AUDIO interface = does it help or not? Options

[riket]

Hello.

Could someone help me understand who I must believe?
My config : iMac DV 400 / 512Ram., Cubase 4.1, electric guitar in audio from Roland GS6.

The scenario :
As I use PPG vsti together with audio guitar lines + other audios (vsti's like Sample Tank piano or other vsti's) my CPU hits the overload, audio cuts off, comes back after I disable one vsit or two to unstuck the stuff.
How can I improve the CPU performance without changing of Mac?
Is an external audio (UA-5 for ex.) a solution (attention, I mean while PLAYING PPG in live processing, not as printed lines, because with many printed audio tracks I have no problem, of course)??  
I have asked already 10 different dealers in Belgium, 50% say it IS the solution, 50% say it doesn't help at all in this case cause what you send to the extern. audio is ALSO processed by yr cpu, thus as much work for it than with an internal audio : it moves the problem to another place but won't help.
The others say the dsp of UA-5 will take so much in charge that yr CPU will work seriously faster, while the processing of the PPG play occurs on the external card, they say.
Does anyone have any experience with a configuration close to mine?
Thank you for any input.
riket

[macmax]

The Bad news is. VSTis use a considerable amount of CPU overhead whatever , because the cpu is doing the processing involved in actually generating the digital signal.
all the interface will do is convert from Digital to analogue and interface with the outside world.
It is true that a small amount of overhead will be saved doing this, but not enough t make a real difference.

Ok Good news time.
There are ways to reduce the CPU overhead by a significant amount.
1) as you finish each midi part for a VSTi , you can RECORD the Audio output, as a track and then free up a certain amount of CPU for processing The VSTi on the next track.
While each new track will consume a proportion of resource, it is less than the useage of generating Audio in real time from MIDI.
You may need to do a little nudging around of the audio once recorded, as it will have the latency recorded into it. So it will need compensating for.
Once recorded, you can mute out the midi track as well (Dont delete in case you want to edit) and then store them in a folder track where relevant.
Thus you reduce the MIDI overhead as well as the Audio processing overhead.

2) Get a processor upgrade from Sonnet.
AND use the above technique, that should seriously extend your capabilities.

3)
I have heard that OS9.1 has better USB support that is more efficient than 8.6, I cant immediately substantiate this, as i run 9.1 on ALL my machines. And i dont have a copy of 8.5/6 to test.
This will only be an issue if you do decide to go with a USB interface.
If your iMac-DV is the SE version you will also have 2 Firewire Ports, which would allow use of things lioke the MOTU 828 , which i recommend as Firewire has a Much greater Bandwidth, thus is less restricting in terms of channels and sample rates/bit depth.
I have heard, although again i cant substantiate, that firewire Audio interfaces impose a slightly lower CPU load, I have no idea why that should be so, or even if its true, So take it with a pinch of salt........
(given the larger data transmission requirements, i would have supposed the opposite to be the case......)

Hope i've been off use.
macmax