Learning tab in Tools : Options provides options affecting the way you learn:

• Forgetting index - determine the default forgetting index given to all elements introduced into a collection. Forgetting index determines the speed of learning. When you first run SuperMemo, it is set to 10%. This means that SuperMemo will tune the learning process in such a way that you will stand 10% chance of forgetting a given element at repetitions. You can reduce the forgetting index to 3% at the cost of significant slow-down of the learning process. You can also increase it up to 20% to greatly increase the speed of learning at the cost of knowledge retention. Increasing the forgetting index further makes little sense as both retention and the speed of learning will decrease (you can read about it in Theoretical aspects of SuperMemo or see it for yourself by using Tools : Statistics : Simulation).
  All individual elements can have their individual forgetting index set with Edit : Edit parameters on element pop-up menu (Ctrl+Shift+P). Before you change that value, however, their forgetting index will be determined by the default value set at Tools : Options : Learning : Forgetting index. Read overview: Forgetting index
• Classic layout at learning - upon pressing the button Learn, align the element window with statistics windows in the classic manner (introduced yet in SuperMemo 3.0). Check this box if you like to follow all the learning statistics during repetitions. If you want to see the classic layout before you make up your mind, choose Window : Classic (F5)
• Full repetition history - keep the full history of repetitions of all individual elements. Uncheck this box if you would like to spare some hard disk space (you can see the size of repetition history file by inspecting <collection directory>/info/reps.dat (please do not delete this file manually, use File : Reset : Repetition history instead). History of repetitions can be viewed by double clicking element data window or by choosing History in Edit : Edit parameters on element pop-up menu (Ctrl+Shift+P)
• Always randomize final drill - scramble the sequence of repetitions in the final drill before moving to the final drill stage
• Sound feedback - decide the way SuperMemo will react to passing and failing grades:
  • None - provide no sound feedback
  • Default - use default Windows sounds to indicate bad and good grades
  • Custom - define your own sounds with Options : Learning : Custom sounds (see below)
• Custom sounds - if Options : Learning : Sound feedback is checked, Custom sounds makes it possible to pick sound registry members for grade sound feedback. For example, if you have a low beep in sound registry member named Fail, and a cheerful Tada signal named Tada, you can type in those two names at Custom sounds: Success=Tada, Failure=Fail. You can test the sounds by pressing play buttons on the right. To import sounds to sound registry use Search : File : Sound and choose Import files on the registry pop-up menu