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I had started this discussion in the digital thread, now it evolved to basic pc audio. Are USB based DACs equal to sPDIF interfaces? I wanted to add a DAC to my ibook based system.
A discussion on sterophile forum had me confused. Comments anyone?
Follow Ups:
Veejay,Basically there is allot going on here as far as highend and most of it is pretty new. My first USB DAC was 4 years ago and the newer version of that one is much better.
I did respond to your stuff at the Stereophile site.
But just a few things... USB is capable with Full Speed (12MHZ) of only 24/96. If you do the design correctly this will work for any data upto 24 bits and sampling rates that you enumerate for. Enumeration is the initialization of the USB device. You can tell the computer what it is that you support (i.e. 16/44.1 or 16 bits at 32, 44.1, 48 what ever).
The problem with most USB High End is that they are just converting to SPDIF and then doing the same old thing.
It is really best not to do this but to take the USB stream and convert it to a logical output to the dac and or filter if you are into that stuff.
There are also different USB devices many of which are plagued with a couple of issues. The first series of devices had terrible jitter. The second generation where much better but included dacs that interferred with the clocks and also shared the clock between the USB and the AUDIO. Well 12MHZ doesn't really go into the audio clocks easily (i.e. 11.2896MHZ, 24.576MHZ etc...).
So what's best to do is engineer around these problems or use what I am calling the 3rd generation parts which require custom programming and the clocking problems go away but then their are software issues to face.
The biggest problem we are all faced with in High End is the fact that the accountants at these semiconductor companies feel we aren't enough buisness and therefore they cater to the high volume companies who make pretty low end units.
The good fact is that with each day we are excelling at a higher rate. Let's face it... having all those error free ripped cd's on a hard drive is much better than any CD player or transport ever would be and at a significant savings in $.
Gordon, Have you looked into the new (soon to be released) Airport Extreme with its networked hard drive capability? What I'm wondering is if you can have a hard drive with all of the music on it connected to the AE and use iTunes on a networked computer with one of your USB DACs for playback. And if you can have multiple of these setups around the house. This would allow you to store your hard drive away from the music system, and for it to be shared in more than one audio system.Based on experience I'm not terribly confident in wireless connectivity for music listening (mainly, drop outs), but the idea of the wirelessly networked drive shared across more than one computer/audio system is clearly useful for media. I've studied some of the available NAS products, but most seemed too technical. No doubt Apple will make it consumer friendly.
In between the listening room and the dining room. Even the little IBook is noisy. I have it connected via a mini-hub and CAT5 to our MAC ITunes Server in our basement. The IBook is certainly a lot quieter than our G5 server.I have never found a case where running wireless works for music playback.
Thanks for you post. I was curious about the new Airport Extreme and wondered if one could run wirelessly with it, and how noisy it is...
Cheers,
In arenas he kills for a prize, Wins a minute to add to his life. But the sickness is drowned by cries for more, Pray to God, make it quick, watch him fall
Sordidman,I have a G4 iBook, several MacBooks and a G5 dual 2GHZ. The G5 is a little noisey but the G4 never has it's fan on and the MacBooks are only noisey when I run Windows in parallels or book camp.
As for wireless... I have never had a problem. I have an AE-G model with a DrBott antena and I am like 80 feet away from the basement server.
Never had a drop out ounce.
The newer Macbooks are completely silent (I think the g3 and 4 are too) unless they are accessing a disc, which they don't have to do when used wirelessly.Sorry to hear you have had trouble with wireless but I use it with great success. I can stream from iTunes to any or all 4 Airport Expresses in my house with no problems.
Andrew,If you mean use the new AE-N as a hard drive server then yea... I am on the list...
Presently I have a LaCie NAS server and do that it works fine connected to the back bone and then stream over my AE-G system. But the server itself sucks and is very noisey.
Anyway G is fine for audio as you are only really requiring it to transfer at 2MBS. The computers have plenty of buffer space and so this is not a problem.
I have not see how the setup for the drive will be but I am looking forward to getting one.
nt
;-)
You state 'USB is capable with Full Speed (12MHZ) of only 24/96', implying USB 1.1. Is there any reason why 2.0 isn't used?
Crimson,With USB 2.0 you have more time slots so you can do things better. But there are no USB 2.0 Audio controllers because the various companies paying USB.org are wimpering over what they want in the specification. Stuff like multiple channel, midi crap, you name it... it's like a polical bill going to the house with pork barrel written all over it.
You could use a bulk transfer capable USB 2.0 controller like an ARM9 unit and then write custom drivers for it. But TI showed the results can be kinda of poor because bulk transfer has the lowest priority.
Whereas Audio streaming has the highest.
Gordon - isnt' there a way to make bulk transfers a higher priority?Even if they are a low priority, if the blocks are big enough will this not be good enough?
You can make all other processes low priority as well, correct?
Steve,I have used some of these ARM based controllers and tried this out. It is very simple to setup a bulk based system if it resides on a USB link that is not taxed by other things.
Basically what it comes down to is the buffering on the DAC side of things. What I did was use one of these Atmel AT91SAM7S128 which has 64K of SRAM and 128k or program space. IAR.com has a real nice dev kit for it with C eval and a USB JTAG emulator.
Basically what I did was setup 2 endpoints one bulk and one hid. The bulk would fill the buffer to like 75% then the HID would send a wait to the computer until the buffer would fall below 50% then the HID would send a ready.
This worked pretty well but the ap on the mac side would have needed to be written as a driver.
Is it better? well I guess if I wanted to sit around and write PC code all day. I would say a week of work on the mac and I could have had the driver done. Then what about 6 months before getting the PC to work.
There is not way that I know of to increase the priority of any of the USB devices.
Thanks Gordon. I have a friend that will do this for me. I just wanted to understand the pitfalls.
Steve,Sure thing... the Atmel ARM parts are pretty nice. There is a bunch of open source code for them and several modular platforms that have embeded linux in them.
If you need any help just ask.
Thanks Gordon. I was planning to have the driver talk to a TUSB3200. It has lots of buffering features already built-in. What do you think?
Steve,I have the dev system for the TUBS3200 if you want it I would be happy to sell it too you. I only looked at it for a couple of days. Comes with board and stuff. I linked the page below.
The TUSB3200 is better than the TAS1020 as far as doing Streaming Async. Both of these parts require the KEIL "C" compiler to compile the sample code which is basically standard 1.1 audio streaming.
You can change the enumeration code to make these work in any capacity. You may want to get an emulator to do much more than the standard audio stuff.
The thing about the TUSB3200 that's nice is that the clocking is better suited for ASYNC and bulk type transfers. In the TAS1020 there are several gotcha's that don't allow certain things, like slave mode in I2S and MCLK1 in for certain stuff. With the 3200 that is not the case.
I also have a parallel port Xeltek SuperproZ programmer if you need one of these. I bought the more expensive USB one and use that now for everything like PLD's and stuff not compatible with the Z model.
Thanks
Gordon
J. Gordon Rankin
Gordon email with your price on these items.
nugent@empiricalaudio.com
Makes sense.In your previous post you say: 'It is really best not to do this but to take the USB stream and convert it to a logical output to the dac and or filter if you are into that stuff.'
I assume this what you do in your dacs. Is converting the USB datastream to I2S the same thing?
Thanks.
Crimson,Well yes I prefer I2S as this protocol is better in my experience by the WCLK (Word Clock) delay of one clock cycle. This means you can with a really good BCLK (Bit clock) you can over come much of the problems with jitter. Because on I2S the WCLK only enables the latching of data into the dac. BCLK actual does the latching, as well as shifting in each data bit.
But with the new Crimson I am not limited to I2S. It can do any of the protocol's required for what ever dac chip I want to use.
VeeJay:Here is what I gather about current USB technology.
1. It's not all created equal. There are different USB controllers out there, some are better than others... much of it is digital audio circuit "engineering level" discussion and lost on me. One thing they often talk about is whether the USB controller first converts to spdif before going to the DAC or if it converts to I2S. The latter is the much preferred method. There is no "spreadsheet" on google which shows which USB vendor does "what and how" yet... this is still relatively new technology.
2. If you need more than two channels, it's not the best way to go... unless you get a PROSUMER USB solution, but then it gets back to how they handle the data transfer. Some prosumer USB solutions are supposed to be not-so-good, like some prosumer fire-wire solutions that have reportedly TERRIBLE jitter figures.
3. If you need 24/48, 24/96 or 24/192 capability, you're hooped with the 'high-end' USB DACs. I think USB dacs (the good ones anyways) are currently only supporting Redbook CD (16/44.1) and stereo LPCM from DVD-Video at 16/48. Again, only prosumer solutions handle these formats - and there is much doubt as to how well they do this.
Now... if you are doing two-channel (stereo) playback of CD or losslessly compressed music, USB could be your trick. No kmixer, and none of the jitter issues that can plague SPDIF *IF* the DAC goes to I2S at the other end.
Hope this helps. I don't know THAT much but what I DO KNOW I can write in laymans terms and not "digital audio engineering speak".
Don't get me wrong - we appreciate them... we just can't always UNDERSTAND them! :D
Presto,Empirical Audio's Spoiler USB Dac can do 24/96. Wavelength Audio's Crimson will also do 24/96 when the new module is available.
nt
discussions on various forum, and pseudo scientific explaination are the same bullshit..
take a good dac , try a good CD drive with it C.E.C , wadia , etc..
than listen the same dac with a good USB/spdif converter ( empirical, redwine,db systems,trends , hagerman,etc..)
and juge by yourself.. everything else is just blahblah...
Pepe:There are many many folks who are very adverse to using SPDIF - especially with an asynchronous sample rate conversion (ASRC) chip in the signal path to deal with two different clocks - one in the receiver/DAC and the other one that was used to clock the data in the tranmitter.
If you ask me, the "bullshit" is when 2-wire SPDIF became a consumer standard. It was originally designed as a "test point" or some darned thing - not as a digital transmission method. Even in Europe they use the AES/EBU which is much more of a studio oriented solution than consumer spdif. Just look at the higher tranmission voltages alone...
Why do *most* professional audio solutions (DACs, soundcards, etc) all have wordclock I/O and master/slave selectivity? It's to permit syncing to ONE GOOD CLOCK which has tremendous advantages over "slightly different clocks all over the place" and all kinds of compensation and compromise circuits to make up for it. The whole consumer audio realm has it backwards - they put the master clock in the CD transport and slave the DAC instead of the other way around.
Now your point about 'sonics is what matters at the end' is valid. That IS what matters around here. > > > How does it sound versus how much does it cost and is it good value or plain expensive? < < < I get that. But there is good science behind all of the digital transmission stuff. And some of it is good science trying to make up for bad design decisions made back when digital was in its infancy. Some of it, however, is "Hey - there is a right way to do this..."
I don't know. Maybe I'm buying into some engineering bullshit. But I work in engineering - so it's okay...
I guess I am just used to it! :P
when you appreciate a coffe , the most important is the taste of it , not the engeniering
behind it, nespresso or socks filter ,
same for audio , some 80' old dacs sounds better than brand new call "jitter free" ones
why ? i don't care..
i only want the best sound in my house...
Pepe:How do you think good audio products are built? Musicians randomly popping semiconductors into circuit boards until it "just sounds good"?
Some of us happen to believe that good digital circuit design, good amplifier design, good crossover and speaker design, and even good PC audio server design all require a certain amount of "art" to get mixed in with the science for them to result in truly beautiful musical reproduction.
Saying "Blah blah blah... I just want audio equipment that gives me good sound" is just like saying:
"Blah blah blah - all I want is a rocketship to take me to the moon."
I'll take the properly engineered rocket ship thank you. And the properly engineered audio equipment too...
Now go and have a nice cold beer. You've been drinking way too much of that delicious coffee...
Did you ever think your coffee was delicious because the temperature of the water and the rate at which the water was passed through the filter was DECIDED UPON and not just allowed to occur randomly?
Even a cup of coffee is a result of engineering. The vacuum seal on the coffee can. Engineering. The coffee maker. Engineering. The cup you are drinking from - even if made by hand was fired in an electric kiln... ENGINEERING.
You can run. But you can't hide...
from ENGINEERING.
Nyuk nyuk nyuk.... I MEAN....
BWAH HAAAH HAAAH HAAAAAAAAAA!!!
try to buid a Stradivarius with math and enginiering without a touch of "arts"
and good ears...
i know a good engineered and "savoir faire" are always necessary but i disagree to
follow the marketing "hype" that claims that the last technology is the better .
it's not always the case. ( musical instruments, hifi source, media format,television, ....wine.. i don't drink beers.. )and stay cool , presto it's just hifi....
Cheers..
...is that is does not always sound better!Look at MP3 players.
Small, convenient, fast, cheap, music to go! Better!
Microscopic amplifier. Lossy compressed music. Shitty ear-buds. Not better?
Here we agree.
But the work the fine men of science are doing to reduce jitter is to attack bad digital sound at the very source.
My point was that the efforts of these men should be applauded and not viewed with contempt or disdain. The fact someone will undoubtedly take their accomplishments and PUT them into cheap, dirty and crappy sounding circuits is not their fault or responsibility, and does not devalue their work.
And yes, many engineers will say "Well, it meets the specs, but it sounds dry and I liked our last design better".
And now Pepe, in lieu of the standard beer, may I recommend to you the winner of 4th Annual Wines of Chile Awards:
Best Cabernet Sauvignon: Hacienda Araucano Reserva 2005 (Lolol, Colchagua Valley)Please try this for me and tell me if it's as good as it sounds.
I quit drinking alcohol in 1995 due to medical reasons, and don't miss beer or hard liquor, but do miss the wonderful bouquet and flavour of wines - especially the flavour and aroma enhancement that the suitable wine can offer various culinary creations.
Damn, now I am hungry.
Big J.
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