Do It Yourself

• If you have the means, the simplest way to gather a sound effect of any kind is to make it yourself with a digital recorder or a microphone plugged directly into your computer. In the case of a barking dog, this means that you must find either a dog that barks often or can be induced to bark, or a person that can do a decent impression of a dog barking. Whether you can get away with a human imitation of a dog depends on what you will be using the sound for -- it will do for a background sound in a movie but perhaps not for a home-invader deterrent.
  
  

Creative Commons

• Creative Commons is a nonprofit in San Francisco that aims to protect and help artists in work distribution and resource sharing. There are many websites --- including Creative Commons's own --- to which artists have uploaded various sound effects that are protected by Creative Commons licenses. Some of these licenses allow you to use the sounds for commercial purposes and modify them as you see fit. The Free Sound Project is a good source of Creative Commons-licensed sounds, and has dog-barking sounds from Chihuahua yips to mastiff growls.
  
  

Royalty Free

• The downside to Creative Commons-protected sound bites is that since nonprofessional recorders produce them, the quality may be not as good as what you need. In these cases, turn to professional sound effect houses. You can buy sound effects in downloadable files or CD collections. Search for "royalty free" sound effects. This allows you to use the effect in commercial productions without paying royalties to the sound's creator every time it is played or sold. Partners in Rhyme has several varieties of dog-bark sound effects, including both public domain sounds available for free download and royalty-free sounds available for purchase. Sound Snap and Soungle are other popular sources of royalty-free sound effects, and both have many varieties of dog barks.
  
  

File Types

• In general, uncompressed audio files are best for use in sound collages, music or film soundtracks. Microsoft Wave, also known as WAV format, is the most common, and most sound effect houses will allow you to download sound effects in WAV format. Audio Interchange File Format, or AIFF, is the native uncompressed file format on Mac OSX.