How would you feed two USB devices from one USB source ?

Eldam

Banned
2012-09-13 12:25 am
France
Hi,

How would you feed two USB devices playing at the same time from one USB source ?

MiniDSP just launched a two way device wich accept usb streaming ! With two devices you can make an active 3 or 4 ways.... But you need to feed two usb devices from one streamer ! https://www.minidsp.com/products/minidspkits/2-x-in-4-x-out-hd

Is it possible ? (two outputts needs more voltage level ? synchronised buffers for the two outputts to play at the same time ?

If yes, can it be better to use some isolator chips made to isolate the ground from the source to have quieter noise floor ?

So USB input-> isolator chip -> two USB outputts
with inputt of the isolator chip feeded by the USB source and the outputt of the isolator chip powered by a standalone low noise reg ?

Thanks if any ideas
 
No.

Also I caution that USB is not USB is not USB. For instance not all USB 2.0 can handle 192k. For example, high speed USB 2.0 is limited to two channels of 24/96 audio for instance. Your computer may need to have USB 3.0 to actually get the throughput that miniDSP is advertising... but manual and datasheet are moot on this point, or requirements therefore. I would really like to see miniDSP clarify this.
 
Actually you might be able to do THIS:
Don't use USB to "feed" the 2x4HD, instead use the toslink input.
spdif is an analog signal really, and you can "copy" it in the electrical domain (coax spdif) or the optical domain (toslink spdif), although I only know of a way to do the first one.

So, for example if your computer has coax spdif out you can connect that to something like a 74HC04, use a couple channels to buffer the input, then connect two more channels in parallel, and finally use two more channels to buffer the output. Some hints at the end of this page:
S/PDIF Digital to Analogue Converter
Now you have two identical spdif electrical signals. You simply use two TOTX modules to convert to light and send the signals on their way.

The only drawback would be that you can't do staggered crossovers where the output of one section is used as the input as the next. The topology would be like a parallel input with the same signal feeding both miniDSP units.

So if you really have to use two 2x4HD units instead of buying a single 24/192k capable unit with 8 output channels, that might work.

And now that I think about it, what is stopping your computer from having two output devices? Probably your player. For instance MPD can have more than one output device that is running concurrently. So it could send the audio to TWO 2x4HD units, assuming that there could be TWO on the same system at the same time (who knows? ask miniDSP in the forum at their web site) and direct the audio to both of them simultaneously. One can handle the crossover for the left channel and the other the crossover for the right channel.
 

Eldam

Banned
2012-09-13 12:25 am
France
Thanks a lot Charlie, very usefull inputts.

La mariée était trop belle indeed ! Maybe I should get a MiniSHarc with three I2S 9023 chip DACs from Curryman instead if wanting simpliest active 3 ways still at "cheap" price, although I don't know if the Minisharc has one I2S outputt or more ! They launched also a 8 ways dac for it : https://www.minidsp.com/products/minidspkits/minidac8
 
There seems to be a fair bit of concern about phase coherence (or lack of it) when using multiple USB DACs together, since their clocks aren't slaved together in any way. Here's one thread on the JRiver forum, for example.

-- Jim

Only if they are those latest-and-greatest USB asynchronous types!

I use multiple USB adaptive mode DACs with a Raspberry Pi and they remain 100% synchronized.
 
OP, you might look at Voicemeeter if using Windows.

...high speed USB 2.0 is limited to two channels of 24/96 audio for instance.
I believe you're thinking of USB 1, not 2.0. 2*24*96k = 4.6Mbps. Lots of info here.

FWIW, the U-DAC8 (8 channels @ 24/192 over USB2.0) manual does include this disclaimer:
Note that while multiple U-DAC8s can be connected to a single PC, they should not use the same USB Controller in order to avoid any chance of overloading the bandwidth of the controller.
 
If you need a good solution for an active cross over you might have a look at Najda.

It has good built in dac. And if you don't like you you can use

1x I2S input via a USB2I2S adapter and three I2S outputs feeding to other dacs.

It is more expensive than mini dsp, but has much more to offer.

On the other hand if you want there should be a multi channel USB output an a multi channel USBI2S adaptor, diyhk as an example which can provide 6 or 8 channels via 3-4 output I2S singals
 

GDO

Member
2009-07-23 2:16 pm
And now that I think about it, what is stopping your computer from having two output devices? Probably your player. For instance MPD can have more than one output device that is running concurrently. So it could send the audio to TWO 2x4HD units, assuming that there could be TWO on the same system at the same time (who knows? ask miniDSP in the forum at their web site) and direct the audio to both of them simultaneously. One can handle the crossover for the left channel and the other the crossover for the right channel.

Brutefir on Linux can convert a 2ch programm into a 4ch, 6ch, 8ch, etc, simply copying respective inputs to outputs. But you must create before this a virtual soundcard combining the physical ones. I don't thins this is allowed on Windoz/Mac...

Btw, 2X4HD works in async mode so that there might be sync issues combining various units.

Regarding the routing, yes 2X4HD allows any matrix, but as i am not a purist i would use the analog input which is by far the most easy way to combine various 2X4HD...:cool:
 

twest820

Member
2009-06-24 10:49 pm
2X4HD works in async mode so that there might be sync issues combining various units
Not might, will. Without a word clock even if the internal 96k sample rate is delivered by ASRC the two units will get out of sync with each other. The simplest way round this is any audio interface type gizmo with 6-8+ line outs, be it from Focusrite, MiniDSP, MOTU, or several other manufacturers.

Depending on data flow, hardware capabilities, and software support it is sometimes possible to bond separate units together. This is quite a rare feature, however.

I use multiple USB adaptive mode DACs with a Raspberry Pi and they remain 100% synchronized.
The downside is it's a software sync where the host adds or removes samples to keep different hardware clocks aligned within a few samples. I'm not up on the implementation details of current Linux drivers on this but, at least historically, such clock management in USB audio stacks has been high error compared to hardware ASRC or word clock locked PLLs.

Also, and to my not insignificant surprise, I've found in some cases reliable ABX discrimination of timing errors down to about 5us. One might as well call that one 192k sample. At the common 44.1k sample rate maintaining sync within this tolerance requires fractional resampling, which is rather involved and rarely supported.

One can usually mitigate these issues when choosing which interconnect goes where. Mathematically there will be some impact on imaging and, psychoacoustically, it's plausibly audible. I haven't listened to such a configuration so can't personally comment on subjective preference, neutrality, or dislike. I have handled user complaints about poor audio quality where use of spread spectrum clocking results in different times being perceived by USB devices and the host. But spread spectrum timing mismatches are an order of magnitude larger than drifts against the fixed frequency clocks usually employed in mid-fi and up devices.

I believe you're thinking of USB 1, not 2.0
It's a confusion of full speed with high speed, actually. The table of versions and speeds you link is correct, as is the math there showing full speed supports more than stereo 24/96. Though the ability to fit, say 3 x 24/96, into a full speed isochronous frame is rarely useful. And increasingly obsolete.
 

GDO

Member
2009-07-23 2:16 pm
Not might, will. Without a word clock even if the internal 96k sample rate is delivered by ASRC the two units will get out of sync with each other. The simplest way round this is any audio interface type gizmo with 6-8+ line outs, be it from Focusrite, MiniDSP, MOTU, or several other manufacturers.

Sure, "might" was an euphemism. But i have not observed any problem combining several adaptative usb devices based on PCM29XX or Tenor TE7022.

Yes these might be obsolete, like TDA1541 and stuff like that which are still quite usable and enjoyable...:cool: