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DAC on Wireless USB


Steve_S
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I'm trying to send audio to my USB DAC wirelessly. My brilliant idea was to use a wireless USB hub at the audio rack and connect the transmitter to my laptop's USB port. Sounded good on paper! But...

 

While the Wireless USB hub works well with normal USB devices such as hard drives, it seems to have issues with USB audio devices. The laptop (Win XP SP2) sees the DAC but Windows cannot load and assign the drivers. Plugging the DAC directly into the laptop with USB works perfectly. I've tried this on another computer with the same results.

 

Has anyone tried anything like this, or possibly have information or tips on how to get this working? My next step will be to get rid of the Wireless USB and go to "USB over WiFi". I don't like WiFi but it seems like the next best thing.

 

Oh, to answer a question before it's asked... I'm trying to avoid putting a computer into the audio rack. If I can't get the DAC itself to work wirelessly then I will probably go that route, with a remote desktop device of some sort.

 

Ah, nuts! sys64738

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There is only one device that I have tested that actually works, the WiRanger. Gordon has no experience with this one. I collaborated with Icron to make it work for audio streaming (provided the USB audio interface):

 

http://www.icron.com/products/usb_new/wireless-usb.php

 

I have one of these and I have tested it at 44.1 and 96. It works perfectly, except for really bad jitter. It MUST be reclocked. A bit expensive new.

 

http://www.kvm-switches-online.com/00-00228g.html

http://industrialcomponent.com/icron/0000228G.html

http://www.techorium.com/wiranger-cable-free-usb-20-hub-p-926.html

 

If you want to give one a try, I'll sell it to you for $200.00 plus shipping and PayPal.

 

Steve N.

Empirical Audio

 

 

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I spotted those things on the web recently but was unsure about them. Seems to be a fancy version of a USB-over-wireless device, no? While I typically despise WiFi and use it only when necessary, I was actually considering trying the less expensive IoGear version... http://www.iogear.com/product/GUIP201/ ... which can be had for around $60. Coupled with a small USB hub it would do everything the more expensive units would for under $80. Admittedly I have no experience with this thing nor do I know if it would work with a DAC. I don't suppose anyone has tried it?

 

Steve, your comments on jitter have me concerned about the wireless USB path because I don't want to spend $1K on a reclocking device. This is just one new issue that has me a bit up in the air on how to proceed with a music server at this point, and perhaps I'll start a new thread about this. Hmmm...

 

Ah, nuts! sys64738

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I've looked into the Airport Express but two potential deal breakers for me are the requirement of iTunes as a player and the fact that it converts the music to ALAC, which is in my opinion an unnecessary step that could potentially degrade the sound quality. I relate it to having multiple short audio cables tied together instead of one longer cable. The more connections, the more potential for something to degrade the signal. I have no data to support my concerns about the Airport Express, just an uneducated guess. :)

 

Ah, nuts! sys64738

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You can always use Airfoil to send audio from any application to the AE - on Mac OS X or Windows. So choose your player. The format conversion to ALAC is ONLY for transmission - what comes out on the optical output of the AE is plain old PCM data. The main drawback is the limitation to 16 bit, 44.1ksps stereo.

 

Max

 

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Interesting, I didn't know about that app, thanks! Still, the conversion (twice) is a concern of mine and I hate paying money to take unnecessary steps. If I can send the data wireless without processing it more than necessary then I'd rather go that route. I haven't completely ruled out the Airport Express, I've just moved it down on the list. The convenience is the only attraction of the Apple solution but I'm willing to put up with some R&D and a bit of configuring to get a better ultimate sound. If I can't send the audio unaltered then I'll probably pursue placing a physical server in the rack.

 

Ah, nuts! sys64738

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Steve, I think you are absolutely correct to have reservations about airport express. I do use them and they are brilliant little devices for covenience based use-cases. However, I would never consider using one for my main listening scenario / for critical listening. In may experience the SQ degrdation is not at all subtle. Ymmv of course. - John.

 

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Considering that the audio data on the hard disc has to be encoded in some form to be compatible with the characteristics of the magnetic medium (it used to be 'run-length limited' coding back when I was involved with disc); and must be wrapped with TCP/IP headers, MAC layer pre- and post-ambles, before application of the packet-level error-correcting convolutional encoding & Barker-code spread-spectrum modulation so it can be sent over the WiFi radio link; it's a bit much to complain about a simple little thing like ALAC compression of the transmitted audio data affecting the sound! It is

    lossless encoding, you know?

     

    It reminds of the old joke: "A tongue sandwich! I'm not eating that: it's been in somebody else's mouth. I'll have an egg instead"

     

    ;-)

     

    Max

     

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Max, I do find a flaw in this logic because everything done during the digitizing process is controlled to produce the highest possible quality. The data on the hard drive is as good as it can possibly get based on what is within our control. When this data is output, various steps are taken to get the data from the hard disc to the drive controller, then through a ribbon cable to the motherboard's controllers, through the PCB to the chipset, etc etc etc and finally to the USB cable itself. Very little control is offered in these steps but fortunately they are not altering the data but rather transfering it bit for bit between different data transmission formats. The data itself has not been altered, it's still the same 1's and 0's.

 

Now that the exact same ones and zeros that were on the hard drive are leaving the computer, it makes the most sense, in my opinion, to not deliberately alter them. Lossless compression "should" cause no change to the sound but unfortunately that has been proven untrue from what I've learned.

 

I guess what I'm saying is that just because the data has to go through a lot of electronics before reaching the USB cable, that doesn't mean we should ignore deliberate manipulation fo the data itself, which surely has the potential to do far more damage to sound quality than anything else it has gone through!

 

You could relate the same argument to CD players. There is a lot going on from the time the CD is pressed to the time it leaves the player. But you wouldn't want to wirelessly stream it to your preamp if you didn't have to because it would be an unnecessary manipulation of the audio data.

 

Of course I've been known to be full of crap... :)

 

Ah, nuts! sys64738

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I have a bit of experience with AirPort Express since I have both modded it and sold this as a product. Many of my customer do this, as well as Apple TV.

 

The stock AE has some of the worst jitter of any WiFi device. Simply atrocious. Even a $50 CD player is better. This is why the SQ sucks. It's the PCM270X parts again, same as used in many cheap plug-and-play USB interfaces. There is simply no help for this part. It's beyond help IMO.

 

If you want to do WiFi with a stock device, use a Squeezebox.

 

Steve N.

Empirical Audio

 

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Using the digital output of the AE isn't the worst thing in the world. According to Stereophile, "However, this performance becomes moot when the AE's digital output is used. The grayed-out trace in fig.7 shows a similar spectral analysis of the Musical Fidelity X-DACV3's analog output while it was driven by the AirPort Express via the Monster TosLink cable. The noise floor has dropped by 4–5dB, the word-clock jitter to a respectably low 258ps, which is actually better than the case with the standalone D/A processor driven directly by my PC's S/PDIF output (provided by an RME PCI card). "

 

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Chris,

 

Yes actually we have tested a bunch of these and none of them are very good, most do not work at all.

 

Steve, actually more than a year ago I have emails from several of the engineers at icron. Well actually the company that designed the product for icron since Nov07.

 

But there are at least two problems that all of these devices have including many of the optical units.

 

1) The power supply is a switching unit which will inject noise in the audio system. Some people are making outboard linear supplies for these which is a requirement from the start.

 

2) The delivery of packets especially for Adaptive mode DACS (this also includes the Airport Express since it is a USB to PCM270x unit) is not timed as critical and therefore the amount of jitter injected is much more significant as compared to a directly connected unit. For example all adaptive mode dacs use the SOF frame as the timing reference to derive the Master Clock. With a computer this is timed almost dead on at 1ms. Even with the icron this is more irratic ending up with more jitter on the output of the USB Audio Receiver.

 

Steve grab a USB Analyzer and check out the timing of the SOF frames. It will directly correlate to the Word Clock jitter coming out of the TAS1020B using your Adaptive code from Centrance.

 

Guys spend a little more money and get a computer. I bought a little EEE pc to do some testing and can carry that around anywhere. Run the Airfoil on it as a client plug the USB DAC into that and you can have a pretty damn good system. Or go to eBay and pick up a good condition mac for cheap. Either way Airtunes/Airfoil is just data and they present that to the USB Audio Stack and the jitter will be reduce tremendously.

 

You can also look at JACK Audio as a transport the same way you do Airtunes. It is open source and works (??) on OSX, Windows and Linux. The nice thing about Jack is it is 32 bit audio and any sampling rate. The bad news is it is open source and there are some bugs and learning curve.

 

Thanks

Gordon

 

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It's bit perfect on Windows XP, bypassing the k-mixer.

 

As far as the effects of lossless compression, I'm dead certain that nothing has been proven about its sonic inferiority. Just a handful of anecdotal reports--not the majority of anecdotal reports, mind you--and a lot of anxieties.

 

I'll tell you this, I run an Airport Express through a mini-TOS cable to an Adcom GDA-700, and HDCD material engages the HDCD light on the DAC, which means nothing is lost. As pointed out above, given all the other processing that goes into transmitting by wi-fi, the ALAC step seems trivial.

 

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Gordon - The first WiRangers did not work for audio, so I sent icron one of my USB adapters. Then they fixed the code and they work now.

 

Like I said, the AE jitter is high, but it can be fixed with a reclocker. It does use Synchronous adaptive mode.

 

Steve N.

Empirical Audio

 

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I looked into an EEE PC as an audio server but was concerned about the lack of horsepower for handling a decent front end application. I would be very interested in any reports to the contrary!

 

Ah, nuts! sys64738

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Guys,

 

Newegg sells the EEE for from less than $300 to about $700. I bought one of the 10" and I use the damn thing all the time. Put in a 2mmb stick and this puppy is pretty darn fast. I have a 32GB SSD IDE in one of my linux PC's I am going to yank out and put in mine. The Intel Atom is pretty powerful for doing this kind of stuff.

 

Steve, no USB dac chips use synchronous except the ones from USB 1.0 times. The PCM2705 uses Adaptive mode. Also remember just like upamplers, reclockers can only get rid of so much jitter. The more there is the more that goes through. The typical jitter from the PCM2705 is really off the charts high. It's even more so out the toslink port.

 

The only silver bullet for jitter is making sure it's not there in the first place.

 

Guys if your going high end then the AppleTV, AE and Icron are not going to send you into nirvana.

 

Thanks

Gordon

 

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For those interested, I run a Samsung NC10 netbook as my music server. (Intel® Atom™ processor N270 (1.6GHz, 533MHz, 512KB, 2.5W), 1gb, 802.11b/g)

 

It has run just about every front-end known to man and has streamed everything I've ever thrown at it with absolutely no problems whatsoever. Cool, quiet and more than up to the task of 24/196 audio. It currently runs the Squeezecentre server for my Squeezebox, streaming the data via 802.11g to the receiver.

 

As an aside, I eventually intend to build a small computer to house a top-end soundcard, the Samsung will then become the remote via VNC. I can't speak highly enough of mine and can't think that any of the other similar brands will be much different. In the UK they retail at around the £300 pound mark for a well specified machine, so $450 ought to do it.

 

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Gordon wrote:

"Also remember just like upamplers, reclockers can only get rid of so much jitter."

 

Gordon - there are reclockers and there are reclockers. Reclockers the use PLLS to resample or upsample or track a data stream are certainly to some extent sensitive to jitter in that stream. They can reduce jitter, but always have some sensitivity.

 

There are however more clever ways that this to skin a cat. Reclockers whose output contains absolutely no artifacts from the original data stream are possible. I'm not claiming zero jitter because of course, this is impossible. It is however possible to get to the threshold of audibility.

 

Steve N.

Empirical Audio

 

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Steve,

 

Since you are using the serial stream input the same way a upsampler would then you are also prone to the same problems.

 

If it were true like everyone says and their upsampler/reclockers remove the jitter then why is that their jitter numbers are not cosistent over each interface (i.e. USB, SPDIF)?

 

In all the tests performed by Stereophile including several with the Centrance code you the USB selected interface always had more significant jitter than the SPDIF counterparts.

 

In testing what we found was that ... ahh easy with some basic numbers. The input jitter on a dac we have that has the Centrance USB interface is 4x that of the SPDIF input. The Stereophile jitter measurements put the USB at 250ps and the SPDIF at 150ps. Why??? well because the USB input was significantly higher into the jitter elimination system and therefore less was removed.

 

We tested the Word Clock jitter with the Wavecrest going into the the jitter elimination system and the determination was that all jitter elimination systems only remove a certain amount. The higher it is going in the less is removed.

 

Steve, you can make claims but without the test equipment to back that up, then it is merely claims.

 

Thanks

Gordon

 

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"In all the tests performed by Stereophile including several with the Centrance code you the USB selected interface always had more significant jitter than the SPDIF counterparts."

 

That may be true, but they have never tested my USB converters.

 

Besides, this has nothing to do with my Pace-Car reclocker. This is the cleverness I was talking about, not my USB interface although it is clever too.

 

Steve N.

Empirical Audio

 

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Steve,

 

Then why don't you give us some numbers?

 

If you clock the data and word clock into the FIFO with a jittery bit clock like you do then there are going to be problems on the other side when it comes out.

 

Ounce you told me that investing in expensive test equipment meant less net gain ($) from your products. I want to say that this is not true. For example so far this year I spent $20k on new test equipment. I have been able to lift the products that are coming out of development easily 10 fold. I just received a new TEK MSO 4000 series and bought both the DPO4AUDIO and DPO4EMBD modules so I can test I2S on the fly as well as use the logic analyzer to verify I2C/SPI and other protocols required for all these new dac chips. I recently turned in my USB 1.1 Analyzer for a USB 2.0 unit and bought 4 new development systems for USB and other processors. I also had my Wavecrest overhauled and bought new firmware that can measure jitter down to less than 100fS.

 

Steve all these investments help your product to become better.

 

Come on Steve, tell us some numbers.

 

Thanks

Gordon

 

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Guys spend a little more money and get a computer. I bought a little EEE pc to do some testing and can carry that around anywhere. Run the Airfoil on it as a client plug the USB DAC into that and you can have a pretty damn good system. Or go to eBay and pick up a good condition mac for cheap. Either way Airtunes/Airfoil is just data and they present that to the USB Audio Stack and the jitter will be reduce tremendously.

 

You can run Airfoil as a client and plug a USB DAC into the computer and Airfoil will send a data stream from a media player to the DAC in a unique, more favorable manner? Is it bit perfect?

 

Thanks.

 

- Rand

 

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