And DSD+ sees the voice call flag and starts decoding. The codec in the scanners (Uniden, Whistler) listen and when they se a stream of CRC errors it then says "yeah that is RAS" and decodes. I think UpMan had a write up on the Uniden Tech support forum on this site.Put simply, DSD+ ignores the section of the header where RAS lives and goes on to decode the audio.
Since with RAS the header packet at beginning of transmission is variable the scanner cannot automatically ignore the RAS info and go on to decode. The Motorola radio on the other hand knows what to expect as far as the placement in the header and length of the RAS key so no problem there. You cannot decode the RAS key over the air. It is programmed into both the radio and repeater. Only a variable length CRC checksum is sent over the air.