[wdmaudiodev] Re: USB Audio Class 2.0
- From: Børge Strand-Bergesen <borge.strand@xxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Tue, 25 Mar 2014 08:55:10 +0100
My impression is that a practical UAC2 device is one that works on OS X.
With OS X support in place, tweak it to work wil Linux, after that write a
Windows driver which emulates the other two.
I have seen parts of the descriptor interpreted very differently on
different OSes. There might be a bug in the firmware I'm using, or it may
be the different OSes interpret it differently. The above method at least
rendered a working device.
Børge
On Mon, Mar 24, 2014 at 6:37 PM, Geert Knapen <geert@xxxxxxxxxxxxxxxxxxx>wrote:
> Hi Jerry,
>
> The example document was never finished (not even really started :-(). So
> I am afraid that nothing is available and the Audio working group is not
> active at this time...
>
> Kindest Regards,
>
> [image: D&A] <http://www.designandadvice.com> [image: JW House]
> <http://www.jwhouse.org> *Geert Knapen*
> President/Owner
>
>
> *Design & Advice, L.L.C.* <http://www.designandadvice.com>
> 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 Mar 23, 2014, at 12:26 PM, Jerry Evans <jerry@xxxxxxxxxxx> wrote:
>
> 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 <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
> <~WRD000.jpg>
> <http://www.designandadvice.com/><~WRD000.jpg><http://www.jwhouse.org/>*Geert
> Knapen*
>
>
>
> *Design & Advice, L.L.C.* <http://www.designandadvice.com/>
> 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 <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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