There are two things, AFAIK with portaudio. One is, that portaudio is a callback based library. PD uses it in write/read mode, which is definitely not optimal.
The second thing is that I headr rumours that portaudio by default is configured to have a pretty high latency. You might be able to change this in some portaudio file. (This is really only a guess).
Hi Guenter, these the results of my test with a quickly sketched PortAudio test program (it might not be too clean....)
Portaudio latency (with ASIO - RME HDSP digital loopback): hdsp buffer = 256 samples -> latency 516 samples (= 11.1 ms) hdsp buffer = 128 samples -> latency 260 samples (= 5.9 ms) hdsp buffer = 64 samples -> latency 132 samples (= 3.0 ms)
The choice of the portaudio buffer size doesn't seem to have an influence (tested with 16,32,64). D/A and A/D conversion (RME Multiface) adds another 60 samples (what surprises me a lot).
best greetings, Thomas