Bad sound when playing through Jack transport


-Jack 0.4.5
-Ardour 5.12.0
-Carla 1.9.13
-Loopcloud VST

If I simply connect the Loopcloud VST to Ardour via Jack, I can get the sound through Ardour just fine. However, If i sync them through jack transport, sound quality deteririorates substantially, anoying crackling ensues, as if many xruns would be happening consecutively. However, no x-runs shown by qjackctl.

Situation doesn’t improve when increasing frames per period.

What could it be?

Would appreciate some help.

Thank you in advance.

That jack version does not make sense. The two current versions are 0.125 from the original implementation (now referred to as Jack 1) and 1.9.12 from an alternate implementation of the API (now referred to as Jack 2, originally called JackDMP in case you see that name).

Are you perhaps using QJackCtl and referring to the version of that? If so that is just a utility for starting jackd, it is not actually related to the version of jackd, or even the jack audio project, it is completely independent, and you can use jackd without that application.

I cannot tell which top level topic this post was filed under, so I cannot see which OS platform you are using. Searching for Loopcloud (it would have been helpful if you had provided a link, I have never heard that app mentioned before) it appears to be available for Mac and Windows. I am more familiar with linux, so perhaps someone who has used this app before on the same OS as you can confirm, but…

How did you set up JACK transport sync in Loopcloud? I looked through the FAQ pages, and I do not see any indication that Loopcloud supports JACK at all. Perhaps Ardour was just free-running with regard to Loopcloud.

Also, did you try using the VST version? Right at the top of the FAQ titled “Using Loopcloud with your DAW” it states “If you are using Loopcloud with your DAW software, then you really should be using the Loopcloud plugin!” If you use a plugin then you don’t need jack at all.


Yeah, i gave you the qjackctl version number, sorry about that. The jack version is 1.9.12. I am on linux Ubuntu Studio. I am trying the VST version of Loopcloud, bridged thought Carla, It does work pretty decently, namely the BPM syncing, reponse to controls (play , rewind, etc) work fine, except for the quality-when-jack-transporting issue.

Oddly enough, upon further examination, audio quality seems to improve when increasing buffer size INSIDE Ardour (window>audio/midi config). However even when increased to, say, 4096 samples there is still some crackling. This only happens with Jack Transport. Simple playback of Loopcloud VST through Ardour works fine with no crackling at all at my usual setup (512 frames per second).

What could be the origin of this discrepancy?

Is there a native Linux VST of Loopcloud, or does Carla have the ability to load Windows VST (using Wine libraries, I would assume, if so)?

If it is using Wine to bridge Windows VST to linux perhaps there is something with unpredictable delay in wine. Just guessing I will admit, I have never tried running Windows plugins on Linux. Using Windows plugins on Linux is definitely one of those “use at your own risk” kind of endeavors, the Windows developers aren’t going to help you debug a problem that comes from something outside their control, the Linux developers can’t help much since the plugin is completely black box to them. Maybe you get lucky and some combination of Carla and wine developers can help. I feel bad, that doesn’t seem very constructive when I re-read it, but successfully running audio software on a platform where it was never designed to run is a difficult problem to get right in all cases.