Re: [linux-audio-dev] RFC: API for audio across network - inter-host audio routing

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Subject: Re: [linux-audio-dev] RFC: API for audio across network - inter-host audio routing
From: Richard C. Burnett (burnett_AT_tality.com)
Date: Fri Jun 14 2002 - 21:00:24 EEST


I agree. The more efficient and faster you make the cycle time minimums
in a program, as you are taxing the software with more options and
plugins and the like, each little millisecond counts. And when you cannot
count on the OS to give you low latency in itself, it makes your efforts
futile.

Rick

On Fri, 14 Jun 2002, dgm4 wrote:

> Going back to the issue of latency, it should be pointed out that while
> it might not be a big deal if your softsynth takes 25 ms to trigger,
> latency on the PCI bus is a big problem. If you can't get data from
> your HD (or RAM) to your soundcard fast enough, you _will_ hear dropouts
> in the audio. The more tracks, the higher the sampling rate, and the
> longer the wordlength, the greater the problem becomes. I think this is
> what people mostly are worried about when they talk about latency
> problems. A 25 ms dropout in the audiostream is quite noticeable and
> annoying. The discussions (which I did contribute to) on latency in
> acoustic instruments touched on the subject that trained performers of
> those instruments have learned to compensate for the inevitable delay
> between articulation and sound. Bus latency, however, is a completely
> different story....
> -dgm
>
>
> Richard C. Burnett wrote:
>
> >Actually you are quite wrong about 192 kHz being a hype. Granted if you
> >are going back down to 44.1 you are not getting much of a benefit. But if
> >you are say creating music for SACD or DVDA formats, it is
> >essential. There are three problems caused by lower bit rates; greater
> >clock jitter distortion, non-linearities in the D/A, especially in
> >Delta-Sigma single bit converters, and the number of sample points of say
> >a 20khz audio signal. At 40Khz sampling that would give you 2 points on
> >the wave to reconstruct it. What if you're sampling intervals are 180 out
> >of phase with that signal? You would lose it completey. There are also
> >all sort of phase distortion problems at higher frequencies for the same
> >reason.
> >
> >Now, let's take signal processing. Have you ever worked with video or
> >image files? A few of my professional friends work with this stuff
> >everyday. Their experience is to work in the highest resolution possible
> >for all image transforms and then scale down to what you need. The reason
> >is multiple signal processing techniques suffer the addition of round off
> >related distortion. In that I mean there are less points of interest in
> >the data and the result can and will be different in the end.
> >
> >And to point out something about low-latency, if it really wasn't an
> >issue, people wouldn't be working on it for free. It's extremely
> >noticable to almost everyone I know.
> >
> >Rick
> >
> >
> >On Thu, 13 Jun 2002, xk wrote:
> >
> >>>There's a psychoacoustic phenomenon known as the Haas effect which states
> >>>that a direct sound and it reflections (echos) are percieved as a single
> >>>sound by the brain, where the time difference between the two is less than
> >>>about 30ms. So if the brain can't distinguish between sounds at this level
> >>>
> >>I
> >>
> >>>think you'd get away with a 10ms delay in your instrument without the rest
> >>>
> >>of
> >>
> >>>the band calling you names :-)
> >>>
> >>How about the 1.0-1.5 ms latencies that everbody tries to obtain (or already
> >>has) in both Linux/Win world? That always made me wonder if this isn't just
> >>hype like the 192 kHz issue.
> >>
> >>I'm not a professional musician, but a 25 ms latency makes me more than
> >>happy.
> >>
> >>
> >>
> >>
> >
> >+------------------------+-----------------------+
> >| T a l i t y | +------+ |
> >+------------------------+ +----+-+ | |
> >| Richard Burnett | +-+ | |
> >| Senior Design Engineer +---+ +----+ |
> >| burnett_AT_tality.com | | |
> >| | | |
> >| Phone: 919.380.3014 | |
> >| Fax: 919.380.3903 | | |
> >+------------------------------------------------+
> >
>
>
>
>

+------------------------+-----------------------+
| T a l i t y | +------+ |
+------------------------+ +----+-+ | |
| Richard Burnett | +-+ | |
| Senior Design Engineer +---+ +----+ |
| burnett_AT_tality.com | | |
| | | |
| Phone: 919.380.3014 | |
| Fax: 919.380.3903 | | |
+------------------------------------------------+


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