Jelle de Jong wrote: > Hello everybody, > > I have been testing several scenarios to find some glues why some usb > audio devices did not fully work and gave stuttering sounds I found the > following: > > usb devices define a max power attribute during there enumeration > process. I have some usb devices that have this at 500mA and some that > have this on 100mA. > > I also have some usb hubs that have external extra power supply and some > that are only a hub with bus power. > > Here it comes: > > Make sure the 4 port usb hub is full with for example: > - usb keyboard (100mA) > - usb mouse (100mA) > - usb audio (100mA or 500mA) > - usb stick (200mA/500mA) > > - usb hub with external power (500mA MaxPower) (AC adapter delivers 1A) > - usb hub without external power (100mA MaxPower) > > Make sure to use audio with several tones low tones (most dvds will do) > > When connecting a 100mA usb audio devices on a hub with external power > it will give stuttering sound!! (most usb audo devices are 100mA and > most hubs are external powered due to more then one usb stick) > > When connecting a 500mA usb audio device on a hub with external power it > will work perfectly. > > When connecting a 100mA or a 500mA usb audio device on a hub without > external power it will work perfectly. > > I have the idea there is something wrong with the power distribution > system when using external powered usb hubs... > > Any ideas how to correctly address this problem/bug? > > Best regards, > > Jelle > I did some more debugging, it think the 100mA/500mA behavior is just an effect of the real problem the usb isochronous audio bandwidth under Linux is doing some things that make usb audio not working very well. I wanted to be able to use 4 usb audio device on one usb at the same time. using a powered usb hub this gives shuttering sound. What are the max usb bandwidth limits on Linux? I also found out that the only what that all usb audio device work is to connected them directly without any hub between them. This takes up a lot of resources. Would somebody have to possibility to take a good look at the usb audio issues with multiple devices and isochronous transfers? Thank in advance, Jelle _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
