4. low-latency audio I/O for Windows (3)

[Lorenzo Picinali <LPicinali@xxxxxxxxx>]

Dear Dan,
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!
Yours
Lorenzo

--
Lorenzo Picinali
PhD Student
Music, Technology and Innovation Research Centre
De Montfort University
Clephan building, CL 0.19
The Gateway
LE1 9BH Leicester
UK
tel. +44.0116.2551551, internal 6770
e-mail	lpicinali@xxxxxxxxx
web	http://www.mti.dmu.ac.uk/members-postgrad.htm