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Old 09-12-2017, 03:13 PM   #1
MixR
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Default [Solved] Reaper Live Mixer Delay Comp Problem - please help!

I am trying to run Reaper as a processing machine on a slave computer connected to my main computer via MADI. The idea is to process live inputs with AU/VST plug-ins - treating Reaper as though it was a multichannel FX box connected to my Pro Tools HD rig. All tracks are monitoring input, there is no playback of any kind (Audio/VI). No recording is taking place.

Here is the problem:
When I try to use plug-ins that report a delay other than zero the whole thing falls apart. The PDC is not working as expected: The live audio on the tracks with zero latency plug-ins is not compensated (delayed) to remain aligned with the audio on the track with the extra plug-in delay.

The manual says this under 6.17 Plug-In Delay Compensation:

"For example, a display of 256/512 spls would mean that one of the FX requires a latency of 256 samples: REAPER rounds this up to a number of blocks based on your buffer size. All other tracks will be delayed to match the track with the greatest latency."

This is not true for live audio tracks. Presumably Reaper only delays playback tracks correctly?

I am new to Reaper and may well be overlooking something here. But it seems that there is no such thing as an Aux track so in order to monitor live audio through plug-ins I have to use track arm and input monitor?

Any help appreciated!

Last edited by MixR; Yesterday at 02:53 AM. Reason: making clear that no recording is taking place
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Old 09-12-2017, 10:52 PM   #2
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Its perfectly normal and unavoidable that for live usage plugins that introduce a noticeable delay will introduce an appropriate latency to the complete mix, as the (any) DAW needs to take care that the correct samples get mixed at any mixing point in the signal flow.

That is why e.g. ReaVerb features a "Zero Latency" ("ZL") check box that changes the algorithm to use up more CPU power to avoid introducing latency between the in and the out signal.

For Live Usage you simply can't use plugins that introduce a considerable latency.

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Old 09-13-2017, 03:27 AM   #3
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Thank you for your reply. Unfortunately it has nothing to do with my question.

My question is why Reaper does not apply PDC to the *other* audio tracks - the ones who's plug-ins are not causing extra delays?

Please see the attached screen shot from a Pro Tools session. There are four stereo Aux tracks procesing external audio. Aux 4's plug-in is causing the biggest amount of processing delay. All other Aux inputs are offset by the correct amount so the *entire* mixer remains in sync.

I am perfectly happy with plug-ins causing latency as long as the latency is compensated as you would expect - across the entire mixer.

Re-creating the above example within Reaper doe not work .It appears that in Reaper PDC is only applied to disk based audio tracks, *not* live inputs - unless I am doing something wrong of course in which case I am grateful for any help. I am new to Reaper so I may very well be overlooking something!
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Old 09-13-2017, 06:07 AM   #4
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Quote:
Originally Posted by MixR View Post
My question is why Reaper does not apply PDC to the *other* audio tracks - the ones who's plug-ins are not causing extra delays?
AFAIK, there is a way to configure Reaper to ignore PDC. This is (obviously) necessary when creating a loop somewhere in the routing, which otherwise is forbidden.

If you did not configure this, not handling PDC appropriately (i.e. synchronizing all tracks) would be a bug (but I did not check this recently).

OTOH, when you use a plugin with considerable latency and PDC is handled appropriately, live mixing/playing supposedly would very likely be impossible.

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Old 09-13-2017, 07:06 AM   #5
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Hi Michael,

thank you for your answer. I am not sure I understand: Are you saying it would be a bug if Reaper worked the way I described in my earlier post (keeping the all mixer channels aligned - even with extra latency)?

My plan is to simply use Reaper for processing - no live playing of any kind. I am simply running audio from my Pro Tools HD mixer to Reaper in order to use VST/AU plug-ins to expand my current Pro Tools HD rig.

Latency will be compensated for within the Pro Tools mixer. This latency is obviously dependent on the buffer size of the slave machine (Reaper). Everything will work fine if Reaper keeps it's mixer channels time-aligned. But as it does not do that (unfortunately) I have to look elsewhere I think.
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Old 09-13-2017, 08:14 AM   #6
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Your latency sits at the block size you entered.

Any plugins that have an internal latency of less than your block size are fine. PDC can adjust everything within that block size limit. The latency doesn't vary with different plugins. It sits at the block size and you need to use plugins that have less internal latency than your block size.

If you try to use a plugin that has a larger lag than the current block size you have set is when this breaks.

For live use, you have a minimum block size you can use because you need to keep any latency under the threshold of perception. Thus you are limited in the plugins you can use with such settings.
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Old 09-13-2017, 11:43 AM   #7
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Quote:
Originally Posted by MixR View Post
I am simply running audio from my Pro Tools HD mixer to Reaper
via what kind of interface ?

Quote:
Originally Posted by MixR View Post
in order to use VST/AU plug-ins to expand my current Pro Tools HD rig.
Sending audio back from reaper to Pro Tools ? Using Reaper as an outboard device ?

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Old 09-14-2017, 03:10 AM   #8
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via what kind of interface ?

I have 3x SSL Delta Link on my Pro Tools HD rig giving me 160 I/O. 64 of those channels are connected to the Reaper slave via MADI. The Reaper computer uses an RME HDSPe MADI FX.

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Sending audio back from reaper to Pro Tools ? Using Reaper as an outboard device ?
That is precicely what I am doing!
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Old 09-14-2017, 03:56 AM   #9
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Your latency sits at the block size you entered.

Any plugins that have an internal latency of less than your block size are fine. PDC can adjust everything within that block size limit. The latency doesn't vary with different plugins. It sits at the block size and you need to use plugins that have less internal latency than your block size.

If you try to use a plugin that has a larger lag than the current block size you have set is when this breaks.
That is exactly how I expected it to work. Except it seems to work slightly differently - at least if you are coming from Pro Tools.

For example (64 samples Block Size): Most plug-ins I have currently installed report 0 samples latency. I can insert as many as I want and this does not change at all. The Performance Meter shows 0 under PDC. When I insert a plug-in with extra latency (SPL Vializer MK2 in this example) the plug-in window shows "CPU 16/64 spls." PDC for that track changes to 64 in the Performance Meter.

If I understand the manual correctly this means that the plug-in takes 16 samples of extra latency and Reaper rounds this up to the nearest block size. If I change the block size to 32 samples the above changes to "CPU 16/32 spls" and 32 under PDC in the Performance Window.

What I don't understand is why the extra latency of 16 samples does not go away when I increase the buffer size? Is it a case where a plug-in basically adds an offset latency? I.e. 16 extra samples on top of the buffer size? I would expect a plug-in's latency to be an absolute number of samples and if the host has a smaller buffer size than that latency one would have to increase the buffer size in order for PDC to be working correctly. That is how Pro Tools works.

Which is also why I am expecting PDC to be applied to all other tracks in the project. With Reaper, however, it seems that PDC is applied on a per-track basis (as can be seen in the Performance Window) - which means that I will have to restrict myself to using plug-ins that work within one buffer's worth of latency. Otherwise things will get very messy as Pro Tools won't know that a certain track within the 64 I am bussing to and from Reaper has a higher latency than all the others.

Last edited by MixR; 09-14-2017 at 04:02 AM.
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Old 09-14-2017, 05:21 AM   #10
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edit:
Explaination from Justin below.

Last edited by nofish; 09-14-2017 at 06:16 AM.
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Old 09-14-2017, 05:47 AM   #11
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Quote:
Originally Posted by MixR View Post

The manual says this under 6.17 Plug-In Delay Compensation:

"For example, a display of 256/512 spls would mean that one of the FX requires a latency of 256 samples: REAPER rounds this up to a number of blocks based on your buffer size. All other tracks will be delayed to match the track with the greatest latency."
This is actually inaccurate -- REAPER implements PDC by looking ahead on the existing track, if possible, rather than delaying other tracks. When live monitoring, it can't look ahead obviously, so you hear that track delayed (but it will not affect other tracks since they are not delayed).
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Old 09-14-2017, 05:51 AM   #12
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I have just checked Ableton Live. It works in the same way as Pro Tools does:

PDC is applied to *all* tracks in the arrangement. Furthermore, the delay is absolute and does not get rounded up to the nearest buffer size. In my case from above the extra latency caused was 16 samples.

In Reaper this would have gotten rounded up to the next block size. In my case 64 samples. However, the buffer size I will normally be running when I am mixing will be higher, at least 128, possibly more samples.

The problem is that if I insert more than one plug-in causing extra delay the added PDC will spiral: 3 plug-ins with 16 samples of delay will cause 384 samples of delay at 128 Block Size; 768 samples at 256 Block Size and 1536 samples at 512 Block Size and so on.

I suppose Reaper's audio engine is just working differently to that of other DAW's.
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Old 09-14-2017, 05:55 AM   #13
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This is actually inaccurate -- REAPER implements PDC by looking ahead on the existing track, if possible, rather than delaying other tracks. When live monitoring, it can't look ahead obviously, so you hear that track delayed (but it will not affect other tracks since they are not delayed).
Thank you for clearing that up, Justin. Unfortunately this means that I will not be able to use Reaper in the way I had imagined - unless I restrict myself to using plug-ins with zero latency. I am not sure that this will be practical though.
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Old 09-14-2017, 06:40 AM   #14
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Quote:
Originally Posted by MixR View Post
When I insert a plug-in with extra latency
For a test in Reaper you can easily do (or even find) a JSFX plugin with variable latency, intendedly controllable the claimed PDC and the factually introduced latency.

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Last edited by mschnell; 09-14-2017 at 06:46 AM.
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Old 09-14-2017, 06:45 AM   #15
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Which is also why I am expecting PDC to be applied to all other tracks in the project.
I understand the DAW is supposed to handle the PDC at all summation points. Hence it might issue different delays in case of completely interdependent audio paths (if something like that is even possible).

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Old 09-14-2017, 06:48 AM   #16
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, so you hear that track delayed (but it will not affect other tracks since they are not delayed).
What will happen when you route such tracks towards a new track and sum the signals ?

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Old 09-14-2017, 06:51 AM   #17
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Unfortunately this means that I will not be able to use Reaper in the way I had imagined - unless I restrict myself to using plug-ins with zero latency. I am not sure that this will be practical though.
While to me it is astonishing as well that no delay is automatically applied in this situation, you can do that manually by using an appropriate delay plugin.

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Old 09-14-2017, 07:00 AM   #18
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While to me it is astonishing as well that no delay is automatically applied in this situation, you can do that manually by using an appropriate delay plugin.

-Michael
Thank you for the tip! I have found the plug-in "JS Time Adjustment Delay".

As A workaround I could have this plug-in inserted on all my Reaper tracks. That way I can reserve one extra block size worth of PDC. Once a plug-in with extra latency is inserted I can turn off the JS Time Adjust Delay on that track and the whole mixer will be in sync.
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Old 09-14-2017, 07:02 AM   #19
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What will happen when you route such tracks towards a new track and sum the signals ?

-Michael
You will hear the tracks out of sync with each other - one of them is delayed, the other one isn't.
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Old 09-14-2017, 07:05 AM   #20
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I understand the DAW is supposed to handle the PDC at all summation points. Hence it might issue different delays in case of completely interdependent audio paths (if something like that is even possible).

-Michael
There should at least be the option to keep all tracks in sync. This is the case in Ableton and Pro Tools. I assume most other DAW's behave in this way, too but I currently do not have access to any other ones.

Reaper might be the odd one out?

Worth investigating.
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Old 09-14-2017, 07:22 AM   #21
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There should at least be the option to keep all tracks in sync. This is the case in Ableton and Pro Tools. I assume most other DAW's behave in this way, too but I currently do not have access to any other ones.

Reaper might be the odd one out?

Worth investigating.
REAPER does a lot of things differently, including allowing free routing between tracks. Live with it, I guess?
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Old 09-14-2017, 09:31 AM   #22
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So...

PDC doesn't work on live input for what I consider obvious reasons. If the drums have no latency, and my guitar has like 1.28567 beats of latency, how do I play in time? Me, I play to the beat I'm hearing, not the beat that's 1.28567 beats later. Haven't heard that beat yet. And if you delay that drum track by 1.28567 beats, I'm still playing to the beat I'm hearing now.

So...

The time adjuster plug was going to be my suggestion. Any changes you make in realtime will STILL be heard late, but you could get the tracks themselves to line up. Just don't try to use negative numbers.

I'm wondering if it wouldn't be quicker and easier to just bounce the audio over to reaper, or just record to Reaper before adding plugs.
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Old 09-14-2017, 10:19 AM   #23
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So...

PDC doesn't work on live input for what I consider obvious reasons. If the drums have no latency, and my guitar has like 1.28567 beats of latency, how do I play in time? Me, I play to the beat I'm hearing, not the beat that's 1.28567 beats later. Haven't heard that beat yet. And if you delay that drum track by 1.28567 beats, I'm still playing to the beat I'm hearing now.

So...

The time adjuster plug was going to be my suggestion. Any changes you make in realtime will STILL be heard late, but you could get the tracks themselves to line up. Just don't try to use negative numbers.

I'm wondering if it wouldn't be quicker and easier to just bounce the audio over to reaper, or just record to Reaper before adding plugs.
I have edited the original post to make it clearer that there is no recording and/or overdubbing taking place. Reaper is solely used as a multichannel FX unit.

As far as I can see the problem I am having stems from the fact that, unlike other DAW, Reaper applies negative PDC. Pro Tools and Ableton delay all tracks (and busses, etc.) to keep them in sync with each other.

The suggested workaround using the Time Adjust plug-in works fine. I have created a default INPUT plug-in chain with three (bypassed) instances of the Time Adjust Delay.

Each instance is set to one of the block sizes I am working at. If a plug-in with extra latency is inserted on a channel I need to toggle the Time Adjusters on the other tracks active and the entire mixer stays in sync.

So far so good. The only thing I need to figure out now is how to select multiple tracks/mixer channels and toggle bypass of their specific inserts - ideally in one go. Does anybody have a tip for me?? :-)
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Old 09-14-2017, 02:29 PM   #24
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. Live with it, I guess?
I am a "technical" person and do have a lot of experience with Reaper in Live usage (did multiple plugins to support my Live playing setup).

So my statement is:

When really use Reaper "live" (on stage), the latency needs to be (1) very short, and (2) as short as ever possible. So it does not harm and in fact even is beneficial not to delay any audio stream to sync it with others.

The situation described here (using Reaper as an outboard effect with not-live mixing/rendering) is something that supposedly is not used very often, so we can live with what might be perceived as a workaround.

The Workaround would be using additional delay plugins. That is doable, the only drawback might be that it could be quite a pain to set them correctly.

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Last edited by mschnell; 09-14-2017 at 10:26 PM.
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Old Yesterday, 02:51 AM   #25
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The Workaround would be using additional delay plugins. That is doable, the only drawback might be that it could be quite a pain to set them correctly.

-Michael
After searching around the net and watching Reaperblog.net videos (massive thank you to Jon for this!) I have installed SWS Extensions.

It makes it very easy and transparent to see which tracks have aditional delay on them and offsetting the others accordingly - down to a couple of clicks and/or commands in console.

It is simply a matter of selecting the tracks and pasting the correct preset as an input FX to the relevant channels - no problem with the help of the resources window with the following workflow:

1) Sort tracks in Track Manager by PDC
2) Select tracks without PDC
3) using Resources window double-click to "Paste/replace as Input FX to selected tracks" the relevant preset to offset tracks/keep mixer in sync

Quote:
Originally Posted by mschnell View Post
The situation described here (using Reaper as an outboard effect with not-live mixing/rendering) is something that supposedly is not used very often, so we can live with what might be perceived as a workaround.
Maybe I am the only one using Reaper in this way. But Reaper is incredibly well suited for the task - compared to the Pro Tools system it replaces.
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Old Yesterday, 01:49 PM   #26
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Reaper is incredibly well suited for the task - compared to the Pro Tools system it replaces.
In fact after taking a look at the recent update I discussed with a friend and we both agree that Reaper is suited incredibly well for close to any task compared to close to any other DAW

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