This is basic breathing technique for singers, voice actors, or just general good breathing technique. 

Do an "sss" sound with light intensity that increases to strong intensity over 5 seconds and then back to light intensity over 5 seconds. Then do a quick szforzando (a strong, sudden emphasis - in this case all the way from the lightest intensity you can do to your strongest and then back to light) as fast as you can while making it clear. Then repeat on the same breath the exercise again.

To make it harder, change the intensity over 10 or 20 seconds - it takes real control to maintain and move slowly.

NOTE: Didn't use a sensitive mic so clip doesn't show too much intensity contrast. So just be sure to make your biggest intensity contrast possible!

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http://wevoiceup.wordpress.com/2014/03/01/basic-breathing/

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