content to as low as 4 Kbps at 8 kHz.
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CompatibilityThe following table outlines what your audience will experience when playing Windows Media Audio 9 Series content on earlier Microsoft Windows operating systems than Windows XP or with earlier versions of Windows Media Player. This table also lists the compatibility for Apple Mac OS X and Windows CE–based platforms.
| Codec | Feature | Player backward compatibility |
|---|
Windows Media Audio 9
| Constant-bit rate (CBR) encoding
| Windows Media Player 6.4 or later on non-portable devices (using transcoding as needed)
Windows Media Player 9 for Mac OS X
Windows Media Player 9 Series and Windows Media Player 9.1 for Pocket PC*
Windows Media Player 9 Series and Windows Media Player 9.1 for Smartphone*
|
| Variable-bit-rate (VBR) encoding
| Windows Media Player 7 or later on all devices that support the Player (using transcoding as needed)
| Windows Media Audio 9 Professional
| General
| Windows Media Player 7 or later
Windows Media Player 9 for Mac OS X
|
| Discrete channel playback (for instance, 5.1)
| Requires Windows Media Player 9 Series (or SDK) or later, Windows XP, and a multichannel audio card.
|
| High-resolution audio (24-bit, 96 kHz)
| Requires Windows Media Player 9 Series (or SDK) or later, Windows XP, and a high-resolution audio card.
|
| Dynamic range control
| Requires Windows Media Player 9 Series (or SDK) or later and Windows XP.
| Windows Media Audio 9 Lossless
| General
| Windows Media Player 7 or later
Windows Media Player 9 for Mac OS X
|
| Discrete channel playback (for instance, 5.1)
| Requires Windows Media Player 9 Series (or SDK) or later, Windows XP, and a multichannel audio card.
| Windows Media Audio 9 Voice
| General
| Windows Media Player 6.4 or later
Windows Media Player 9 for Mac OS X
Windows Media Player 9 Series and Windows Media Player 9.1 for Pocket PC*
Windows Media Player 9 Series and Windows Media Player 9.1 for Smartphone*
|
* All versions of Windows Media Player for Pocket PC and Smartphone are shipped as part of the Microsoft Windows Mobile operating system. Windows Media Player for Pocket PC and Windows Media Player for Smartphone are not available for download from Microsoft.
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