[Ardour-Dev] how to precisely align the audio output of a Jack MIDI client in Ardour?

Robin Gareus robin at gareus.org
Thu Nov 9 20:56:00 PST 2017

Hi Markus,

It looks like you're sending and receiving data in the same jack client.

  your client -> Ardour -> your client.

This cannot happen in the same process cycle. Jack will break the cycle
and either run Ardour first or your client first. So a delay of 1 cycle
is expected.


On 11/09/2017 11:56 PM, Markus Grabner wrote:
> 	Hi!
> I recently made some effort to measure the latencies of my audio equipment to 
> get perfectly aligned capturing and playback with Ardour (version 5.11), and 
> so far it worked well. However, I failed at a task which I thought should be 
> one of the easiest. I have a Jack client which takes MIDI input and produces 
> audio output (actually LinuxSampler, but the same issue can be demonstrated 
> with the attached minimal Jack client and Ardour session). When recording the 
> audio output of the Jack MIDI client into an Ardour audio track, I noticed 
> that the signal is delayed by one Jack period, regardless of the latency set 
> by the client for its ports. When I change the alignment mode of the audio 
> track to which I'm recording from "Automatic (Capture Time)" to "Align With 
> Existing Material", the signal is recorded too early by (m-1)*n+o frames, 
> where m is the number of periods, n the frame size, and o the output latency 
> of the Jack server. Latency of the Jack MIDI client does have an effect now, 
> but only shifts the signal even earlier in time.
> To summarize:
> *) In "Align With Capture Time" mode, the audio signal created by the Jack 
> MIDI client is too late, and latency settings of the Jack MIDI client are 
> ignored.
> *) In "Align With Existing Material" mode, the audio signal created by the 
> Jack MIDI client is too early, and can only be shifted to an even earlier time 
> by setting the latency of the Jack MIDI client.
> So what is the recommended way to get frame-accurate recordings of the audio 
> output of a Jack MIDI client receiving input from an Ardour MIDI track (aside 
> from manually nudging the recorded regions)?
> 	Thanks & kind regards,
> 		Markus
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