[wdmaudiodev] Re: USB Audio Class 2.0

  • From: Geert Knapen <geert@xxxxxxxxxxxxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Fri, 14 Feb 2014 15:09:25 -0800

May I suggest to have a look at Section 2.1 in the Audio 2.0 spec:
2.1 Overview of Key Differences between ADC v1.0 and v2.0

The following list is not an exhaustive list of all changes that have been 
introduced. For complete information, refer to the full specification. Pay 
special attention to Sections 1 through 6!

Complete support for high speed operation - no longer are audio class devices 
limited to full speed operation.

The notion of physical and logical Audio channel clusters.

The number of predefined spatial locations has increased. In addition, a 
virtual spatial location

called Raw Data was introduced.

Use of the interface association descriptor - The standard Interface 
Association mechanism is used

to describe an Audio Interface Collection. The former class specific mechanism 
was deprecated.

Descriptor updates: fixed offsets associated with many descriptors and enlarged 
three byte fields

into four bytes.

Extensive support for interrupts to inform the host about dynamic changes that 
occur on the

different addressable Entities (Clock Entities, Terminals, Units, interfaces 
and endpoints) inside

the audio function.

More clarification text on the audio function.

Audio Control Changes.

–  Control attribute changes.

–  Mixer Unit control request (set/get pairs changed).

–  Many updates in the control descriptions.

Added support for clock domains, clock description and clock control.

Added additional Audio Controls inside a Feature Unit (Input, Gain, Input Gain 
Pad ...)

Added bit pairs in descriptors to indicate presence and programmability of 
every Control

Prohibited the use of Alternate Setting switching to change sampling 
frequencies. Instead, Clock

Entities are introduced that can be manipulated (through the AudioControl 
interface) to select

operating sampling frequencies.

Split off the examples in a separate document.

Allowed binding between physical buttons on the audio function and the 
corresponding Audio

Control. Prescribed how this is done.

Added an Effect Unit to group algorithms that work on logical channels 
separately but require

multiple parameters to manipulate the effect (as opposed to basic (single 
parameter) manipulation,

performed in a Feature Unit).

Introduced Parametric Equalizer Section Effect Unit.

Rearranged Reverb, Modulation Delay and Dynamic Compressor PUs under the new 
Effect Unit.

Added the concept of audio function Category. The Category indicates the 
primary use of the

audio function as envisioned by the manufacturer.

Added the Sampling Rate Converter Unit.

Added a means to express Latency of individual building blocks within the audio 
function.

Added Encoder support. 

Of course, these are all technical differences and do not necessarily directly 
translate in specific reasons to invest in Audio 2.0 :-)

Kindest Regards,

Geert Knapen
USB Audio DWG Chair

  Geert Knapen 


Design & Advice, L.L.C.
1725 Martin Avenue, San Jose CA 95128
e-mail: geert@xxxxxxxxxxxxxxxxxxx | Tel: +1-408-297-3731 | Cell: 
+1-408-507-7852 | Google Voice: +1-408-805-4320

On Feb 14, 2014, at 2:45 PM, Matthew van Eerde 
<Matthew.van.Eerde@xxxxxxxxxxxxx> wrote:

> Specific reasons to invest in USB Audio 2.0:
> 
> * Higher bit rate enables more formats
> * Dynamic jack presence detection
> * Anything else?
> 
> -----Original Message-----
> From: wdmaudiodev-bounce@xxxxxxxxxxxxx 
> [mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Børge Strand-Bergesen
> Sent: Friday, February 14, 2014 2:38 PM
> To: wdmaudiodev@xxxxxxxxxxxxx
> Subject: [wdmaudiodev] Re: USB Audio Class 2.0
> 
> Thank you Phil.
> 
> The market demands Hi-Res, science of not.
> 
> Microsoft will sell more OS licenses with UAC2 support. Apple will
> sell less Macs with Windows UAC2 support. Enough to justify the
> investment? I think yes. Enough to get a measurable peak on the first
> quarterly report? Probably not.
> 
> 
> Børge
> 
> P.S. I'm sorry for going OT with the mention of megapixels and MHz.
> I'm just trying to see the world of electroncis through the eyes of
> the people browsing the shelves at Best Buy. Having a number to
> compare will tip their scale. Lots of users will ignore the not easily
> quantifiable quality of the optics if the other camera has more
> pixels. Currently, UAC2 DACs don't play out of the box, and they sell
> to customers who care about the quality of the optics. Make them play
> out of the box and they will sell to the much larger crowd which
> doesn't.
> 
> P.P.S Don't forget the placebo effect. This DAC has more X than that
> other one, so it _must_ sound better. No UAC2, no cake!
> 
> 
> On Fri, Feb 14, 2014 at 7:42 PM, Philip Gruebele <pgruebele@xxxxxxx> wrote:
>> Three points worth making:
>> 
>> 1. Whether or not it is technically necessary to support higher sample rates
>> is not relevant.  What is relevant is whether the market demands it, and it
>> undeniably does.  Otherwise why would so many companies - hardware
>> manufacturers and download services - invest so many resources to make it
>> happen?
>> 
>> 2. Using Nyquist and human hearing to make a case for not supporting higher
>> sample rates is looking at the issue too narrowly.  The reason higher sample
>> rates can be better are complex and include things like simplifying DAC
>> design and out-of-band filtering. Also some protocols like DSD64 over DoP
>> require 176.4Khz and DSD128 requires double that just to get the data
>> across.  UA2.0 also supports certain use cases which are not possible with
>> UA1.0.  The minimum sample rate that should be supported is at least 384Khz
>> and UA2.0 has handled all these cases for many years.
>> 
>> 3. The lack of USB Audio 2.0 support causes a headache for consumers because
>> they have to deal with low quality, poorly test, third party drivers.  These
>> drivers are not going away because of point (1). There are a LOT of high-end
>> audio enthusiasts who voted against Windows by using Apple products because
>> they provide a better end-user experience.
>> 
>> -phil
>> 
>> Tim Roberts wrote:
>>> 
>>> Børge Strand-Bergesen wrote:
>>>> 
>>>> I'm sorry Tim, but this is like saying Canon & Co. should have stopped
>>>> adding megapixels once their cameras got 4 or so of them.
>>> 
>>> No, this is not a valid comparison.  Our eyes can tell the difference
>>> 
>>> between 300dpi and 600dpi, and a 4MP camera can only do about 200dpi
>>> when printed at 8.5x11.  Those extra pixels ARE being put to use.
>>> 
>>> The same is simply not true of audio.  You don't "zoom in" on an audio
>>> track.  The concept doesn't make sense.  The best human ears are
>>> physically unable to sense frequencies above about 20kHz.  Per Nyquist,
>>> anything above twice that frequency serves no purpose at all.  They
>>> CANNOT, physically, alter what we sense in the sound.
>>> 
>>> It reminds me of the "Dominator DMX 10" scene from Ruthless People:
>>>     http://www.youtube.com/watch?v=mNzr6lfiHJE
>>> (Caution: language)
>>> 
>>> 
>>>> kHz is a simple number. Comparing the kHz of your audio system will be
>>>> done in the consumer crowds just like they compared the MHz of their
>>>> CPUs and the megapixels of their cameras. The more you have of that
>>>> simple metric, the better they will feel.
>>> 
>>> That's voodoo, not engineering.  Those MHz and megapixels are being
>>> 
>>> used.  Those extra kHz are utterly pointless.  Unlike the other two, we
>>> have reached a physical limit.
>>> 
>> 
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