Re: PCI a Bottleneck in USB 2.0 for Audio?, RT Os Issues

Previously Veli-Pekka Tätilä <vtatila@xxxxxxxxxxxxxxxxxxxx> wrote:
Arno Wagner wrote:
Previously Veli-Pekka Tätilä <vtatila@xxxxxxxxxxxxxxxxxxxx> wrote:
Hi,
Briefly put, can the real world bandwidth or latency of a PCI-based USB
2.0 card be a problem for high speed USB devices in soft realtime
applications like audio and softsynths? For optimal performance, should
I use the USB on the mobo or the ports on the add-on card?

I have an Asus M2V mobo (using a Via chipset), an Ati Radeon X300
graphics card, and among the USB devices are an E-Mu 0404 sound card, an
M-Audio MidiSport 4x4 interface (USB 1.1) and an Evolution UC-33 MIDI
knob box (USB compatibility unknown), plus a Lacie hard drive for
permanent media storage. The kbd and mouse, as well as a headset and
scanner, are USB as well.

Having added USb ports, I decided to put everything audio on the new
ports relying on the PCI card. Lately I have been geting audio dropouts
in Sonar 4 LE with small buffers of 4 ms, and crackles when a screen
reader program (speech synth with DirectSound or MME) and non-ASIO audio
are used simultaneously. This being the Windows world, and since I have
also updated drivers, I'm unsure whether the crackles are a result of
USB changes or something else, thus my question.

I've read a couple USB FAQs and the Wikipedia articles on PCI and USb
but still cannot figure out whether it could be the bandwidth or not.
Especially since the ideal data rates are never reached anyway.
It is not the bandwidth, but bandwidth allocation. USB devices may
have to wait a bit to send or receive on USB. Buffers of 4ms are
very likely too small, expecially when you also have storage on the
bus.
I see. Then one logical solution would be to use the disk with the USB
ports on the mobo, and use those on the add-on card for the sound card,
for instance.

That could work.

On the other hand, 4ms is pretty tight. Microsoft Windows is a toy
and not intended to handle anything like this.
Put less subjectively, Microsoft Windows is a general purpose operating
system originally intended for business applications, it is not a
multimedia OS like BeOS let alone a true soft or hard real time
operating system like QNX. Even Apple thinks of audio having a higher
priority compared to MS.

I should rephrase: Anything leaving the scope of a glorified
single-user typewriter is problematic in Windows. Even the
typewriter is problematic today.

I don't think you can change scheduling strategies and speeds
And there are far too few process priority levels, too. Well actually
you can tell the OS not to give the process owning the foreground window
a priority boost which most audio guides recommend (control panel,
system, advanced, settings, advanced, processor scheduling = backround
services). Also, precisely because of driver issues before we had WDM
kernel streaming, Steinberg deviced the ASIO driver standard for
Windows.

Well, so solving this by sheduling priorities is out.

I do know the actual latency surely is not 4 MS. USb probably adds to
that, as does the PCI bus hosting the USB card, I presume, not to
mention the DACs and any other possible delays.

On Linux you could ty incrrease the sheduling frequency to
something like 10000Hz (default used to be 100Hz,
Interesting, I've heard that many musically oriented distros already
contain a lot of real time and other kernel patches such as preemption.

There is a lot you can do in Linux. For me kernel-level scheduling
with generous buffers has been enough so far, but I do not do
adudiom except as a consumer.

Best would be to use a real-time OS like QNX for it,
Agreed, QNx is seriously cool at any rate. I've seen the amazing 1
diskette demo of the OS. But the choice of Os is not just a match of
technical features, the problem is that I use the OS because of the
software, not for its accessories or most other user features:

Linux still lacks apps for wave editing, MIDi sequencing and soft synths
at all seriously comparable to Sonar, Sound Forge and VST plugs, which
is what I'm using and have invested some money in. There are some apps,
but nothing much better than in Windows. Another sad real world problem
are drivers, those for my USB sound card are experimental at best. LAst
but not least, accessibility is something I'll have to worry about being
sight impaired, and while the basic gnome desktop is accessible with
Orca, music software is not.

Some real concerns there, yes. I actually have sound driver issues
as well. I have been wanting to buy a Creative X-FI card for
some time for gaming, but until there is Linux support, not
possible. It seems Creative is not even giving datasheets to the
Linux sound developers. Pretty sad.

QNX is much worse in terms of hardware support and screen reader
accessibility. But thanks for the advice anyway. I was kinda hoping that
after five years or so I might be able to use LInux for serious music
making with screen reader access to KDE. But that's OT at any rate. and
we'll see in five years or so how accessible they've managed to make KDE
and the music apps by then.

It is really a mess. Good software on bad foundation or bad software
in good foundations. Were there is good Linux software, it at least
stays available, since typically it can be ported with minimal effort
to newer versions or does not need porting at all. So the situation
should indeed get better.

Arno

.

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