[wdmaudiodev] Re: USB Audio Class 2.0

  • From: "Jerry Evans" <jerry@xxxxxxxxxxx>
  • To: <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Sun, 23 Mar 2014 19:26:22 -0000

Hello Geert

 

I wonder if you might be able to help with a more general AC2 issue. In the
list of ‘Key Differences’, the Release 2.0 ‘device class definition for
Audio Devices’ document states that ‘split off the examples in a separate
document’. Did any such document ever get published? Is there a draft
available perhaps? Given the (sad) paucity of AC2 compliant devices such a
document would be extremely helpful for implementors …

 

Many thanks

 

Jerry

 

From: wdmaudiodev-bounce@xxxxxxxxxxxxx
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Geert Knapen
Sent: 14 February 2014 23:09
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Re: USB Audio Class 2.0

 

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. 

o    –  Control attribute changes. 

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

o    –  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

 <http://www.designandadvice.com> Image removed by sender. D&A
<http://www.jwhouse.org> Image removed by sender. JW HouseGeert Knapen 


 <http://www.designandadvice.com> Design & Advice, L.L.C.
1725 Martin Avenue, San Jose CA 95128
e-mail:  <mailto:geert@xxxxxxxxxxxxxxxxxxx> 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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