Latency or ???

128 samples is extremely taxing for your CPU, hence the artefacts. Try to increase the sample to 256 or 512 in logic. I usually use 256 when film scoring and 512 when mixing.

 

You latency is VERY low. Remember that sound travels about one foot per 1 ms. So your 4.9 ms latency is the same as if you were standing about five feet from a drummer. Would you ever notice the speed of sound delay over such a short distance? It is like the "lag" you get when speaking to some one across a large dinner table. It is SO CLOSE TO ZERO you can't notice.

What I'm saying is you have room for a larger buffer. You can make the buffer 4X longer and never notice the 20 ms latency (which is the same as a 20 foot speed of sound delay. Some musicians can detect a 40 ms delay. But most humans can't and it has to be over 50 ms before normal people can begin to notice.

The key to remembering is that speed of sound is about 1 foot per ms. If you think of it this way it is kind of nuts to worry about a few ms of "lag".

Try this experiment to determine how much "lag" you can detect. Get a buddy to play a steady beat with big wide hand claps that are easy to see. Stand close and you will hear the see the claps at the same time. Now walk 50 feet away and the sound will "lag" by 50ms. Do you notice? Try 100 feet and you should notice. But maybe your ears are golden and you can notice at 25 feet? Now you know your tolerance for latency.