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: Phil Kerr (phil_AT_plus24.com)
Date: Thu Jun 13 2002 - 20:57:05 EEST


Not really hype, they are slightly different issues.

(I work with Barry and we discussed this issue earlier)

Achieving system latencies down to 1 - 2 ms is good as it's an indication of
the overall latency of the system. Typically a system can spike at a lot
higher than the values you mention which *are* noticeable.

The Haas effect covers the way the brain differentiates between reflected
sounds (with reference to previous posts it works out at about 5 metres) and
the way it distinguishes between different sources. There are other factors to
take into account such as frequencies of the sounds (is the networked audio
stream two similar sounds or different) and the brain processes them
differently. There are more factors to take into account such as the way the
brain interprets spatial positioning and you can detect timeshifts as low as 10
microseconds. This isn't one of my core area's so others may correct me on
certain points here :)

With regards to MIDI, not audio, there are other latency issues relating to the
UART and opto-isolator chips as well as the time needed for a MIDI device to
respond to an event (we couldn't find any specs on the 16450 UART chips
though). IIRC the Yamaha TX81Z has delays of upto 250 ms from event reception
to hearing a sound.

There was a good posting a while ago by Paul Davis covering work done by RedHat
on achieving very good latency results which explains system latencies quite
well. [http://www.linuxdevices.com/news/NS4928110118.html]

So, system latencies bad, the wetware ones we have to live with!

Cheers

Phil

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.


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