Re: Inadmissible sound dropouts on 2.2.18

From: Pavel Machek (
Date: Sat Feb 10 2001 - 17:32:55 EST


> I found that 2.2.18 probably rudely drops samples (lets ocassionally one sample
> be played several times) on the Gravis Ultrasound output device. I use 2.2.18
> and the native kernel drivers. I wrote this program that should produce a clean
> sine tone. Instead I hear a sine interspaced with crackling. The crackling
> repeats at 100Hz I guess. There runs nothing CPU-consuming. The sound process
> takes 5% CPU. It's funny Linux drops sound samples just at 5% of CPU load. I
> got AMD K6-2 3D 400Mhz at 400Mhz, 4*100MHz, running stably between 20-35 deg C
> of case temperature. I got PCI / AGP board FIC VA-503+. There are three serial
> ports, none of them was transceiving at that time. There is one ISA
> NE2000 NIC

And receiving?

There are tools for measuring latency problems. Look at kernel archives.

> The crackling is not dependent on the buffer size you can set up in the C code.
> The crackling is dependent on the frequency of the sine. It's clearly audible
> (read: annoying) at 10kHz, audible at 1kHz, inaudible at 100Hz. So I think
> they are sample dropouts - the card stops playing and repeats one sample until
> kernel gets the breath and whips itself up to supply next audio
> data.

Or it is just Graivs driver bug...

> There are no custom changes in the drivers - no buffer tweaking, nothing. The
> Gravis plays modules, midules and mp3 with nearly no problems (apart from when
> Loreena Mc Kennith sings too high and too loud, I hear something that looks like
> MP3 frames bounds, but I can't surely tell who's responsible for this - if the
> Fraunhofer Institute or Linux Kernel)

;) Or maybe problem is in your application. Can you generate sample
file than "play" it with cat samples > /dev/dsp? You can do it on
different machines to learn if it is gravis or something else.

PS: I think it is your app that is buggy. You write to soundcard, then
you do _lots_ of floating point computation, then you write
again.... If your computtation takes too long, you'll hear
cracking... Of course. You wrote latency critical app!

I'm "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents at
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