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Old 26th November 2007, 02:46 AM   #921
hbarki is offline hbarki  Indonesia
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"The XO is a 24.576mhz extremely low jitter crystek part which is perfect for doing 96/24(256fs) or 192/24(128fs)."

I am trying to figure out how the ASRC in Metronome works, but somewhat confused.

Could someone explain to me where does the number 256fs and 128fs above come from, and what does it mean?

Thanks!
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Old 26th November 2007, 03:19 AM   #922
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Quote:
Originally posted by hbarki
"The XO is a 24.576mhz extremely low jitter crystek part which is perfect for doing 96/24(256fs) or 192/24(128fs)."

I am trying to figure out how the ASRC in Metronome works, but somewhat confused.

Could someone explain to me where does the number 256fs and 128fs above come from, and what does it mean?

Thanks!
"fs" stands for "sampling frequency". Specifically since we are using the output in master mode to take advantage of the low jitter clock, we will be using that clock as the reference.

256fs = 256 x sampling frequency which at 96khz = 24.576mhz.

Likewise 192khz x 128 = 24.576mhz.

So to get 96khz output you set the metronome for 256fs on the output in master mode.

To get 192khz output you set the metronome for 128fs on the output in master mode.

Hope that helped.

Cheers!
Russ
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Old 26th November 2007, 04:26 AM   #923
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Which are parts from Twisted Pear Audio what I can build the complete Opus DAC with:
- coaxial and USB digital input signal
- I2S input signal (for CD transport's I2S output signal, is it better?, I think because it is raw signal)
- RCA and XLR balanced analog output
Thank you
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Old 26th November 2007, 05:36 PM   #924
hbarki is offline hbarki  Indonesia
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Default SRC metronome setup

Thanks, Russ!

I placed in my order for the Metronome and Opus set - cannot wait

Is the Metronome using SRC4192 chip?
So if it is using SRC4192, in order to upsample to 24bit 192kHz, I will then setup as follow:

mode2=0
mode1=0
mode0=1

OWL0=OWL1=0
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Old 26th November 2007, 05:43 PM   #925
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Default Re: SRC metronome setup

Quote:
Originally posted by hbarki
Thanks, Russ!

Is the Metronome using SRC4192 chip?
So if it is using SRC4192, in order to upsample to 24bit 192kHz, I will then setup as follow:

mode2=0
mode1=0
mode0=1

OWL0=OWL1=0
Yes it is the SRC4192.

Your setup info (MODE and OWL) is correct but not complete. You would want to be sure to setup IFMT and OFMT to whatever format you need.

For Opus that would probably be I2S 24bit.


Cheers!
Russ
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Old 26th November 2007, 07:28 PM   #926
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Thanks Spartacus for your information, I should have pointed to your post in my original email.

So let me get this correct, is the Metronome an unsampler or re-clocker? Or perhaps both?

Also thanks to you analog_sa for your help, but i'm still a little confused.

If I want to use the Metronome with my other Opus stuff should I put it between the USB input via I2s to Metronome to OPUS Dac via 12s? If this is correct? How is the Metronome powered? If it is re-clocker is there a clock? Do I need anything else?

Sorry if I'm being a bit dense, digital electronics are new to me and if I don't ask I won't know.
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Old 26th November 2007, 07:47 PM   #927
VT67 is offline VT67  Belgium
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I'm glad you're asking these questions because now I don't have to.
I was struggling with the same issues.

Regards
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Old 26th November 2007, 08:10 PM   #928
OneyedK is offline OneyedK  Belgium
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Quote:
Originally posted by rjbaldwin
So let me get this correct, is the Metronome an unsampler or re-clocker? Or perhaps both?
Both...

Datasheet says:
The input data is passed
through interpolation filters which up-sample the data, which
is then passed on to the re-sampler. The rate estimator
compares the input and output sampling frequencies by
comparing LRCKI, LRCKO, and a reference clock. The
results include an offset for the FIFO pointer and the coefficients
needed for re-sampling function.


I ordered a "metronome" myself, just to see if it's an actual improvement.
I really don't know what to expect, half of the functions of the SRC4192 are already in the WM8804 receiver, the other half of the functions are already performed by the WM8740.
If it's a really audible improvement, we'd simply know that the WM8740 is not the best choice as a DAC.
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Old 26th November 2007, 08:25 PM   #929
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Quote:
Originally posted by OneyedK
I really don't know what to expect, half of the functions of the SRC4192 are already in the WM8804 receiver, the other half of the functions are already performed by the WM8740.
If it's a really audible improvement, we'd simply know that the WM8740 is not the best choice as a DAC.
Well not exactly correct...

The way things are done are not the same at all, but you will still get very good results even without a metronome.

What I mean is you can't put 44.1/16 into WM8804 and get out a 192/24 sample. With the metronome you can.

At first the metronome was an experiment purely for my own pleasure/curiosity, but it seems to have grown legs. I don't expect everyone will think its as fun as I do. I also happen to think it makes things sound a bit better, at least thats my subjective opinion.

One Key benefit is that instead of the clock being "generated" by a PLL (ala WM8804/PCM2707) you get a nice clean low jitter master clock. I think that is probably one of the key benefits. Also the whole metronome has its own VREG so its supply is very clean. You can even power it completely separately from the rest of your stack if you so choose.

Cheers!
Russ
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Old 26th November 2007, 08:30 PM   #930
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Another key point. I wanted to provide the metronome for cases where people only had (easily accessable) the bit clock, word clock, and data PCM signals. No master clock. In this situation the metronome provides the master clock. All is well.

An example is some of the Opus owners who have CDPro transports etc.

It also seems to clean up the USB module I2S signal very very well.

Cheers!
Russ
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