[music-dsp] DOS [or DOS mode] for low latency on PC?

David Olofson david at olofson.net
Tue Jan 6 10:59:01 EST 2004


On Tuesday 06 January 2004 18.59, Rob Belcham wrote:
> The input - output latency largely depends on your sound card. If
> you've got a cheap, or built in sound card, the latency is likely
> to be quite high.

Actually, it depends pretty much only on the drivers and OS. For some 
reason, the Windows drivers for most sound cards are just plain crap. 
The same hardware usually works just fine at 2-5 ms on 
Linux/lowlatency with the standard OSS/Free or ALSA drivers.

That said, there *are* some audio chipsets that have weird limitations 
on buffer sizes. Not much any driver can do about that, but AFAIK, 
very few cards have any serious limitations of that kind.


> Typical modern soundcards with ASIO drivers can achive a latency in
> the order of a few ms. Is this low enough for your needs ?

A typical PCI card usually goes all the way down to the PCI busmaster 
DMA burst size, which means 64 bytes per buffer. That is, 0.33 
ms/buffer. Most ISA cards DMA two bytes at a time, so they have no 
practical lower latency limit.


> I understand Linux is also good for real-time, low latency audio,
> might be worth checking out.

Yeah - especially considering that the limits usually are in the OS, 
rather than the hardware. :-)

And either way, if DOS is an option, so is any other OS, I guess, 
including RTLinux/Free, RTAI, Linux/lowlatency, and (if cost is not 
an issue) any of the commercial RTOSes and RT kernels, such as 
RTLinuxPro, QNX, AMX, SMX and whatnot.


//David Olofson - Programmer, Composer, Open Source Advocate

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