Two audio interfaces with Jack and Ardour? Your recent experiences?

Hello everyone, I found this video very interesting. I remember in the past reading somewhere that this approach could be problematic but that was an old article and both Linux and Jack have improved a lot since then. Has anyone used this approach recently? Is there a problem or downside to doing this? A friend o f mine and I have 2 input interfaces each so plan is to try it for drum recording using 4 mics with Ardour. Thanks in advance.

Forgot to add the video link :joy: , here it is

That might be problematic. As far as I understand the interfaces won’t be in sync with each other so you might get all kinds of phasing problems as the channels slowly drift out of sync from each other.

Four input interfaces are cheap and problem free, my recommendation is to always use only one interface with enough inputs for what you are doing. For example Behringer UMC1820 has 8 mic inputs and it costs less that 200 euros. By adding a Behringer Ultragain ADA8200 you can add 8 more Mic channels via Adat. I have both of these devices and this combination works in Linux and is dirt cheap. When talking about Behringer you need to add: the first device you get might be broken and you need to return it (this also happened to me :slight_smile:

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Its still interesting. I myself have 16 analog inputs (Scarlett 18i20 along with the OctaPre mkII via ADAT), but I have been looking for more MIDI inputs. This same method should work for a MIDI interface and something like the Scarlett, right? Thanks for sharing :slight_smile:

yes that will work. It does take care of out of sync cards by using SRC to correct. However, I would rather use the zita-ajbridge package which has zita-a2j instead of alsa_in and zita-j2a instead of alsa_out. The advantage with zita-ajbridge is that is has better quality SRC while at the same time using less cpu power. It also allows not using the SRC if you have a word clock link between your devices and they are synced. Another note is that jackd 1 has this built in already though jackd 2 does not yet.

Any time SRC is used, there is no longer a sample for sample path. The difference for most cases is not audible but I would not use sources across two device for stereo or other surround tricks. Left and Right for any source should always be on the same device. A second left and right can be from another device.

SRC = Sample Rate Conversion

MIDI is a different animal. You can use as many MIDI devices as you like and jack with a2jmidid will show all of them with no problems. It is even possible to use a midi port on a card and not use the audio part. for example I have an old pciaudio card that has a joystick/midi connector that I use only for MIDI no audio.

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Interesting, any links or videos you recommend on using the zita-a2j and zita-j2a ? Thanks in advance.

/usr/bin/zita-j2a -j AudioPCI-out -d hw:AudioPCI -r 48000 -p 128 -n 2 -c 100 &
Will add a set of outputs with as many as 100 channels (likely a lot less), 2 periods, 128 samples per period at 48k. These outputs will show up in jack as AudioPCI-out and expect the audio card to be hw:AudioPCI.

in a terminal type:
man zita-a2j
for more info… the man page applies to both zita-a2j and zita-j2a
as a note you generally want -p to be half of what jackd is using if the device will handle it. -r should be the sample rate the card sounds best at. It does not have to be the same as jackd, but 48000 is a good number for most anything unless you have a card that only does 44100 (they do exist and there are some others that are 48000 only too)

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Thanks, I will check this out. Another thing I can see myself using this is to workaround the fact that most of the affordable recording interfaces have a single headphone output (which is also the same monitors output) that I need to send to my drummer (I was trying drum recording yesterday for my first time, lots of fun) but I needed an additional headphone myself AND to be able to send him his own custom mix.

Upstream it is called zita-ajbridge. There is a Quick Guide from the original author. As well as a paper-presentation at the Linux Audio Conference about the tool. Both are rather technical and for background information.

@lenovens’ example as well as the man-page should be sufficient to get you started. (Note that zita-ajbridge can be used as drop-in replacements for alsa_in/alsa_out and also be launched fom qjackctl’s “after start-up” script).

Just FYI if you are looking for a cheap multi-input interface with 2 headphone outputs with separate volume controls, then take a look at Behringer UMC1820.

Forgot to mention: you can individually select Ardour outputs 1+2 or 3+4 for each of the two headphone jacks, so you can listen to two different mixes on UMC1820 also.

Thanks, I am aware of that kind of interfaces, just trying to make the most out of what we already have before buying something else. Actually the 2 mic recording test was better than we expected, the DIY acoustic treatment improved the sound of the room so now we feel more comfortable with the idea to save some money to improve it. Maybe we will spend some money on better mics and see how it goes before buying the bigger and better interface.

So my friend lend me his Behringer UMC202HD and I am pairing it with my Focusrite2i2 to compare zita-j2a and alsa_in, I just played bass thru a DI box with two outputs one for each interface. About zita-j2a, well it initially does perform better as it seems to have no noticeable delay between the main (jack) interface and the one coming thru zita-a2j but after some 10 or 20 min it stops working, it happened every time. On the other hand alsa_in does have a little noticeable delay but it is usable and it is been rock solid stable, left it running all night and I came back to computer and it is still working.

I am not sure if all these details about alsa_in and zita-a2j should be on a different forum or just a different area of this forum but my I idea was to share my comments for those using Ardour trying to use 2 interfaces. I will try to do my best to investigate and try to get zita-a2j running stable as alsa_in does and just come back with my final comments to avoid making this a ling thread.

By the way, the UMC202HD did a good job recording a drum set with two mics in a bedroom, I know Behringer gets a lot of bad comments but this interface gets the job done.

The only thing I can think of is that zita-ajbridge seems to work better is the latency is shorter than the jack server it is connected to. I like to run it at half… So if I have jackd set to 1024, then I set zita-ajbridge to 512.

I have had zita-ajbridge run over night or even for days without crashing. However you say it “stops working” which may mean it still looks like it is there but audio doesn’t pass through or something like that. My second card is the standard computer internal with tiny 1/8 stereo plugs which are in short supply around here.

It means no sound comes from the interface into Ardour. When running running zita-a2j using the -v (verbose) and the sound stops I get this recurring message over and over in the terminal…

Detected excessive timing errors, waiting 10 seconds.
Starting synchronisation.

I will try a different computer with a fresh install of UbuntuStudio, I have messed a bit with this one. By the way, QJackCtrl settings are sample rate 44.1k, frames/period 128, periods/buffer 2. When I launch zita-a2j I use same rate but periods set to 64.

I have been paying around with KXStudio and AVLinux and found that maybe my settings where wrong or too ambitious and I ran into similar issues. I have stick with AVLinux for my latest test then I tried Jack 44.1k, frames/period 512, periods/buffer 3, then for zita-a2j a sample rate of 44.1k, frames/period 256, periods/buffer 3 while also increasing the Ardour abuffers a little bit. So far I have done recording runs of 30 mins or so with the verbose option of zita-a2j and I have not had any audio drop or Jack/Ardour xrun, I think this is the winner settings to keep it stable with zita-a2j. Thanks a lot.