Measuring Latency, Scarlett 6i6, DiGiGrid, etc.

[guitardom]

Originally Posted by Amack

Like Pro Tools HD Native and HDX with AVID interfaces, standard Pro Tools is capable of achieving “audible” tracking latencies less than 1ms (millisecond) at 96 kHz sample rates with some third party audio interfaces. These interfaces contain internal mixers which enable tracking without the delay added when passing the monitored audio signal thru the host computer/software.

The black arrows in the figure below represent the two audio signal flow options available for tracking with these types of interfaces – one directly thru the interface and the other thru the host software and computer. The figure does not show any details about the signal flow path(s). Such things as analog to digital and digital to analog converters, faders, auxiliary buses, plugins, effects processing, multiple inputs/outputs, etc. were purposely omitted. The effect of anything (plugins, effects processing, etc.) that adds additional delay to the monitored input – output path would cause an increase in the “audible” tracking latency.

When monitoring directly thru the Audio Interface, track playback delays caused by the output buffer, plugins, etc. will not be audible. So, when punching into a track, the effect of any plugins on the track will be heard during playback except during the actual punch-in (recording) process. HDX likely allows the effects of its resident plugins on that track to be heard during the punch-in process as well (in addition to any latency that they contribute). Does it? Does it also enable the simultaneous recording of the dry (pre-plugin) and wet (post-plugin) audio signals?

September 5, 2015 update/correction - Windows 12.1 added "Input Monitoring", it should be left in the default OFF/AUTO state when tracking. When PT's "Low Latency Monitoring " (LLM) is ON the record enabled track will be muted in PT and only the path thru the interface (upper path) will be heard when recording. If LLM is OFF both the record enabled track's input (delayed lower path) and the path thru the interface (direct upper path) will be heard during recording. The following table provides more details.

Post #171 of the “Measuring Latency, Scarlett 616, DiGiGrid, etc.” thread shows latency measurement procedures and results for Roland’s Studio Capture which demonstrate that it achieves 0.844ms of “audible” latency when monitoring directly through the interface. The Motu 1248 http://www.motu.com/products/avb/1248 claims a round trip host latency of 1.4 ms thru 32 sample input and output buffers. That says that if the host was bypassed, the “audible” tracking latency should be less than 1.4 – 2*32/96 ms = 0.733ms (comparable to HDX’s advertised 0.7ms). The Focusrite Scarlett 6i6, which uses an analog mixer, achieves 0.182ms.

The minimum H/W Buffer Size that PT currently supports at a 96 kHz sample rate is 64 samples (128 for HDX?). So, the minimum added delay going thru the PT host would be 2*64/96 ms = 1.33ms (2.66ms for HDX?)

Again, STOP with the HDX claims!!!! When are you going to understand that the HW Buffer size does not matter until you use Native plugins!!! It's all handled by DSP. Tracking with it set to 64 or 1024 does not matter, tracking latency is the same as long as no native plugins are being used!

Second, they did not "add" input monitoring. It has always been there (alt+k shortcut to toggle on and off). They just changed it from a universal to per track basis. Nothing changes except the ability to have tracks to monitor input and not record them.

[Amack]

guitardom,

Sorry if I didn't make it clear enough that HDX, like other third party interfaces with internal mixers and plugins/effects, can monitor over the low latency (0.7ms) upper path. It, also like they the others, can operate over the high latency lower path through PT (adding another 2.33ms of latency when native plugins are used with HDX). Thanks for pointing out the need for some clarification - please let me know if you still disagree.

Do you (and others) understand the table? Is it correct? How do the AVID interfaces that support LLM work with PT, PT HD native, and PT HDX?

Thanks for correcting me on the Input Monitoring thing!

Amack

Originally Posted by guitardom

Again, STOP with the HDX claims!!!! When are you going to understand that the HW Buffer size does not matter until you use Native plugins!!! It's all handled by DSP. Tracking with it set to 64 or 1024 does not matter, tracking latency is the same as long as no native plugins are being used!

Second, they did not "add" input monitoring. It has always been there (alt+k shortcut to toggle on and off). They just changed it from a universal to per track basis. Nothing changes except the ability to have tracks to monitor input and not record them.

[YYR123]

Why is thread still active ?

[Amack]

Apparently it was re-opened to move my "Low Latency Tracking without Pro Tools HD Native or HDX" thread to it. See post #253 in this thread.

Originally Posted by YYR123

Why is thread still active ?

[Matt Hepworth]

Not really. Native plugins are completely disabled on any armed/monitored channels during recording with HD TDM and HDX.

It's a completely different beast. Buffer is irrelevant when speaking of *recording* through plugins on PT DSP systems.

I certainly understand what your point is, but it doesn't apply to HDX, as HDX does not work in the manner you describe when recording, unless you trick it into doing so.

Originally Posted by Amack

guitardom,

Sorry if I didn't make it clear enough that HDX, like other third party interfaces with internal mixers and plugins/effects, can monitor over the low latency (0.7ms) upper path. It, also like they the others, can operate over the high latency lower path through PT (adding another 2.33ms of latency when native plugins are used with HDX). Thanks for pointing out the need for some clarification - please let me know if you still disagree.

Do you (and others) understand the table? Is it correct? How do the AVID interfaces that support LLM work with PT, PT HD native, and PT HDX?

Thanks for correcting me on the Input Monitoring thing!

Amack

Can you agree that setting DA/AD track insert with latency compensation on, using PT shows actual and reliable RTL figures? This is when PT uses full output and input paths to phase align tracks. There is nothing to hide using this method - all latencies present whereever have to be inluded!
Results are audible - 2 identical tracks are either aligned or comb filtered.
Am I missing something?