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Old 17th August 2012, 11:48 AM   #201
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I don't know about the ESS - does it share a clock or run of the wm8805 mclk ?

For the wm8805, the datasheet says the best performance is when r = 8, and iirc my calculations got r as 8.35374 and 8.7075 for 44.1/48 input with a 22.5792 xo , so I decided this was the best xo freq, not least because it means you can use a cchd-957 xo.

I'd need to re-study that datasheet to work out if this is in fact 100% the best choice, and I don't have time for that. All my projects are on hold as I have no spare time.
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Old 18th August 2012, 05:37 AM   #202
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Quote:
Originally Posted by KlipschKid View Post
I don't know about the ESS - does it share a clock ...
Generally, no. But forum member EUVL reports a benefit from the WM8804 S/PDIF receiver sharing the same external clock as the ESS DAC. In EUVL's implementation, the XO is 48 MHz, divided down to 12 MHz for the WM8804.

But with a software-controlled WM8805 we are not limited to 12MHz, and I'm asking if we can use more suitable clock-rates for both the S/PDIF receiver, and the DAC? This would be taking the "synchronous" concept to its optimum.
And of course, the samplerate of the source material must also be considered when applying a "synchronous" regime.

Let me apply some numbers, and hope I understand this correctly -

For 44.1 kHz material (and 88.2), I'm thinking that a 22.5792 XO would be the best to share between the WM8805 and a DAC;
- PRESCALED to 11.2896, you could use an N-value of 8, and K-value of 0. This lets the WM8805's PLL do a straightforward multiplication to 90.3168 MHz (within spec) for its S/PDIF RX, and this is a neat multiple of optimal clock rate for 44.1 kHz material.
- and the 22.5792 XO is a also a suitable clock rate for the DAC, when dealing with 44.1 kHz material.

For 48 kHz material (and also 96), a 24.576 XO would be best;
- configure the WM8805 to PRESCALE to 12.288, PLL_N "8", PLL_K "0".
The f2 value is then 12.288 x 8 = 98.304 (within spec) and suitable for 48 kHz / 96 kHz sources.

Am I right?
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Old 18th August 2012, 06:04 AM   #203
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For 44.1/88.2/...khz it is common to use 22.5792Mhz because there is no rounding for the multiple; it is an integer (512, 1024, ..), and for 48/96/... it is usual to use 24.576 for the same reasons.

Some devices (like the Via pci receivers in some sound cards) can have two external xo's, which to me seems like the best solution, but then they are not great receivers. I wonder if it would be possible to configure the wm8805 to do this ? I don't think so.

So which clock to choose ? I guess it depends on what most of your material is. Mine is mostly CD and SACD with only a few DVD-A, so for me I think this is why I preferred the 22.5792Mhz to 24.576, but I have a nagging thought that the maths told me I'd get closer to 8 with 22.5972 and that's what the wm wants. What does the ESS want ?

Anyway, I honestly can't remember if the pll in the wm8805 works the usual way above. I seem to remember it does something unusual so I'm afraid I'm not able to say if you are 100% correct. Have you checked the data sheet for this ?

Also consider - who's writing the code ? If you're doing it yourself then of course you can try both, and measure/listen to decide. If not you, what does the programmer say ? Also, IIRC the wm8805 is a bit of a pig for 88.2khz, 192khz material as it requires a reset (or something like this - my memory is fuzzy), so going with the programmers advice would make sense to me.
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Old 18th August 2012, 10:37 PM   #204
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Quote:
Originally Posted by KlipschKid View Post
Hi,

Well, software is going to be a headache it seems. There's no available code for LCDuino. Linux Works says it is hard to program, so it must be extremely hard to program ! He says he hasn't given up... but that sounds like he wants to !
hey all

yes, its true, I am not looking forward to doing software for this chip. but I do PLAN to. I even bought a few more samples to burn^Htry.

I also do have this ebay/hongkong kit. its assembled and waiting for my code, in fact. I can switch between the included PIC controller and my own LCDuino, but I just have not finalized a few details of the code, so its not runnable yet.

if I get into trouble, I got myself a logic analyser and so, worst case, I could i2c-sniff what the 'factory firmware' does and see if I can at least do the same in my code.

has anyone confirmed that the factory code DOES actually lock-in and work at all samplerates?

one of the detours I took was wanting to get some source of all the samplerates. I got into the Audio Widget project, then created an spdif transmitter for it using the wolfson chip, but in hardware mode. it sends all samplerates if you give it i2s. I've personally confirmed that. but its the other way that we want: we want spdif IN and i2s or spdif OUT. in that mode, hardware won't support all the samplerates (as we all know). but I wonder if the ebay board in software mode DOES work in all rates?
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Old 18th August 2012, 11:24 PM   #205
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update: I just tried playing every samplerate other than 32k. this is what I see from the ebay firmware and the wolfson chip:

44,48,88,96: all ok

176, I -think- gets passed thru (spdif meter says 176k but my dac does not play)

192 seems to get stopped and even mapped to 44k!

so, that's a first pass, informally, testing this ebay unit. I'm not convinced they have done a good job with firmware at all. unless I did something wrong, they did not support 176/192 properly.
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Old 19th August 2012, 02:12 AM   #206
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linuxworks, there's Arduino code for WM8805 here -
https://github.com/kabturek/WM8805
Does this help?
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Old 19th August 2012, 03:57 AM   #207
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yes, I did see that and I saved it away.

looking at it again, I see:

uint8_t WM8805::frequency(){
if(!is_locked()){
return 0;
}
//frequency is the 5:4 bits of pll6, we use the mask 48
uint8_t freq_bits = (this->spdstat & 48) >> 4;
if(freq_bits == 0){
return 192;
} else if( freq_bits == 1){
return 96;
} else if( freq_bits == 2){
return 44;
}
return 32;
}

unless I'm missing something, he's also leaving out 176. isn't that the 'thorn' in everyone's paw?

I also don't see 88k in there. I'll have a better look at the code to see what's going on. anything that compiles is a good start, isn't it?
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Old 19th August 2012, 06:30 AM   #208
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Mine locks onto 44.1, 48, 88.2 and 96. I don't have any 192 discs to try, sorry, but I wouldn't be at all surprised if it didn't. IIRC the Taobao/Ebay ads don't mention any of them at all.

It's great to see you're working on code for this. Do you have a best xo freq in mind ? 22.5792 ?
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Old 19th August 2012, 08:38 AM   #209
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Quote:
Originally Posted by KlipschKid View Post
Some devices ... can have two external xo's, which to me seems like the best solution,
...
I wonder if it would be possible to configure the wm8805 to do this ?
Yes, this is what I was really suggesting. That's how the Audio-Widget works - its microcontroller detects the source samplerate, then activates either of two XO's which is most suitable. This activation logic is via the "enable" pins on the XO's. Apparently the inactive XO has also has its outputs shorted.

So the big question is: can the WM8805 detect the samplerate of the incoming S/PDIF stream, and properly report this to a controller (such as Arduino) -
then the controller can be programmed to do the necessary enable/disable function for the two XO's.
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Old 19th August 2012, 08:43 AM   #210
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Quote:
Originally Posted by linuxworks View Post
unless I'm missing something, he's also leaving out 176.
...
I also don't see 88k in there.
Yes ... there's no "48" listed, either.
As I read the WM8805 datasheet, the "Recovered Frequency Flag" (REC_FREQ) cannot differentiate between 44.1 and 48, neither between 88.2 and 96.

To determine the exact samplerate, I'm guessing you would need to read from a different parameter of the WM8805;
possibly "Original Sampling Frequency" (ORGSAMP)
or "Indicated Sampling Frequency" (FREQ)
I see a danger with "Indicated Sampling Frequency" - it would rely on the incoming S/PDIF source to have properly implemented this flag in its transmitted stream.

But in the case of the Arduino code from kabturek, differentiating between 44.1/48 and 88.2/96 might not actually matter. It just depends on what he is using the "freq_bits" variable for.

In our case, however, we're aiming to use optimised XO's, and possibly dual XO's as I described in my previous post. In this case, determining the correct source samplerate is critical.
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