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Old 2nd November 2012, 12:26 PM   #331
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Lets se if I have understood this right then
If I want to run a pair of external stereo dacs from the second I2S port
in asyncronus mode that will not be a problem ?
The six channels was clear, but why not all eight ?
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Old 2nd November 2012, 12:37 PM   #332
chaparK is offline chaparK  Luxembourg
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Can you explain what you mean with 'asynchronous' in the context of I2S? That's not clear to me.

There are 6 outputs on this expansion port because only 3 I2S data lines are available, with 2 channels per data line.
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Old 2nd November 2012, 01:43 PM   #333
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Quote:
Originally Posted by chaparK View Post
Can you explain what you mean with 'asynchronous' in the context of I2S? That's not clear to me.

There are 6 outputs on this expansion port because only 3 I2S data lines are available, with 2 channels per data line.
I think what he is asking is if you can run an external dac in addition to the onboard dacs ?

regards
Trev
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Old 2nd November 2012, 03:03 PM   #334
ChrisPa is offline ChrisPa  United Kingdom
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I interpret asynchronous to mean the DAC controlling the clock/data rate rather than the dsp board
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Old 2nd November 2012, 04:37 PM   #335
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Quote:
Originally Posted by ChrisPa View Post
I interpret asynchronous to mean the DAC controlling the clock/data rate rather than the dsp board
Yepp
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Old 2nd November 2012, 04:56 PM   #336
TNT is offline TNT  Sweden
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So its still synchronous but the master is the DAC or do You want to disconnect the clocks and introduce some memory to compensate for the two clock domain differences?
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Old 2nd November 2012, 08:07 PM   #337
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Hi Nick
I have been following this thread for some time now with interest. This is a fairly simple question but will make life easy for me at least:

Are you planning a nice case for this board?

Cheers

Aidan
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Old 3rd November 2012, 02:04 AM   #338
chaparK is offline chaparK  Luxembourg
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Quote:
Originally Posted by ChrisPa View Post
I interpret asynchronous to mean the DAC controlling the clock/data rate rather than the dsp board
No this is not possible. The reason is simple: the master clock is onboard.
You simply cannot request samples from a system that has its own clock without going through a sample rate converter.

Quote:
Originally Posted by Trevor White View Post
I think what he is asking is if you can run an external dac in addition to the onboard dacs ?
Trev
This is absolutely possible. The data transiting through this expansion port is independent of what's going to the DACs - but they share the same clock. The cool feature is that, if we decide to expand the number of channels, then we can effectively have 14 analogue outs (8 + 6).


Quote:
Originally Posted by TNT View Post
So its still synchronous but the master is the DAC or do You want to disconnect the clocks and introduce some memory to compensate for the two clock domain differences?
You must set your external DACs is slave mode: they get the data lines, the frame sync, the bit clock and the master clock.

Quote:
Originally Posted by chalkandtalk View Post
Hi Nick
I have been following this thread for some time now with interest. This is a fairly simple question but will make life easy for me at least:

Are you planning a nice case for this board?

Aidan
Hi Aidan,

There's no plan for a finished product at this point at least. We'll make a demo unit and we'll display all the details so that you build your own unit with confidence.

Cheers

Nick
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Old 3rd November 2012, 08:31 AM   #339
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From a differrent thread.
Quote:
The center of all functions will be the dsp filter that "Chapark" is working on
and at the I2S input I will have "Loriens" usb reciver. I will also be in need of
both digital and analog inputs of the dsp. If I'm not misstaken that will
disqualify the possibility to use the Wave IO as a masterclock, right? The
plan for outputs are to connect two stereo dacs to I2S and use ESS digital
volume control before sending this to four channels of John Broskie's "Unballancer".

Could someone with more experience in digital clocking please describe the
best way to clock a setting like this. I don't mind bying an external clock
if that's needed.
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Old 3rd November 2012, 12:51 PM   #340
chaparK is offline chaparK  Luxembourg
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Quote:
Originally Posted by dahlberg
The center of all functions will be the dsp filter that "Chapark" is working on and at the I2S input I will have "Loriens" usb reciver. I will also be in need of both digital and analog inputs of the dsp.
So far no problem

Quote:
Originally Posted by dahlberg
If I'm not misstaken that will disqualify the possibility to use the Wave IO as a masterclock, right?
Well yes and no.
I assume Wave IO and Lorien's usb receiver are the same unit.
In the first version of the board software, the central clock is internal. This is what disqualifies any external clock as master clock.
So, with the first software, you just connect your USB receiver to the I2S port and data is converted to the internal rate. You can also use any of the analogue/spdif inputs and you can anytime switch between all 4 inputs (analogue, coax, optical, I2S).
This works perfectly but uses the onboard clock.

In a forthcoming software revision, there will be the option for feeding an external clock to the system through the expansion port.
With this setup:
- Analogue audio will be AD converted using that external clock.
- SPDIF will be rate converted to the system rate
- I2S input data will bypass the sample rate converter because it's expected to be at the rate of the supplied external clock.

In this second setup, you're responsible for supplying a clock that has the proper rate. This means that if you actually supply a clock different from the one that you told the system you would supply, then it's not going to work as expected. Also, if the rate of your clock changes (for example because the clock is regenerated from chunks of digital data sampled at various rates), then you are going to hit problems as well.
I want here to stress that if you're making the choice of supplying an external clock, you're also taking on the responsibility of that clock. It's not going to be plug and play.

Quote:
Originally Posted by dahlberg
The plan for outputs are to connect two stereo dacs to I2S and use ESS digital volume control before sending this to four channels of John Broskie's "Unballancer".
Ok so here we have another device who wants a clock.

I'd like first to briefly mention that the term 'asynchronous' doesn't fit nicely the context of I2S coms. Indeed, I2S is inherently 'synchronous' in the sense that both endpoints use the same clock transmitted along data and synchronously to it.

So this is it: there are 2 endpoints (external DAC and DSP board) but only one clock, so we must decide whether the clock comes from the DSP or from the DAC. We'll call 'Master' the endpoint supplying the clock and we'll call 'Slave' the endpoint sync'ed with the Master's clock.

I said here in a previous post that the expansion port that has 6 extra outs will only work in Master mode. This actually means that data on this port is at the system's central rate, which is derived either from the onboard PLL or from the external clock supplied via the other expansion port (future software revision as discussed above).

You understand now that if you want this port to work in Slave mode (i.e. clock supplied by your DACs), then you're introducing a 3rd clock in the system.
We have to set now who's the 'boss of it all', as would say Lars Von Trier. Do you want the master clock to be generated from the onboard PLL? Do you want that clock to be supplied by the USB receiver? Or do you want the master clock to be supplied by the DACs? This is the question you must answer.

My guess is: just feed your DACs with the system's central clock - which can be either PLL generated or supplied by the receiver. For allowing this, you set your DACs in Slave mode and let the DSP board be the Master of this I2S com.

Last edited by chaparK; 3rd November 2012 at 01:00 PM.
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