Frequently asked questions

What error correction does SuperMAC have?

In SuperMAC, the audio data is arranged in Ethernet frames (rather than packets as with IP-based audio systems), and a Cyclic Redundancy Check (CRC) is used to provide error detection. A CRC checksum is calculated at the transmitting end of the link and sent with the corresponding Ethernet frames. HyperMAC employs two levels of CRC check for error detection, at the Ethernet frame level and at the audio data level.

SuperMAC additionally features a robust Hamming Code error correction scheme that allows individual bit errors can be corrected at the receiving end of the link. Extra data is sent along with the audio, such that if a small amount of data is corrupted on the link (e.g. by external interference), the receiver is able to completely recover the transmitted data. This is not error concealment - it is true lossless error correction. This can correct up to 8 total line corruptions in a given 11 μs period.

SuperMAC also “scrambles” the audio data in such a way that adjacent bits relate to different samples, which allows burst errors to be fully corrected. This means that a poor quality link (due to a bad cable or external interference) can be detected by the receiver, while still passing perfect audio.

These approaches are in contrast to IP-based audio systems which assume that if a packet is dropped, it is OK to re-send it later. Fine for Internet downloads, but not much use if you needed an audio sample at a particular moment in time. In addition, both the SuperMAC and HyperMAC cores report status information about the link – noting data errors, clock synchronisation and so on. This makes it very easy to provide health reporting to the user, and to implement dual-redundant links with manual or automatic change-over.

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