SuperMAC is a proprietary point-to-point digital audio connection technology operating over 100 Mbit/s Ethernet. Originally developed by Sony Pro-Audio Lab in Oxford and now owned by Klark Teknik, it forms the basis of the Audio Engineering Society’s AES50 open standard (AES50, AES standard for digital audio engineering - High-resolution multi-channel audio interconnection (HRMAI). Published by Audio Engineering Society, Inc. Copyright ©2005 by the Audio Engineering Society, New York, NY., USA. www.aes.org).

SuperMAC networks can be created using specialised routers, such as the Midas DL461 Audio System Signal Router, which can provide channel-by-channel audio routing (like a patch bay), as well as packet switching for the auxiliary data messages. This approach offers robust, low-latency and deterministic latency audio routing, with the benefits of a true packet-switched network for the control data.

Routing is centralised, not distributed, giving better latency control, better reliability and finer routing granularity than distributed audio networks. It uses Ethernet frames transmitted over the physical layer only of the Ethernet technology – the cables and transceivers at each end. A deterministic protocol is used that is essentially a time-division multiplex (TDM) at the hardware level.

This approach allows for simultaneously high channel counts and very low deterministic (fixed) latencies. At 96 kHz operation (as adopted by Klark Teknik and Midas), SuperMAC offers 24 bidirectional channels with an individual link latency of 62.50 μs. The full list of channel counts and link latencies at each sampling frequency supported are as follows:-

48-channel	44.1 kHz	24-bit PCM	3 Samples	68.02 μs
48-channel	48 kHz	24-bit PCM	3 Samples	62.50 μs
24-channel	88.2 kHz	24-bit PCM	6 Samples	68.02 μs
24-channel	96 kHz	24-bit PCM	6 Samples	62.50 μs
12-channel	176.4 kHz	24-bit PCM	12 Samples	68.02 μs
12-channel	192 kHz	24-bit PCM	12 Samples	62.50 μs
6 Channels	352.8 kHz	24-bit PCM	24 Samples	68.02 μs
6 Channels	384 kHz	24-bit PCM	24 Samples	62.50 μs

It should be noted that SuperMAC differs from the AES50 standard with regard to the number of samples delay incurred for the link latencies at sampling frequencies above 96 kHz and that the Direct-Stream Digital (DSD) format is not specifically supported.

The AES50 standard specifies base sampling frequencies of 44.1 kHz and 48 kHz and multiples thereof, Midas and Klark Teknik have internally standardised on 96 kHz operation (twice the base sampling frequency of 48 kHz) for both SuperMAC and HyperMAC, to minimise latencies when converting between analogue and digital domains.

At 96 kHz, the latency per link of SuperMAC is fixed at six samples at twice the base sampling frequency, which for 96 kHz is 6 x 10.42 μs (one sample at 96 kHz), or 62.50 μs. Additionally, depending on the implementation of the interface to the SuperMAC core at both ends of the transmission link, a further delay up to of one base sampling frequency sample and one sampling frequency sample will be incurred converting to and from an internal data format such as I²S, although typically this can be limited to just the base sampling frequency sample in most implementations. SuperMAC can be transmitted over standard unscreened Cat 5 cable for short distances. For longer distances, up to 100 metres (the maximum specified by the IEEE 802.3 Ethernet standard for twisted-pair copper cables), the use of high-grade Cat 5e or Cat 6 cable is recommended.

SuperMAC provides accurate phase-aligned clock distribution utilising separate copper pairs in the Cat 5/Cat 5e cable for audio data and clock. This allows reliable, low-jitter clocks to be delivered to the end-points of the system. As digital audio systems develop from the current “islands” of digital electronics connected by analogue cables into fully digital systems, this ability to deliver high-quality clock signals with the audio will become increasingly critical.

Clock synchronisation is very simple to configure, units equipped with SuperMAC interfaces are either master (internally clocked) or slave (externally clocked). All that is necessary to create an operational audio network is to connect up the SuperMAC interfaces and select the clock source.

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 data frames.

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.

SuperMAC supports both dual redundant and N+1 redundant networking. Error and Link status information such as CRC error detection, clock synchronization status, link status and so on makes it very easy to provide health reporting to the user, and to implement redundant links with manual or automatic change-over.

SuperMAC has the in-built capability to relay auxiliary control data, including TCP/IP and similar IP-based data packets, at a data rate of 5 Mbit/s. The auxiliary data is embedded in the same frame as the audio data. This fixed allocation means that there is no risk of the audio streams being swamped by control data messages. The control data packet contents are irrelevant to the operation of the SuperMAC audio streams, so any format of control message received can be relayed.