That depends on what type of codecs you are using for your calls..
High complexity codecs include g729. For a detailed list of codecs and their complexity please refer to this link
http://www.cisco.com/c/en/us/support/docs/voice/h323/14069-codec-complexity.html
For a better understanding of how dsp allocates credits refor to this link
https://supportforums.cisco.com/document/123126/cisco-pvdm2-and-pvdm3-dsp-creditmips-allocation
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