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

Paul Davis paul at linuxaudiosystems.com
Thu Nov 9 15:21:19 PST 2017

What version of Ardour is involved?

On Thu, Nov 9, 2017 at 5:56 PM, Markus Grabner <mg.2849 at w42.at> 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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