MOD period

Well, I was just wondering how to read the period from a mod file. If you are initiated in this subject you probably know that a ''note'' is written in this format Byte 1 Byte 2 Byte 3 Byte 4 --------- --------- --------- --------- 7654-3210 7654-3210 7654-3210 7654-3210 wwww XXXX xxxxxxxxx yyyy ZZZZ zzzzzzzzz wwwwyyyy ( 8 bits) : sample number XXXXxxxxxxxx (12 bits) : sample ''period'' ZZZZzzzzzzzz (12 bits) : effect and argument this I copied from Modfil11.txt. As you can see the first bytes low nibble and the second byte make up the period but howdo I use this period?. I have read this: 7093789.2 ----------- = x Hz period * 2 But I have to divide by period*4 to make it sound right. Why?