[linux-audio-user] Re: [Ardour-users] Re: [Alsa-devel] usb audio sound quality

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Subject: [linux-audio-user] Re: [Ardour-users] Re: [Alsa-devel] usb audio sound quality
From: Patrick Shirkey (pshirkey_AT_boosthardware.com)
Date: Fri Nov 08 2002 - 23:54:08 EET

Jesse Chappell wrote:

> What is the nature of the quality degradation? I assume that
> no xruns are occurring in all cases... you are sensing
> degradation that occurs with no obvious suspect?

Yes no xruns. It seems to be directly related to the amount of available
physical memory. I have been talking with AthlonRob about how the Linux
memory management works and it seems that the kernel will cache almost
all the available memory up to between 10 and 4 MB before it starts

It also appears that the kernel stores a certain amount of recently used
data and I guess that by playing an audio stream it stores that to
memory until something which needs it, like a gui app request the space.
It will then transparently give up the memory it has cached giving the
impression that no memory has been used to open an application.

So It seems I am in a bit of a catch22. In order to use JACK with no
sound degredation I have to run with no gui. However the kernel will
eventually use up the memory space which will probably cause
degredation. However I haven't tested this as I haven't had the time.
 From here it seems the kernel will cache memory at around 1MB per
minute. Sometimes more, sometime less.

Patrick Shirkey - Boost Hardware Ltd.
For the discerning hardware connoisseur
http://www.djcj.org - The Linux Audio Users guide

Being on stage with the band in front of crowds shouting, "Get off! No! We want normal music!", I think that was more like acting than anything I've ever done.

Goldie, 8 Nov, 2002 The Scotsman

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