Article by Damien.
Published: March 8, 2009 at 17:41
Category: Audition 3, Flash, Flash Media Server, Flex

So, What exactly is a .wav file?

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Until recently, I thought a .wav file was for uncompressed digital audio data on windows, while .mp3 file would be the compressed version of the audio clip.  That was probably too simple to be true!!

The first time I used Adobe Audition to export a mixdown of a multitrack session, an export dialog box poped-up and asked me to choose a format in which to export my music.  I wanted to choose the “.wav”  format, but, when I opened the ‘Save as type’ drop-down, I found a dozen of different formats that were all using the “.wav” file extention.  Obviously the world in which a “.wav” file only  is one thing (uncompressed audio data) was not anymore the one I was living in!  I told you, too simple to be true (and another lost illusion about our world!).

So What exactly is a “.Wav” file.

The “.wav” file has been invented by Microsoft and IBM.  It is an implementation of  the RIFF bitstream format.

RIFF (for Ressource Interchange File Format) is a generic meta-Format.  In other words, RIFF describes how RIFF compliants file formats should store and organize information (a bit like an action script interface describes how a class that implements it should look like).  RIFF was introduced by Microsoft and IBM in 1991.

Many different multimedia file formats implements the RIFF specification.  The “.wav” file is one of them, but the “.avi” file format on windows and the “.aiff” file format on Macintosh are other examples.

RIFF describes a way to store data in ‘chuncks’ into a file that wraps all the chunks together.

So, a “.wav” file just is a wrapper for whatever audio data we want to put in it.

Yes! That’s it.  The “.wav” file just is a wrapper for audio data.  As such a “.wav” file can contain compressed audio data.  For example, we could imagine audio data compressed with the MP3 codec being stored in a “.wav” wrapper.  This explains that there is more that one “.wav” file format.  It all depends on the codec used on the audio data the Wav format has to wrap.

How a “.wav” file is generally used?

Most of the time, a “.wav” file is used to warp audio data in the LPCM format (Linear Pulse Control Modullation – Also called PCM format).  LPCM is a particular method of pulse code modulation which represents an audio waveform as a sequence of amplitude values recorded at a sequence of times.

Event thougt a .wav file can hold audio data coded otherwise, the most common audio format that a .wav file holds is a PCM audio stream.  The weight of the file as well as the quality of the sound depends on 2 things

1. The number of samples per second.  Usually 44.1Khz (44 thousands samples per second!!) for CD quality, but Audition allows for a sampling frequency up to 192Khz.
2. The number of BITs used to code each sample’s amplitude (called the bit definition).  Usually 16 bits for CD quality, but Audition uses a 32 bits mixing engine.

What are the other formats usually found on a “.wav” file

While most ‘.wav’ files are used to wrap PCM data, other popular .wav file formats include

• a Law / mu Law
• ACM
• ADPCM (Adaptive Differential Pulse Control Modulation)
• MP3
• …

Limitations of a Wav File

The WAV format is limited to files that are less than 4 GB in size, because of its use of a 32 bit unsigned integer to record the file size header.  This is a problem for video applications that use a 5.1 or even 7.1 surrond sound (6 or even 8 channels of sound that in the same file)

Wav files and Audio CD

A .wav file can not be burned directly on an audio CD.  Even though the audio CD also uses PCM audio data, it does not wraps it in a Wav.  Instead, it used the ‘Red book Audio’ format.  When burning a wav file on an audio CD, the burner Application first converts the Wav into ‘Red Book audio’ format.  Basicly, this operation consist in removing the PCM data from their WAV wrapper and place them into a ‘Red book audio’ format.

Since we usually use a higher sampling frequency than 44.1 kHz and a higher bit definition than 16 bits when we record and mix our sounds, the CD burner application must also ‘downSample’ the audio data so that the 44.1 kHz 16 bits requirement of an audio CD is met.

I hope this will help you understand the different option Adobe Audition and other sound Editors provide to you.

Musically yours

Damien

External links :

More on WAV
More on PCM
More on Audio CD

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