Subject: Re: [linux-audio-user] ALSA and usb-audio
From: Patrick Shirkey (pshirkey_AT_boosthardware.com)
Date: Wed Jul 31 2002 - 18:09:44 EEST
Paul Winkler wrote:
> Hi Joseph, congrats on getting alsa to work with your USB gear!
> Sorry you had to be an unwilling pioneer in this area.
>
> On Tue, Jul 30, 2002 at 11:56:42PM -0700, Joseph Zitt wrote:
>
>>However, when I try to play CDs (by selecting CDDA from the menu that
>>comes from the box with the little horizontal lines on it), the CD
>>plays but stutters, with it sounding like the sound is cutting in and
>>out at a steady pace several times a second. Any clues?
>
>
> You're getting dropouts. Dropouts are commonly a symptom
> of the computer not being able to deliver enough audio data
> to fill the soundcard buffer before the buffer needs to be played.
> Remember that in order to get a continuous stream of sound, the
> computer needs to be
>
It seems extremely unusual to get drop outs with a cd. you definitely
shouldn't need to tune your machine for this. Streaming sound from a cd
is completely different than using your computer to run multiple fx and
apps while recording off the same processor and hdd.
> Any number of things could cause this to fail:
>
> * not using lowlatency-patched kernel with a realtime-priority app.
> In your case, addressing this is probably overkill for playing CDs.
>
> * Output buffers aren't big enough. I would try to adjust this before
> trying anything else. I don't have alsaplayer here
> at the moment so I'm not sure how you'd adjust buffer size in this case.
> Maybe there's a command-line or config option.
> Bigger buffers means it takes longer to hear the sound (very bad
> for realtime synthesis, but probably quite acceptable for CD playing).
> The benefit is the audio is less likely to glitch if CPU usage
> gets really intense occasionally, because there's probably time
> to catch up before the next buffer period.
>
>
> * a disk device or data bus can't deliver data fast enough to fill
> the audio buffers. How fast is your cd drive?
> Are you running other USB devices that send a lot
> of data down the USB bus? One way to check would be to set
> up alsaplayer to use the built-in laptop soundcard (assuming you've
> got that working with alsa). If it works better there, then you
> have a problem somewhere in the USB chain. If not, then at
> least you know it's not the USB soundcard, driver, or bus.
>
> * The CPU is being asked to do more work than it has time for in each
> buffer period. This can happen easily with software synthesizers, even on
> high-end modern hardware. I'd be surprised if CDDA extraction caused
> this, but try running top in an xterm while you're running alsaplayer.
> If cpu usage climbs up to 90 percent or so, you have found the limits
> of your processor. Nothing you can do about that but upgrade the
> hardware or use less cpu-intensive software.
>
> as a point of reference, I remember running alsaplayer years ago
> on a celeron 333 MHz machine with a cheap ISA soundcard,
> and the CDDA worked fine, even playing
> with the speed control and playing backwards. IIRC you have a PII 266
> so I suspect that should be OK.
>
-- Patrick Shirkey - Boost Hardware Ltd. For the discerning hardware connoisseur http://www.boosthardware.com http://www.boosthardware.com/LAU/guide/ ========================================
This archive was generated by hypermail 2b28 : Wed Jul 31 2002 - 17:57:11 EEST