In USB audio, I know of no way of 'slaving' the host computer's transmission rate other than using the Asynchronous mode of feedback/synchronization in the Isochronous mode of operation.
As of now none of the mass market (the ubiquitous PCM27xxx) usb chips offer that kind of synchronization. I believe they all just do the Adaptive mode of synchronization, which is nothing but adjusting the DACs clock to match the PC's transmission rate. Basically the DAC follows the PC (insert chilling shiver here).
So what's the point in doing an I2S conversion from USB ? There no reverse feedback possible anyway!
In fact in those terms it would be just like spdif. What would one acheive by 'converting' spdif to I2S ?
As of now none of the mass market (the ubiquitous PCM27xxx) usb chips offer that kind of synchronization. I believe they all just do the Adaptive mode of synchronization, which is nothing but adjusting the DACs clock to match the PC's transmission rate. Basically the DAC follows the PC (insert chilling shiver here).
So what's the point in doing an I2S conversion from USB ? There no reverse feedback possible anyway!
In fact in those terms it would be just like spdif. What would one acheive by 'converting' spdif to I2S ?
ok I should have been more clear - when I said I2S I was referring to the use of I2S for the purpose of slaving the source as well.
I agree that I2S would still be better than spdif any day, but when converting from USB all that it will do is provide a better interface, but still no advantage in terms of using your own clock.
I agree that I2S would still be better than spdif any day, but when converting from USB all that it will do is provide a better interface, but still no advantage in terms of using your own clock.
I see three ways of looking at it:
Your DAC may not accept SPDIF input, and you may need a I2S input for it (TDA1543, PCM1792, etc).
If it does, converting USB (1.1) to I2S should not provide any benefit at all, over USB to SPDIF.
If it offers both, there may be differences in the way it handles SPDIF versus I2S, and then it may or may not make sense to use USB->I2S.
You cannot reclock a PC source with a USB 1.1 connection, not with a mass-market product (if at all). Since it is a mass-market product, reclocking is probably an extravagance, anyway. However, two-way communication does happen on USB 1.1 - since thumb drives can do it, there may be a way to write some kind of a driver for a USB controller. It's still a lot of work.
IMO nothing beats Firewire for getting a signal out of the PC today, as long as you have drivers and the right device. Zero latency, external clock and everything is outside the PC environment.
Your DAC may not accept SPDIF input, and you may need a I2S input for it (TDA1543, PCM1792, etc).
If it does, converting USB (1.1) to I2S should not provide any benefit at all, over USB to SPDIF.
If it offers both, there may be differences in the way it handles SPDIF versus I2S, and then it may or may not make sense to use USB->I2S.
You cannot reclock a PC source with a USB 1.1 connection, not with a mass-market product (if at all). Since it is a mass-market product, reclocking is probably an extravagance, anyway. However, two-way communication does happen on USB 1.1 - since thumb drives can do it, there may be a way to write some kind of a driver for a USB controller. It's still a lot of work.
IMO nothing beats Firewire for getting a signal out of the PC today, as long as you have drivers and the right device. Zero latency, external clock and everything is outside the PC environment.
Is there any such thing as a sound card with a word clock input?? If so could you have a converter with Is2 on your end that feeds its word clock back to the sound card and forces it to transmit (whether USB or SPDIF) in sync with your local clock? Just thinking out loud here. I'm not sure if such a card exists for consumer PC's but, in the pro audio world, digital audio gear that syncs to an external clock is pretty common.
Plenty soundcards have a word clock input, and some even have word clock outputs.
The E-mu1212m, for example, interfaces with an add-on card with BNC connectors for word clock sync.
But then the SPDIF output of that card is pretty good.
Soundcards normally don't have USB connectors for passthrough, only SPDIF. Normally the controllers on the cards determine the clock of the DACs on them so even though the chips are separate it's a closed system, difficult to get in to.
The E-mu1212m, for example, interfaces with an add-on card with BNC connectors for word clock sync.
But then the SPDIF output of that card is pretty good.
Soundcards normally don't have USB connectors for passthrough, only SPDIF. Normally the controllers on the cards determine the clock of the DACs on them so even though the chips are separate it's a closed system, difficult to get in to.
Hi there,
I'm using a M-audio transit to get I2s from a TAS1020A chip (USB) and it sound quite good into a TDA1541A. Much better than an EMU 1212m internal card. Get one of those, follow the datasheets and you get the pinout.
Make sure that the USB card has the proper grounding with the DAC board, other than that, happy listening.
Regards,
Lucian
I'm using a M-audio transit to get I2s from a TAS1020A chip (USB) and it sound quite good into a TDA1541A. Much better than an EMU 1212m internal card. Get one of those, follow the datasheets and you get the pinout.
Make sure that the USB card has the proper grounding with the DAC board, other than that, happy listening.
Regards,
Lucian
I have come across pci soundcards with a word clock input. But I haven't found any 'external' (or atleast sanely priced external) soundcards that have word clock input.
Even having just a word clock input isn't enough, unless you want to stick with the DACs and opamps of the soundcard itself. But to do what we mostly do around here, it would only make sense for a soundcard to have a word clock input AND an I2S output(but beware, read below). Or atleast bidirectional I2S that will allow you to slave the soundcard to an external clock. But I suppose if a card has a word clock input it most likely has an I2S output as well.
It's possible that some firewire or ethernet soundcards could exist that would have a word clock input but I would be very surprised to see a USB soundcard. And if you find a USB soundcard you might want to be careful how in the world would they do that because of what I said earlier about the whole Asynchronous synchronization/feedback (or)deal in USB.
I don't know much in detail about Firewire and Ethernet but it sounds like it has the feedback built into the nature of the protocol.
Even having just a word clock input isn't enough, unless you want to stick with the DACs and opamps of the soundcard itself. But to do what we mostly do around here, it would only make sense for a soundcard to have a word clock input AND an I2S output(but beware, read below). Or atleast bidirectional I2S that will allow you to slave the soundcard to an external clock. But I suppose if a card has a word clock input it most likely has an I2S output as well.
It's possible that some firewire or ethernet soundcards could exist that would have a word clock input but I would be very surprised to see a USB soundcard. And if you find a USB soundcard you might want to be careful how in the world would they do that because of what I said earlier about the whole Asynchronous synchronization/feedback (or)deal in USB.
I don't know much in detail about Firewire and Ethernet but it sounds like it has the feedback built into the nature of the protocol.
There are firewire with BNC word clock inputs. My Mackie 400f has them and I am pretty sure the focusrite and presonus cards had them too when I was looking.
I only know of the Black Lion external clock that is intended to be used to improve jitter or clock performance.
http://www.blacklionaudio.com/microclock.html
I only know of the Black Lion external clock that is intended to be used to improve jitter or clock performance.
http://www.blacklionaudio.com/microclock.html
It's part of the USB audio standard. Unless you use asynchronous isochronous mode (which needs special hardware ie not PCM27xx) your clock will be derived from USB ticks.
USB audio standard 2.0 should correct this.
I'm building a FPGA based USB soundcard which will do it the right way (ie clock in the DAC)...
USB audio standard 2.0 should correct this.
I'm building a FPGA based USB soundcard which will do it the right way (ie clock in the DAC)...
peufeu said:
I thought the problem was pre-Vista Windows operating systems and also the unavailbility of hardware (like usb interface chips) that can provide the Asynchronous feature in a 'ready to use' form. I believe the standard always had the capability. Or in other words - what changed in 2.0 that would correct something ?
iirc, there have been successful implementations of Asynchronous feedback in USB in Linux and in usb v1.1 .
I seem to remember from reading the specs that, while 1.0 allows it, USB Audio 2.0 makes it a lot easier to use asynchronous mode. Maybe that's the reason why...
USB Audio 2.0 should correct this because it specifies asynchronous mode in much more detail, and hopefully driver developers at M$ will implement the complete standard this time... and maybe get it right ? who knows.
USB Audio 2.0 should correct this because it specifies asynchronous mode in much more detail, and hopefully driver developers at M$ will implement the complete standard this time... and maybe get it right ? who knows.
peufeu said:
With all that I have been reading here and in other threads, I am of the opinion that it would be useful to majority of people on this board to find some external firewire card that will be suitable for modification. Than use their fire wire protocol and than work and develop something from there. So in the another words, have obvious benefits from firewire that seems to be untouchable part for majority of us and work on the part we can. Just an idea.
lucpes said:
I got one of these M-Audio Transits.
1. It is USB powered. IMO - NoGo.
2. It is noisy. IMO - NoGo.
3. It is isync. IMO- ??? It depends heavily on your PC setup
4. It delivers 24/96 - OK
I2S I havn't tried yet.
I currently feed my Buffalo DAC with I2S from a PCM2707 receiver ( Old DDDAC).
This sounds better than SPDIF from USB 0404 USB (async USB) to Buffalo.
I havn't managed to get the M-Audio transit working with my Opticis USB cable under Linux.
(I am connecting all my USB PCM 270x based receivers via Opticis)
This way I feed it with clean 5V regulated battery power. I figured out that the galvanical USB isolation plus a clean local USB 5V supply, will improve performance quite heavily. Unfortunately these Opticis devices ( with a downstream PS) are USB 1.1 only.
Anyhow I'll give M-Audio Transit - I2S a try. (I'd appreciate if you could PM me to give directions - picture? of your mod)
Cheers
AR2 said:
I'm on a budget... this is the one i've been looking at.
http://www.rolandus.com/products/productdetails.aspx?ObjectId=731&ParentId=114 (excuse the b^&%$# flash)
I have the USB one in the same paxkage and it is nice.
dave
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