Stuttering 100mA and 500mA MaxPower usb audio investigation on bus powered and external powererd usb hubs

[Jelle de Jong <jelledejong@powercraft.nl>]

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