Knowledgebase: Audio Interfaces
How many Firefly 808 units can I daisy-chain at once?
Posted by Rick Shao on 16 November 2015 06:26 AM

The short answer is: it all depends on the sampling rate you use.

The maximum data rate of the IEEE1394a (FireWire) interface on the Firefly 808 and Firefly 808 Universal is 400 Mbit/sec This means that 200Mbit can be sent every second in each direction direction (ie. Half duplex).

When a sampling rate of 192kHz is selected, 32 samples are sent for every ISO packet. We have 8000 ISO packets/sec. Every sample has 4 bytes.

Practically, the usable bandwidth for ISO traffic is only 70% of the total. So 70% of 400MBits/sec is equal to 280MBit per second is equal to 140MBit per second in each direction. Size per channel: 4 x 8 x 32 x 8000 + (8000 x 20 byte Headers) = 8'352'000 bit/sec => 140Mbit/sec/ 8'35 Mbit/sec = 16.76 channels (each direction)

So to summarize and simplify the situation, the maximum numbers of channels supported by IEEE 1394a (FireWire) are:

  • At 192kHz Sampling Rate = 16 channels (or two Firefly 808s)
  • At 96kHz Sampling Rate = 32 channels (or four Firefly 808s)
  • At 48kHz Sampling Rate = 64 channels (or eight Firefly 808s)
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