Variable delay using USB interface and click test

I’m trying to reign in the USB latency on a two computer systems that I’ve install ardour 8.2 on. I’ve been following the guidelines set out in System configuration [Linux-Sound] as a starting point to attempt to get the USB to behave consistently.
One complication to my setup. I have Audio out going to one USB device and audio in (record) coming from several devices (Spark 40, Focusrite 2i2) For my experiments, I only been working on lining up the timing from Click → headphone → mic plugged into Spark40->USB In.

I’ve attached an example of this problem. I think I have the “calibration” figured out and then the machine shifts latency. You’ll note in the attached screen capture, it moved from lagging to almost perfect alignment.

In this second example. Using the same loop path as described above, the second computer gapped and inserted additional buffering in loop. Buffer sizes were a minimum of 1024 samples.

There may be links back to the following post: Inconsistent systemic latency measurements - without usb device restart

Hello and welcome! Does this also happen with just one USB interface connected? When using multiple devices you might want to read and Problem with audio interfaces - #5 by paul

Hi Jeremy: Good points. Technically my passing any analog through either the Focusrite / spark 40 would make it a USB microphone/source. I’ll keep reading and see what other configuration may work better.

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So I’m testing a revised workflow. All USB <-> Analog IO only goes through the focusrite. This device gets initially put in “looped back” (Headphone to line in) mode and the Ardour latency tuner seems to do a very good job of correcting it.

The Spark40 output is taken as analog from the headphone jack to the Focusrite line in. No further use of the its USB.

Subsequent overdub recordings use the Focusrite line in to record vocal or instrument (from the Spark) and the headphone jack to listen/align to the click / other tracks in the recording.

I’ll see how well this improves the timing. Thx!!

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