Buffered read for audio from SD card

eliminating the MSB the LSB and the 7th bit

Why do that?

They are all 16 bit numbers which are only missing the high order zero. If you insert the missing high order zero, split it into bytes and convert the result as ASCII characters you get this:

01000010 01000001 BA
01000100 01000011 DC
01000110 01000101 FE
01001000 01000111 HG
01001010 01001001 JI
01001100 01001011 LK

The Arduino is a little-endian device, so this is the ASCII string "ABCDEFGHIJKL"

Pete