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Help Me Understand latency & compensation?


CwC Studio

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Hi folks

I'm trying to understand latency through a couple of different avenues and hoping someone could help with a little insight. 

A couple of different scenarios:

1. Using the i/o plugin to process audio through external hardware as a track / bus insert 

2. Using channel outputs to send to a passive summing mixer (to then process and sum) and then record back in

To test these scenarios, I set up a click track to send to the interface outputs, looped directly back into the interface inputs and recorded to audio tracks (i.e. no hardware processing, just round trip out and in). Zooming into the waveforms has given me different results (screen grab of results attached)

 

Scenario 2 is fairly simple in my mind. The round trip has caused the returned audio to have a small delay, i.e. track 1 is a few ms after track 4 (raw click). This I understand - there's inherent latency in the system and this method does not compensate - all good (although I'd love to compensate somehow)

 

Scenario 1 has me a bit baffled. In this test, I sent audio out via the i/o plugin. On one track, I did not use the ping function to compensate for latency. On the other track, I did use the ping function. On this track, the i/o plugin compensated with -80 samples which I find odd but it lines up with the raw track. With the track that did not use ping to compensate, the audio is actually early by a few ms.

For the attached screen grab , track 2 was sent via i/o plugin with latency offset at 0. Track 3 was sent via the i/o plugin with -80 samples of latency offset.

My questions are this:

1. What is it about the i/o plugin that causes the negative latency compensation? (could it be the interface and Mac OS is not communicating the correct round trip latency?)

2. Is this something that can be adjusted / fixed / messed with?

click latency test.pdf

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