[wdmaudiodev] Re: The latest in acheiveable latencies using Windows?

  • From: "Voelkel, Andy" <andy.voelkel@xxxxxxxxxxxxxxx>
  • To: <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Thu, 8 Feb 2007 08:48:10 -0800

Thanks for the info. 


Has anyone tried this audio driver, which claims to bypass usbaudio.sys?


www.usb-audio.com <http://www.usb-audio.com/> 


Also, can anyone comment on best case Firewire latencies?




- Andy



From: wdmaudiodev-bounce@xxxxxxxxxxxxx
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Jerry Evans
Sent: Thursday, February 08, 2007 8:14 AM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Re: The latest in acheiveable latencies using


Hi Andy


This is a question that has perplexed me for years as well. 


Off the shelf the best results are had with PCI hardware and a
well-written ASIO driver. RME Hammerfall cards are apparently reliable
at latencies of 64 samples or so. Consumer hardware like a decent
Creative Audigy comes bundled with an ASIO drvier that should get you
latencies in the low hundreds of samples


USB should be equally low latency but suffers from the hardwired 10ms
buffering built into the USB stack on Win2K/XP. (discussed some years
back in this NG). 


A quick test can be done with ASIO4ALL (www.asio4all.com) and PCI/USB
hardware if you use PortAudio or somesuch to give you a quick way to
read and write audio data.


What _really_ burns me is that the Vista guys decided to write an
entirely new API to do near realtime audio. Which gives Windows no fewer
than _4_ audio interfaces (MME/DirectSound/KS/Core Audio).  So far I've
not had the chance to try it out but a posting some time back by one of
the PortAudio crew suggested performance was far from advertised. See
here: http://msdn2.microsoft.com/en-us/library/ms678518.aspx and here:


You'd have thought the simplest way to get sound out quickly was to give
users (or latency sensitive apps) the option to bypass the wretched
KSMixer, which is the bottleneck in the entire bodge (see DDK docs for
grisly details). My utter frustration with Windows audio is compounded
by the fact that Windows has had a very stable, very low latency MIDI
implementation since NT 4.0. Which was _guaranteed_ to operate with 1ms
accuracy, that being a requirement of the MIDI spec. If reliable MIDI
delivery then why not the equivalent for audio? 






----- Original Message ----- 

        From: Voelkel, Andy <mailto:andy.voelkel@xxxxxxxxxxxxxxx>  

        To: wdmaudiodev@xxxxxxxxxxxxx 

        Sent: Wednesday, February 07, 2007 9:12 PM

        Subject: [wdmaudiodev] The latest in acheiveable latencies using



        I am looking into the feasibility of using Windows as a realtime
development platform for audio algorithms. The stumbling block for this
approach for some time now has been latency. I am wondering what the
current state of affairs is in the Windows world regarding this issue. A
few year ago, I acheived latencies of a few milliseconds using a MOTO
2408 and (tuned) 500 MHZ P3. So I figured this problem would be largely
solved by now, but it appears that this not the case, based on some
quick internet research.

        I am interested in the answers to questions like:

        1.      Which audio interface HW types (USB, Firewire, PCI) have
the lowest latencies, and what latencies are achievable in each
        2.      Is DirectKS streaming still the best way to achieve low
latencies, or has it been replaced by something better? 
        3.      What are achievable latencies in Windows Vista vs.
Windows XP? Would I get an enormous payoff going to Vista, or could I
get close by tuning XP and using the fastest driver interfaces? 
        4.      How much Windows system tuning is required to achieve
low latencies? 
        5.      What are the best information resources to consult for
(up to date) system tuning tips? 
        6.      If I write my own audio host program (desirable for many
reasons), are there good information sources on how to achieve the
lowest possible latencies? 

        Thanks in advance for any help on this issue. I really
appreciate it!

        - Andy Voelkel

        Principal DSP Engineer

        Plantronics, Inc.

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