Omnia .9 Installation & User Manual page 180

SYSTEM MENU CHAPTER 23 |
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Resyncs indicates that the time code on the majority of the packets we received do not match our expectation, and that we had
to resynchronize rather than try to adapt.
If you see Lost packets alone, packets are getting lost between the Livewire audio source and the Omnia.9. This is usually can by
faulty network cables or switches.
If you see Lost and Discarded both tick up in tandem, packets are arriving out of order. In this case, you can increase the Packet
Buffers slider until you instead see Late ticking up while Discarded and Lost hold steady. This works around the problem and
will yield glitch-free audio, at the expense of more delay.
The Sample Rate Converter and the FIFO buffer are one unit, and statistics include Overruns, Underruns, Margin In and
Margin Out.
Margin In is how many samples of free space we had in the buffer after we just wrote the last input frame. This number can go
negative, because the buffer is internally much bigger than it needs to be for a given Fifo Buffer setting. Why throw away good
audio if we have it, right? So, it has to go quite a lot below zero before we'd throw away an incoming block of audio and count it
as an Overrun.
Margin Out is how many samples of audio remained in the buffer after we pulled the last output frame. This number cannot
go below zero – if it did, that means there were not enough samples available in the buffer when we needed them, and we must
instead use silence. We count this as an Underrun. If this happens frequency, you will want to increase the Fifo Buffer setting.
Packet buffers is different from the FIFO buffer. Packet buffers instructs the Omnia.9 to hold back N livewire packets before
stuff their contents in the FIFO buffer, which guards against packets arriving out of order. As mentioned earlier, if Lost and
Discarded increment in tandem, a packet arrived out of order. It wasn't there when we needed it, so we substituted it with
silence and counted it as lost. It later arrived, but we didn't need it anymore so we discarded it. If that happens, increase Packet
Buffers until they start showing up as "Late" instead. That means "Late, but got here in time."
Of course, while we're waiting for a single late packet, we can't let its younger counterparts (which have already arrived) into
the Fifo Buffer because FIFO means First In First Out, meaning they will come out in the same order they went in. Thus, if fed
into the fifo in the wrong order, they would also come out the wrong order. And so we must wait, while the fifo potentially runs
out of buffer and has an underrun (and an audio drop-out). This is why the Packet Buffers and and Fifo Buffer controls are
separate in Omnia.9 MKII.