MADI interface card, distorted audio?

Summary of the defect:

Using MADI in slot 4 of the Gemini system. When a physical MADI loopback is made in slot 4 (either BNC or Fibre) and a tone is routed from an AEB to MADI and then MADI to an AEB for monitoring, the tone has what appears to be a higher frequency modulating on the sine wave tone.

Reason for the defect:

The problem was found to be timing problem where the receive buffers on the MADI card switch memory sections right at the point where the buffer contents is selectively copied to the transmit buffers. It is consistently slot 4 because the MADI stream is clocked by Gemini. If the MADI stream comes from a different source, it could happen elsewhere (not necessarily slot 4) and it will also change in behaviour.

The solution:

Update to the FPGA firmware for the MADI card, fixed in version V6 (July 2019)

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