In some cases when inserting a plug-in containing a very high PDC latency value your MIDI instruments may not be audible. Examples of plug-ins dependent on high PDC are Waves DeBreath or Perfect Space when its latency is configured to the maximum setting of 32,768 samples.

If you have plug-ins with high PDC that are causing this to happen, you can work around the issue by increasing SONAR's MIDI buffer size. You can do this from Edit > Preferences > MIDI - Playback and Recording by adjusting the Prepare Using N Msec Buffers value to around 700 msec.

Note that if you are using MIDI effects you will typically want to set this setting to smaller values. For example, 100 milliseconds. Setting this to a smaller value means that if you change a property for a MIDI effect, such as the Arpeggiator, there will be less delay before you hear the new value take effect.