Type 3 : Silence

 ┌────┬──┬──┬──┬───┬───┬────┐
 │ 03 │ BLKLEN │ PERIOD│ SR │
 └────┴──┴──┴──┴───┴───┴────┛

 This sub-block defines silence period in the voice data.

 The length of the silence period (period, 2 bytes) is stored after the
 BLKLEN field in units of sampling cycle. Its value is one less than the
 silence period. The sampling rate (SR) is defined as above.

 The BLKLEN for this sub-block is always 3.