[Ardour-Users] USB C Guitar Interface Recommendations?

Ralf Mardorf ralf.mardorf at alice-dsl.net
Thu Aug 23 01:13:47 PDT 2018


On Thu, 23 Aug 2018 09:15:42 +0200, David Kastrup wrote:
>"Chris Caudle" <chris at chriscaudle.org> writes:
>> On Wed, August 22, 2018 5:11 pm, Ralf Mardorf wrote:  
>>> When buying an USB audio
>>> interface for an iPad, I experienced that it has got an USB current
>>> limitation, so some audio devices only work with an USB hub.  
>> I have not looked at details of currently available USB interfaces,
>> do any come with external power connections so that you will not
>> deplete the battery of your ipad so quickly?  It seems that any
>> interface which supports USB or something else (S/PDIF, or ADAT, or
>> maybe Ethernet) must have a power supply.  
>Is there an inherent reason if you need a power supply anyway that you
>don't use the iPad power supply?  I mean, if the "USB current
>limitation" hits, "deplete the batter of your iPad" would not get to
>the state of an issue anyway, would it?

Yes, there are reasons.


The USB current limitation does check the device information, it
doesn't care of anything else.

The Scarlett works with an iPad, without an USB hub.

[root at archlinux rocketmouse]# lsusb -v 2>/dev/null | grep "Scarlett
18i20 USB" -A10 | grep MaxPower MaxPower                0mA
    MaxPower                0mA
[root at archlinux rocketmouse]# usb-devices | grep Scarlett -A9 | grep -v
SerialNumber S:  Product=Scarlett 18i20 USB
C:  #Ifs= 6 Cfg#= 1 Atr=c0 MxPwr=0mA
I:  If#=0x0 Alt= 0 #EPs= 0 Cls=01(audio) Sub=01 Prot=20
Driver=snd-usb-audio I:  If#=0x1 Alt= 0 #EPs= 0 Cls=01(audio) Sub=02
Prot=20 Driver=snd-usb-audio I:  If#=0x2 Alt= 0 #EPs= 0 Cls=01(audio)
Sub=02 Prot=20 Driver=snd-usb-audio I:  If#=0x3 Alt= 0 #EPs= 0
Cls=01(audio) Sub=01 Prot=00 Driver=snd-usb-audio I:  If#=0x4 Alt= 0
#EPs= 2 Cls=01(audio) Sub=03 Prot=00 Driver=snd-usb-audio I:  If#=0x5
Alt= 0 #EPs= 1 Cls=ff(vend.) Sub=01 Prot=10 Driver=(none)

Some devices report higher consumption. I guess it's reported in
x mA units, the Scarlett seems to need less than x mA, aless than a
unit. I don't know how much 'x' is. It at least seems to be is less than
100 mA.

[root at archlinux rocketmouse]# usb-devices | grep =...mA -B1
S:  Product=USB Optical Mouse
C:  #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA


When using an iPad that is connected to the battery charger, more
current is consumed, than charged. If the battery is empty, an iPad
cannot be used.


The iPad has got no USB output, a so called Camera Connection Kit is
needed. When using the Camera Connection Kit, it's not possible to use
the battery charger, too. Btw. my experiences with faked Apple cables
and a faked Camera Connection Kit are way better, than with an original
Apple cable. One audio equipment vendor provides interfaces that could
be connected to the iPad and that do charge the iPad during usage. IIRC
those are MIDI interfaces and/or less good audio interfaces.

You might wonder why somebody wants to use an iPad, especially why
experienced Linux audio users decide to use an iPad. The reason for me
is less expensive proprietary software that provides what I need, but
can't get for Linux. There was a lot of talk about the advantage of
modular synths with CV/gate over non-modular MIDI synth. Often a modular
synth and  CV/gate isn't needed, a feature like a LFO that could be
synced to the DAW's midi clock and similar features do the job. MIDI is
not that bad as often claimed by the Linux community. Linux just
suffers from dreadful MIDI and audio plug-in support.

However, it's off-topic for this thread, so lets not continue this

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