Setting the various parameters involved with latency is
very important, regardless of the relative speed of the computer, and the exact values for the various parameters depend on the specific computer, so there is no universally correct set of values . . .
For the 2.8-GHz 8-core Mac Pro here in the sound isolation studio, I leave the key NOTION 3 parameter at the factory default value, which specifically has the Audio Buffer Size set to 256 samples, because if I increase it, then the problem you described is quite likely to occur . . .

Similarly, I keep the buffering in Digital Performer 7.24 (MOTU) small, where I set the Buffer Size to 1024; Host Buffer Multiplier to 2; and Work Priority to High, which works nicely . . .

[
NOTE: If you are observant, you will observe that the settings for NOTION 3 have the MOTU 828mk3 Hybrid selected as the output device, but "Built-in" audio is set for the output device in Digital Performer 7.24, and this is done because I have the system configured so that I can switch back and forth from using CoreAudio (a.k.a., "Built-in") to the MOTU 828mk3 Hybrid, which is done in part because the Melodyne Editor (Celemony) requires CoreAudio, and I use the Melodyne Editor. And when I am not doing ReWire from NOTION 3 to Digital Performer 7.24, NOTION 3 tends to work better with CoreAudio, since (a) NOTION 3 uses a non-standard pair of output channels for its Master stereo output track and (b) I tend to forget how to set it correctly for use with the MOTU 828mk3 Hybrid . . . ]
In both instances (NOTION 3 and Digital Performer 7.24), these are low settings, and this works because the 2.8-GHz 8-core Mac Pro is a reasonably fast machine with highly optimized hardware and firmware, including fast internal hard drives, so the parameter settings for other machines probably will be different, although in some respects the Mac Pro here in the sound isolation studio is slower than a new iMac, with the exception of the memory and hard drive busses and all that stuff, which for all practical purposes is the only actual advantage of a Mac Pro as contrasted to an iMac, although being able to swap internal hard drives easily is very nice . . .
Yet another reality is that due to both NOTION 3 and Digital Performer 7.24 currently being 32-bit applications, the Mac Pro here in the sound isolation studio typically runs at approximately 15 percent of its capabilities, which maps to using the equivalent of around 100 percent of 1 of the 8 cores at any given time, although the work typically is spread over 2 or 3 of the 8 cores since there is a tiny bit of multiprocessing being done, all of which is due to the 32-bit application workspace limitation, as well as to multiprocessing and multitasking considerations, where as a general rule digital music production software tends to be single-threaded or whatever, which is the consequence of (a) some of the work being so time sensitive that it must be single-threaded and (b) multithreading, multicore programming, and parallel processing require software engineers to have vastly advanced skills and expertise, which makes such folks not so easy to find at the dawn of the early-21st century, but so what . . .
So what! Another very important consideration involves the limitations of 32-bit application workspaces with respect to VST effects plug-ins and VSTi virtual instruments, where the high-level overview is that NOTION 3 can handle approximately 25 "heavy" VSTi virtual instruments in a single project or score, and the practical solution when you need more "heavy" VSTi virtual instruments is (a) to clone the original NOTION 3 score and (b) to use a
set of cloned NOTION 3 scores while keeping everything synchronized, which when done correctly maps to the ability to have 500 to 1,000 "heavy" VSTi virtual instruments in a song, with a key part of the strategy being to record the NOTION 3 generated audio as soundbites in Digital Performer 7.24 via ReWire, with this basically being is the strategy where you construct a song in layers . . .
For reference, sometime in the future when NOTION 3 and Digital Performer are true 64-bit applications and all VST effects plug-ins and VSTi virtual instruments are true 64-bit components, which includes the sampled sound libraries being higher resolution, it will be easy to overwhelm state-of-the-art computers, although it might take a while to discover how to do this . . .
Explained another way, no matter how it is done, it is
not so difficult to overwhelm a computer, so the key is to discover how to do a
lot of stuff within the constraints and capabilities of the hardware, firmware, and software . . .
For example, if sometime in the future there are computers which are trillions of times faster than the fastest supercomputers on this planet today, someone will have the idea of putting each musician of a symphonic orchestra inside a "microphone megapod" which has inner walls that look a bit like the compound eye of honey bee, where each individual "eye" is a separate and independent microphone, which might map having one million microphones for each microphone megapod . . .
But instead of having just one symphonic orchestra, the same person would have the bright idea of having 1,000 symphonic orchestras, each with 1,000 musicians, and then what you have is 1,000 times 1,000, times 1 million tracks, which since the microphones might as well be stereo microphones, maps to needing a Digital Audio Workstation (DAW) application that can handle 1 trillion stereo tracks, and best wishes on setting the latency parameters for that system, where the reason for having 1,000 musicians per symphonic orchestra is that it requires 8 musicians to play the "sparkled" notes for what otherwise would be one instrument, which makes little if any sense until you discover how I use the term "sparkled", really. . .
Really!
SUMMARYThere are a few scenarios that fit the problem you described:
(1) Your computer is entirely too slow and outdated, in which case I recommend getting a new iMac (Apple), where the least expensive new iMac will be very nice, since you can add some memory from Other World Computing to make it nicer . . .
(2) You are using more than 25 "heavy" VSTi virtual instruments and some number of "heavy" VST effects plug-ins in your NOTION 3 score, in which case I refer you to my ongoing topic on "Notion 3, DISCO Songs, and Sparkles" in this FORUM, which will be helpful no matter which operating system you are using, although the focus specifically is on how to do a virtually absurd festival of advanced stuff with a Mac, where the "virtually absurd festival" refers to the general concept of having 1,000 instruments for a song, which actually is
not so absurd as one might imagine, since fully "sparkling" an instrument requires 8 staves, hence if you divide 1,000 instruments by 8, then it is more in line with this being the number of staves required for a fully "sparkled" symphonic orchestra, or perhaps more correctly for 8 complete symphonic orchestras positioned in 8 locations within a spherical concert hall where you are sitting in a floating chair in the center of the sphere . . .
Notion 3, DISCO Songs, and Sparkles (Notion Music FORUM)(3) You tinkered with the Audio Buffer Settings, in which case you set it too high or too low, so put it back to 256 samples . . .
With a bit more information about what you are doing, it will be possible to provide specific advice on what is happening and how to solve the problem, which is fabulous . . .
Fabulous! 
P. S. This is Part 2, and there might be a Part 3, but it depends on how many cups of Massimo Zanetti Master Chef® coffee I enjoy, which for reference I make at the ratio of 1/2 cup of ground coffee to 12 ounces of water at the ideal brewing temperature of 200 degrees Fahrenheit, which works for me since I have the
full array of what I call the "South American Coffee Achiever Gene Matrix™", even though I am not South American and have never visited South America, and as a bit of a warning for those folks who do
not have the full array of the
South American Coffee Achiever Matrix, consuming as little as one cup of coffee this strong could be a fatal endeavor, hence is strongly discouraged . . .
