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PCM4222 adc and ADAT transmitter
PCM4222 adc and ADAT transmitter
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Old 3rd October 2019, 08:31 AM   #1
Dimitree is offline Dimitree  Italy
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Default PCM4222 adc and ADAT transmitter

I'm trying to understand if I can use a V1401 ADAT transmitter with the PCM4222 ADC.

They will be communicating by their PCM audio serial port interfaces, using Left-justified mode. The ADC will be set as master, and it will get a master clock from an external oscillator.
Doing so, it will generate LRCK ( = Fs) and BCK (256*Fs and 128*Fs, depending on the mode).
V1401 only needs word clock, it generates its own internal BCK using a PLL (f = 64xWDCLK).

Can I connect V1401 clock input to PCM4222 LRCK output?

my doubts are about the rate of data output of the ADC. Even if I don't use the output BCK from the ADC, and only use LRCK, I don't understand if the data rate is correct for the V1401.

https://www.ti.com/lit/ds/symlink/pcm4222.pdf

http://www.coolaudio.com/docs/COOLAU..._DATASHEET.pdf
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Old 6th October 2019, 03:15 PM   #2
weissi is offline weissi  Austria
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I was searching for something similar, but didn't find anything. Forget the Behringer stuff, these ICs are way outdated and will not deliver decent performance.
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regards / servus
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Old 7th October 2019, 02:12 PM   #3
mhelin is offline mhelin
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Quote:
Originally Posted by Dimitree View Post
I'm trying to understand if I can use a V1401 ADAT transmitter with the PCM4222 ADC.

They will be communicating by their PCM audio serial port interfaces, using Left-justified mode. The ADC will be set as master, and it will get a master clock from an external oscillator.
Doing so, it will generate LRCK ( = Fs) and BCK (256*Fs and 128*Fs, depending on the mode).
V1401 only needs word clock, it generates its own internal BCK using a PLL (f = 64xWDCLK).

Can I connect V1401 clock input to PCM4222 LRCK output?

my doubts are about the rate of data output of the ADC. Even if I don't use the output BCK from the ADC, and only use LRCK, I don't understand if the data rate is correct for the V1401.

https://www.ti.com/lit/ds/symlink/pcm4222.pdf

http://www.coolaudio.com/docs/COOLAU..._DATASHEET.pdf
That sound fine. V1401 is actually an improved version of Wavefront AL1401 which was know to have problems with some audio interfaces.

V1401 has internal PLL that's why you won't need BCLK signal at all. Well, the PCM4222 needs though. With a V1401 (alone) you are limited to 44.1 kHz / 48 kHz sample rates as at higher sample rates ADAT uses SMUX protocol which V1401 don't support though it can be used as transmitter for SMUXed signal. SMUX simply sends the 96kHz sample data over two channels @48 kHz so when using it the number of channels get halved. Otherwise V1401 is just fine and not outdated by any means. You don't want to use ADAT as clock source anyway because of jitter, so you better use the buffered LRCLK as Word clock signal output. If you have some other master clock source use Cirrus CS2300CP PLL to generate the master clock instead of the local oscillator(s).
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Old 7th October 2019, 02:36 PM   #4
Dimitree is offline Dimitree  Italy
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Quote:
Originally Posted by mhelin View Post
That sound fine. V1401 is actually an improved version of Wavefront AL1401 which was know to have problems with some audio interfaces.

V1401 has internal PLL that's why you won't need BCLK signal at all. Well, the PCM4222 needs though. With a V1401 (alone) you are limited to 44.1 kHz / 48 kHz sample rates as at higher sample rates ADAT uses SMUX protocol which V1401 don't support though it can be used as transmitter for SMUXed signal. SMUX simply sends the 96kHz sample data over two channels @48 kHz so when using it the number of channels get halved. Otherwise V1401 is just fine and not outdated by any means. You don't want to use ADAT as clock source anyway because of jitter, so you better use the buffered LRCLK as Word clock signal output. If you have some other master clock source use Cirrus CS2300CP PLL to generate the master clock instead of the local oscillator(s).
thank you!
not a problem being limited tu 44.1/48kHz

Quote:
V1401 has internal PLL that's why you won't need BCLK signal at all. Well, the PCM4222 needs though.
what do you mean? if the PCM4222 is set as master, it only needs a master clock, right? then I can ignore its BCLK output, and just use its LRCLK output and feed it to V1401 word clock input, along with DATA.
is that correct?
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Old 7th October 2019, 08:31 PM   #5
mhelin is offline mhelin
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Yes that is correct. I thought you are doing multichannel with a single ADC as master and the other as slaves...
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Old 7th October 2019, 08:47 PM   #6
Dimitree is offline Dimitree  Italy
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Yes indeed I will connect to V1401 other PCM4222s, and they will be slave of the first PCM4222 and of course they will take BCKL from the master. Would that be a problem in uour opinion?
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Old 8th October 2019, 06:25 AM   #7
mhelin is offline mhelin
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Quote:
Originally Posted by Dimitree View Post
Yes indeed I will connect to V1401 other PCM4222s, and they will be slave of the first PCM4222 and of course they will take BCKL from the master. Would that be a problem in uour opinion?
No, that is how it is supposed to be done. The PCB design is the most critical part here.
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Old 8th October 2019, 07:47 AM   #8
Dimitree is offline Dimitree  Italy
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this is a quote I found on the web that I didn't understand and so that's why I made this topic..it made me doubt

"The AL1401A is a bit unusual, it interally generates the bit clock from an externally applied word clock. The disadvantage is that it only supports a 64Fs BCLK, so if you want to use a converter like the TI PCM4202 which wants a BCLK of 128Fs in single-rate mode (which is all that you can use over ADAT without S/MUX), you'll need a CPLD between the ADC and transmitter to re-shuffle the bitstream. Other converters, like the Cirrus CS5362/5382 or the older TI PCM1804, directly support a 64Fs BCLK"

but I think it only applies when you don't use the ADC in master mode so you need to provide your own BCLK to ADC and ADAT and they should have different rates
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Old 8th October 2019, 01:00 PM   #9
mhelin is offline mhelin
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Yeah, the PCM4202 and PCM4204 (quad version) are odd chips. It means in master mode they send actually 64-bits data / channel and at double rate compared to "normal" converters. I think that in slave mode they still accept 64x fs BCK anyway. In this thread the PCM4202 (PCM4204 is typo) is actually operated at the 64xfs BCK rate in slave mode and the results in the end are rather good.

Not sure what would V1401 do if you feed it data at 128 x Fs, most probably it would just skip every other bit. Guess you could use a shift register or FIFO which puts data in at 128 FS and when you divide the BCK by 2 you could use that for reading the data out to ADAT chip input. Then at every LRCK transition you would have to reset the FIFO because the that point it would have 32 zero bits.

Last edited by mhelin; 8th October 2019 at 01:12 PM.
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Old 8th October 2019, 01:58 PM   #10
Dimitree is offline Dimitree  Italy
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Thank you for the explaination and the help!
I will use PCM4222 anyway so I’m ok

Working on the layout right now!
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