Digital audio

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Draft

1 Audio file formats

“It is important to distinguish between a file format and a codec. A codec performs the encoding and decoding of the raw audio data while the data itself is stored in a file with a specific audio file format” (Wikipedia).

1.1 Formats

Read:

Example of lossy compression
  • MP3 - MPEG Layer-3
  • OGG - Vorbis (most often with OGG container, therefore also known as OGG-Vorbis)
  • AAC, MP4, M4a - MPEG 4 audio
Lossless examples
  • WMA - Microsoft
  • FLAC
  • WAV mostly for Windows PCs. Can use several compression codecs (most often uncompressed PCM as in standard audio CDs)
  • AIFF (The Mac equivalent of WAV)

2 Overview of CD Formats

Most of these are called CD Rainbow Books (referring to the color of the specification documents)

  1. Red Book (CD Digital Audio). The basic standard for all CDs, including music CDs. Digital audio encoding: 2-channel signed 16-bit PCM sampled at 44,100 Hz.
  2. Yellow Book (CD-ROM and CD-ROM XA). CDs for data (software)
  3. Orange Book (CD-R and CD-RW). Recordable CDs
  4. White Book (Video CD). CDs with video content that plays in most DVD players.
  5. Blue Book (Enhanced CD, CD+G, and CD-Plus). Music CDs with extra features like videos or photos.
  6. Beige Book (Photo CD). Kodak's format for storing photos on a CD.
  7. Green Book (CD-i). Rarely used. CD-Interactive contains educational material and games.
  8. Purple Book (DDCD) hold more storage than CDs and require a special reader, not popular
  9. High Density CD (HDCD), an alternative to DDCD, not popular
  10. Scarlet Book (SACD). Super Audio CDs uses Direct Stream Digital (DSD) recording, a proprietary Sony/Philips format. Quality is superb but needs a special player to work. There are three separate versions, one of which includes a red-book layer so that music will also play on an old CD player.
  11. DVD-Audio (DVD-A) is a Digital Versatile Disc (DVD) format that is specifically designed to hold high-quality audio data. An alternative to SA-CD

3 Audio in web pages

3.1 HTML5 Audio

Audio works quite nicely in HTML5

3.2 HTML4 and XHTML1 Audio

3.2.1 Audio URLs

This is quite a nightmare. If you just use normal URLs, behavior will entirely depend on the configuration of your navigator and your system set-up. In any case, if you use firefox, you must install a mediaplayer plugin, e.g. Real Player, Quicktime, Windows Media.

E.g. in Firefox, select "Edit->Preferences" 'or "Tools->Options" (depending on your version). Then select the "Applications" tab. It will show how various audio files will be played and you can change that. E.g. on windows I use "Quicktime" and on Ubuntu the "mplayer" plugin.

3.2.2 Using the embed tag

Using the embed tag is probably the best solution for HTML4 audio, even if this tag is not an official part of HTML 4.x. Since the embed tag is official in HTML 5 it will survive, but it has different attributes. It also allows to adopt a user-friendly strategy, i.e. you can show a little control widget for playing the sound.

Attributes:

src= "URL"
The URL of the sound file
loop= "true/false/N"
Whether it should loop or how many times
autostart = "true/flase"
Whether it should automatically start.
controls = "console|smallconsole|pausebutton|stopbutton|volumelever"
Whether it will display a full console, a small one, juste a stop button or a volumelever
hidden = "true/false"
Hide/unhide. Hide if you really need background music
height=XX
defines the height of the player in pixels
width=XX
defines the width of the player in pixels
border
frameborder
align = "top|bottom|baseline|left|right

3.3 Using Flash

Simply include a Flash file. Make it very small if you don't want controls...

3.4 Using JavaScript

Source: Demonstration of Different Ways to Play a Sound from a Web Page:

<script>
function PlaySound(soundobj) {
  var thissound=document.getElementById(soundobj);
  thissound.Play();
}
</script>

<embed src="sound.mp3" autostart=false width=0 height=0 id="sound1"
enablejavascript="true">

Then call this function, e.g. from a button

<form>
<input type="button" value="Play+" onClick="PlaySound('success.wav')">
</form>

3.5 Using the object tag

In HTML4.x and XHTML 1.x, this should be the "standard" solution, but not as well implemented as the unofficial embed. Read HTML5 audio and video for better approach.

4 Software

4.1 Editing tools

4.2 Clients

  • All web browsers can support audio in one or another way. HTML4/XHTML 1.1 only supports audio through plugins, HTML5 has built-in support for some formats
  • A lot of audio players (by default each OS includes a player).

5 Links

5.1 Overviews

5.2 Information about audio file and compression formats

  • WAV (Wikipedia).


5.3 Information about CD standards

  • SA-CD FAQ. Quote: This FAQ aims to be the most comprehensive concerning SA-CD on the web, but also independent, unbiased, practical and readable

5.4 HTML embedded sound

5.5 Other