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Old 5th December 2008, 07:09 PM   #11
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6 months ago I did some basic research with my buddy for a "pass D1 Clone"......we stopped the planning and after a drunk summer I remember only this :-)

A) the SRC4192

Its a great Sample Rate Converter which integrates a DIR and a multifeature SRC. It has many Inputs and able to mux. We planned to use a PCM2707 (as USB receiver) -> SRC4192 -> PCM1794

A PLL can feed the SRC and PCM. The SRC4192 can Upsample to eliminate some kinds of jitter....it can recreate the clock based on the input signal (up to 192khz) or with extern clock (up to 212Khz).

The signal to noise ratio and many other specs are very good. Although DIR9001 has very low jitter....the SRC is a real Jitterkiller.

To place a small PCM2707 as USB Receiver would make your microDAC more versatile......for PC or Mac User. Just a thought!

My opinion, regarding your great tiny-micro-dac-work.....give it a try.

I am not a pro......but thats what I remember from the Tech Talk of my DIY friend in Germany.

Have to tell my friend about your Project....he will love it!

have nice evening

Alan
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Old 5th December 2008, 07:57 PM   #12
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I do plan on making one with the PCM2707 eventually. For right now I need SPDIF input because my source (a PC as DSP) has three SPDIF outputs.

I've read about the capabilities of the SRC and get what it does (sort of), but my original question still stands; is it worth the effort?

My source is 16-bit 48kHz; will I (a non-believer of audiophile magic) be able to tell the difference if I include the SRC to upsample to say 96kHz?
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Old 5th December 2008, 09:43 PM   #13
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Upsampling is not voodoo - it is measureable, sometimes hearable.

1) Measurement

Conversion 16bit to 24 bit (and almost the same wit 44,1 to 192khz)

Pictures from Hoerwege Website - german audio manufacturer at www.hoer-wege.de

16bit

Click the image to open in full size.

24bit

Click the image to open in full size.

The 44,1 to 192Khz Conversion works similar.....not the same but similar. Esxcuse my bad english.

2) can your hear it?

The rule of thumb says - what isnt in the music will be not better due to upsampling....if your source is just average it will still be average in 192khz. To avoid Jitter in your Player is the best way to kill jitter :-)

I switched completely to PC based audio.......FLAC files.....ASIO driver for bit-perfect playback...USB....etc!

For me.....just my experience.....with my EZDac.....is that the sound gets smoother with 192Khz....with Headphone I believe that noise is less with low volume music....but questions stays.....is the noise from your DAC, source, Amp, cable, PSU, Headphone etc?

just my 2 cents :-)

regards

Alan
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Old 5th December 2008, 11:25 PM   #14
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To be honest, I doubt I would be able to tell the difference. Lets say I did want to add the SRC though, is it worth doing using the DIR9001 recovered clock signal? If I really have to add an external clock then I wouldn't want to bother.

What should the output clock from the DIR9001 be set at, 128Fs? Should I resample to 192kHz? Why does the ezDAC only resample to 96kHz?

Sorry for all the questions and thanks for the help, I'm still trying to a grasp on this digital stuff.
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Old 6th December 2008, 02:12 AM   #15
JC951t is offline JC951t  Taiwan
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Sorry I'm no expert but after auditioning a couple
of cdp with upsampling, I felt that the sound is too
hifi. Maybe it's just me.
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Old 6th December 2008, 08:12 AM   #16
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Hello,

the SRC can reclock internally based on the input signal (Recovering clock!)....so no external Clock needed.....its just another option.

Maybe I did understand you wrong - do you want to use the DIR and SRC together? Because SRC has a DIR built-in!

The DIR9001 cant upsample to 192Khz. It can only play what is coming in....if 48Khz is on the inputs then only 48Khz on the outputs.

192 Khz is not a must......96Khz upsampling is also okay....but many companies are using higher values (192Khz instead of 96 Khz) to imply "better". 96 Khz is okay....with 96Khz you can use 256fs....some people use only 48Khz with 768Fs......never compared the sound of the different settings......i think its just a "measuring" thingie!

But your suspicion is right....if you build a basic microDac....maybe SRC is not relevant because the benefit of an SRC would be.....using a external clock to reclock the DAC and SRC...to get more exact DA results. Drawback......your micro DAC Design will be larger in size.

So, let the SRC out.......Micro1794DAC V1.0 (without SRC) :-)

cya

Alan
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Old 6th December 2008, 08:15 AM   #17
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OK, I've modified my schematic to include the SRC4192 using the recovered clock from the DIR9001. I have hardwired all the jumper settings for what I need, hopefully I have them correct.

I would really appreciate it if someone could take a look and tell me if this will work. The only thing I am really unsure of is the reset of the SRC4192. In the datasheet it says it needs a clock signal present during reset, but the clock is coming from the DIR9001 that also gets reset at the same time.

Here is a rundown of all the jumper settings.....

DIR9001

CKSEL -> ERROR : Auto Mode
FMT0 = 1, FMT1 = 1 : 24-bit, MSB-first, I2S Output
PSCK0 = 0, PSCK1 = 0 : SCKO = 128Fs

SRC4192

IMFT0 = 1, IMFT1 = 0, IMFT2 = 0 : 24-bit I2S Input
MODE0 = 0, MODE1 = 0, MODE2 = 0 : Clock I/O Slave Mode
OMFT0 = 1, OMFT1 = 0 : I2S Output
OWL0 = 0, OWL1 = 0 : 24-bit Ouput

PCM1794A

MONO = 0, CHSL = 0, FMT0 = 0, FMT1 = 0 : I2S, Stereo, Sharp
DEM = 0 : De-Emphasis OFF


Thanks
Attached Files
File Type: pdf microasrc_dac.pdf (46.7 KB, 919 views)
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Old 6th December 2008, 08:32 AM   #18
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Alan,

Sorry, was busy typing when you posted above.

I guess I am not understanding some things here. I do not see where the SRC4192 has the ability to input a SPDIF signal, hence the need for the DIR9001? I also don't understand how to determine what the DIR9001 output clock Fs needs to be.

I see a mistake I made already with the SRC mode selection. It should be....

MODE0 = 1, MODE1 = 1, MODE2 = 0 : Clock IN Slave Mode/Clock OUT Master Mode 256Fs

Maybe I should stick to the basics and just finish the active I/V and stop trying to show off.
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Old 6th December 2008, 09:15 AM   #19
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I *think* I have finally figured out what xxxFs is now (something that should have been obvious), it is the sampling frequency times a multiplier. For instance, if the sampling rate of the SPDIF signal to the DIR9001 is 48kHz and I have PSCK[1:0] set for 256Fs, then the output clock frequency will be 12.288MHz.

This makes sense now because when I play around with the settings of PSCK[1:0] with my working DAC it doesn't seems to change anything. I see that is because the PCM1794A can accept all the different clock frequencies that creates.

One baby step at a time I guess.
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Old 6th December 2008, 09:35 AM   #20
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Eureka, I've got it! (proclaims the noob)

I think I have it all figured out now.....

The maximum sampling rate the DIR9001 can handle is 96kHz. If I set PSCK[1:0] to 512Fs, that will make the clock output 49.152MHz. With the SRC4192 set to slave input with a master output of 256Fs, the PCM1974A will be receiving a 192kHz sampling rate.

I will ask one more time to be sure though, will using the recovered clock from the DIR9001 make this whole exercise pointless?
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