Old 09-18-2009, 04:37 AM   #1
DaveG
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Default PDC ???

I'm confused by the way REAPER compensates plugins that add delay. Can someone please explain how REAPER actually handles PDC and what the actual latency ends up being.

Tanks David
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Old 09-20-2009, 01:31 AM   #2
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REAPER automatically doubles your system latency regardless of if the plugin itself only adds 1 sample of latency. It has to do with the way it processes audio blocks, and is one of the reasons why I am looking into something else because it makes tracking with the SSL e-channel impossible unless you can deal with the latency (i can't)
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Old 09-20-2009, 04:15 AM   #3
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As far as i'm aware the overall latency is never bigger than the channel with the most latency on it though. There are ways round large latencies but i'm not the one to tell you about it since i run my system at 64 buffer and don't really use large latency plugs apart from linear eq's.

Hopefully someone else can chime in and offer a way out.
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Old 09-20-2009, 04:39 AM   #4
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Thanks, that seems to be my experience. I imagine that other DAW's only add the the actual plugin latency.
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Old 09-20-2009, 05:53 AM   #5
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I remember a comment somewhere on this saying that doing it this way dramatically improves performance. But maybe we should get a choice at somepoint
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Old 09-20-2009, 06:30 AM   #6
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Quote:
Originally Posted by future fields View Post
REAPER automatically doubles your system latency regardless of if the plugin itself only adds 1 sample of latency. It has to do with the way it processes audio blocks, and is one of the reasons why I am looking into something else because it makes tracking with the SSL e-channel impossible unless you can deal with the latency (i can't)

So what exactly do you mean by "doubling the latency?!
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Old 09-20-2009, 06:44 AM   #7
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Originally Posted by adXok View Post
So what exactly do you mean by "doubling the latency?!
I think it adds another block of buffers eg. if asio buffer is set at 64 and plugin ads one sample of latency Reaper increases latency to 128 samples. Is this correct?
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Old 09-20-2009, 08:47 AM   #8
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Quote:
Originally Posted by DaveG View Post
I think it adds another block of buffers eg. if asio buffer is set at 64 and plugin ads one sample of latency Reaper increases latency to 128 samples. Is this correct?
More or less.. but just for that channel, when monitoring.

Note that as far as I know there's no real way around this for any application (when dealing with blocks of audio, no software can add "just one" sample of latency).

However, the situation where you have 3 plugins in series that each add 1 sample, could be improved (REAPER would add a few ASIO blocks of latency to that track, whereas the theoretical minimum latency added would still be one ASIO block).

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Old 09-20-2009, 09:38 AM   #9
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Is there a way to disable PDC in Reaper?

I could actually get around all of this if I could disable PDC, set up my template with the 1-sample e-channels, and then manually offset where i need to. The rest of my plugins are zero latency.

EDIT: might not even have to offset for 1 sample. I know people that use PTLE that just throw them on there and dont even bother to offset because 1 sample latency doesnt cause any audible differences.
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Old 09-20-2009, 03:16 PM   #10
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[QUOTE=future fields;375842]Is there a way to disable PDC in Reaper?
[QUOTE]

A per-VST instance option for "disable PDC" might be coming soon
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Old 09-20-2009, 06:41 PM   #11
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Wouldn't it make sense if REAPER did the realignment of the audio streams to compensate to for plugin latency instead of adding extra buffers.
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Old 09-20-2009, 07:28 PM   #12
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Reaper is frighteningly flexible, as it allows people to arm, record, add tracks, add fx, change automation modes, add parameter modulation and so much more, all on the fly, that I imagine this block based approach is necessary.

Perhaps this flexibility will mean that Reaper will not do what Logic does, which is running unarmed tracks at a latency of 1024 and the armed tracks at whatever you picked.

And when it comes to turning PDC off, 3.11 has just come out and whaddaya know, it's in there per-instance .
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Old 09-20-2009, 10:50 PM   #13
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I see that, but can't find where the option is...
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Old 09-20-2009, 11:40 PM   #14
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Default i cant find the pdc off per vst from 3.11

Quote:
Originally Posted by Justin View Post
More or less.. but just for that channel, when monitoring.

Note that as far as I know there's no real way around this for any application (when dealing with blocks of audio, no software can add "just one" sample of latency).

However, the situation where you have 3 plugins in series that each add 1 sample, could be improved (REAPER would add a few ASIO blocks of latency to that track, whereas the theoretical minimum latency added would still be one ASIO block).
i cant find the new pdc off, its actually i believe not there?

anyone found it?

also: if one track has a 1 sample plugin, isnt the ENTIRE MIX delayed one block relative to the input sample (when input monitoring) with default PDC?

because your saying that that the one channel would be the only one delayed, then its out of phase with the rest!

in realtime streaming, (input monitoring), and PDC on, doesent reaper delay the entire tracks by that channels delay, so theyre all in sync?

and turning PDC OFF in this instance, wouldnt THAT make only the one channel delayed and the rest coming earlier? thats what i want, IE, i have a 64 sample delayed 'allocator light' in the master section, so everything mixed into the master will be delayed, but i have 4 monitor receive tracks (receiving sends from the rest of the board) earlier on in the mixer that then send out to their own hardware out and do not get to the master section. i would like these to remain NOT delayed, whereas now they are.
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Old 09-21-2009, 01:42 AM   #15
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Quote:
Originally Posted by evanrabby View Post
i cant find the new pdc off, its actually i believe not there?

anyone found it?
Rightclick on the inputs/outputs button in the plugin wrapper
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Old 09-21-2009, 02:09 AM   #16
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that's really neat, using reafir with no added latency and such, what do you lose doing this though?
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Old 09-21-2009, 04:40 PM   #17
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it works!!!

ok, as i said: with pdc off on a channel (in my case the master section), the entire mixer will have no delay, EXCEPT the channel with the plugin that has latency. ONLY that channel, will be delayed by the actual delay amount added by that plugin

it doesent magically stop the plugin from having latency, it just stops the syncing up of all other channels by delaying them all by the longest additive latency of any channel, as is done with PDC, so that the output of all channels arrive at the same time. it stops that so in my case, i have a delay on a plugin i have to use (a crossover) on the master for a live show, which is front of house sound, which is already 10 to 30 feet or more away from the band (delayed) so its not noticeable, BUT, the stage monitors, which send out through another channel on the mixer, and have no delayed plugins, arrive without that delay. DJs especially can notice 10.5 ms total latency, but when i can turn off PDC for the latency ridden master plugin, now the stage monitors are delayed by 128 samples less (2x the delay of the master plugin 'round trip') so they only hear 7.5 ms, the latency of my asio buffers only, which starts to be short enought that they dont complain....

yay!
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Old 09-21-2009, 05:20 PM   #18
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So the trade off of having some material technically out-of-sync during your performances doesn't have any negative impact? Basically, you can't hear the out-of-syncness?
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Old 09-21-2009, 05:39 PM   #19
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I'm guessing it could potentially cause phase issues when using different delay times on the same sound source. But other then that, anything under 20ms is not noticeable to human hearing as 'out of sync'.

For example: When the bas guitar note hits 20ms later then the Kick, because of latency differences, no one in the audience will notice it.

I think...
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Old 09-21-2009, 05:48 PM   #20
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Quote:
Originally Posted by future fields View Post
So the trade off of having some material technically out-of-sync during your performances doesn't have any negative impact? Basically, you can't hear the out-of-syncness?
correct. with pdc off, the outputs to stage will have one latency, and the outputs to front of house will have a little more. but the front of house speakers, say you are at mid stage, are 20 feet or more from you, so the sound is already delayed by 20 or 30 MS, plus wall reflections in the room or even outdoors come back later.

whereas, the stage monitors are usually 6 feet or less from you, and with a dj sometimes only 3 feet, and if they use headphones, they hear their source material right away, and can hear any delay between that and the live monitor 3 feet away. and musicians with in ear monitors that i feed them can hear any delay between their voice and the in ear right at their ear. so these mixes need to be as latency free as i can get.

same in the studio, i find that headphone mixes with only 7.5 ms delay are unnoticeable to almost everyone, whereas say a plugin brought it to 10.5, it is just over the wire for someone with a drum machine to hear it.

however, once again as the engineer, i can monitor in a separate room and id have no idea that there is a delay if i had some latency plugins on in the master section, since i only hear the reproduced sound, and even if im listening through headphones in the same room, i can tolerate hearing a little more delay since im not the performer.

this means i can now add fx with latency in subgroups and on the master while tracking, and it wont be heard now by the musicians who are tracking!
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Old 09-21-2009, 09:30 PM   #21
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is there a way to globaly disable PDC or to disable it in a project and save it as a template?

and also, could one expect any negative artifacts from running a 1-sample latency plugin without any PDC?
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Old 09-21-2009, 09:51 PM   #22
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1 sample wouldnt even be a phasing issue, except on absolutely identical data, IE a null test.

i believe PDC is only per vst, i couldnt find any other setting.
and its only per instance, and not a global setting for the plug itself.

this is definitely good to have per instance, but its true that for my use id like it disabled globally. i happen to know which plugs cause latency, and the only drawback is that if i add one on the fly, i notice it requires a save and then reload project for a per instance pdc to go into effect. that means if im running a live board, i have to have all delayed plugs preloaded that i expect to use.
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Old 09-21-2009, 11:29 PM   #23
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phew the disable PDC option has really saved my butt

thank you!
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Old 09-22-2009, 12:46 AM   #24
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Quote:
Originally Posted by evanrabby View Post
...this is definitely good to have per instance, but its true that for my use id like it disabled globally. i happen to know which plugs cause latency, and the only drawback is that if i add one on the fly, i notice it requires a save and then reload project for a per instance pdc to go into effect. that means if im running a live board, i have to have all delayed plugs preloaded that i expect to use.
You could save an FX chain for each of those plugs with PDC disabled. So you can load them on the fly.
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Old 07-06-2012, 01:20 PM   #25
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Just out of curiosity, is there a DAW which audio engine doesn't have the doubling latency issue?
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Old 07-06-2012, 04:36 PM   #26
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audio in from sound card has one latency, audio out to sound card also must have some latency. each requires going thru the computer which has many tasks to do and requires that latency time. (this all excludes hardware/soundcard asio direct monitoring of course).
the daw only creates processing requests that your computer has to provide. the daw itself Adds no latency. if your computer required less than half a sample or so of time to process, you would be back to hardware only latency, whereas when computer requires say maximum 127 samples or so, including getting the data from the sound card, and writing it back until it arrives At the pci bus output, then your soundcrd driver will have to create buffers to make sure no samples get lost.
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Old 07-06-2012, 09:58 PM   #27
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I know something about how latency works, i haven't asked "Is there a daw without latency?", i've asked "Is there a daw without the doubling latency issue?".
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Old 07-07-2012, 12:23 AM   #28
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Quote:
Originally Posted by ThePriest View Post
Just out of curiosity, is there a DAW which audio engine doesn't have the doubling latency issue?
Pro Tools.

PT is sample based. If the longest latency of a plug-in chain in a session is 30 samples, the maximum compensation value will be exactly 30 samples. This is separate from the throughput latency of the hardware.

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Old 07-07-2012, 01:57 AM   #29
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what do you mean then by "the doubling latency issue"
i was referring to how whatever the soundcard latency is in samples in your driver, it is always double that "round trip", ie in to out, as a neccesity of these host based systems
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Old 07-07-2012, 02:40 AM   #30
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Quote:
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what do you mean then by "the doubling latency issue"
I think he was referring to post 2, 7, & 8 in regards to block based audio processing.

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