What is the difference between Siren7 and G.722.1?
G.722.1 is the formal name for the codec, as approved by the ITU. Siren7 is an informal name which refers to the same codec. There was an earlier form of Siren7, which is licensed to Microsoft and is included in the Microsoft Windows operating system. For purposes of clarity, we will call that earlier version Siren7pre. The differences between Siren7pre and G.722.1 are in the header information. In Siren7pre, the first 2 bits in its 20 ms payload packet indicate the bit rate of the codec. The last 4 bits of the packet are a checksum to check for bit errors in the packet. In contrast, in G.722.1, there is no 2 bits for the header and there is no 4 bits for the checksum. Thus, the total available bits per packet is 6 bits more for G.722.1 compared to Siren7pre. Otherwise, the actual codec algorithm is identical. Because the number of bits for the actual codec differs by 6 bits per packet, compatibility between G.722.1 and Siren7pre must be accomplished via transcoding. This is true for a
