Impact on CPU processing power
OASYS PCI Website
Contents
Host Processing in Patches & Effects
Audio I/O
All bus-mastering audio cards, such as the OASYS PCI, work in basically the same fashion. The card reads and writes audio data directly to and from the main RAM, bypassing the CPU. This process is known as Direct Memory Access, or DMA.
This means that the CPU doesn't do much at all to make the audio I/O itself happen, although the DMA transfers do take up a very slight amount of bandwidth.
The CPU still has to do all of the normal audio tasks, such as dealing with the hard drive, mixing, effects, etc.
Also, the more inputs and outputs you use, the more work the program's mixer has to do. Depending on the audio program being used, the work required to generate each output is roughly equivalent to playing back a single track from disk.
Some programs, such as Cubase VST, allow you to specifically enable and disable inputs and outputs, so that you can adjust the amount of processing power spent on the mixing process. Other programs, such as Digital Performer and Deck, automatically enable and disable inputs and outputs as necessary.
Because of the additional work required to handle additional inputs and outputs, one should expect to see slightly less CPU performance when using a multi-channel card (OASYS PCI, 1212 I/O, AW8, etc.) than when using stereo audio hardware (AMIII, Apple Sound Manager with built-in I/O, etc.). In general, the difference should not be very great - but with slower computers, using additional inputs and outputs may cause a noticeable difference in performance.
Audio Buffer Size/Latency
Latency is adjustable from 1.5ms/3ms to 12ms/24ms
The Audio Buffer Size parameter sets the size of the buffers used when sending audio data between the OASYS PCI and digital audio programs. The smallest setting of 64 samples is equivalent to about 1.5ms output latency (for CPU-based software synths), or about 3ms input-to-output latency (for CPU-based effects). The largest setting, 512 samples, is equivalent to about 12ms output latency, or about 24ms input-to-output latency.
You can set the Audio Buffer Size in the ASIO Control Panel, or in the OASYS PCI Editor's Audio Settings dialog. After changing this setting, you'll need to reboot before using the OASYS PCI.
Audio Buffer Size affects CPU processing power
Smaller settings allow you to decrease CPU input-to-output latency, at the expense of slightly higher CPU loading.
Larger settings allow you to maximize CPU efficiency, at the expense of higher CPU input-to-output latency.
Depending on the speed of the CPU, the amount of host-based plug-ins you are running, the speed of the audio disk, and other factors, some computers may require higher Audio Buffer Size settings than others. You may need to experiment to find the best setting for your system.
Audio Buffer Size does not affect OASYS PCI synths and effects
The Audio Buffer Size affects only CPU-based synths and effects. The amount of time that it takes to trigger notes when playing OASYS PCI synths, or to route live audio inputs through OASYS PCI effects, is unaffected by the Audio Buffer Size.
Host Processing in Patches & Effects
Most OASYS PCI Patches and Effects use almost no processing power on the CPU. A few, however, may use the main CPU for small amounts of controller processing, such as LFOs. These algorithms will increase the CPU processing load by a small amount, which may be noticable on slower computers. You can use the OASYS PCI's Resource Monitor window to see the amount of CPU processing power being used.
Copyright 1999-2002 Korg Inc. FAQ Version: 8/19/02