The following classes, CRecordSound and CPlaySound, record sound and play PCM sound simultaneously. An example dialog-based program is provided that records, saves to disk and then echos sound. This example also contains two more classes, CWriteSoundFile and CPlayMMSound. CWriteSoundFile receives sound buffers from CRecordSound and writes them to a WAV disk file. CPlayMMSound opens these WAV files and plays them to the sound device. All sound files are currently PCM samples. Be careful with the sample application as it records a PCM WAV file. The PCM WAV file can grow at 16 kilobytes a second, so keep the recorded samples short.