2 interfaces, 2 jackd, couple them

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khz
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Re: 2 interfaces, 2 jackd, couple them

Postby khz » Thu Nov 28, 2019 7:50 am

The different audio/MIDI interfaces must be synchronized with each other.
khz wrote:Synchronisation your cards: with SPDIF, word clock or an internal sync port.
Is there anything about this in the manual of your used sound card?
(Personal, unverified and possibly false assumption: "? I think you need to synchronize the soundcards over one of the possibilities mentioned above. If it doesn't offer your sound card it won't work. The audioadapter does not do this. ?") IMHO
https://en.wikipedia.org/wiki/Word_clock
https://www.rme-audio.de/english/techinfo/sync.htm (German: https://www.rme-audio.de/techinfo/sync.htm); (https://www.rme-audio.de/download/hdspeaio_e.pdf)
http://manual.ardour.org/synchronization/
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merlyn
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Re: 2 interfaces, 2 jackd, couple them

Postby merlyn » Thu Nov 28, 2019 3:28 pm

khz wrote:The different audio/MIDI interfaces must be synchronized with each other.

Not many soundcards have that option, especially not budget USB cards. alsa_in, zita-a2j and audioadapter are ways of using multiple soundcards that don't have word clock or S/PDIF sync.

I have found that alsa_in is quite rubbish, zita-a2j is better and audioadapter so far has been usable, even for recording. zita-a2j is OK for a simple monitor, but fell down when I tried to use it as an input to Ardour. audioadapter works as an Xrun free input to Ardour so far. I've had three soundcards going at the same time -- one PCI card as the master, a USB synth through audioadapter and a USB interface with zita-a2j.

How can two or more cards that don't have a sync input be synced? -- They can't.

The solution is to let them drift out of sync and resample the slave card. That is what those three bits of software do with varying degrees of success.

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Re: 2 interfaces, 2 jackd, couple them

Postby tavasti » Fri Nov 29, 2019 7:05 am

merlyn wrote:zita-a2j is better and audioadapter so far has been usable, even for recording.
...
The solution is to let them drift out of sync and resample the slave card. That is what those three bits of software do with varying degrees of success.

1) Is audioadapter also doing resample?
2) what happens if clocks run out of sync?
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merlyn
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Re: 2 interfaces, 2 jackd, couple them

Postby merlyn » Fri Nov 29, 2019 2:15 pm

First of all I should probably say that audioadapter does not turn two Scarlett Solos into a 2i2 :D

If you want four inputs a four input soundcard is the best solution. If you already have two soundcards and want to use them together audioadapter lets you do that. I use audioadapter to allow me to record my guitar synth over USB. The alternative would be to use the synth's analogue outs into my soundcard's analogue ins. There is no option for sync with my guitar synth.

tavasti wrote:1) Is audioadapter also doing resample?

Yes. It uses Secret Rabbit Code. To avoid using an anti-aliasing filter I set the master and slave cards at the same sample rate, so the quality of the filter is not relevant.

tavasti wrote:2) what happens if clocks run out of sync?

I think the developers would assume the clocks are out of sync. The two clocks are running at a fractionally different speed and phase. The rate will be (very nearly) constant on both, so all three implementations have a calibration stage at the start, where the difference is measured and calculated out. In addition to the JACK buffer there is now a resampling buffer on the slave input introducing extra latency.


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