[quadrifoglio]

Today I measured loopback latencies on my system, here are the results:

Saffire Pro 40

44.1khz ; 32 samples buffer size ; 305 samples / 6.916 ms latency ; Reaper reports 3.6/2.4

44.1khz ; 64 samples buffer size ; 368 samples / 8.344 ms latency ; Reaper reports 4.3/3.1

44.1khz ; 128 samples buffer size ; 496 samples / 11.247 ms latency ; Reaper reports 5.8/4.6

44.1khz ; 256 samples buffer size ; 752 samples / 17.052 ms latency ; Reaper reports 8.7/7.5

***

48khz ; 32 samples buffer size ; 304 samples / 6.333 ms latency ; Reaper reports 3.3/2.2

48khz ; 64 samples buffer size ; 367 samples / 7.645 ms latency ; Reaper reports 4.0/2.9

48khz ; 128 samples buffer size ; 496 samples / 10.333 ms latency ; Reaper reports 5.3/4.2

48khz ; 256 samples buffer size ; 3751 samples / 15.645 ms latency ; Reaper reports 8.0/6.9

I can work with any of those buffer sizes, 32, 64, 128, on my system this simply works.
Later tonight we will check this problematic MacBook Pro and I will post the results.

As for the smallest block size, we can play multiple files at 64 samples buffer size. As soon as we introduce one plugin, it starts crackling. But not every plugin, for example Waves SSL Channel does not make problems, but Fab Filter Pro L makes everything unusable. Well, all plugins with larger latency makes Reaper crackle.
It is the same with files located on external USB 3.0 HD, and with files on internal SSD drive.

I thought about bad SSD, and we will check it for sure, but everything else works normal, system is fast and responsive, Logic works like a charm at 32 samples buffer size.
When playing 13 44.1 16 bit audio channels in Reaper it shows 1.6 MB/s Read Speed, and around 1.8 MB/s write speed when we record all those tracks to another 13 empty tracks.
The same project and the same session on my bronze age i3, 4gb RAM, spinning drive laptop shows 1.98 MB/s Read Speed and 2.14 MB/s Write Speed. Maybe it is nothing, but I noticed this yesterday.