iPad Class 1 Audio---Corrections
iPad Class 1 Audio---Corrections
- Subject: iPad Class 1 Audio---Corrections
- From: Gordon Rankin <email@hidden>
- Date: Mon, 03 May 2010 10:30:13 -0400
- Organization: Wavelength Audio, ltd.
Gang,
Spoke a little early.... Put the Total Phase Beagle USB 480 Analyzer on
the link.
1) Even though the iPad + Camera USB Connection kit selects the
Asynchronous DAC and plays out of it... it does fail to send the
feedback pipe any in's (0x83) which means there is no feedback
associated with the link and in some cases this will cause over or
underruns sometime down the pike. In my case it must be because I do
some stuff internally to pre-buffer the interface and therefore I did
not hear anything.
Endpoint 0x01 - Isochronous Output
Address: 0x01 (OUT)
Attributes: 0x05 (Isochronous asynchronous data
endpoint)
Max Packet Size: 192
Polling Interval: 1 ms
Class-Specific AS Audio EndPoint - Control output
Attributes: 0x00
bLockDelayUnits: 0x00 (UNDEFINED)
wLockDelay: 0 Endpoint 0x83 -
Isochronous Input Address: 0x83 (IN)
Attributes: 0x01 (Isochronous no synchronization
data endpoint)
Max Packet Size: 3
Polling Interval: 1 ms
2) The suspend sequence does work but it is a little weird... When the
iPad is turned off, it sends like 10 seconds of standard zero packets
(i.e. 44.1 nine 176 + one 180) for silence and then set's the interface
to OFF waits for the ACK then delays 10 more seconds and does a Host
Disconnect.
3) Standard HID stuff like volume, mute etc... seem to work fine.
4) Multichannel... I plugged the Creative Labs xFi/xMod into the iPad
which does 5.1 virtual stuff at 44.1/16. The iPad did select it and it
did send the correct amount of data (i.e. nine 528 byte and one 540
byte) per 1ms frame. But the data was not sequenced right and it sounded
like the chipmunks. This is also an async unit and it did verify #1 and
the iPad did not send in's (0x81) to the xMod.
Endpoint 0x01 - Isochronous Output
Address: 0x01 (OUT)
Attributes: 0x05 (Isochronous asynchronous data
endpoint)
Max Packet Size: 540
Polling Interval: 1 ms
Class-Specific AS Audio EndPoint - Control output
Attributes: 0x00
bLockDelayUnits: 0x00 (UNDEFINED)
wLockDelay: 0 Endpoint 0x81 -
Isochronous Input Address: 0x81 (IN)
Attributes: 0x01 (Isochronous no synchronization
data endpoint)
Max Packet Size: 3
Polling Interval: 1 ms
5) First attempt at multiple interfaces (i.e. 16 bit and 24 bit) did not
work. I will have to try a couple more things as I did still offer up
44.1, 48, 88.2 and 96 which we know are not all supported. But basically
it loops in a reset, get Descriptor, Set Interface then loop. Audio
comes out of internal speakers.
6) I had an old iMic from Griffin here and plugged that in. It has
stereo Adaptive output and mono microphone. Both iPod and Videos output
at 16/44.1. I did not see any activity on the in port for the
Microphone. But I have seen elsewhere were someone tested a USB headset
ok. So I imagine that depends on if an application opens the microphone
input on the iPad.
More soon, but it looks like presently only Adaptive is really supported.
Thanks
Gordon
--
J. Gordon Rankin
Owner and Chief Scientist
====== Wavelength Audio, ltd ======
--
J. Gordon Rankin
Owner and Chief Scientist
====== Wavelength Audio, ltd ======
High-End Audio since 1981
SET Tube Amplifiers, DACS & Preamps
http://www.WavelengthAudio.com
===================================
Computer USB DACS
http://www.USBDacs.com
===================================
SET Tube Guitar Amplifiers
NAMM Member since 1998
http://www.Guitar-Engines.com
===================================
3703 Petoskey Avenue
Cincinnati, Ohio 45227 USA
mailto: email@hidden
(513) 271-4186 phone/voicemail
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