[LAU] (Ardour) How to get rid of delay when recording ?

[Harry van Haaren]

On Sun, Feb 14, 2016 at 2:24 PM, jonetsu at teksavvy.com <jonetsu at teksavvy.com>
wrote:
> the web page it is mentioned, and shown, that an input and output (in
> this case from the mb audio interface, and USB) are not made to be
> connected together and doing so could/can damage the card.

In that case its a line output, and microphone input, which are different
levels.

> Then I have
> to ask before doing anything: is it possible to simply use a plain
> stereo RCA cable to connect the stereo out pair to the stereo in pair
> of a 1010LT card ?

So long as they're both the same level, no problem.
For the Art USB Dual Pre, just a normal guitar jack lead:
http://openavproductions.com/loopback_cable.jpg

> If so, then how is jdelay connected and told to measure these connected
> ports ?  The man page mentions to connect the jdelay in and out
> together and that's all.  I guess this connection is used as a
> reference to measure the actual audio connections. The web page doe snot
> mention any argument to jdelay. Will it detect which ports are
> connected?

jack_iodelay is "just" a JACK client. You connect it to whatever you want,
in this case, we wish to measure the soundcard latency:

1) Patch RCA cable system-output-1 to system-input-one
2) connect jack_iodelay output to system:playback_1
3) connect jack_iodelay input to system:input_1

The *output* of jack_iodelay (it generates a sine-wave) gets played
through the output of the audio interface, the analog signal is recorded
again by the input, which is passed to jack_iodelays *input* port.

jack_iodelay compares how many samples have passed since it sent
that output, and can very accurately calculate how much time has passed.


The resulting audio path of this setup:
software playback -> ADC -> DAC -> software record.

Recording & playback with Ardour is:
ADC -> software record -> software playback -> DAC.

Note that the overall amount of work done is the same: its only
in a different order. The latency measurement taken is the exact
amount of latency you will experience when recording music.


Hope that clears up exactly whats going on :) -Harry

--

http://www.openavproductions.com
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