Home Messages Index
[Date Prev][Date Next][Thread Prev][Thread Next]
Author IndexDate IndexThread Index

Re: Low-latency audio on Linux

  • Subject: Re: Low-latency audio on Linux
  • From: "Larry Qualig" <lqualig@xxxxxxxxx>
  • Date: 11 Mar 2006 07:21:01 -0800
  • Complaints-to: groups-abuse@google.com
  • In-reply-to: <dutjq1$1b6o$1@godfrey.mcc.ac.uk>
  • Injection-info: u72g2000cwu.googlegroups.com; posting-host=; posting-account=I0FyeA0AAABAUAjJ9vi7laKRssUBoQA3
  • Newsgroups: comp.os.linux.advocacy
  • Organization: http://groups.google.com
  • References: <PqrQf.1038$X7.489@bignews7.bellsouth.net> <1142049123.281591.249230@p10g2000cwp.googlegroups.com> <dutjq1$1b6o$1@godfrey.mcc.ac.uk>
  • User-agent: G2/0.2
  • Xref: news.mcc.ac.uk comp.os.linux.advocacy:1090210
Roy Schestowitz wrote:
> __/ [ Larry Qualig ] on Saturday 11 March 2006 03:52 \__
> >
> > TheLetterK wrote:
> >> Well, since t would be best to avoid feeding the troll... Would anyone
> >> like to have an intelligent discussion about Linux's low-latency audio
> >> capabilities, as they relate to that available on Windows?
> >
> > My computing audio needs are fairly simple but I'm no slouch when it
> > comes to audio equipment. In computers latency is like a "big balloon"
> > in that if you take your finger and poke somewhere, the rest of the
> > balloon needs to take up the difference. Same with latency, if you
> > decrease the latency (ie. response time) of audio then the response
> > time (latency) of something else is going to increase.
> But why miss the point that latency was too high in previous (and current)
> versions of Windows? While Microsoft boast a 'feature' in Vista, I call it a
> bugfix. Small things matter.

Miss what point? I never mentioned anything about Microsoft or Vista.

> > The goal isn't to get latency to zero because that simply will never
> > happen. Most people can't hear or perceive latency that's less than
> > 1/8th of a second anyway. (Many claim they detect <1/8th second latency
> > can but most simply can't. It's like the guy who can claims to hear
> > 16khz tones.)
> I think you are justifying to self here. You can't get 0 latency (duh!), but
> approaching it while not entailing a performance penalty is more than
> worthwhile.
> > When it comes to latency buffers are the double-edged sword. A large
> > buffer makes CPU usage more efficient in that the CPU writes a whole
> > bunch of data to the buffer than goes away. The problem with a large
> > buffer is that all this buffered data is what's creating the latency in
> > the first place. Minimum latency is achieved when there is no (or
> > absolutely minimal) buffering. The CPU would write the audio data as
> > soon as it was available. Problem here is that it takes many, many,
> > many interrupts in order to do this and the OS would have to do it
> > pretty darn fast. If the OS doesn't respond fast enough you get
> > momentary pauses and clicks in the audio and neither Windows or Linux
> > was ever intended to be a real-time OS.
> A good start would be to trim the bloat off the operating system. Windows is
> always busy doing *something.* My system monitor in Linux indicates that the
> CPU is purely idle (memory is static too) unless I do something particular.
> I am very well-aware of this because all my panels are automatically hidden
> while the only thing visible (apart from the Desktop/wallpaper, which has no
> items on it) is the system monitor and the pager. 'Tune in' to your system
> and you will notice the same thing. Fan burnouts are more of a Windows
> issue, for a reason.

Why in the world are you talking about Windows and fan burnout???? We
are talking about audio latency!!!!

> > The best solution IMO is to make extremely smart audio cards. Throw a
> > dedicated processor on these audio cards and perhaps some DSP
> > capabilities. The micro-OS that runs on these cards would be capable of
> > real-time interrupt handling so it could work with small buffer
> > (==short latency). The software running on the main OS (Linux, Windows,
> > OSX, <whatever>) would essentially 'program' the processor/DSP on the
> > audio card as needed. Once programmed, the card would handle nearly all
> > of the audio with minimal intervention from the host computer.
> That's already being done. Ethernet takes a similar approach.
> > Bottom line is that I don't believe a general purpose OS like
> > Linux/Win/OSX is ever going to get latency down to a level that serious
> > musicians need. The best alternative is to offload this onto
> > specialized hardware that is built specifically for this. Then use the
> > host computer to program/configure this hardware as needed but have all
> > of the actual processing done on the dedicated card.
> While we're on the subject of media latency in Linux, check out this shiny
> new Linux-based device, which has just been unveiled:

Is Linux what you're talking about now? Because up until now you didn't
mention Linux at all. Not one time. It was nothing but Windows and

> http://www.linuxdevices.com/news/NS2786595347.html
>         [ Linux PMP boasts impressive playback times ]
> Makes you wonder why they picked Linux, doesn't it?

What exactly does this device have to do with audio latency??  The
headline says it "boasts impressive playback times" but this is a
portable media player and the impressive playback times are 10-hours of
battery life.

I'm failing to see what this has to do with audio latency and audio
signal processing? It doesn't matter if the latency is 500 mSec. It's
simply playing streaming audio and there user has no idea what the
latency of the audio stream is.

[Date Prev][Date Next][Thread Prev][Thread Next]
Author IndexDate IndexThread Index