Latency in one file only

I wonder if anyone can cast light on this, or suggest what settings to look at. I recently decided to work again on a song I recorded last year. It has 29 tracks, mostly audio, one or two MIDI and FX tracks. When I went to add a bass guitar part, it had such latency I couldn't play accurately. I assumed it was something to do with my sound card (M-Audio 2496) and tried different buffer settings but the latency remained. By latency I mean the note I heard from monitoring came late, maybe a quarter-second after I'd played it. Enough to make it impossible to play in time. I then went on to a MIDI track and found the same issue. I closed this file and started a new one. No latency on audio or MIDI. Monitoring was easily good enough to play accurately. Reopened the original file, the latency was still there. I must have inadvertently changed something in this song file to cause this, as it doesn't happen in any other songs. I rarely change any settings in Reaper as I'm too scared of, well, things like this! I've had a look at Project Settings and a quick trawl through Preferences to see if there's anything obvious but it's quite difficult to compare every setting in two different files. Any idea where I should look for the cause?

Hi, Could the track that you have the problem file on have any fx on it? If so, bypass the fx. GL

It sounds like you aim to record an overdub monitoring through the Reaper mixing board. You dial your latency (block size) down to your acceptable setting for live work. Except it doesn't seem to be responding to the block size control? FYI If you insert a plugin with an inherent latency that is larger than the block size you set for the system, Reaper will add blocks of latency until that plugin can be run. (The other choices would be to silence the plugin or to deliver audio output from it laden with dropouts. Reaper is programmed to add blocks.) You may have a plugin in the project that has higher latency than what you need to set to for live recording. If yes, render the track in question to a stem so you can offline that plugin.

Thanks for your reply, Lugnut The new track I'm trying to add is just a straight bass guitar input through my mixer. 1) create new track 2) arm for recording 3) monitor input to ON No FX on this track, no sends either. I play and there's a delay in hearing it. The delay only happens in this song. It's the same for MIDI in this song. (By 'delay' I don't mean a delay FX, I mean that I don't hear the note as soon as I play it.)

Thanks Ser Is it worth going through every track that has plugins and disabling the plugins? I can give that a try and see if it makes a difference. I'll let you know when I've done it. UPDATE That worked! - I've disabled all FX on all tracks and the latency has vanished. Now to re-enable them one by one and see which one is causing it. UPDATE I found it, and it should have been obvious! I mentioned that this is an old song that I've decided to finish. At the time I was doing it I had just bought Ozone Elements, for mastering. I mistakenly thought you should add it as an FX on the master track. I don't do that at all nowadays, but I must have forgotten to look for it in this old song. Ozone was there on the master track as an FX, and as soon as I disabled it, the latency disappeared. Obviously all tracks feed the master track, and it takes time to process them there. Thanks very much both of you for telling me where to look!

Glad that you found it. :) Out of curiosity: how much latency did Ozone Elements add. I've just put Ozone 8 Elements on the Master and got a PDC of 721 (round up to 768 (256 * 3). That is about 17.4 milliseconds.

Hi Dark Star I don't know how to measure it, I'm afraid, but it was enough to make playing accurately in time to the track impossible.

You can see the latency value (strictly the Plug-in Delay notified by the plug-in) in any of these places (and disable it too): 721 samples is the value notified by the plug-in. Reaper rounds that up to the number of samples in an integral number of buffers (3 x 256 in my case).