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62.143.40.17
Hi there.
The iPad allows to connect external USB DACs via CCK... ...under certain conditions.
iPeng - the iPad player app - meanwhile supports up 2 24/96 playback (even as PCM stream) (- iPhone is limited to 48khz.)
To me all this looks quite attractive on the first glance.
As usual, there's always a "but".
Problem:
USB power.
Obviously the iPad won't power USB DACs with rather high (>100mA???)power consumption.
The problem is that even self powered devices ( not all -- but many ) - if directly connected - won't work.
iOS will complain about too much power consumption.
I did a test by using a USB cable with cut off 5V. No change.
I did another test by powering up the iPAD with DAC connected ( somebody suggested this). No change.
The only way to make it work was by hooking up a selfpowered USB-Hub in between iPAD and DAC.
Scratching my head, hmmh... ...I guessed - it must be a software/firmware issue.
Finally I stepped over a comment that stated that USB devices
need to announce estimated power consumption to the host.
Question:
Could it be that all those selfpowered USB-DACs that just work with
a hub in the line, don't announce the power consumption to the host??
That's just a thought. Would be nice if affected manfuctarers would look into the subject. Similar things might happen on Android devices soon.
Cheers
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::: Squeezebox Touch Toolbox 3.0 and more ::: by soundcheck
Follow Ups:
A little progress.I looked up the TI TAS 1020B datasheet.
Page 21. The EEPROM header got a field called MaxPower given in n * 2mA.
That's probably the relevant parameter in the firmware.
But that means 1 parameter = 1 hardcoded value.You most probably wouldn't be able to handle bus and external power on the same device with this.
The manufacturer would have to choose the worst case scenario (bus power).On a first glance it looks to me that the 1020B would support 2 scenarios only.
Bus PS only or External PS only. A combined scenario wouldn't be possible......except you'd fake that value. Though I doubt that any manufacturer would do/risk that.
Let see how Tenor and XMOS are doing.
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::: Squeezebox Touch Toolbox 3.0 and more ::: by soundcheck
Edits: 08/18/12 08/18/12
Hi
A brief update.
I've been in contact with the guy who is building the real well done WaveIO interface (You'll find it on DIY audio).
He confirmed that you can set that MaxPower parameter inside XMOS firmware.
He even did it... ...and it worked on the iPad.
The main challenge though remains - at least for now:
You can't just change that header parameter on the fly. That would be required to run USB power and external power from the same device.
Anyhow. He'll be offering an iPad compatible (no need for a USB-hub) version of his Wave-IO device.
Cheers
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::: Squeezebox Touch Toolbox 3.0 and more ::: by soundcheck
Apple was concerned that there were USB devices that would draw a good bit of power from the iPad. They didn't want the battery life to become an issue and thus face the bad PR after touting the battery's long life, so some time back they made a change to iOS (I believe it was iOS 4) that basically dropped the current draw support to 100 mA from the earlier higher amount.
I do know that if you use the camera connector and a Turtle Beach Audio Advantage Micro II, you can feed a DAC via an optical cable. Not High End by any means, but it does work and there are people who use these and similar to feed the optical input of the DAC in their vehicle (lots of YouTube videos online).
They also don't want people to use their product for off-label use...they never intended for the iPad to be used to drive anything via USB esp audio products.
Now when/if the day comes where Apple sees profit in Audio related USB products then they will work something out that will enable the USB to work [with their product].
Dynobots Audio
Music is the Bridge between Heaven and Earth - 音楽は天国と地球のかけ橋
.
Yes of course
I see it clearly now
Apple is an evil money grabbing monster and all other companies are altruistic love machines who only care about the wants and needs of their customers
Thanks for opening our eyes!
.
I never said anything pro or con about any other company...so please don't put words into my mouth.
In fact what I said about Apple is neither pro or con. It may be viewed either way depending on the persons perspective. An investor might see it as a pro for example while a consumer might see it as a con.
Again please don't forcefully assign your assumptions on my words.
It is no revelation that in a Capitalistic world most if not all companies seek profit in order to survive. Some people might call them Money Grabbing Monsters others might not. IMO no need for labels, they are what they are... It takes a special talent to make a profit and run a business that operates with the best interest of consumers.
Dynobots Audio
Music is the Bridge between Heaven and Earth - 音楽は天国と地球のかけ橋
.
So after all of your relentless Apple bashing you are going to try and take the high road and say this one just happens to be a neutral observation?
Good one.
.
If I wanted to bash Apple it would be obvious. I would not need you to twist my words, add words into my mouth or try to make implications.
Dynobots Audio
Music is the Bridge between Heaven and Earth - 音楽は天国と地球のかけ橋
You must realise by now that these are his posting attributes. Alternatively, he just cannot comprehend properly what others are saying.
Edits: 08/18/12
.
At least someone around here has a sense of humor and doesn't get his panties in a wad like, well like fmak !!!
it was a good depiction of himself?
.
That's the best you can come up with?
I thought the British were known for their wit and clever insults?
.
.
.
Dynobots Audio
Music is the Bridge between Heaven and Earth - 音楽は天国と地球のかけ橋
Would you please keep us up to date regarding developments on that front, too?
It's quite convenient (and satisfying) if you use both hands.
SC,
In the enumeration process the connecting unit tells the host computer how much current it draws. So not matter what you are doing the problem will exist because the iPad is seeing that the device draws X amount of current and if X > max limit then the iPad sends the shut down command and ignores the connection.
The only way is to put a smart powered hub in front of it so the iPad see's that the unit is not drawing any current directly.
Thanks
Gordon
J. Gordon Rankin
"...."
That's what I figured already.
The question is if I can make the USB audio interface chip (probaly depends on brand and firmware) announcing two different modes (external/USB powered) with related power consumption.
If the USB audio device is externally powered it should be able to announce
zero consumption. Obviously many devices fail on this feature.
Cheers
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::: Squeezebox Touch Toolbox 3.0 and more ::: by soundcheck
"Obviously many devices fail on this feature."
Feature? Does the device in question have a separate power input besides the USB connection? In that case it at least could do it. However some designs use both. I think Ayre does for instance and runs the USB transceiver and some other glop from the host power then opto-isolates that from the self-powered chunk.
If not it would be unable to devine that the user has hacked up his interface to not draw power from the host which I believe was your test case.
Regards, Rick
My device allows to switch bus vs. extern.
I'd expect all devices with external PS - switchable or fixed - to announce 0 current consumption to the host. That's not the case.
My cut-the-line test had shown that the host doesn't measure the actual current draw.
My guess that somehow the client firmware must get involved was confirmed by Gordon.
Cheers
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::: Squeezebox Touch Toolbox 3.0 and more ::: by soundcheck
I don't know the answer to your question but I have a question of my own.
Do you actually plan to use the iPad with an external DAC?
How many people actually walk around with an iPad, iPhone, iPod Touch, or other similar device with an external DAC and cable hanging off it? Just a question. Not meant to be insulting. I can't imagine this scenario for most users.
The idea might not be to walk about with a Dac hanging off a iPad but to instead dock the iPad into a Dac while at home.
Some people might prefer to use a traditional computer [keyboard, mouse etc] while at home...
Dynobots Audio
Music is the Bridge between Heaven and Earth - 音楽は天国と地球のかけ橋
Here is a Dac that hangs off my iTouch
Dynobots Audio
Music is the Bridge between Heaven and Earth - 音楽は天国と地球のかけ橋
Good observations. I don't see that an iPad is a good place to store a music collection either.
Something new to tinker with.
Bill
For most folks on this forum, I would agree..... iPad (or any tablet) is probably not the best place to store your music collection for your main audio system. And if you store music on it for portable use, I can't see hanging a DAC and cables from it.
I tried the iPod + digital dock + DAC setup in my main audio system for a couple months then decided it made better sense to set up a more flexible music server instead. The iPod, iPhone, iPad, or Android device would then be used as a remote control only.
iPhone Remote Control for music server
There are many people who have high quality audio systems in their vehicle. Some people might want to take their iPad in the vehicle and have it output digital audio to a better DAC.
Many people have second systems or headphone systems set up for music playback. Some of these people might want to have an iPad with music on it to plug into a DAC for better sound quality.
As cool as my iPad is, it never leaves the house. I use it to control the Sonos system and experimented with it to see if I could use it as a source to feed various DACs with the same dismal results. Will play with the powered USB hub idea. If it works, that would be an acceptable hack.
.
How many people actually walk around with an iPad, iPhone, iPod Touch, or other similar device with an external DAC and cable hanging off it?
You might not understand this Abe but some people just care about sound quality and not how "cool" something is....
I certainly would hang all kinds of cables off my ipad if it would sound better than my main rig doing so.
Afterwards we discovered faith; it's all you need
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