Sound
From MobileRead
This page covers the Sound capabilities that are found in some eBook Readers. It is not intended to be a complete page technical page on digital sound.
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[edit] Sound Use
Many eBook reading devices do not support sound. Those that do tend to support sound for music background while reading eBooks. Some, however, consider it another format for eBooks themselves (called audio books). For example MP3 books are readily available as an alternative to reading. Audible is a company that specializes in producing audio books using a highly compressed proprietary format.
For readers that are trying to learn a new language having the audio playing while reading a book can aid in learning the language pronunciation. Some eBook readers even support reading a book aloud by synthesized TTS (text to Speech) technology. This permits the text pages to be synced exactly with the sound although some may argue that synthesized sound does not produce good pronunciation for many words.
This page covers the digital formats used in the recording and reproduction of sounds. It is also possible to define music using a notation system and then create music directly from the notations. See the article on MIDI for a discussion of this system.
[edit] Sound Formats
[edit] AAC
Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. AAC is promoted as the successor to the MP3 format by MP3’s creator, Fraunhofer IIS.
AAC generally achieves better sound quality than MP3 at the same bitrate, particularly below 192 kbit/s.
AAC’s most famous use is as the default audio format of Apple's iPhone, iPod, iTunes, and the format used for all iTunes Store audio (with extensions for proprietary Digital Rights Management (DRM) where used).
AAC is also the standard audio format for Sony’s PlayStation 3 and the MPEG-4 video standard. HE-AAC is part of digital radio standards like DAB+ and Digital Radio Mondiale.
The extensions that can be used for AAC files include: .m4a, .m4b, .m4p, .m4v, .m4r, .aac, .3gp, .mp4
[edit] MP3
MPEG-1 Audio Layer 3, more commonly referred to as MP3, is an audio encoding format.
It uses a lossy compression algorithm that is designed to greatly reduce the amount of data required to represent the audio recording, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners. It was invented by a team of European engineers at Philips, CCETT (Centre commun d'études de télévision et télécommunications), IRT and Fraunhofer Society, who worked in the framework of the EUREKA 147 DAB digital radio research program, and it became an ISO/IEC standard in 1991.
MP3 is an audio-specific format. The compression removes certain parts of sound that are outside the hearing range of most people. It provides a representation of pulse-code modulation — encoding audio in much less space than straightforward methods, by using psychoacoustic models to discard components less audible to human hearing, and recording the remaining information in an efficient manner. This is quite different from the principles used by, say, JPEG, an image compression format, which are purely frequency domain based.
The lower the bitrate of an MP3 recording the lower the frequency response and the smaller the file. For reading the text a low bitrate, small file is adequate. A monophonic format will also reduce the file size and should always be used for audio books.
The standard bitrate for music in MP3 is 128K bps. This offers good quality but many audiophiles prefer higher bitrates like 192K or even 320K. There are less artifacts in these higher bitrates but, of course, they will have a larger file. The quality is dependent on the bitrate but also on the quality of the encoder used to create the file. In addition the sample rate effects the quality of the file. Some files use a variable bit rate to increase the quality for difficult waveforms while using a lower bitrate for simple waveforms to provide better quality while decreasing the size of the file.
For audio books the use of 64K provides high quality voice and even lower bitrates can be used with good results. Bitrates supported in the MP3 standard include 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 192, 224, 256 and 320 kbit/s. The available sampling frequencies are 32, 44.1 and 48 kHz with 44.1 being the most used since it matches a CD.
[edit] WMA
Windows Media Audio is an audio format developed by Microsoft to compete with MP3. Currently it is a widely accepted format available on a number of hardware platforms. WMA can refer to the data or to the codec that encodes and decodes the data.
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. Today it is one of the most popular codecs, together with MP3 and MPEG-4 AAC.
- 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. This is a newer more efficient replacement for the original Microsoft WAV format.
- WMA Voice, targeted at voice content, applies compression using a range of low bit rates.
The file itself is a container with data in one of the 4 codec forms and a header that specifies which one is used. The container can optionally contain DRM. Not all players can play all 4 forms or support DRM.
[edit] WAV
WAV or WAVE files, short for Waveform audio format, is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs using the .wav extension. It is a variant of the RIFF bitstream format method for storing data in “chunks”, and thus also close to the AIFF format used on Macintosh computers. It is the main format used on Windows systems for raw and typically uncompressed audio. Though a WAV file can hold compressed audio, the most common WAV format contains uncompressed audio in the pulse-code modulation (PCM) format. PCM audio is the standard audio file format for CDs, containing two channels of 44,100 samples per second, 16 bits per sample. Since PCM uses an uncompressed, lossless storage method, which keeps all the samples of an audio track, professional users or audio experts may use the WAV format for maximum audio quality.
[edit] Audible
Audible, http://www.audible.com, provides audio books for playing on a wide variety of platforms. Audible files have a .AA extension. They have 4 formats available depending the fidelity required by the user. The higher the format number the higher the quality and the larger the file. Not all players can read all 4 formats nor are all books available in all formats. DRM is always employed on audible files even if they are free. Multiple devices can use the same audible file. Any or all of the available formats can be downloaded and the site has a backup of all files owned by the user.
Some Magazines, Newspapers, and radio shows are supported using a subscription plan.
Formats:
| format | size/hour | quality |
|---|---|---|
| 1 | 1.8 MB | telephone |
| 2 | 3.7 MB | AM Radio |
| 3 | 7.2 MB | FM Radio |
| 4 | 14.4 MB | MP3 standard |
