11 Aug
2008
11 Aug
'08
1:59 p.m.
Hi dear LAU and LAD users,
I read somewhere that it was possible to change the USB bus sample
rate. I tried to do this with the 'setpci' command by changing the
'latency_timer' PCI register of my USB controllers, but I don't think
I am on the right way. Does anyone knows if that is possible and makes
sense, and if so, how to do it ?
Thanks.
Regards,
Adrien
12 Aug
12 Aug
3:16 a.m.
New subject: [LAU] How to change the USB bus sample rate ?
Adrien DANIEL wrote:
I read somewhere that it was possible to change the
USB bus
"universal serial bus bus"? ;-)
sample rate.
USB doesn't have a built-in sample rate; audio samples are transported
in packets.
USB does have a bit rate and a frame rate, but neither of these can be
changed. The only exception is the frame rate on UHCI controllers; to
change the frame length, change the initialization of the USBSOF
register in the configure_hc() function in uhci-hcd.c.
Why would you want to do this?
Regards,
Clemens
4:03 a.m.
New subject: [LAU] How to change the USB bus sample rate ?
On Tue, Aug 12, 2008 at 9:16 AM, Clemens Ladisch <cladisch(a)fastmail.net> wrote:
Yes. I am interested by the frequency at which these packets are send.
"universal serial bus bus"? ;-)
Yes, in France, it is usual to say "bus USB", because in many minds
(mine only ?) USB do not relate to a bus, but to a technology (which
is wrong, of course), sorry for the mistake ! :)
sample rate.
USB doesn't have a built-in sample rate; audio samples are transported
in packets. USB does have a bit rate and a frame rate, but neither
of these can be
changed.
I think that I was talking about the frame rate, sorry ! In fact I
read a post on another list that I could report here :
--
First of all - USB based sound cards are notoriously terrible for temporal
accuracy. Your best bet really is to get an PCMCIA-based card.
The reason is, the data bus of the USB is not all that fast - it's high
bandwidth, but has a slow sample rate - default is only 125 Hz.
This means you can only "deliver" a sound to begin roughly every 7.5 ms...
So if the sound delivery from the hsystem does not line up appropriately,
you will have a gap while it "waits" to sync w/ the USB data bus.
Now there is hope!
In Windows, you CAN change the USB sample rate, using an applet.
This one here will do it:
http://www.softpedia.com/get/Tweak/System-Tweak/USB-Mouserate-switcher.shtml
It allows changing the data rate up to 1000 Hz (1 ms resolution).
Note - this changes the access rate for ALL USB devices; mice, remote
drives, access keys, etc. It may also decrease the time you get out of the
battery, due to larger power consumption.
--
The only exception is the frame rate on UHCI
controllers; to
change the frame length, change the initialization of the USBSOF
register in the configure_hc() function in uhci-hcd.c.
Why would you want to do this?
I did not try this applet, since I do not use Windows, but I was
wondering if it was possible in Linux. However, I don't think that
altering the kernel code is a good idea (for me) ! :D
Regards,
Adrien
5:58 a.m.
New subject: [LAU] How to change the USB bus sample rate ?
Adrien DANIEL wrote:
On Tue, Aug 12, 2008 at 9:16 AM, Clemens Ladisch
<cladisch(a)fastmail.net> wrote:
That post is wrong, audio data packets are always sent at 1000 Hz (every
1 ms), in both Windows and Linux (input devices use a different transfer
type).
Regards,
Clemens
USB doesn't have a built-in sample rate;
audio samples are transported
in packets.
Yes. I am interested by the frequency at which these packets are send.
[...]
I read a post on another list that I could report here :
--
The reason is, the data bus of the USB is not all that fast - it's high
bandwidth, but has a slow sample rate - default is only 125 Hz.
This means you can only "deliver" a sound to begin roughly every 7.5 ms...
7:02 a.m.
New subject: [LAU] How to change the USB bus sample rate ?
On Tue, Aug 12, 2008 at 11:57 AM, Clemens Ladisch <cladisch(a)fastmail.net> wrote:
That post is wrong, audio data packets are always sent
at 1000 Hz (every
1 ms), in both Windows and Linux (input devices use a different transfer
type).
Ok, thank you !
Adrien
5742
days inactive
5743
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linux-audio-dev@lists.linuxaudio.org
4 comments
2 participants
participants (2)
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Adrien DANIEL -
Clemens Ladisch