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USB depth and rate limitation with Mac os lion.
post Mar 17 2013, 18:17
Post #1

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Joined: 17-March 13
Member No.: 107268

Hi everyone,
First i'd like to apologize if there's is an introduction thread, I didn't see it.
and excuse me for sometimes misusing English, as i'm french and also for being a learner !

I've recently set up an audio rig with: MacBook pro running lion, audirvana plus and fidelia (trial for now), a Mav-audio TubeMagic D1 plus (up to 24/96 in USB, 24/192 for optical/spdif) and akg k701.

here's my problem : ( I also post it in head-fi, no offense meant)

With every configuration, USB input can't handle 24/96, whereas 24 / 41 or 48 is ok, and 16/96 is ok (when i set 24/96 for the input in Audi midi set up, the dac doesn't "boot" and no music can be played).
When players are set to automatic control of bit/rate, they lower bit depth from 24 to 16bit.
The spdif work fine up to 24/96 using the optical out from the macbookpro, but with sound limitation from not bypassing coreaudio.

i browsed the internet forums and i've got the impression that it might be kind of a saturation of USB bus.
The tenor 7022l (interface used by the dac) datasheet says:
- it is USB 2.0 audio class 1 FULL SPEED
- "Due to 12Mbps bandwidth limitation of the USB full speed operation, only one I2S input or output can be set for 24bit/96KHz application, under this condition, for simultaneous multiple-channel applications, rest of I2S interfaces has to be configured at the combination of 16-bit / 48KHz, 16-bit/96KHz and even lower resolution/sampling rate. In the application of USB internet telephony, lower resolution and sampling rate are needed."

When i look into "system profiler" then USB i see all USB bus. MacBook pro has only 2 USB ports. No matter which port i choose :
- maverick appears as USB full SPEED (not high SPEED) with 12mbps : So normal as i understand.
- it is always a shared USB bus (with iSight or internal keyboard or trackpad). Disabling iSight with isight disabler didn't make any change.

is it possible that, by being shared, USB bus is limiting bandwidth , leading to incapacity of habing full 24/96 ?
Is there anything to do ?

Thank you

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post Mar 20 2013, 11:30
Post #2

Group: Members
Posts: 3
Joined: 17-March 13
Member No.: 107268

Hi, thanks for answering.
With help from GFEC (who's manufacturing the tenor 7022l interface) I think I found the answer.

For audio interfaces ( input and output or D to A and A to digital, like in recording interfaces) USB full speed have limitations :
- 2 Inputs and 0 Outputs at 24Bit / 96kHz
- 0 Inputs and 2 Outputs at 24Bit / 96kHz
- 4 Inputs and 2 Outputs at 24Bit / 44.1 or 48kHz
- 2 Inputs and 4 Outputs at 24Bit / 44.1 or 48kHz
- 4 Inputs and 4 Outputs at 16Bit / 44.1 or 48kHz
- 2 Inputs and 8 Outputs at 16Bit / 44.1 or 48kHz (Sonica Theater)
- 4 Inputs and 4 Outputs with every other sample rate up to 16Bit/44.1kHz.

THe problem is, since os x 10.6, some audio DAC, though only having output capacity (d to a), are wrongly recognized as having both input and output. That's why I see both in and out in "audio midi settings"!!

Then the player, in hog mode, matching depth qnd rates to file played, try to equalize input and output.... Leading to 24/96 +24/96 = USB full speed saturation!!!

The same problem apparently occured with udac2 users!

I'll take you informed of new s if you want to !

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