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4. low-latency audio I/O for Windows (3)
If you want a "standard" interface, I think that you'll have the best
results using RME or Motu products, and buying the interfaces with a PCI
card (or PCI Express) and an external rack unit (communicating each
other using a proprietary bus and format), and not with firewire or,
even worst, USB connections.
RME and Motu offer products with an integrated DSP (for example, in the
Motu products is called Cuemix DSP) for the routing of the IO: this is
usually useful if you want to automatically route an input to an output
without processing it, and in this case has absolutely no perceivable
latency. Although, these DSP for the routing can help even when you need
to do some internal processing, but they can't achieve 0 latency...
The problem is that the latency is also given by your system (computer)
and by the software you are using. The input-output buffer size is
essential: if you have a really short buffer, you system will have to
work much more, but the latency will be less, while if you have a big
buffer, the system will be more "relaxed", but you'll have bigger
latency. Nowadays, it's a good habit, for playback systems or for
processing which does not require realtime performances, to use a IO
buffersize of 512 samples, which means nearly 10ms of latency: this is
of course audible if you are trying to do direct processing and
monitoring in realtime.
Then, the software you are using is another really important thing to
consider: using MaxMSP, for example, you'll have to choose a vector
size, and this means the same thing of the buffer size explained before.
I think that with one of the two interfaces listed before (RME and Motu,
with the PCI or PCIe card), with a fast PC and a good amount of RAM, and
with a well calibrate software for the processing, you can easily
achieve a latency of 128 samples (which means, in your case, at 48kHz, a
bit less than 3 ms).
The only other solution to achieve real time processing with no latency,
is to use a DSP processing system based on PC, such as Digidesign Pro
Tools, Sadie, ecc...
For example, with a Digidesign Pro Tools TDM or HTDM (it means that you
don't only have to buy the interface, but even the dsp card for the
processing) you can easily achieve a latency < 1ms. The problems of
these systems is that they are a bit expensive (the basic setting could
be around 6000 euros)...
Anyway, if you have a good audio card (as the RME or Motu), it depends
everything on the speed and memory of your computer, on the software and
on the kinof processing you need to perform!
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