以前用的时候好像是可以随时修改播放频率, 不过不能修改主缓冲的播放频率, MSDN上说的, 参见 http://msdn.microsoft.com/archive/default.asp?url=/archive/en-us/directx9_c/directx/htm/idirectsoundbuffer8setfrequency.asp
Increasing or decreasing the frequency changes the perceived pitch of the audio data. This method does not affect the format of the buffer.
Before setting the frequency, you should ascertain whether the frequency is supported by checking the dwMinSecondarySampleRate and dwMaxSecondarySampleRate members of the DSCAPS structure for the device. Some operating systems do not support frequencies greater than 100,000 Hz.
This method is not valid for the primary buffer.