From: Jonathan W. <jw...@ju...> - 2013-10-12 10:54:04
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On Sat, Oct 12, 2013 at 12:37:43PM +0200, Arnold Krille wrote: > Hi, > > On Sat, 12 Oct 2013 00:40:26 +0200 Thomas Orgis > <tho...@or...> wrote: > > I don't see that mentioned in the documentation (neither wiki, nor > > `jackd -d firewire --help`; also no section for firewire in `man > > jackd`). Can one specify two devices in order with the -d parameter on > > jack command line? > > > > jackd -d firewire -d hw:0 -d hw:1 > > > > Or are they just sorted by some other means? > > They are sorted in semi-random order. Meaning the ordering 'could' be > stable but is not guaranteed to be. > > But why do you care? > FFADO aggregates all devices found by default. And last time I checked, > it created port-names including device-specific details (like name or > guid). So regardless if the device is "first" or "second", sync-master > or sync-slave, the ports of that device (or one of the alias-names) > should always be the same. The device-specific port names (at least when using jack1) are in the port aliases. The actual names are generic: the names are "system:capture_1" and so on, while it's the aliases with the device-specific names: firewire_pcm:C0_000a350076e71193_cap_analog-1 etc. The difficulty is that the aliases are not visible in some software, which means you have to know which generic system port name corresponds to the channel on the desired device. For software which knows about the aliases and makes them available to users, I agree that the guid-based aliases should not change when a different device is added. > > Bonus question: Are there experiences about synchronization behaviour > > of the Edirol boxes? I am playing safe by linking them via S/PDIF (the > > initial clock coming from a stereo A/D connected to FA-101 input, then > > FA-101 output to FA-66 input). Are they expected to play nice without > > that connection, being in sync via firewire? > > I think (I don't have the devices) when both are edirol, they can use > the same fw-clock for syncing. So you get sample sync without extra > connection of the devices and without loosing one spdif-in/out. Ah. I was not aware the BeBoB platform could derive the audio clock from the firewire bus clock - thanks for the information. I wonder what the jitter is like though, but I guess this could be minimised through a hardware PLL (which would be needed anyway to derive multiples of 44.1 kHz from the 24.576 MHz bus clock). How does one tell the devices to sync like this in preference to their internal clock? Do the Edirols just do this by default? Regards jonathan |