Dear customers,
about Mac OSX RAM Management:
as explained before by chriskard, physical memory is paged to the so called Swap-file (in 4096k blocks), whenever physical memory is being over subscribed. The swap file is located somewhere on the system HD (its estimated size is shown as VM = virtual memory). Continuous swapping will affect the system performance and the performance of all applications - errors might occur "without cause".
The situation will become worse when it happens that sample data is swapped! The access time of an internal HD is way too slow in order to play back audio samples smoothly (that is why the beginning of the samples is loaded into RAM - - the rest of the sample is streamed from HD). Result: samples wonĀ“t play back properly anymore = clicks and pops will occur.
(There is a mechanism called memory protection for data that should not be swapped, but to my knowledge this protection can be overruled by the OS).
Since excessive swapping makes an impact on the performance it is necessary to install more RAM to avoid it.
The actual number of page outĀ“s is displayed either in activity monitor OR in the last line of the header in Terminal when entering the UNIX command <top>. The UNIX command <vm_stat> provides more detailed information about the swapping activity of OS X.
Moreover OS X RAM Management tries to allocate free memory ideally, it will analyze which data is used frequently and give important data a higher priority (as chriskard already mentioned). This behaviour explains why VI and other applications appear to perform better with increasing time of usage and it also explains why OS X will require almost all RAM, no matter how much is installed.
Apparently Mac OS X RAM management is not optimized for RAM intense realtime operations which need to handle a large number of very short files.
@chriskard said:
I got the information from an Apple engineer that the more RAM you have installed the better, because when physical RAM is still free, the Swap File Technology starts to use this free ram for its page file. So the samples are just moved from the Real memory of the thread "VSL-Server" to another area in the physical RAM.
Yes!
Some customers said that problems with clicks and pops would not occur with EXS. But most EXS programs arenĀ“t as large as Vienna Instruments matrices or presets can be! Therefore significantly less RAM is needed and its rather unlikely to run into swapping problems. We did some tests with EXS where we forced the system to swap data from EXS and it showed the same behaviour like VI does when physical memory is overwritten (clicks and pops).
The only solution_at the moment_is to add more RAM (if possible). Hopefully the situation will change with upcoming operating systems and improved memory protection- and we are also investigating in order to find a solution (which might however reduce the possibilities in VI to load many samples).
It is also recommendable to use VI as efficiently as possible and to create your own customized matrices and presets out of the patches you really need for your arrangement and to remove all unused (!) playing techniques. The factory presets are extremely "RAM intense" and therefore they are not always the best choice - but they are great examples for showing the keyswitch-possibilities and functionalities of VI programs.
Besides all of this we mentioned that VI does not perform as good in Digital Performer 5.12 as it does in Logic Pro 7.2.3 or Cubase 4.
Best regards,
Maya VINSON
